\vskip 10mm {\Large \boldmath Search for the Decay $B^0 \rightarrow \gamma \gamma$} %\begin{center} % Temporary fix for Collaboration name problem %\vskip 10mm %The \babar\ Collaboration %\end{center}
The \babar\ Collaboration
We present a limit on the branching fraction for the decay $B^0 \rightarrow \gamma \gamma$ using data collected at the $\Upsilon(4S)$ resonance with the \babar\ detector at the PEP-II asymmetric--energy $e^+e^-$ collider. Based on the observation of one event in the signal region, out of a sample of 21.3 $\times$ 10$^6$ $e^+e^- \rightarrow \Upsilon(4S) \rightarrow B\overline B$ decays, we establish an upper limit on the branching fraction of ${\cal B}(B^0 \rightarrow \gamma \gamma ) < 1.7 \times 10^{-6}$ at the 90\% confidence level. This result substantially improves upon existing limits.
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\title{ 
\vskip 10mm
{\Large \bf\boldmath Search for the Decay $B^0 \rightarrow \gamma \gamma$}
%\begin{center} % Temporary fix for Collaboration name problem
%\vskip 10mm
%The \babar\ Collaboration
%\end{center}
}

%\author{\large The \babar\ Collaboration}
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\date{\today}% It is always \today, today, but you may specify any date with \date.

\begin{abstract}
We present a limit on the branching fraction for the decay $B^0 \rightarrow \gamma \gamma$
using data collected at the $\Upsilon(4S)$ resonance with the \babar\ detector at the PEP-II 
asymmetric--energy $e^+e^-$ collider.
Based on the observation of one event in the signal region, out of a sample of 
21.3 $\times$ 10$^6$ $e^+e^- \rightarrow \Upsilon(4S) \rightarrow B\overline B$ 
decays, we establish an upper limit on the branching fraction of
${\cal B}(B^0 \rightarrow \gamma \gamma ) < 1.7 \times 10^{-6}$
at the 90\% confidence level. 
This result substantially improves upon existing limits.
\end{abstract}

\pacs{12.15.Hh, 11.30.Er, 13.25.Hw}% PACS, the Physics and Astronomy Classification Scheme.

\maketitle

\begin{figure}[ttt]
\begin{center}
\epsfig{file=fig1.eps,width=0.46\linewidth}\hfill
\epsfig{file=fig3.eps,width=0.46\linewidth}
\end{center}
\caption
{Examples of possible diagrams responsible for 
the decay $B^0 \rightarrow \gamma \gamma$. In these diagrams
q = u, c, or t, and  H is a hypothetical charged non-Standard Model Higgs boson.
\label{fig:feynman}}
\end{figure}

%
% INTRODUCTION
%
In the Standard Model the decay  $B^0 \rightarrow \gamma \gamma$ proceeds via a
second-order weak transition, including gluonic penguins, followed by annihilation 
(Fig.~\ref{fig:feynman}).
Standard Model predictions for the branching fraction of 
these effective flavor--changing weak neutral current processes
range from 0.1 to $2.3\times 10^{-8}$ \cite{b0gammagammaSUSY}.

Physics beyond the Standard Model can enhance this branching fraction  
by as much as two orders of magnitude, particularly in the case of 
two--Higgs models \cite{b0gammagamma2Higgs}.
Other particles from the supersymmetric spectrum can further modify the Standard Model
expectation \cite{b0gammagammaSUSY}.
The current best limit on the branching fraction for $B^0 \rightarrow \gamma \gamma$,
from the L3 experiment \cite{L3} at the CERN LEP collider, is
${\cal B}(B^0 \rightarrow \gamma \gamma ) < 3.9 \times 10^{-5}$ (90\% confidence level).

%
% DATA SAMPLE
%
In this Letter we present an analysis based on 
data taken with the \babar\ detector \cite{detector}, which operates at the 
PEP--II asymmetric--energy $e^+e^-$ collider at the Stanford Linear Accelerator Center
\cite{pep}. 
The sample
consists of 19.4\invfb\ taken at the $\Upsilon(4S)$ resonance,
corresponding to $21.3\times 10^6$
$e^+e^- \rightarrow \Upsilon(4S) \rightarrow B\overline B$ events. 
An additional sample of 2.2\invfb\ accumulated 
%approximately 
40\mev\ 
below the $\Upsilon(4S)$ resonance is used to estimate non--$B\overline B$ background.

Charge conjugation invariance is assumed for all channels quoted in this
paper, and the charge conjugate reactions are included in the analysis.
%Charge conjugation is 
%implied throughout this paper and equal production of charged and neutral $B$ mesons at the 
%$\Upsilon(4S)$ resonance is assumed. 
%Quantities are calculated in both the laboratory frame and the $\Upsilon(4S)$ rest frame.
Quantities evaluated in the $\Upsilon(4S)$ rest frame are denoted by an asterisk; 
{\it e.g.}, $E^*_{b}$ is the energy of the $e^+$ and $e^-$ beams in the 
$\Upsilon(4S)$ rest frame.

The \babar\ detector, a general purpose solenoidal magnetic spectrometer, is 
described in detail elsewhere \cite{detector}. A silicon  vertex detector and a
cylindrical drift chamber in a 1.5-T solenoidal magnetic field are used to measure momenta and 
ionization energy loss of charged particles. 
%A Cherenkov ring imaging detector covering the central region provides K--$\pi$ separation.
Electrons and photons are identified by a 
CsI electromagnetic calorimeter (EMC). 
%Muons are identified in the instrumented flux return.

This analysis exploits in particular the information provided by the
%%%%electromagnetic calorimeter 
EMC
consisting of 6580 CsI crystals, covering 90\% of 4$\pi$ 
in the $\Upsilon(4S)$ rest frame. 
The energy resolution has been measured directly with a radioactive source at low energy
and with electrons from Bhabha scattering at high energy.
% yielding values of $\sigma_E/E = (5.0 \pm 0.8) \%$ at 6.13 \mev\ and 
%$\sigma_E/E = (1.90 \pm 0.07) \%$ at 7.5 \gev,
%%%The energy dependence of the resolution is extracted from a variety of processes.
The mass resolution of $\pi^0$ and $\eta$ candidates in which the two photons 
in the decay have approximately equal energy can be used to infer the energy resolution
at an energy less than 1\gev; the decay $\chi_{c1}\rightarrow J/\psi\gamma$ provides
an additional measurement at 500\mev. 
A fit to the energy dependence results in $\sigma_E/E = (2.3 \pm 0.3)\%/^4\sqrt{E} \, \oplus \, 
(1.9 \pm 0.1)\%$ \cite{detector}.

%Photon identification is performed 
Energy deposits in the EMC are reconstructed
by grouping adjacent crystals with energy deposits greater than 
1\mev\ into {\it clusters}. Clusters with more than one local energy maximum are then split 
into {\it bumps}. 
The energy of each crystal is divided among the bumps by an iterative adjustment of the 
centers and energies of the bumps assuming electromagnetic shower shapes \cite{detector}. 
Next, all tracks reconstructed in the tracking volume are extrapolated to the 
%electromagnetic calorimeter 
EMC entrance and a track--bump matching probability is calculated for each pair.

All bumps with a matching probability smaller than $10^{-6}$ are treated as photon candidates.
Photons are selected  by requiring the bump shape to be compatible with an electromagnetic
shower, and by requiring the bump to have a minimum energy of 30\mev. 
In addition we accept only photon candidates which are isolated from any other bump in the event. 
This requirement selects against background from high--energy $\pi^0$ mesons, where the two 
photons from the decay of the $\pi^0$ meson strike the calorimeter in close proximity 
({\it merged $\pi^0$}).

The \babar\ detector is simulated by a {\tt GEANT}--based Monte Carlo procedure \cite{geant} that includes
beam--related background by mixing random trigger events into the Monte Carlo generated events.
The simulated events are processed in the same manner as data. 
The simulation is used to study background and optimize selection criteria, but
only enters the analysis directly through the calculation of the signal efficiency.

In order to select $B\overline B$ events, we require at least three tracks of good quality
in the event. The quality requirements for these tracks include a small impact parameter with respect to
the collision point along the beam direction (10\cm) and transverse to it (1.5\cm), 
a minimum number of 13 hits in the drift chamber and a momentum of 
$p<10\gevc$ in the laboratory frame. To help reject continuum background, the ratio of the 
second Fox--Wolfram moment to the zeroth Fox--Wolfram moment \cite{FoxWolfram} must be less than 0.9. 
We further require that there be two high--energy photon candidates with
an energy in the $\Upsilon(4S)$ rest frame between 1.5 and 3.5\gev. 
%After this preselection all the remaining photons are combined to $B$ meson candidates. 
At this point, all remaining pairs of photons are considered candidates
for the decay $B^0 \rightarrow \gamma \gamma$.
If the event contains more than one such $B$ candidate all of them are kept for further analysis.

After this preselection additional requirements are imposed on the 
$B^0 \rightarrow \gamma \gamma$ candidates.
Photon bumps from the $B$ candidate must not contain noisy crystals or crystals which produce no
signals.
The second moment of the energy distribution around the cluster's centroid 
%\cite{definitionOfSecondMoment}
must be smaller than 0.002. This value has been optimized
to
reject 
%select against 
remaining background from merged $\pi^0$ mesons.

Since $B$ mesons at the $\Upsilon(4S)$ resonance are produced nearly at rest, the decay 
$B^0 \rightarrow \gamma \gamma$ will contain two nearly back--to--back photons with 
$E^*_\gamma \approx 2.6 \gev$ in the $\Upsilon(4S)$ rest frame. This represents a clean signature and
makes this channel relatively easy to study experimentally. We  exploit this 
feature by considering only $B^0 \rightarrow \gamma \gamma$ candidates
which have at least one photon with $2.3 < E^*_\gamma < 3.0 \gev$.

In order to reject photons from $\pi^0$($\eta$) decays 
we combine each photon from the $B$ candidate with all the other 
photons in the event having energy greater than 50(250)\mev. The resulting $\pi^0$($\eta$)
candidates are required to have an invariant
mass beyond three standard deviations, or $3 \times 8.8 (18) \mevcc$, 
of the nominal $\pi^0$($\eta$) mass \cite{PDG}.

% In order to reject photons from $\pi^0$($\eta$) decays
% the combination of the high energy photons from the $B$ candidate with each other 
% photon in the event having energy greater than 50 (250)\mev\ is required to have an invariant
% mass beyond 
% %that does not lie within 
% three standard deviations, or $3 \times 8.8 (18) \mevcc$, 
% of the nominal $\pi^0$ ($\eta$) mass.
% We have determined with single $\pi^0$ Monte Carlo that the overall $\pi^0$ rejection is better than
% 97\% in the photon energy range of interest. 
% This has been confirmed by comparing the single $\pi^0$ Monte Carlo with $\tau$ lepton
% decays to $\rho (\pi\pi^0) \nu_\tau$  from data and Monte Carlo which have both a purity of greater 
% than 99\%.
% This has been confirmed by comparing 
% $\tau$ lepton decays to $\rho (\pi\pi^0) \nu_\tau$ 
% between samples of greater than 99\% purity
% from generic $\tau$ Monte Carlo and $\tau$ data.

Reconstruction of exclusive final states from $B$ mesons produced at the \Y4S\ resonance benefits
from the beam energy constraint $E^*_B = E^*_{b}$. Thus, in the 
$\Upsilon(4S)$ rest frame the energies of the $B$ meson decay products must add up to the beam energy.
We calculate the energy difference $\Delta E \equiv E^*_{\gamma,1} + E^*_{\gamma,2} - E^*_{b}$
between the candidate $B^0$ meson and the beam energy 
in the \Y4S\ rest frame. The distribution of this quantity peaks at 0 GeV for true $B$ mesons,
and has a tail towards negative 
$\Delta E$ due to 
shower leakage in the EMC.
%energy loss of the photons in the detector material.
The resolution in $\Delta E$ is obtained from signal Monte Carlo events with a fit of the $\Delta E$ 
distribution to an empirical function \cite{CrystalBall} and
is $\sigma_{\Delta E} = 73\mev$.

The $B$ meson mass resolution is improved 
%by an order of magnitude 
with the use of the 
beam energy constraint. 
We use the beam energy substituted mass
\mes\ $ \equiv \sqrt{E^{*2}_{b}-({\mathbf p}^*_{\gamma,1} + {\mathbf p}^*_{\gamma,2})^2}$.
The resolution on \mes\ is obtained from signal Monte Carlo events with a fit of the \mes\ distribution 
to an empirical function \cite{CrystalBall} and 
is $\sigma_{\mes} = 3.9\mevcc$.

For the purpose of determining numbers of events and efficiencies a rectangular 
signal region is defined. This region extends 2$\sigma$ 
in $\Delta E$ about 0\mev\ and 2$\sigma$ in \mes\ about the nominal mass $m_{B^0}$ of the $B^0$ meson.

The search for $B^0 \rightarrow \gamma \gamma$ was performed as a blind analysis by hiding
a 3$\sigma$ region in $\Delta E$ and \mes\ in on--resonance data until the development of 
the selection procedure was complete. 
This allows optimization of the selection and estimation of the background 
without the bias of knowing the number of events in the signal region.

Monte Carlo studies indicate that the main background arises from the process 
$e^+e^- \rightarrow q\overline q$ ($q = u$, $d$, $s$), referred to as continuum background
and modeled with the JETSET event generator \cite{JETSET}.
Such events 
%usually 
exhibit a two--jet structure and contain
high momentum, approximately back--to--back tracks. 
%In about 50\% of the cases the 
%Background sources include photons
One source of background includes photons
from initial-state radiation, others are photons from $\pi^0 \rightarrow \gamma \gamma$ 
and $\eta \rightarrow \gamma \gamma$ decays, where the decay is very asymmetric in the 
final-state photon energy.
%Background from high energy $\pi^0$ mesons which merge in the EMC into one cluster 
%is negligible. 
Background from merged $\pi^0$ mesons is negligible. 

\begin{table}[tttt]
\caption{
Cumulative signal reconstruction efficiency as selection criteria are applied.
The first row shows the cumulative event selection efficiency. The additional rows give 
individual contributions to the $B$ candidate selection efficiency. The cumulative signal
reconstruction efficiency is 
given by the product of event selection and final $B$ reconstruction efficiency.
}
\label{tab:efficiency}
\begin{tabular}{lc}
  \hline
  \hline
  selection criteria& efficiency [\%] \\
  \hline
  cumulative event preselection             & 39.8   \\
  \hline
  photon energy $E^*_\gamma$                & 92.9   \\
  bump quality and second moment            & 86.8   \\
  $\pi^0$ and $\eta$ veto                   & 72.8   \\
  $|\cos(\theta_B)|$ and $|\cos(\theta_T)|$ & 40.1   \\
  signal region                             & 27.0   \\
  \hline 
  cumulative                                & 10.7   \\ 
  \hline
  \hline
\end{tabular}
\end{table}

To reduce continuum background, we calculate the angle $\theta^*_T$ between one of the photons
(chosen randomly) of the $B^0$ candidate and the thrust axis of the remaining tracks and neutral bumps 
in the event. The distribution of $|\cos\theta^*_T|$ is uniform for signal events and 
strongly peaked at 1 for continuum background events. 
We also calculate the angle $\theta^*_B$ between the momentum vector of the $B^0$ candidate 
and the beam axis in the $\Upsilon(4S)$ rest frame.
The distribution of $|\cos\theta^*_B|$ is uniform
for continuum background and  follows a $\sin^2\theta^*_B$ distribution for signal events.
The requirements for both $|\cos\theta^*_T|$ and $|\cos\theta^*_B|$ have been 
optimized to maximize the statistical significance $N_S/\sqrt{N_S+N_B}$, where $N_S$ is the number of 
signal candidates expected assuming for the branching fraction 
${\cal B}(B^0 \rightarrow \gamma \gamma ) = 1 \times 10^{-8}$ \cite{b0gammagammaSUSY}
and $N_B$ is the expected number of background candidates determined from continuum 
Monte Carlo simulation and  off--resonance data. 
We require $|\cos\theta^*_T|<0.57$ and $|\cos\theta^*_B|<0.81$.
If more than one $B$ meson candidate per event remains after this selection, which occurs in 
less than 0.1\% of the events analyzed, we select the candidate with the smallest $|\Delta E|$.
After all these selection criteria
the overall efficiency for $B^0 \rightarrow \gamma \gamma$ decays is determined from 
the Monte Carlo simulation to be $( 10.7\pm 0.2 )\%$, where the error is purely statistical.
Table \ref{tab:efficiency} shows the cumulative signal reconstruction efficiency as the 
selection criteria are applied.


\begin{figure}[ttt]
%  \begin{center}
    \epsfig{file=final3_j_2.eps,width=\linewidth}   
    \caption{
      Energy difference 
      $\Delta E$
%$\Delta E \equiv E^*_{\gamma,1} + E^*_{\gamma,2} - E^*_{b}$
      between the candidate $B^0$ meson and the beam energy 
      in the \Y4S\ rest frame versus
      beam energy substituted mass
      \mes\ 
%$\equiv \sqrt{E^{*2}_{b}-({\mathbf p}^*_{\gamma,1} + {\mathbf p}^*_{\gamma,2})^2}$
      for on--resonance data. 
      We observe one event in the signal region, outlined as a black dashed box about $\Delta E = 0$\gev,
      consistent with the expected background. The dashed box on the left shows the sideband used
      for background estimation.
      \label{fig:final}
     }
%  \end{center}
\end{figure}

\begin{figure}[ttt]
\epsfig{file=polyFit_2.eps,width=\linewidth}
\epsfig{file=argusFit_2.eps,width=\linewidth}
\caption{
  a) Fit to the $\Delta E$ distribution in the grand sideband
  to a first-order polynomial; b) fit of the \mes\ distribution in the lower 
  sideband 
  with the ARGUS function \cite{Argus}. See text for the definition of the
  sidebands.
  \label{fig:background}}
\end{figure}



A single event in the on--resonance data meets these selection criteria, as shown in Fig.~\ref{fig:final}.
%After the full set of selection criteria has been applied, we find one event in the signal region
%for on--resonance data, shown in Fig.~\ref{fig:final}, 
%compared to a continuum Monte Carlo expectation of 0 events. 
%Due to the limited statistics
%of the continuum Monte Carlo sample, however, the observation of one data event in the signal 
%region is not inconsistent with the Monte Carlo prediction of 0 background events. 
A number of 
exclusive decay modes that can mimic $B^0 \rightarrow \gamma \gamma$ decays have been studied
with high statistics (equivalent to $1.2-1.7 \times 10^4\invfb$ assuming branching fractions 
of the order of
10$^{-6}$). We expect negligible contributions from  
$B^0 \rightarrow \eta\eta$, $K^{*0}\gamma$, $\rho^{0}\gamma$, and $\pi^0\pi^0$, and a combined 
contribution of $0.7\times 10^{-3}$ events from $B^\pm \rightarrow \rho^\pm(\pi^\pm\pi^0)\gamma$ and 
$B^0 \rightarrow \omega(\pi^0\gamma)\gamma$.
To further explore the question of remaining background in the signal region, 
%as well as to verify the accuracy of the Monte Carlo background simulation, 
we define the {\it grand sideband} 
consisting of a rectangular region within the limits 
$-1.0 < \Delta E < 1.0 \gev$ and $5.20 < \mes < 5.26 \gevcc$ 
(see Fig. \ref{fig:final}, left dashed box).
In this region we find a prediction of $34\pm 9$ events from continuum 
Monte Carlo simulations, in good agreement
with the observation of $43\pm 7$ ($44\pm 20$) events from on--resonance data (off-resonance data
of 2.2 fb$^{-1}$ scaled to the full analyzed luminosity of 19.4 fb$^{-1}$).
We parameterize the background using on--resonance data.
The background in  $\Delta E$ is parameterized in the grand sideband 
with a first-order polynomial (see Fig. \ref{fig:background}a); the background in \mes
is parameterized in the {\it lower sideband}, which is a rectangular region within the limits 
$-1.0 < \Delta E < -0.2 \gev$ and $5.20 < \mes < 5.29 \gevcc$, with an empirical threshold function
first employed by the ARGUS collaboration \cite{Argus} (see Fig. \ref{fig:background}b).
Both parameterizations describe the corresponding distribution very well with a $\chi^2$, normalized
to the number of degrees of freedom, of about 0.8.
Using this parameterization we are able to extrapolate the on--resonance grand sideband data 
into the signal region and find an expectation of $0.9^{+0.4}_{-0.3}$ events. 
%Using a parameterization of the background in $\Delta E$ and \mes\ outside the signal region \cite{Argus}
%we are able to extrapolate the on--resonance sideband data into the signal region and find 
%an expectation of 
%$0.9^{+0.4}_{-0.3}$ 
%%$0.89^{+0.40}_{-0.26}$ 
%events. 
This is consistent 
with the hypothesis that the observed event in the signal region is due to continuum background.
Nevertheless, 
%in light of the limited Monte Carlo statistics in the signal region, 
we choose to 
quote a conservative upper limit, assuming that the observed event in the signal region is 
in fact due to the decay $B^0 \rightarrow \gamma \gamma$. 
We use Poisson statistics to set an upper limit on the branching fraction.
%  as follows.
% If $n_0$ is the number of observed events and $\mu_B$
% is the known expectation for the background mean, the upper limit $N_{lim}$ on the number of
% signal events is obtained from the expression
% $$
% \alpha
% =
% \frac{e^{-(N_{lim}+\mu_B)} \sum^N_{i=0} \frac{(N_{lim}+\mu_B)^i}{i!}}
% {e^{-\mu_B}\sum^N_{i=0}\frac{\mu_B^i}{i!}}
% $$
%The upper limit on 1 observed event from Poisson statistics at the 90\% confidence level is $N_{UL}$ = 3.49. 
The upper limit on the branching fraction $\cal B$ is obtained from 
${\cal B} = N_{UL}/(\epsilon \cdot (N_{\Bz}+ N_{\Bzb}))$,
where $N_{UL}$ is the upper limit on the number of observed events, $\epsilon$ 
the signal reconstruction efficiency of (10.7 $\pm$ 0.2)\% and 
$N_{\Bz}+ N_{\Bzb}$ is the number of produced \Bz and \Bzb mesons. 
$N_{\Bz}+ N_{\Bzb}$ is equal to the number
of $\Upsilon(4S)$ events since we assume the number of \Bz\Bzb events to be 50 \% of the number
of produced $\Upsilon(4S)$ events.
This yields an upper limit on the branching fraction, based on statistics alone,
of ${\cal B}(B^0 \rightarrow \gamma \gamma ) < 1.7 \times 10^{-6}$
at the 90\% confidence level.

\begin{table}[ttt]
\caption
{Summary of systematic uncertainties on the signal efficiency and the number
of produced \FourS\ as an error on the branching fraction determination.
The total systematic uncertainty is the sum of the individual contributions added
in quadrature.}
\label{tab:systematics}
  \begin{tabular}{ l r }
    \hline
    \hline
      systematic uncertainty                   & ($\Delta${$\cal B$}/{$\cal B$})\% \\
    \hline
    Number of produced \FourS\           &  1.6 \\
    Photon detection efficiency          &  6.5 \\ 
    $\eta$ veto                          &  2.0 \\
    $\pi^0$ veto                         &  2.0 \\
    $\Delta E$ selection                 &  5.3 \\
    \mes\ selection                      &  2.6 \\
    Track finding efficiency             &  1.8 \\ 
    Number of signal Monte Carlo events  &  2.0 \\
    \hline
    Total                                &  9.6 \\
    \hline
    \hline
  \end{tabular}
\end{table}
% %
% % RESULTS
% %
Systematic effects arise from the modeling of the signal efficiency and the estimation 
of the number of $B$ mesons in the data sample.
A summary of all systematic errors
is provided in Table~\ref{tab:systematics}.
%The systematic uncertainties we have considered in this study are listed
%in Table~\ref{tab:systematics} in terms of their effect on the branching fraction determination.
The most significant sources are
%systematic uncertainties 
%are introduced by 
the photon detection efficiency 
and 
%by 
the $\Delta E$ selection 
%as a consequence of the
due to the
uncertainty in the photon energy scale and photon energy resolution.
The systematic uncertainty on the photon detection efficiency has been 
determined from a study which compares the precisely know ratio \cite{PDG} of 
the $\tau \rightarrow \pi\pi^0\nu_\tau$ and $\tau \rightarrow \pi\pi^0\pi^0\nu_\tau$ rate
in Monte Carlo events and data. 
This uncertainty depends on the event multiplicity, whose effect is estimated by embedding 
photon bumps from radiative Bhabha events into both generic $B$ meson
and generic $B$ meson Monte Carlo events.
%, and is included in the systematic uncertainties
%listed in Table~\ref{tab:systematics}.
%The systematic uncertainty on the photon detection efficiency has been 
%determined from hadronic $\tau$ lepton 
%decays. The study compares the rate of $\tau \rightarrow \pi\pi^0\nu_\tau$ relative to that of
%$\tau \rightarrow \pi\pi^0\pi^0\nu_\tau$, which is precisely known \cite{PDG}, 
%in Monte Carlo events and data. 
%The photon detection and $\pi^0$/$\eta$ veto efficiency depend
%on the event multiplicity. This effect is estimated by embedding 
%photon bumps from radiative Bhabha events into both generic $B$ meson
%and generic $B$ meson Monte Carlo events.
The uncertainty in the energy scale is estimated with a study of symmetric 
$\eta \rightarrow \gamma \gamma$ decays,
where both photons are within a narrow energy range. 
%To measure the uncertainty in the energy scale symmetric
%$\eta \rightarrow \gamma \gamma$ decays were used, for which both photons were within a narrow
%energy range.
%These are $\eta$ meson decays in which both photons are within a given energy range. 
Systematic shifts of the reconstructed 
$\eta$ mass from the nominal value measure the uncertainty in the energy scale in this 
energy range. 
% The charged track finding efficiency 
% affects this study via the initial event selection which requires at least 
% three good charged particle tracks.

In order to include our systematic uncertainty in the determination of the upper limit,
we follow a prescription given by \cite{Cousins}.
The branching fraction $\cal B$ is calculated as  ${\cal B} = n / S$, where $n$ is the number of 
observed events and $S = 2.3\times 10^6$ is the sensitivity, 
given by the product of the number of $B^0$\Bzb\ 
events 
and the overall $B^0 \rightarrow \gamma \gamma$ selection efficiency.
Assuming a normal distribution for the uncertainty in $1/S$,
the systematic uncertainty is accounted for by convoluting the Poisson probability
distribution for the assumed branching fraction with a Gaussian error distribution for $1/S$.
Our total systematic uncertainty of 9.6\% included in this way has a negligible effect on the upper limit.
%The results of this analysis are summarized in Table~\ref{tab:efficiency}.

% \begin{table}[tttt]
% \caption{Summary of results and branching fraction upper limit.
% The number of expected signal events assuming a branching fraction
% of $1 \times 10^{-8}$ is  $N_{\rm exp}$, the number of observed 
% events $N_{\rm obs}$, with the upper limit on 1 of $N_{\rm UL}$ and a  
% signal efficiency $\epsilon$ we derive the 
% upper limit on the branching fraction ${\cal B}$.
% }
% \label{tab:efficiency}
% \begin{tabular}{l c c c c c c }
% \hline
% \hline
%  $N_{\rm exp}$ & $N_{\rm obs}$ & $N_{\rm UL}$ &  $N_{\rm bkg}$ & $\epsilon$ [\%] & 
%  ${\cal B}(B^0 \rightarrow \gamma \gamma)$ upper limit \cr
% \hline
%  0.02      & 1         & 3.89     &  $0.9^{+0.4}_{-0.3}$ & $10.7\pm 0.2$ & $1.7\times 10^{-6}$ (90\% CL) \cr
% \hline
% \hline
% \end{tabular}
% \end{table}


In summary, 
we have performed a search for the decay $B^0 \rightarrow \gamma \gamma$. We observe one event in 
the signal region and infer an upper limit on the branching fraction
of $${\cal B}(B^0 \rightarrow \gamma \gamma ) < 1.7 \times 10^{-6}$$
at the 90\% confidence level.
This result improves the existing limit 
%from the L3 collaboration 
\cite{L3} 
%at the CERN LEP collider 
by over a factor of 20.

\input pubboard/acknow_PRL.tex

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%   $
%   $\Delta \theta_i$ and $\Delta \phi_i$ are the angular distances between the center of crystal $i$
%   and the cluster centroid in $\theta$ and $\phi$,
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\end{document}


authors_0116.tex
%% author list as of 08-Jun-2001 (616 authors)
%
\author{B.~Aubert}
\author{D.~Boutigny}
\author{J.-M.~Gaillard}
\author{A.~Hicheur}
%\author{A.~Jeremie} per J.P.Lees
\author{Y.~Karyotakis}
\author{J.~P.~Lees}
\author{P.~Robbe}
\author{V.~Tisserand}
\affiliation{Laboratoire de Physique des Particules, F-74941 Annecy-le-Vieux, France }
\author{A.~Palano}
\affiliation{Universit\`a di Bari, Dipartimento di Fisica and INFN, I-70126 Bari, Italy }
\author{G.~P.~Chen}
\author{J.~C.~Chen}
\author{N.~D.~Qi}
\author{G.~Rong}
\author{P.~Wang}
\author{Y.~S.~Zhu}
\affiliation{Institute of High Energy Physics, Beijing 100039, China }
\author{G.~Eigen}
\author{P.~L.~Reinertsen}
\author{B.~Stugu}
\affiliation{University of Bergen, Inst.\ of Physics, N-5007 Bergen, Norway }
\author{B.~Abbott}
\author{G.~S.~Abrams}
\author{A.~W.~Borgland}
\author{A.~B.~Breon}
\author{D.~N.~Brown}
\author{J.~Button-Shafer}
\author{R.~N.~Cahn}
\author{A.~R.~Clark}
\author{M.~S.~Gill}
\author{A.~Gritsan}
\author{Y.~Groysman}
\author{R.~G.~Jacobsen}
\author{R.~W.~Kadel}
\author{J.~Kadyk}
\author{L.~T.~Kerth}
\author{S.~Kluth}
\author{Yu.~G.~Kolomensky}
\author{J.~F.~Kral}
\author{C.~LeClerc}
\author{M.~E.~Levi}
\author{T.~Liu}
\author{G.~Lynch}
\author{A.~B.~Meyer}
\author{M.~Momayezi}
\author{P.~J.~Oddone}
\author{A.~Perazzo}
\author{M.~Pripstein}
\author{N.~A.~Roe}
\author{A.~Romosan}
\author{M.~T.~Ronan}
\author{V.~G.~Shelkov}
\author{A.~V.~Telnov}
\author{W.~A.~Wenzel}
\affiliation{Lawrence Berkeley National Laboratory and University of California, Berkeley, CA 94720, USA }
\author{P.~G.~Bright-Thomas}
\author{T.~J.~Harrison}
\author{C.~M.~Hawkes}
\author{D.~J.~Knowles}
\author{S.~W.~O'Neale}
\author{R.~C.~Penny}
\author{A.~T.~Watson}
\author{N.~K.~Watson}
\affiliation{University of Birmingham, Birmingham, B15 2TT, United Kingdom }
\author{T.~Deppermann}
\author{K.~Goetzen}
\author{H.~Koch}
\author{J.~Krug}
\author{M.~Kunze}
\author{B.~Lewandowski}
\author{K.~Peters}
\author{H.~Schmuecker}
\author{M.~Steinke}
\affiliation{Ruhr Universit\"at Bochum, Institut f\"ur Experimentalphysik 1, D-44780 Bochum, Germany }
\author{J.~C.~Andress}
\author{N.~R.~Barlow}
\author{W.~Bhimji}
\author{N.~Chevalier}
\author{P.~J.~Clark}
\author{W.~N.~Cottingham}
\author{N.~De Groot}
\author{N.~Dyce}
\author{B.~Foster}
\author{J.~D.~McFall}
\author{D.~Wallom}
\author{F.~F.~Wilson}
\affiliation{University of Bristol, Bristol BS8 1TL, United Kingdom }
\author{K.~Abe}
\author{C.~Hearty}
\author{T.~S.~Mattison}
\author{J.~A.~McKenna}
\author{D.~Thiessen}
\affiliation{University of British Columbia, Vancouver, BC, Canada V6T 1Z1 }
\author{S.~Jolly}
\author{A.~K.~McKemey}
\author{J.~Tinslay}
\affiliation{Brunel University, Uxbridge, Middlesex UB8 3PH, United Kingdom }
\author{V.~E.~Blinov}
\author{A.~D.~Bukin}
\author{D.~A.~Bukin}
\author{A.~R.~Buzykaev}
\author{V.~B.~Golubev}
\author{V.~N.~Ivanchenko}
\author{A.~A.~Korol}
\author{E.~A.~Kravchenko}
\author{A.~P.~Onuchin}
\author{A.~A.~Salnikov}
\author{S.~I.~Serednyakov}
\author{Yu.~I.~Skovpen}
\author{V.~I.~Telnov}
\author{A.~N.~Yushkov}
\affiliation{Budker Institute of Nuclear Physics, Novosibirsk 630090, Russia }
\author{D.~Best}
\author{A.~J.~Lankford}
\author{M.~Mandelkern}
\author{S.~McMahon}
\author{D.~P.~Stoker}
\affiliation{University of California at Irvine, Irvine, CA 92697, USA }
\author{A.~Ahsan}
\author{K.~Arisaka}
\author{C.~Buchanan}
\author{S.~Chun}
\affiliation{University of California at Los Angeles, Los Angeles, CA 90024, USA }
\author{J.~G.~Branson}
\author{D.~B.~MacFarlane}
\author{S.~Prell}
\author{Sh.~Rahatlou}
\author{G.~Raven}
\author{V.~Sharma}
\affiliation{University of California at San Diego, La Jolla, CA 92093, USA }
\author{C.~Campagnari}
\author{B.~Dahmes}
\author{P.~A.~Hart}
\author{N.~Kuznetsova}
\author{S.~L.~Levy}
\author{O.~Long}
\author{A.~Lu}
\author{J.~D.~Richman}
\author{W.~Verkerke}
\author{M.~Witherell}
\author{S.~Yellin}
\affiliation{University of California at Santa Barbara, Santa Barbara, CA 93106, USA }
\author{J.~Beringer}
\author{D.~E.~Dorfan}
\author{A.~M.~Eisner}
\author{A.~Frey}
\author{A.~A.~Grillo}
\author{M.~Grothe}
\author{C.~A.~Heusch}
\author{R.~P.~Johnson}
\author{W.~Kroeger}
\author{W.~S.~Lockman}
\author{T.~Pulliam}
\author{H.~Sadrozinski}
\author{T.~Schalk}
\author{R.~E.~Schmitz}
\author{B.~A.~Schumm}
\author{A.~Seiden}
\author{M.~Turri}
\author{W.~Walkowiak}
\author{D.~C.~Williams}
\author{M.~G.~Wilson}
\affiliation{University of California at Santa Cruz, Institute for Particle Physics, Santa Cruz, CA 95064, USA }
\author{E.~Chen}
\author{G.~P.~Dubois-Felsmann}
\author{A.~Dvoretskii}
\author{D.~G.~Hitlin}
\author{S.~Metzler}
\author{J.~Oyang}
\author{F.~C.~Porter}
\author{A.~Ryd}
\author{A.~Samuel}
\author{M.~Weaver}
\author{S.~Yang}
\author{R.~Y.~Zhu}
\affiliation{California Institute of Technology, Pasadena, CA 91125, USA }
\author{S.~Devmal}
\author{T.~L.~Geld}
\author{S.~Jayatilleke}
\author{G.~Mancinelli}
\author{B.~T.~Meadows}
\author{M.~D.~Sokoloff}
\affiliation{University of Cincinnati, Cincinnati, OH 45221, USA }
\author{T.~Barillari}
\author{P.~Bloom}
\author{M.~O.~Dima}
\author{S.~Fahey}
\author{W.~T.~Ford}
\author{D.~R.~Johnson}
\author{U.~Nauenberg}
\author{A.~Olivas}
\author{H.~Park}
\author{P.~Rankin}
\author{J.~Roy}
\author{S.~Sen}
\author{J.~G.~Smith}
\author{W.~C.~van Hoek}
\author{D.~L.~Wagner}
\affiliation{University of Colorado, Boulder, CO 80309, USA }
\author{J.~Blouw}
\author{J.~L.~Harton}
\author{M.~Krishnamurthy}
\author{A.~Soffer}
\author{W.~H.~Toki}
\author{R.~J.~Wilson}
\author{J.~Zhang}
\affiliation{Colorado State University, Fort Collins, CO 80523, USA }
\author{T.~Brandt}
\author{J.~Brose}
\author{T.~Colberg}
\author{G.~Dahlinger}
\author{M.~Dickopp}
\author{R.~S.~Dubitzky}
\author{E.~Maly}
\author{R.~M\"uller-Pfefferkorn}
\author{S.~Otto}
\author{K.~R.~Schubert}
\author{R.~Schwierz}
\author{B.~Spaan}
\author{L.~Wilden}
\affiliation{Technische Universit\"at Dresden, Institut f\"ur Kern- und Teilchenphysik, D-01062, Dresden, Germany }
\author{L.~Behr}
\author{D.~Bernard}
\author{G.~R.~Bonneaud}
\author{F.~Brochard}
\author{J.~Cohen-Tanugi}
\author{S.~Ferrag}
\author{E.~Roussot}
\author{S.~T'Jampens}
\author{Ch.~Thiebaux}
\author{G.~Vasileiadis}
\author{M.~Verderi}
\affiliation{Ecole Polytechnique, F-91128 Palaiseau, France }
\author{A.~Anjomshoaa}
\author{R.~Bernet}
\author{A.~Khan}
\author{F.~Muheim}
\author{S.~Playfer}
\author{J.~E.~Swain}
\affiliation{University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom }
\author{M.~Falbo}
\affiliation{Elon University, Elon University, NC 27244-2010, USA }
\author{C.~Borean}
\author{C.~Bozzi}
\author{S.~Dittongo}
\author{M.~Folegani}
\author{L.~Piemontese}
\affiliation{Universit\`a di Ferrara, Dipartimento di Fisica and INFN, I-44100 Ferrara, Italy  }
\author{E.~Treadwell}
\affiliation{Florida A\&M University, Tallahassee, FL 32307, USA }
\author{F.~Anulli}\altaffiliation{Also with Universit\`a di Perugia, I-06100 Perugia, Italy }
\author{R.~Baldini-Ferroli}
\author{A.~Calcaterra}
\author{R.~de Sangro}
\author{D.~Falciai}
\author{G.~Finocchiaro}
\author{P.~Patteri}
\author{I.~M.~Peruzzi}\altaffiliation{Also with Universit\`a di Perugia, I-06100 Perugia, Italy }
\author{M.~Piccolo}
\author{Y.~Xie}
\author{A.~Zallo}
\affiliation{Laboratori Nazionali di Frascati dell'INFN, I-00044 Frascati, Italy }
\author{S.~Bagnasco}
\author{A.~Buzzo}
\author{R.~Contri}
\author{G.~Crosetti}
\author{P.~Fabbricatore}
\author{S.~Farinon}
\author{M.~Lo Vetere}
\author{M.~Macri}
\author{M.~R.~Monge}
\author{R.~Musenich}
\author{M.~Pallavicini}
\author{R.~Parodi}
\author{S.~Passaggio}
\author{F.~C.~Pastore}
\author{C.~Patrignani}
\author{M.~G.~Pia}
\author{C.~Priano}
\author{E.~Robutti}
\author{A.~Santroni}
\affiliation{Universit\`a di Genova, Dipartimento di Fisica and INFN, I-16146 Genova, Italy }
\author{M.~Morii}
\affiliation{Harvard University, Cambridge, MA 02138, USA }
\author{R.~Bartoldus}
\author{T.~Dignan}
\author{R.~Hamilton}
\author{U.~Mallik}
\affiliation{University of Iowa, Iowa City, IA 52242, USA }
\author{J.~Cochran}
\author{H.~B.~Crawley}
\author{P.-A.~Fischer}
\author{J.~Lamsa}
\author{W.~T.~Meyer}
\author{E.~I.~Rosenberg}
\affiliation{Iowa State University, Ames, IA 50011-3160, USA }
\author{M.~Benkebil}
\author{G.~Grosdidier}
\author{C.~Hast}
\author{A.~H\"ocker}
\author{H.~M.~Lacker}
\author{S.~Laplace}
\author{V.~Lepeltier}
\author{A.~M.~Lutz}
\author{S.~Plaszczynski}
\author{M.~H.~Schune}
\author{S.~Trincaz-Duvoid}
\author{A.~Valassi}
\author{G.~Wormser}
\affiliation{Laboratoire de l'Acc\'el\'erateur Lin\'eaire, F-91898 Orsay, France }
\author{R.~M.~Bionta}
\author{V.~Brigljevi\'c }
\author{D.~J.~Lange}
\author{M.~Mugge}
\author{X.~Shi}
\author{K.~van Bibber}
\author{T.~J.~Wenaus}
\author{D.~M.~Wright}
\author{C.~R.~Wuest}
\affiliation{Lawrence Livermore National Laboratory, Livermore, CA 94550, USA }
\author{M.~Carroll}
\author{J.~R.~Fry}
\author{E.~Gabathuler}
\author{R.~Gamet}
\author{M.~George}
\author{M.~Kay}
\author{D.~J.~Payne}
\author{R.~J.~Sloane}
\author{C.~Touramanis}
\affiliation{University of Liverpool, Liverpool L69 3BX, United Kingdom }
\author{M.~L.~Aspinwall}
\author{D.~A.~Bowerman}
\author{P.~D.~Dauncey}
\author{U.~Egede}
\author{I.~Eschrich}
\author{N.~J.~W.~Gunawardane}
\author{J.~A.~Nash}
\author{P.~Sanders}
\author{D.~Smith}
\affiliation{University of London, Imperial College, London, SW7 2BW, United Kingdom }
\author{D.~E.~Azzopardi}
\author{J.~J.~Back}
\author{P.~Dixon}
\author{P.~F.~Harrison}
\author{R.~J.~L.~Potter}
\author{H.~W.~Shorthouse}
\author{P.~Strother}
\author{P.~B.~Vidal}
\author{M.~I.~Williams}
\affiliation{Queen Mary, University of London, E1 4NS, United Kingdom }
\author{G.~Cowan}
\author{S.~George}
\author{M.~G.~Green}
\author{A.~Kurup}
\author{C.~E.~Marker}
\author{P.~McGrath}
\author{T.~R.~McMahon}
\author{S.~Ricciardi}
\author{F.~Salvatore}
\author{I.~Scott}
\author{G.~Vaitsas}
\affiliation{University of London, Royal Holloway and Bedford New College, Egham, Surrey TW20 0EX, United Kingdom }
\author{D.~Brown}
\author{C.~L.~Davis}
\affiliation{University of Louisville, Louisville, KY 40292, USA }
\author{J.~Allison}
\author{R.~J.~Barlow}
\author{J.~T.~Boyd}
\author{A.~C.~Forti}
\author{J.~Fullwood}
\author{F.~Jackson}
\author{G.~D.~Lafferty}
\author{N.~Savvas}
\author{E.~T.~Simopoulos}
\author{J.~H.~Weatherall}
\affiliation{University of Manchester, Manchester M13 9PL, United Kingdom }
\author{A.~Farbin}
\author{A.~Jawahery}
\author{V.~Lillard}
\author{J.~Olsen}
\author{D.~A.~Roberts}
\author{J.~R.~Schieck}
\affiliation{University of Maryland, College Park, MD 20742, USA }
\author{G.~Blaylock}
\author{C.~Dallapiccola}
\author{K.~T.~Flood}
\author{S.~S.~Hertzbach}
\author{R.~Kofler}
\author{T.~B.~Moore}
\author{H.~Staengle}
\author{S.~Willocq}
\affiliation{University of Massachusetts, Amherst, MA 01003, USA }
\author{B.~Brau}
\author{R.~Cowan}
\author{G.~Sciolla}
\author{F.~Taylor}
\author{R.~K.~Yamamoto}
\affiliation{Massachusetts Institute of Technology, Laboratory for Nuclear Science, Cambridge, MA 02139, USA }
\author{M.~Milek}
\author{P.~M.~Patel}
\author{J.~Trischuk}
\affiliation{McGill University, Montr\'eal, Canada QC H3A 2T8 }
\author{F.~Lanni}
\author{F.~Palombo}
\affiliation{Universit\`a di Milano, Dipartimento di Fisica and INFN, I-20133 Milano, Italy }
\author{J.~M.~Bauer}
\author{M.~Booke}
\author{L.~Cremaldi}
\author{V.~Eschenburg}
\author{R.~Kroeger}
\author{J.~Reidy}
\author{D.~A.~Sanders}
\author{D.~J.~Summers}
\affiliation{University of Mississippi, University, MS 38677, USA }
\author{J.~P.~Martin}
\author{J.~Y.~Nief}
\author{R.~Seitz}
\author{P.~Taras}
\author{A.~Woch}
\author{V.~Zacek}
\affiliation{Universit\'e de Montr\'eal, Laboratoire Ren\'e J.~A.~L\'evesque, Montr\'eal, Canada QC H3C 3J7  }
\author{H.~Nicholson}
\author{C.~S.~Sutton}
\affiliation{Mount Holyoke College, South Hadley, MA 01075, USA }
\author{C.~Cartaro}
\author{N.~Cavallo}\altaffiliation{Also with Universit\`a della Basilicata, I-85100 Potenza, Italy }
\author{G.~De Nardo}
\author{F.~Fabozzi}
\author{C.~Gatto}
\author{L.~Lista}
\author{P.~Paolucci}
\author{D.~Piccolo}
\author{C.~Sciacca}
\affiliation{Universit\`a di Napoli Federico II, Dipartimento di Scienze Fisiche and INFN, I-80126, Napoli, Italy }
\author{J.~M.~LoSecco}
\affiliation{University of Notre Dame, Notre Dame, IN 46556, USA }
\author{J.~R.~G.~Alsmiller}
\author{T.~A.~Gabriel}
\author{T.~Handler}
\affiliation{Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA }
\author{J.~Brau}
\author{R.~Frey}
\author{M.~Iwasaki}
\author{N.~B.~Sinev}
\author{D.~Strom}
\affiliation{University of Oregon, Eugene, OR 97403, USA }
\author{F.~Colecchia}
\author{F.~Dal Corso}
\author{A.~Dorigo}
\author{F.~Galeazzi}
\author{M.~Margoni}
\author{G.~Michelon}
\author{M.~Morandin}
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\author{M.~Rotondo}
\author{F.~Simonetto}
\author{R.~Stroili}
\author{E.~Torassa}
\author{C.~Voci}
\affiliation{Universit\`a di Padova, Dipartimento di Fisica and INFN, I-35131 Padova, Italy }
\author{M.~Benayoun}
\author{H.~Briand}
\author{J.~Chauveau}
\author{P.~David}
\author{Ch.~de la Vaissi\`ere}
\author{L.~Del Buono}
\author{O.~Hamon}
\author{F.~Le Diberder}
\author{Ph.~Leruste}
\author{J.~Lory}
\author{L.~Roos}
\author{J.~Stark}
\author{S.~Versill\'e}
\affiliation{Universit\'es Paris VI et VII, LPNHE, F-75252 Paris, France }
\author{P.~F.~Manfredi}
\author{V.~Re}
\author{V.~Speziali}
\affiliation{Universit\`a di Pavia, Dipartimento di Elettronica and INFN, I-27100 Pavia, Italy }
\author{E.~D.~Frank}
\author{L.~Gladney}
\author{Q.~H.~Guo}
\author{J.~H.~Panetta}
\affiliation{University of Pennsylvania, Philadelphia, PA 19104, USA }
\author{C.~Angelini}
\author{G.~Batignani}
\author{S.~Bettarini}
\author{M.~Bondioli}
\author{M.~Carpinelli}
\author{F.~Forti}
\author{M.~A.~Giorgi}
\author{A.~Lusiani}
\author{F.~Martinez-Vidal}
\author{M.~Morganti}
\author{N.~Neri}
\author{E.~Paoloni}
\author{M.~Rama}
\author{G.~Rizzo}
\author{F.~Sandrelli}
\author{G.~Simi}
\author{G.~Triggiani}
\author{J.~Walsh}
\affiliation{Universit\`a di Pisa, Scuola Normale Superiore and INFN, I-56010 Pisa, Italy }
\author{M.~Haire}
\author{D.~Judd}
\author{K.~Paick}
\author{L.~Turnbull}
\author{D.~E.~Wagoner}
\affiliation{Prairie View A\&M University, Prairie View, TX 77446, USA }
\author{J.~Albert}
\author{C.~Bula}
\author{P.~Elmer}
\author{C.~Lu}
\author{K.~T.~McDonald}
\author{V.~Miftakov}
\author{S.~F.~Schaffner}
\author{A.~J.~S.~Smith}
\author{A.~Tumanov}
\author{E.~W.~Varnes}
\affiliation{Princeton University, Princeton, NJ 08544, USA }
\author{G.~Cavoto}
\author{D.~del Re}
\affiliation{Universit\`a di Roma La Sapienza, Dipartimento di Fisica and INFN, I-00185 Roma, Italy }
\author{R.~Faccini}
\affiliation{University of California at San Diego, La Jolla, CA 92093, USA }
\affiliation{Universit\`a di Roma La Sapienza, Dipartimento di Fisica and INFN, I-00185 Roma, Italy }
\author{F.~Ferrarotto}
\author{F.~Ferroni}
\author{K.~Fratini}
\author{E.~Lamanna}
\author{E.~Leonardi}
\author{M.~A.~Mazzoni}
\author{S.~Morganti}
\author{G.~Piredda}
\author{F.~Safai Tehrani}
\author{M.~Serra}
\author{C.~Voena}
\affiliation{Universit\`a di Roma La Sapienza, Dipartimento di Fisica and INFN, I-00185 Roma, Italy }
\author{S.~Christ}
\author{R.~Waldi}
\affiliation{Universit\"at Rostock, D-18051 Rostock, Germany }
\author{P.~F.~Jacques}
\author{M.~Kalelkar}
\author{R.~J.~Plano}
\affiliation{Rutgers University, New Brunswick, NJ 08903, USA }
\author{T.~Adye}
\author{B.~Franek}
\author{N.~I.~Geddes}
\author{G.~P.~Gopal}
\author{S.~M.~Xella}
\affiliation{Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, United Kingdom }
\author{R.~Aleksan}
\author{G.~De Domenico}
%\author{A.~de Lesquen} per R.Aleksan
\author{S.~Emery}
\author{A.~Gaidot}
\author{S.~F.~Ganzhur}
\author{P.-F.~Giraud} % per request from Roy Aleksan, Gautier
\author{G.~Hamel de Monchenault}
\author{W.~Kozanecki}
\author{M.~Langer}
\author{G.~W.~London}
\author{B.~Mayer}
\author{B.~Serfass}
\author{G.~Vasseur}
\author{Ch.~Y\`eche}
\author{M.~Zito}
\affiliation{DAPNIA, Commissariat \`a l'Energie Atomique/Saclay, F-91191 Gif-sur-Yvette, France }
\author{N.~Copty}
\author{M.~V.~Purohit}
\author{H.~Singh}
\author{F.~X.~Yumiceva}
\affiliation{University of South Carolina, Columbia, SC 29208, USA }
\author{I.~Adam}
\author{P.~L.~Anthony}
\author{D.~Aston}
\author{K.~Baird}
\author{E.~Bloom}
\author{A.~M.~Boyarski}
\author{F.~Bulos}
\author{G.~Calderini}
\author{R.~Claus}
\author{M.~R.~Convery}
\author{D.~P.~Coupal}
\author{D.~H.~Coward}
\author{J.~Dorfan}
\author{M.~Doser}
\author{W.~Dunwoodie}
\author{R.~C.~Field}
\author{T.~Glanzman}
\author{G.~L.~Godfrey}
\author{S.~J.~Gowdy}
\author{P.~Grosso}
%\author{J.~L.~Hewett}
\author{T.~Himel}
\author{M.~E.~Huffer}
\author{W.~R.~Innes}
\author{C.~P.~Jessop}
\author{M.~H.~Kelsey}
\author{P.~Kim}
\author{M.~L.~Kocian}
\author{U.~Langenegger}
\author{D.~W.~G.~S.~Leith}
\author{S.~Luitz}
\author{V.~Luth}
\author{H.~L.~Lynch}
\author{H.~Marsiske}
\author{S.~Menke}
\author{R.~Messner}
\author{K.~C.~Moffeit}
\author{R.~Mount}
\author{D.~R.~Muller}
\author{C.~P.~O'Grady}
\author{M.~Perl}
\author{S.~Petrak}
\author{H.~Quinn}
\author{B.~N.~Ratcliff}
\author{S.~H.~Robertson}
\author{L.~S.~Rochester}
\author{A.~Roodman}
\author{T.~Schietinger}
\author{R.~H.~Schindler}
\author{J.~Schwiening}
\author{V.~V.~Serbo}
\author{A.~Snyder}
\author{A.~Soha}
\author{S.~M.~Spanier}
\author{J.~Stelzer}
\author{D.~Su}
\author{M.~K.~Sullivan}
\author{H.~A.~Tanaka}
\author{J.~Va'vra}
\author{S.~R.~Wagner}
\author{A.~J.~R.~Weinstein}
\author{W.~J.~Wisniewski}
\author{D.~H.~Wright}
\author{C.~C.~Young}
\affiliation{Stanford Linear Accelerator Center, Stanford, CA 94309, USA }
\author{P.~R.~Burchat}
\author{C.~H.~Cheng}
\author{D.~Kirkby}
\author{T.~I.~Meyer}
\author{C.~Roat}
\affiliation{Stanford University, Stanford, CA 94305-4060, USA }
\author{A.~De Silva}
\author{R.~Henderson}
\affiliation{TRIUMF, Vancouver, BC, Canada V6T 2A3 }
\author{W.~Bugg}
\author{H.~Cohn}
\author{A.~W.~Weidemann}
\affiliation{University of Tennessee, Knoxville, TN 37996, USA }
\author{J.~M.~Izen}
\author{I.~Kitayama}
\author{X.~C.~Lou}
\author{M.~Turcotte}
\affiliation{University of Texas at Dallas, Richardson, TX 75083, USA }
\author{F.~Bianchi}
\author{M.~Bona}
\author{B.~Di Girolamo}
\author{D.~Gamba}
\author{A.~Smol}
\author{D.~Zanin}
\affiliation{Universit\`a di Torino, Dipartimento di Fisica Sperimentale and INFN, I-10125 Torino, Italy }
\author{L.~Bosisio}
\author{G.~Della Ricca}
\author{L.~Lanceri}
\author{A.~Pompili}
\author{P.~Poropat}
\author{M.~Prest}
\author{E.~Vallazza}
\author{G.~Vuagnin}
\affiliation{Universit\`a di Trieste, Dipartimento di Fisica and INFN, I-34127 Trieste, Italy }
\author{R.~S.~Panvini}
\affiliation{Vanderbilt University, Nashville, TN 37235, USA }
\author{C.~M.~Brown}
\author{R.~Kowalewski}
\author{J.~M.~Roney}
\affiliation{University of Victoria, Victoria, BC, Canada V8W 3P6 }
\author{H.~R.~Band}
\author{E.~Charles}
\author{S.~Dasu}
\author{F.~Di Lodovico}
\author{A.~M.~Eichenbaum}
\author{H.~Hu}
\author{J.~R.~Johnson}
\author{R.~Liu}
\author{J.~Nielsen}
\author{Y.~Pan}
\author{R.~Prepost}
\author{I.~J.~Scott}
\author{S.~J.~Sekula}
\author{J.~H.~von Wimmersperg-Toeller}
\author{S.~L.~Wu}
\author{Z.~Yu}
\author{H.~Zobernig}
\affiliation{University of Wisconsin, Madison, WI 53706, USA }
\author{T.~M.~B.~Kordich}
\author{H.~Neal}
\affiliation{Yale University, New Haven, CT 06511, USA }
\collaboration{The \babar\ Collaboration}
\noaffiliation

acknow_PRL.tex
We are grateful for the 
extraordinary contributions of our \pep2\ colleagues in
achieving the excellent luminosity and machine conditions
that have made this work possible.
The collaborating institutions wish to thank 
SLAC for its support and the kind hospitality extended to them. 
This work is supported by
DOE
and NSF (USA),
NSERC (Canada),
IHEP (China),
CEA and
CNRS-IN2P3
(France),
BMBF
(Germany),
INFN (Italy),
NFR (Norway),
MIST (Russia), and
PPARC (United Kingdom). 
Individuals have received support from the Swiss NSF, 
A.~P.~Sloan Foundation, 
Research Corporation,
and Alexander von Humboldt Foundation.

babarsym.tex
%%%%%   Standard symbols for use in BABAR papers and BAD Notes
%%%%%
%%%%%   Revised   05/22/01 P. Dauncey     Added \hepex, etc. and clean up a bit
%%%%%   Revised   12/07/00 D. Hitlin      Added features of D. Kirkby's HEP.sty
%%%%%   Revised   07/13/00 R. Waldi       Corrected \Kbar, \Bbar ... macros
%%%%%   Revised   07/13/00 D. MacFarlane  Replaced incorrect \chic1 symbols
%%%%%   Revised   07/05/00 P. Dauncey     Added \mes, \mec, removed \O
%%%%%   Revised   07/04/00 D. MacFarlane  Added scalable version of BABAR
%%%%%   Revised   07/01/00 D. MacFarlane
%%%%%   Revised   06/21/00 D. Hitlin
%%%%%   Original  06/10/00 D. Hitlin
%%%%%   Revision of TDR and Physics Book symbol file
%%%%%

\RequirePackage{xspace}

%%%%%%%%%%%%%%%%%%%% BABAR ... THE NAME OF THE COLLABORATION %%%%

% Huge boldface
\def\hbabar{\mbox{{\huge\bf\sl B}\hspace{-0.1em}{\LARGE\bf\sl A}\hspace{-0.03em}{\huge\bf\sl B}\hspace{-0.1em}{\LARGE\bf\sl A\hspace{-0.03em}R}}}
% LARGE
\def\Lbabar{\mbox{{\LARGE\sl B}\hspace{-0.15em}{\Large\sl A}\hspace{-0.07em}{\LARGE\sl B}\hspace{-0.15em}{\Large\sl A\hspace{-0.02em}R}}}
% Large
\def\lbabar{\mbox{{\large\sl B}\hspace{-0.4em} {\normalsize\sl A}\hspace{-0.03em}{\large\sl B}\hspace{-0.4em} {\normalsize\sl A\hspace{-0.02em}R}}}
% normal size
%\def\babar{\mbox{\sl B\hspace{-0.4em} {\small\sl A}\hspace{-0.37em} \sl B\hspace{-0.4em} {\small\sl A\hspace{-0.02em}R}}}
% replace normalsize with scalable version       dbm 7/4/00
\usepackage{relsize}
\def\babar{\mbox{\slshape B\kern-0.1em{\smaller A}\kern-0.1em
    B\kern-0.1em{\smaller A\kern-0.2em R}}}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%   LEPTONS   %%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\let\emi\en
\def\electron   {\ensuremath{e}\xspace}
\def\en         {\ensuremath{e^-}\xspace}   % electron negative (\em is taken)
\def\ep         {\ensuremath{e^+}\xspace}
\def\epm        {\ensuremath{e^\pm}\xspace} 
\def\epem       {\ensuremath{e^+e^-}\xspace}
\def\ee         {\ensuremath{e^-e^-}\xspace}

\def\mmu        {\ensuremath{\mu}\xspace}
\def\mup        {\ensuremath{\mu^+}\xspace}
\def\mun        {\ensuremath{\mu^-}\xspace} % muon negative (\mum is taken)
\def\mumu       {\ensuremath{\mu^+\mu^-}\xspace}
\def\mtau       {\ensuremath{\tau}\xspace}

\def\taup       {\ensuremath{\tau^+}\xspace}
\def\taum       {\ensuremath{\tau^-}\xspace}
\def\tautau     {\ensuremath{\tau^+\tau^-}\xspace}

\def\ellm       {\ensuremath{\ell^-}\xspace}
\def\ellp       {\ensuremath{\ell^+}\xspace}
\def\ellell     {\ensuremath{\ell^+ \ell^-}\xspace}

\def\nub        {\ensuremath{\overline{\nu}}\xspace}
\def\nunub      {\ensuremath{\nu{\overline{\nu}}}\xspace}
\def\nub        {\ensuremath{\overline{\nu}}\xspace}
\def\nunub      {\ensuremath{\nu{\overline{\nu}}}\xspace}
\def\nue        {\ensuremath{\nu_e}\xspace}
\def\nueb       {\ensuremath{\nub_e}\xspace}
\def\nuenueb    {\ensuremath{\nue\nueb}\xspace}
\def\num        {\ensuremath{\nu_\mu}\xspace}
\def\numb       {\ensuremath{\nub_\mu}\xspace}
\def\numnumb    {\ensuremath{\num\numb}\xspace}
\def\nut        {\ensuremath{\nu_\tau}\xspace}
\def\nutb       {\ensuremath{\nub_\tau}\xspace}
\def\nutnutb    {\ensuremath{\nut\nutb}\xspace}
\def\nul        {\ensuremath{\nu_\ell}\xspace}
\def\nulb       {\ensuremath{\nub_\ell}\xspace}
\def\nulnulb    {\ensuremath{\nul\nulb}\xspace}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%  PHOTONS  %%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\def\g     {\ensuremath{\gamma}\xspace}
\def\gaga  {\ensuremath{\gamma\gamma}\xspace}  %% changed from \gg, which is >>
\def\ggstar{\ensuremath{\gamma\gamma^*}\xspace}

\def\ega    {\ensuremath{e\gamma}\xspace}
\def\game   {\ensuremath{\gamma e^-}\xspace}
\def\epemg  {\ensuremath{e^+e^-\gamma}\xspace}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%  Other GAUGE BOSONS  %%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\def\H      {\ensuremath{H^0}\xspace}
\def\Hp     {\ensuremath{H^+}\xspace}
\def\Hm     {\ensuremath{H^-}\xspace}
\def\Hpm    {\ensuremath{H^\pm}\xspace}
\def\W      {\ensuremath{W}\xspace}
\def\Wp     {\ensuremath{W^+}\xspace}
\def\Wm     {\ensuremath{W^-}\xspace}
\def\Wpm    {\ensuremath{W^\pm}\xspace}
\def\Z      {\ensuremath{Z^0}\xspace}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%   QUARKS   %%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\def\q     {\ensuremath{q}\xspace}
\def\qbar  {\ensuremath{\overline q}\xspace}
\def\qqbar {\ensuremath{q\overline q}\xspace}
\def\u     {\ensuremath{u}\xspace}
\def\ubar  {\ensuremath{\overline u}\xspace}
\def\uubar {\ensuremath{u\overline u}\xspace}
\def\d     {\ensuremath{d}\xspace}
\def\dbar  {\ensuremath{\overline d}\xspace}
\def\ddbar {\ensuremath{d\overline d}\xspace}
\def\s     {\ensuremath{s}\xspace}
\def\sbar  {\ensuremath{\overline s}\xspace}
\def\ssbar {\ensuremath{s\overline s}\xspace}
\def\c     {\ensuremath{c}\xspace}
\def\cbar  {\ensuremath{\overline c}\xspace}
\def\ccbar {\ensuremath{c\overline c}\xspace}
\def\b     {\ensuremath{b}\xspace}
\def\bbar  {\ensuremath{\overline b}\xspace}
\def\bbbar {\ensuremath{b\overline b}\xspace}
\def\t     {\ensuremath{t}\xspace}
\def\tbar  {\ensuremath{\overline t}\xspace}
\def\tbar  {\ensuremath{\overline t}\xspace}
\def\ttbar {\ensuremath{t\overline t}\xspace}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%% LIGHT MESONS  %%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\def\piz   {\ensuremath{\pi^0}\xspace}
\def\pizs  {\ensuremath{\pi^0\mbox\,\rm{s}}\xspace}
\def\ppz   {\ensuremath{\pi^0\pi^0}\xspace}
\def\pip   {\ensuremath{\pi^+}\xspace}
\def\pim   {\ensuremath{\pi^-}\xspace}
\def\pipi  {\ensuremath{\pi^+\pi^-}\xspace}
\def\pipm  {\ensuremath{\pi^\pm}\xspace}
\def\pimp  {\ensuremath{\pi^\mp}\xspace}

\def\kaon  {\ensuremath{K}\xspace}
%%% do NOT use ensuremath here
\def\Kbar  {\kern 0.2em\overline{\kern -0.2em K}{}\xspace}
\def\Kb    {\ensuremath{\Kbar}\xspace}
\def\Kz    {\ensuremath{K^0}\xspace}
\def\Kzb   {\ensuremath{\Kbar^0}\xspace}
\def\KzKzb {\ensuremath{\Kz \kern -0.16em \Kzb}\xspace}
\def\Kp    {\ensuremath{K^+}\xspace}
\def\Km    {\ensuremath{K^-}\xspace}
\def\Kpm   {\ensuremath{K^\pm}\xspace}
\def\Kmp   {\ensuremath{K^\mp}\xspace}
\def\KpKm  {\ensuremath{\Kp \kern -0.16em \Km}\xspace}
\def\KS    {\ensuremath{K^0_{\scriptscriptstyle S}}\xspace} 
\def\KL    {\ensuremath{K^0_{\scriptscriptstyle L}}\xspace} 
\def\Kstarz  {\ensuremath{K^{*0}}\xspace}
\def\Kstarzb {\ensuremath{\Kbar^{*0}}\xspace}
\def\Kstar   {\ensuremath{K^*}\xspace}
\def\Kstarb  {\ensuremath{\Kbar^*}\xspace}
\def\Kstarp  {\ensuremath{K^{*+}}\xspace}
\def\Kstarm  {\ensuremath{K^{*-}}\xspace}
\def\Kstarpm {\ensuremath{K^{*\pm}}\xspace}
\def\Kstarmp {\ensuremath{K^{*\mp}}\xspace}

\newcommand{\etapr}{\ensuremath{\eta^{\prime}}\xspace}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%% HEAVY MESONS  %%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%% do NOT use ensuremath here
\def\Dbar    {\kern 0.2em\overline{\kern -0.2em D}{}\xspace}
\def\Db      {\ensuremath{\Dbar}\xspace}
\def\Dz      {\ensuremath{D^0}\xspace}
\def\Dzb     {\ensuremath{\Dbar^0}\xspace}
\def\DzDzb   {\ensuremath{\Dz {\kern -0.16em \Dzb}}\xspace}
\def\Dp      {\ensuremath{D^+}\xspace}
\def\Dm      {\ensuremath{D^-}\xspace}
\def\Dpm     {\ensuremath{D^\pm}\xspace}
\def\Dmp     {\ensuremath{D^\mp}\xspace}
\def\DpDm    {\ensuremath{\Dp {\kern -0.16em \Dm}}\xspace}
\def\Dstar   {\ensuremath{D^*}\xspace}
\def\Dstarb  {\ensuremath{\Dbar^*}\xspace}
\def\Dstarz  {\ensuremath{D^{*0}}\xspace}
\def\Dstarzb {\ensuremath{\Dbar^{*0}}\xspace}
\def\Dstarp  {\ensuremath{D^{*+}}\xspace}
\def\Dstarm  {\ensuremath{D^{*-}}\xspace}
\def\Ds      {\ensuremath{D^+_s}\xspace}
\def\Dsb     {\ensuremath{\Dbar^+_s}\xspace}
\def\Dss     {\ensuremath{D^*_s}\xspace}

% Obsolete
\newcommand{\dstr}{\ensuremath{\Dstar}\xspace}
\newcommand{\dstrstr}{\ensuremath{D^{**}}\xspace}
\newcommand{\dsp}{\ensuremath{\Dstarp}\xspace}
\newcommand{\dsm}{\ensuremath{\Dstarm}\xspace}
\newcommand{\dsz}{\ensuremath{\Dstarz}\xspace}


\def\B       {\ensuremath{B}\xspace}
%%% do NOT use ensuremath here
\def\Bbar    {\kern 0.18em\overline{\kern -0.18em B}{}\xspace}
\def\Bb      {\ensuremath{\Bbar}\xspace}
\def\BB      {\ensuremath{B\Bbar}\xspace} 
\def\Bz      {\ensuremath{B^0}\xspace}
\def\Bzb     {\ensuremath{\Bbar^0}\xspace}
\def\BzBzb   {\ensuremath{\Bz {\kern -0.16em \Bzb}}\xspace}
\def\Bu      {\ensuremath{B^+}\xspace}
\def\Bub     {\ensuremath{B^-}\xspace}
\def\Bp      {\ensuremath{\Bu}\xspace}
\def\Bm      {\ensuremath{\Bub}\xspace}
\def\Bpm     {\ensuremath{B^\pm}\xspace}
\def\Bmp     {\ensuremath{B^\mp}\xspace}
\def\BpBm    {\ensuremath{\Bu {\kern -0.16em \Bub}}\xspace}
\def\Bs      {\ensuremath{B_s}\xspace}
\def\Bsb     {\ensuremath{\Bbar_s}\xspace}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%% ONIA %%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\def\jpsi     {\ensuremath{{J\mskip -3mu/\mskip -2mu\psi\mskip 2mu}}\xspace}
\def\psitwos  {\ensuremath{\psi{(2S)}}\xspace}
\def\psiprpr  {\ensuremath{\psi(3770)}\xspace}
\def\etac     {\ensuremath{\eta_c}\xspace}
\def\chiczero {\ensuremath{\chi_{c0}}\xspace}
\def\chicone  {\ensuremath{\chi_{c1}}\xspace}
\def\chictwo  {\ensuremath{\chi_{c2}}\xspace}
\mathchardef\Upsilon="7107
\def\Y#1S{\ensuremath{\Upsilon{(#1S)}}\xspace}% no space before {...}!
\def\OneS  {\Y1S}
\def\TwoS  {\Y2S}
\def\ThreeS{\Y3S}
\def\FourS {\Y4S}
\def\FiveS {\Y5S}

%\def\chic1{\ensuremath{\chi_{c1}}}
%\def\chic2{\ensuremath{\chi_{c2}}}
%\def\chic3{\ensuremath{\chi_{c3}}}
\def\chic#1{\ensuremath{\chi_{c#1}}\xspace} % dbm


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%% BARYONS %%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\def\proton      {\ensuremath{p}\xspace}
\def\antiproton  {\ensuremath{\overline p}\xspace}
\def\neutron     {\ensuremath{n}\xspace}
\def\antineutron {\ensuremath{\overline n}\xspace}

\mathchardef\Deltares="7101
\mathchardef\Xi="7104
\mathchardef\Lambda="7103
\mathchardef\Sigma="7106
\mathchardef\Omega="710A

%%% do NOT use ensuremath here
\def\Deltabar{\kern 0.25em\overline{\kern -0.25em \Deltares}{}\xspace}
\def\Lbar{\kern 0.2em\overline{\kern -0.2em\Lambda\kern 0.05em}\kern-0.05em{}\xspace}
\def\Sigbar{\kern 0.2em\overline{\kern -0.2em \Sigma}{}\xspace}
\def\Xibar{\kern 0.2em\overline{\kern -0.2em \Xi}{}\xspace}
\def\Obar{\kern 0.2em\overline{\kern -0.2em \Omega}{}\xspace}
\def\Nbar{\kern 0.2em\overline{\kern -0.2em N}{}\xspace}
\def\Xb{\kern 0.2em\overline{\kern -0.2em X}{}\xspace}

\def\X {\ensuremath{X}\xspace}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%% TAU BRANCHING FRACTIONS %%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\def\BR         {{\ensuremath{\cal B}\xspace}}
\def\BRtauptoe  {\ensuremath{\BR(\taup \to \ep)}\xspace}
\def\BRtaumtoe  {\ensuremath{\BR(\taum \to \en)}\xspace}
\def\BRtauptomu {\ensuremath{\BR(\taup \to \mup)}\xspace}
\def\BRtaumtomu {\ensuremath{\BR(\taum \to \mun)}\xspace}



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%  LIGHT HADRON DECAYS %%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\newcommand{\etaprepp}{\ensuremath{\etapr \to \eta \pipi}\xspace}
\newcommand{\etaprrg} {\ensuremath{\etapr \to \rho^0 \g}\xspace}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%  B DECAYS   %%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\def\bpsiks     {\ensuremath{\Bz \to \jpsi \KS}\xspace}
\def\bpsikst    {\ensuremath{\Bz \to \jpsi \Kstar}\xspace}
\def\bpsikl     {\ensuremath{\Bz \to \jpsi \KL}\xspace}
\def\bpsikzeropi{\ensuremath{\Bz \to \jpsi \Kstarz (\to \KL \piz)}\xspace}
\def\bpsikpluspi{\ensuremath{\Bu \to \jpsi \Kstarp (\to \KL \pip)}\xspace}
\def\bpsikpi    {\ensuremath{\Bz/\Bzb \to \jpsi (\to \mumu) \Kpm \pimp}\xspace}
\def\bupsik     {\ensuremath{\Bpm \to \jpsi (\to \mumu) \Kpm}\xspace}
\def\bpsiX      {\ensuremath{\Bz \to \jpsi \X}\xspace}

\def\Bzbtomu    {\ensuremath{\Bzb \to \mu \X}\xspace}
\def\Bzbtox     {\ensuremath{\Bzb \to \X}\xspace}
\def\Bztopipi   {\ensuremath{\Bz \to \pipi}\xspace}
\def\Bztokpi    {\ensuremath{\Bz \to \Kpm \pimp}\xspace}
\def\Bztorhopi  {\ensuremath{\Bz \to \rho^+ \pim}\xspace}
\def\Bztorhorho {\ensuremath{\Bz \to \rho \rho}\xspace}
\def\Bztokrho   {\ensuremath{\Bz \to K \rho}\xspace}
\def\Bztokstpi  {\ensuremath{\Bz \to \Kstar \pi}\xspace}
\def\Bztoapi    {\ensuremath{\Bz \to a_1 \pi}\xspace}
\def\Bztodd     {\ensuremath{\Bz \to \DpDm}\xspace}
\def\Bztodstd   {\ensuremath{\Bz \to \Dstarp \Dm}\xspace}
\def\Bztodstdst {\ensuremath{\Bz \to \Dstarp \Dstarm}\xspace}

\def\BtoDK      {\ensuremath{B \to DK}\xspace}
\def\Btodstlnu  {\ensuremath{B \to \Dstar \ell \nu}\xspace}
\def\Btodstdlnu {\ensuremath{B \to \Dstar(D) \ell \nu}\xspace}
\def\Btorholnu  {\ensuremath{B \to \rho \ell \nu}\xspace}
\def\Btopilnu   {\ensuremath{B \to \pi \ell \nu}\xspace}

\def\Btoetah    {\ensuremath{B \to \eta h}\xspace}
\def\Btoetaph   {\ensuremath{B \to \etapr h}\xspace}

\newcommand{\Betaprks}{\ensuremath{\Bz \to \etapr \KS}\xspace}
\newcommand{\Betaprkz}{\ensuremath{\Bz \to \etapr \Kz}\xspace}

\def\btosgam    {\ensuremath{b \to s \g}\xspace}
\def\btodgam    {\ensuremath{b \to d \g}\xspace}
\def\btosll     {\ensuremath{b \to s \ellell}\xspace}
\def\btosnunu   {\ensuremath{b \to s \nunub}\xspace}
\def\btosgaga   {\ensuremath{b \to s \gaga}\xspace}
\def\btosglue   {\ensuremath{b \to s g}\xspace}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%  Y(4S) DECAYS   %%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\def\upsbb   {\ensuremath{\FourS \to \BB}\xspace}
\def\upsbzbz {\ensuremath{\FourS \to \BzBzb}\xspace}
\def\upsbpbm {\ensuremath{\FourS \to \BpBm}\xspace}
\def\upspsikl{\ensuremath{\FourS \to (\bpsikl) (\Bzbtox)}\xspace}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%  TAU DECAYS   %%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\def\tauptoe    {\ensuremath{\taup \to \ep \nunub}\xspace}
\def\taumtoe    {\ensuremath{\taum \to \en \nunub}\xspace}
\def\tauptomu   {\ensuremath{\taup \to \mup \nunub}\xspace}
\def\taumtomu   {\ensuremath{\taum \to \mun \nunub}\xspace}
\def\tauptopi   {\ensuremath{\taup \to \pip \nub}\xspace}
\def\taumtopi   {\ensuremath{\taum \to \pim \nu}\xspace}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%% GAMMA-GAMMA REACTIONS %%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\def\ggtopi     {\ensuremath{\gaga \to \pipi}\xspace}
\def\ggtopiz    {\ensuremath{\gaga \to \ppz}\xspace}
\def\ggstox     {\ensuremath{\ggstar \to \X(1420) \to \kaon \kaon \pi}\xspace}
\def\ggstoeta   {\ensuremath{\ggstar \to \eta(550) \to \pipi \piz}\xspace}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%   KINEMATICS    %%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\def\ptot       {\mbox{$p$}\xspace}
%\def\pxy        {\mbox{$p_{\rm t}$}
\def\pxy        {\mbox{$p_T$}\xspace}
%\def\pt         {\mbox{$p_{\rm t}$}\xspace}
\def\pt         {\mbox{$p_T$}\xspace}
\def\mes        {\mbox{$m_{\rm ES}$}\xspace}
\def\mec        {\mbox{$m_{\rm EC}$}\xspace}
\def\DeltaE     {\mbox{$\Delta E$}\xspace}

\def\pbcm {\ensuremath{p^*_{\Bz}}\xspace}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%   GEOMETRY    %%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\def\mphi       {\mbox{$\phi$}\xspace}
\def\mtheta     {\mbox{$\theta$}\xspace}
\def\ctheta     {\mbox{$\cos\theta$}\xspace}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%% ENERGY AND MOMENTUM %%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\newcommand{\tev}{\ensuremath{\mathrm{\,Te\kern -0.1em V}}\xspace}
\newcommand{\gev}{\ensuremath{\mathrm{\,Ge\kern -0.1em V}}\xspace}
\newcommand{\mev}{\ensuremath{\mathrm{\,Me\kern -0.1em V}}\xspace}
\newcommand{\kev}{\ensuremath{\mathrm{\,ke\kern -0.1em V}}\xspace}
\newcommand{\ev}{\ensuremath{\mathrm{\,e\kern -0.1em V}}\xspace}
\newcommand{\gevc}{\ensuremath{{\mathrm{\,Ge\kern -0.1em V\!/}c}}\xspace}
\newcommand{\mevc}{\ensuremath{{\mathrm{\,Me\kern -0.1em V\!/}c}}\xspace}
\newcommand{\gevcc}{\ensuremath{{\mathrm{\,Ge\kern -0.1em V\!/}c^2}}\xspace}
\newcommand{\mevcc}{\ensuremath{{\mathrm{\,Me\kern -0.1em V\!/}c^2}}\xspace}
%\def\ev   {\ensuremath{\rm \,e\kern -0.08em V}}
%\def\kev  {\ensuremath{\rm \,ke\kern -0.08em V}} 
%\def\mev  {\ensuremath{\rm \,Me\kern -0.08em V}} 
%\def\gev  {\ensuremath{\rm \,Ge\kern -0.08em V}} 
%\def\gevc {\ensuremath{\rm \,Ge\kern -0.08em V\!/c}} 
%\def\gevc {\ensuremath{{\rm \,Ge\kern -0.08em V\!/}c}} 
%\def\tev  {\ensuremath{\rm \,Te\kern -0.08em V}}
%\def\mevc {\ensuremath{\rm \,Me\kern -0.08em V\!/c}} 
%\def\mevc {\ensuremath{{\rm \,Me\kern -0.08em V\!/}c}} 
%\def\gevcc{\ensuremath{\rm \,Ge\kern -0.08em V\!/c^2}} 
%\def\mevcc{\ensuremath{\rm \,Me\kern -0.08em V\!/c^2}} 
%\def\gevcc{\ensuremath{{\rm \,Ge\kern -0.08em V\!/}c^2}} 
%\def\mevcc{\ensuremath{{\rm \,Me\kern -0.08em V\!/}c^2}} 


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%% DISTANCE AND AREA %%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\def\syin {\ensuremath{^{\prime\prime}}\xspace}
\def\inch   {\ensuremath{\rm \,in}\xspace} % \in is taken
\def\ft   {\ensuremath{\rm \,ft}\xspace}
\def\km   {\ensuremath{\rm \,km}\xspace}
\def\m    {\ensuremath{\rm \,m}\xspace}
\def\cm   {\ensuremath{\rm \,cm}\xspace}
\def\cma  {\ensuremath{{\rm \,cm}^2}\xspace}
\def\mm   {\ensuremath{\rm \,mm}\xspace}
\def\mma  {\ensuremath{{\rm \,mm}^2}\xspace}
%\def\mum  {\ensuremath{\rm \,\mum}\xspace}
\def\mum  {\ensuremath{\,\mu\rm m}\xspace}%% mu meter 
%\def\muma {\ensuremath{\rm \,\mum}^2\xspace}
\def\muma       {\ensuremath{\,\mu\rm m^2}\xspace}
\def\nm   {\ensuremath{\rm \,nm}\xspace}
\def\fm   {\ensuremath{\rm \,fm}\xspace}
\def\nm         {\ensuremath{\rm \,nm}\xspace}   %% nanometer
\def\nb         {\ensuremath{\rm \,nb}\xspace}
%
\def\barn{\ensuremath{\rm \,b}\xspace}
\def\barnhyph{\ensuremath{\rm -b}\xspace}
\def\mbarn{\ensuremath{\rm \,mb}\xspace}
\def\mbarnhyph{\ensuremath{\rm -mb}\xspace}
\def\pb {\ensuremath{\rm \,pb}\xspace}
\def\invpb {\ensuremath{\mbox{\,pb}^{-1}}\xspace}
\def\fb   {\ensuremath{\mbox{\,fb}}\xspace}
\def\invfb   {\ensuremath{\mbox{\,fb}^{-1}}\xspace}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%% TIME AND MASS  %%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\def\mus  {\ensuremath{\rm \,\mus}\xspace}
\def\ns   {\ensuremath{\rm \,ns}\xspace}
\def\ps   {\ensuremath{\rm \,ps}\xspace}
\def\fs   {\ensuremath{\rm \,fs}\xspace}
\def\gm   {\ensuremath{\rm \,g}\xspace}

%%\def\s{\ensuremath{\rm {\,s}}} %% second - this displays nothing  - why?
\def\sec{\ensuremath{\rm {\,s}}\xspace}       %% second - this works - jw 4/19
\def\ms         {\ensuremath{{\rm \,ms}}\xspace}     %% millisecond
\def\mus        {\ensuremath{\,\mu{\rm s}}\xspace}    %% microsecond
\def\ns         {\ensuremath{{\rm \,ns}}\xspace}      %% nanosecond
\def\ps         {\ensuremath{{\rm \,ps}}\xspace}  %% picosecond


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%   MISCELLANEOUS %%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\def\Xrad {\ensuremath{X_0}\xspace}
\def\NIL{\ensuremath{\lambda_{int}}\xspace}
\let\dgr\degrees


%\def\m          {\ensuremath{\rm \,m}}    %% meter
%\def\ma         {\ensuremath{\rm \,m}^2}  %% meter squared
%\def\cm         {\ensuremath{\rm \,cm}}   %% centimeter
%\def\cma        {\ensuremath{\rm \,cm}^2} %% centimeter squared
\def\cms         {\ensuremath{{\rm \,cm}^{-2} {\rm s}^{-1}}\xspace}
%\def\mm         {\ensuremath{\rm \,mm}}   %% millimeter
%\def\mma        {\ensuremath{\rm \,mm}^2} %% millimeter squared
%\def\mum        {\ensuremath{\,\mu\rm m}} %% mu meter
%\def\muma       {\ensuremath{\,\mu\rm m^2}}


\def\mic  {\ensuremath{\,\mu{\rm C}}\xspace}
\def\krad {\ensuremath{\rm \,krad}\xspace}
\def\cmc  {\ensuremath{{\rm \,cm}^3}\xspace}
\def\yr   {\ensuremath{\rm \,yr}\xspace}
\def\hr   {\ensuremath{\rm \,hr}\xspace}
\def\degc {\ensuremath{^\circ}{C}\xspace}
\def\degk {\ensuremath {\rm K}\xspace}
\def\degrees{\ensuremath{^{\circ}}\xspace}
\def\mrad{\ensuremath{\rm \,mrad}\xspace}               %% milliradian
\def\rad{\ensuremath{\rm \,rad}\xspace}
\def\mradhyph{\ensuremath{\rm -mr}\xspace}
%
\def\sx    {\ensuremath{\sigma_x}\xspace}    
\def\sy    {\ensuremath{\sigma_y}\xspace}   
\def\sz    {\ensuremath{\sigma_z}\xspace}    

%\renewcommand{\bar}[1]{\overline{#1}}  

% Some more (from Helen)
%\def\O{{\ensuremath{\cal O}}}  !!! This is a predefined LaTeX symbol !!!
\def\order{{\ensuremath{\cal O}}\xspace}
\def\L{{\ensuremath{\cal L}}\xspace}
\def\calL{{\ensuremath{\cal L}}\xspace}
%\def\S{{\ensuremath{\cal S}}}  !!! This is a predefined LaTeX symbol !!!
\def\calS{{\ensuremath{\cal S}}\xspace}
\def\calA{{\ensuremath{\cal A}}\xspace}
\def\calD{{\ensuremath{\cal D}}\xspace}
\def\calR{{\ensuremath{\cal R}}\xspace}

%% Arrows:
\def\ra                 {\ensuremath{\rightarrow}\xspace}
\def\to                 {\ensuremath{\rightarrow}\xspace}


\newcommand{\stat}{\ensuremath{\mathrm{(stat)}}\xspace}
\newcommand{\syst}{\ensuremath{\mathrm{(syst)}}\xspace}


\def\pep2{PEP-II}
\def\BF{$B$ Factory}
\def\abf {asymmetric \BF}
\def\sx    {\ensuremath{\sigma_x}\xspace}     
\def\sy    {\ensuremath{\sigma_y}\xspace}   
\def\sz    {\ensuremath{\sigma_z}\xspace}


\newcommand{\inverse}{\ensuremath{^{-1}}\xspace}
\newcommand{\dedx}{\ensuremath{\mathrm{d}\hspace{-0.1em}E/\mathrm{d}x}\xspace}
\newcommand{\chisq}{\ensuremath{\chi^2}\xspace}
\newcommand{\delm}{\ensuremath{m_{\dstr}-m_{\dz}}\xspace}
\newcommand{\lum} {\ensuremath{\mathcal{L}}\xspace}

\def\gsim{{~\raise.15em\hbox{$>$}\kern-.85em
          \lower.35em\hbox{$\sim$}~}\xspace}
\def\lsim{{~\raise.15em\hbox{$<$}\kern-.85em
          \lower.35em\hbox{$\sim$}~}\xspace}

\def\qsq                {\ensuremath{q^2}\xspace}


% Data processing
\def\kbytes     {\ensuremath{{\rm \,kbytes}}\xspace}
\def\kbsps      {\ensuremath{{\rm \,kbytes/s}}\xspace}
\def\kbits      {\ensuremath{{\rm \,kbits}}\xspace}
\def\kbsps      {\ensuremath{{\rm \,kbits/s}}\xspace}
\def\mbsps      {\ensuremath{{\rm \,Mbits/s}}\xspace}
\def\mbytes     {\ensuremath{{\rm \,Mbytes}}\xspace}
\def\mbps       {\ensuremath{{\rm \,Mbyte/s}}\xspace}
\def\mbsps      {\ensuremath{{\rm \,Mbytes/s}}\xspace}
\def\gbsps      {\ensuremath{{\rm \,Gbits/s}}\xspace}
\def\gbytes     {\ensuremath{{\rm \,Gbytes}}\xspace}
\def\gbsps      {\ensuremath{{\rm \,Gbytes/s}}\xspace}
\def\tbytes     {\ensuremath{{\rm \,Tbytes}}\xspace}
\def\tbpy       {\ensuremath{{\rm \,Tbytes/yr}}\xspace}
%




% QCD parameters

\newcommand{\as}{\ensuremath{\alpha_{\scriptscriptstyle S}}\xspace}
\newcommand{\MSb}{\ensuremath{\overline{\mathrm{MS}}}\xspace}
\newcommand{\LMSb}{%
  \ensuremath{\Lambda_{\overline{\scriptscriptstyle\mathrm{MS}}}}\xspace
}

% Electroweak parameters

\newcommand{\tw}{\ensuremath{\theta_{\scriptscriptstyle W}}\xspace}
\newcommand{\twb}{%
  \ensuremath{\overline{\theta}_{\scriptscriptstyle W}}\xspace
}
\newcommand{\Afb}[1]{{\ensuremath{A_{\scriptscriptstyle FB}^{#1}}}\xspace}
\newcommand{\gv}[1]{{\ensuremath{g_{\scriptscriptstyle V}^{#1}}}\xspace}
\newcommand{\ga}[1]{{\ensuremath{g_{\scriptscriptstyle A}^{#1}}}\xspace}
\newcommand{\gvb}[1]{{\ensuremath{\overline{g}_{\scriptscriptstyle V}^{#1}}}\xspace}
\newcommand{\gab}[1]{{\ensuremath{\overline{g}_{\scriptscriptstyle A}^{#1}}}\xspace}


% CKM, CP violation

\def\eps{\varepsilon\xspace}
\def\epsK{\varepsilon_K\xspace}
\def\epsB{\varepsilon_B\xspace}
\def\epsp{\varepsilon^\prime_K\xspace}

\def\CP                {\ensuremath{C\!P}\xspace}
%\def\CPT               {\ensuremath{C\!P\!T}\xspace}
\def\CPT               {\ensuremath{C\!PT}\xspace} % Looks better without \!

\def\epstag  {\ensuremath{\varepsilon_{\rm tag}}\xspace}
\def\tagfac  {\ensuremath{\epstag(1-2w)^2}\xspace}

\def\rhobar {\ensuremath{\overline \rho}\xspace}
\def\etabar {\ensuremath{\overline \eta}\xspace}
%\def\paramest {\ensuremath{{\hat A}, {\hat \rho}, {\hat \eta} }}
%\def\ssparamest {\ensuremath{{\hat A}, {\hat {\sin 2 \alpha}}, 
%{\hat {\sin 2 \beta}} }}
\def\meas {\ensuremath{|V_{cb}|, |\frac{V_{ub}}{V_{cb}}|, 
|\varepsilon_K|, \Delta m_{B_d}}\xspace}

\def\Vud  {\ensuremath{|V_{ud}|}\xspace}
\def\Vcd  {\ensuremath{|V_{cd}|}\xspace}
\def\Vtd  {\ensuremath{|V_{td}|}\xspace}
\def\Vus  {\ensuremath{|V_{us}|}\xspace}
\def\Vcs  {\ensuremath{|V_{cs}|}\xspace}
\def\Vts  {\ensuremath{|V_{ts}|}\xspace}
\def\Vub  {\ensuremath{|V_{ub}|}\xspace}
\def\Vcb  {\ensuremath{|V_{cb}|}\xspace}
\def\Vtb  {\ensuremath{|V_{tb}|}\xspace}

%\def\sa{${\sin\! 2 \alpha  }$\xspace}
%\def\sb{${\sin\! 2 \beta   }$\xspace}
%\def\sg{${\sin\! 2 \gamma  }$\xspace}

% added by Gautier for tagging, tagmix, and sin2beta
\def\stwoa{\ensuremath{\sin\! 2 \alpha  }\xspace}
\def\stwob{\ensuremath{\sin\! 2 \beta   }\xspace}
\def\stwog{\ensuremath{\sin\! 2 \gamma  }\xspace}
\def\mistag{\ensuremath{w}\xspace}
\def\dilution{\ensuremath{\cal D}\xspace}
\def\deltaz{\ensuremath{{\rm \Delta}z}\xspace}
\def\deltat{\ensuremath{{\rm \Delta}t}\xspace}
\def\deltamd{\ensuremath{{\rm \Delta}m_d}\xspace}

\newcommand{\fsubd}{\ensuremath{f_D}}\xspace
\newcommand{\fds}{\ensuremath{f_{D_s}}\xspace}
\newcommand{\fsubb}{\ensuremath{f_B}\xspace}
\newcommand{\fbd}{\ensuremath{f_{B_d}}\xspace}
\newcommand{\fbs}{\ensuremath{f_{B_s}}\xspace}
\newcommand{\bsubb}{\ensuremath{B_B}\xspace}
\newcommand{\bbd}{\ensuremath{B_{B_d}}\xspace}
\newcommand{\bbs}{\ensuremath{B_{B_s}}\xspace}
\newcommand{\rgbb}{\ensuremath{\hat{B}_B}\xspace}
\newcommand{\rgbbd}{\ensuremath{\hat{B}_{B_d}}\xspace}
\newcommand{\rgbbs}{\ensuremath{\hat{B}_{B_s}}\xspace}
\newcommand{\rgbk}{\ensuremath{\hat{B}_K}\xspace}
\newcommand{\lqcd}{\ensuremath{\Lambda_{\mathrm{QCD}}}\xspace}

%\newcommand{\eqref}[1]{Eq.~(\ref{eq:#1})}
\newcommand{\secref}[1]{Section~\ref{sec:#1}}
\newcommand{\subsecref}[1]{Section~\ref{subsec:#1}}
\newcommand{\figref}[1]{Figure~\ref{fig:#1}}
\newcommand{\tabref}[1]{Table~\ref{tab:#1}}






% Journal References

% These bases are useful for ``submitted to'' when no volume is needed
\newcommand{\epjBase}        {Eur.\ Phys.\ Jour.\xspace}
\newcommand{\jprlBase}       {Phys.\ Rev.\ Lett.\xspace}
\newcommand{\jprBase}        {Phys.\ Rev.\xspace}
\newcommand{\jplBase}        {Phys.\ Lett.\xspace}
\newcommand{\nimBaseA}       {Nucl.\ Instr.\ Meth.\xspace}
\newcommand{\nimBaseB}       {Nucl.\ Instr.\ and Meth.\xspace}
\newcommand{\nimBaseC}       {Nucl.\ Instr.\ and Methods\xspace}
\newcommand{\nimBaseD}       {Nucl.\ Instrum.\ Methods\xspace}
\newcommand{\npBase}         {Nucl.\ Phys.\xspace}
\newcommand{\zpBase}         {Z.\ Phys.\xspace}


\newcommand{\apas}      [1]  {{Acta Phys.\ Austr.\ Suppl.\ {\bf #1}}}
\newcommand{\app}       [1]  {{Acta Phys.\ Polon.\ {\bf #1}}}
\newcommand{\ace}       [1]  {{Adv.\ Cry.\ Eng.\ {\bf #1}}}
\newcommand{\anp}       [1]  {{Adv.\ Nucl.\ Phys.\ {\bf #1}}}
\newcommand{\annp}      [1]  {{Ann.\ Phys.\ {\bf #1}}}
\newcommand{\araa}      [1]  {{Ann.\ Rev.\ Astr.\ Ap.\ {\bf #1}}}
\newcommand{\arnps}     [1]  {{Ann.\ Rev.\ Nucl.\ Part.\ Sci.\ {\bf #1}}}
\newcommand{\arns}      [1]  {{Ann.\ Rev.\ Nucl.\ Sci.\ {\bf #1}}}
\newcommand{\appopt}    [1]  {{Appl.\ Opt.\ {\bf #1}}}
\newcommand{\japj}      [1]  {{Astro.\ Phys.\ J.\ {\bf #1}}}
\newcommand{\baps}      [1]  {{Bull.\ Am.\ Phys.\ Soc.\ {\bf #1}}}
\newcommand{\seis}      [1]  {{Bull.\ Seismological Soc.\ of Am.\ {\bf #1}}}
\newcommand{\cmp}       [1]  {{Commun.\ Math.\ Phys.\ {\bf #1}}}
\newcommand{\cnpp}      [1]  {{Comm.\ Nucl.\ Part.\ Phys.\ {\bf #1}}}
\newcommand{\cpc}       [1]  {{Comput.\ Phys.\ Commun.\ {\bf #1}}}
\newcommand{\epj}       [1]  {\epjBase\ {\bf #1}}
%\newcommand{\epjc}      [1]  {{Eur.\ Phys.\ Jour.\ C~{\bf #1}}}
\newcommand{\epjc}      [1]  {\epjBase\ C~{\bf #1}}
\newcommand{\fizika}    [1]  {{Fizika~{\bf #1}}}
\newcommand{\fp}        [1]  {{Fortschr.\ Phys.\ {\bf #1}}}
\newcommand{\ited}      [1]  {{IEEE Trans.\ Electron.\ Devices~{\bf #1}}}
\newcommand{\itns}      [1]  {{IEEE Trans.\ Nucl.\ Sci.\ {\bf #1}}}
\newcommand{\ijqe}      [1]  {{IEEE J.\ Quantum Electron.\ {\bf #1}}}
\newcommand{\ijmp}      [1]  {{Int.\ Jour.\ Mod.\ Phys.\ {\bf #1}}}
\newcommand{\ijmpa}     [1]  {{Int.\ J.\ Mod.\ Phys.\ {\bf A{\bf #1}}}}
\newcommand{\jl}        [1]  {{JETP Lett.\ {\bf #1}}}
\newcommand{\jetp}      [1]  {{JETP~{\bf #1}}}
\newcommand{\jpg}       [1]  {{J.\ Phys.\ {\bf G{\bf #1}}}}
\newcommand{\jap}       [1]  {{J.\ Appl.\ Phys.\ {\bf #1}}}
\newcommand{\jmp}       [1]  {{J.\ Math.\ Phys.\ {\bf #1}}}
\newcommand{\jmes}      [1]  {{J.\ Micro.\ Elec.\ Sys.\ {\bf #1}}}
%\newcommand{\josa}      [1]  {{J.\ Opt.\ Soc.\ Am.\ {\bf #1}}}
\newcommand{\mpl}       [1]  {{Mod.\ Phys.\ Lett.\ {\bf #1}}}

%\newcommand{\nim}       [1]  {{Nucl.\ Instr.\ and Methods~{\bf #1}}}
\newcommand{\nim}       [1]  {\nimBaseC~{\bf #1}}
%\newcommand{\nima}      [1]  {{Nucl.\ Instr.\ Methods~{\bf A{\bf #1}}}}
\newcommand{\nima}      [1]  {\nimBaseC~A~{\bf #1}}

%\newcommand{\np}        [1]  {{Nucl.\ Phys.\ {\bf #1}}}
\newcommand{\np}        [1]  {\npBase\ {\bf #1}}
%\newcommand{\npb}       [1]  {{Nucl.\ Phys.\ {\bf B{\bf #1}}}}
\newcommand{\npb}       [1]  {\npBase\ B~{\bf #1}}
\newcommand{\npps}      [1]  {{Nucl.\ Phys.\ Proc.\ Suppl.\ {\bf #1}}}
\newcommand{\npaps}     [1]  {{Nucl.\ Phys.\ A~Proc.\ Suppl.\ {\bf #1}}}
\newcommand{\npbps}     [1]  {{Nucl.\ Phys.\ B~Proc.\ Suppl.\ {\bf #1}}}

\newcommand{\ncim}      [1]  {{Nuo.\ Cim.\ {\bf #1}}}
\newcommand{\optl}      [1]  {{Opt.\ Lett.\ {\bf #1}}}
\newcommand{\optcom}    [1]  {{Opt.\ Commun.\ {\bf #1}}}
\newcommand{\partacc}   [1]  {{Particle Acclerators~{\bf #1}}}
\newcommand{\pan}       [1]  {{Phys.\ Atom.\ Nuclei~{\bf #1}}}
\newcommand{\pflu}      [1]  {{Physics of Fluids~{\bf #1}}}
\newcommand{\ptoday}    [1]  {{Physics Today~{\bf #1}}}

%\newcommand{\jpl}       [1]  {{Phys.\ Lett.\ {\bf #1}}}      % dbm
\newcommand{\jpl}       [1]  {\jplBase\ {\bf #1}}
%\newcommand{\plb}       [1]  {{Phys.\ Lett.\ B~{\bf #1}}}   % dbm
\newcommand{\plb}       [1]  {\jplBase\ B~{\bf #1}}
\newcommand{\prep}      [1]  {{Phys.\ Rep.\ {\bf #1}}}
%\newcommand{\jprl}      [1]  {{Phys.\ Rev.\ Lett.\ {\bf #1}}} % dbm
\newcommand{\jprl}      [1]  {\jprlBase\ {\bf #1}}
%\newcommand{\pr}        [1]  {{Phys.\ Rev.\ {\bf #1}}}
\newcommand{\pr}        [1]  {\jprBase\ {\bf #1}}
%\newcommand{\jpra}      [1]  {{Phys.\ Rev.\ A~{\bf #1}}}
\newcommand{\jpra}      [1]  {\jprBase\ A~{\bf #1}}
%\newcommand{\jprd}      [1]  {{Phys.\ Rev.\ D~{\bf #1}}}
\newcommand{\jprd}      [1]  {\jprBase\ D~{\bf #1}}
%\newcommand{\jpre}      [1]  {{Phys.\ Rev.\ E~{\bf #1}}}
\newcommand{\jpre}      [1]  {\jprBase\ E~{\bf #1}}

\newcommand{\prsl}      [1]  {{Proc.\ Roy.\ Soc.\ Lond.\ {\bf #1}}}
\newcommand{\ppnp}      [1]  {{Prog.\ Part.\ Nucl.\ Phys.\ {\bf #1}}}
\newcommand{\progtp}    [1]  {{Prog.\ Th.\ Phys.\ {\bf #1}}}
\newcommand{\rpp}       [1]  {{Rep.\ Prog.\ Phys.\ {\bf #1}}}
\newcommand{\jrmp}      [1]  {{Rev.\ Mod.\ Phys.\ {\bf #1}}}  % dbm
\newcommand{\rsi}       [1]  {{Rev.\ Sci.\ Instr.\ {\bf #1}}}
\newcommand{\sci}       [1]  {{Science~{\bf #1}}}
\newcommand{\sjnp}      [1]  {{Sov.\ J.\ Nucl.\ Phys.\ {\bf #1}}}
\newcommand{\spd}       [1]  {{Sov.\ Phys.\ Dokl.\ {\bf #1}}}
\newcommand{\spu}       [1]  {{Sov.\ Phys.\ Usp.\ {\bf #1}}}
\newcommand{\tmf}       [1]  {{Teor.\ Mat.\ Fiz.\ {\bf #1}}}
\newcommand{\yf}        [1]  {{Yad.\ Fiz.\ {\bf #1}}}
%\newcommand{\zp}        [1]  {{Z.\ Phys.\ {\bf #1}}}
\newcommand{\zp}        [1]  {\zpBase\ {\bf #1}}
%\newcommand{\zpc}       [1]  {{Z.\ Phys.\ C~{\bf #1}}}
\newcommand{\zpc}       [1]  {\zpBase\ C~{\bf #1}}
\newcommand{\zpr}       [1]  {{ZhETF Pis.\ Red.\ {\bf #1}}}

\newcommand{\hepex}     [1]  {hep-ex/{#1}}
\newcommand{\hepph}     [1]  {hep-ph/{#1}}
\newcommand{\hepth}     [1]  {hep-th/{#1}}


%%%%%%%%%%%%%%%%%%%% SOFTWARE PACKAGES %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\def\aslund     {\mbox{\tt Aslund}\xspace}
\def\bbsim      {\mbox{\tt BBsim}\xspace}
\def\beast      {\mbox{\tt Beast}\xspace}
\def\beget      {\mbox{\tt Beget}\xspace}
\def\Bta        {\mbox{\tt Beta}\xspace}
\def\betakfit   {\mbox{\tt BetaKfit}\xspace}
\def\cornelius  {\mbox{\tt Cornelius}\xspace}
\def\evtgen     {\mbox{\tt EvtGen}\xspace}
\def\euclid     {\mbox{\tt Euclid}\xspace}
\def\fitver     {\mbox{\tt FitVer}\xspace}
\def\fluka      {\mbox{\tt Fluka}\xspace}
\def\fortran    {\mbox{\tt Fortran}\xspace}
\def\gcalor     {\mbox{\tt GCalor}\xspace}
\def\geant      {\mbox{\tt GEANT}\xspace}
\def\gheisha    {\mbox{\tt Gheisha}\xspace}
\def\hemicosm   {\mbox{\tt HemiCosm}\xspace}
\def\hepevt     {\mbox{\tt{/HepEvt/}}\xspace}
\def\jetset74   {\mbox{\tt Jetset \hspace{-0.5em}7.\hspace{-0.2em}4}\xspace}
%\def\jetset     {\mbox{\tt Jetset \hspace{-0.5em}7.\hspace{-0.2em}4}}
\def\koralb     {\mbox{\tt KoralB}\xspace}
\def\minuit     {\mbox{\tt Minuit}\xspace}
\def\objegs     {\mbox{\tt Objegs}\xspace}
\def\paw        {\mbox{\tt Paw}\xspace}
\def\root       {\mbox{\tt Root}\xspace}
\def\squaw      {\mbox{\tt Squaw}\xspace}
\def\stdhep     {\mbox{\tt StdHep}\xspace}
\def\trackerr   {\mbox{\tt TrackErr}\xspace}
\def\turtle     {\mbox{\tt Decay~Turtle}\xspace}

symbols.tex
% -----------------------------------------------------------------
% Symbols for BABAR-CONF-0012
%

\newcommand{\deltam}{\ensuremath{\Delta m}}
\newcommand{\deltae}{\ensuremath{\Delta E}}

% Extra Daughter symbols
\def\D       {\ensuremath{D}}
\def\Dp      {\ensuremath{D^+}}
\def\Dm      {\ensuremath{D^-}}
\def\Dstar   {\ensuremath{D^{*}}}
\def\Dstarp  {\ensuremath{D^{*+}}}
\def\Dstarm  {\ensuremath{D^{*-}}}
\def\DDstar  {\ensuremath{D^{(*)}}}
\def\DDstarp {\ensuremath{D^{(*)+}}}
\def\DDstarm {\ensuremath{D^{(*)-}}}
\def\rhop    {\ensuremath{\rho^+}}
\def\rhom    {\ensuremath{\rho^-}}
\def\aonep   {\ensuremath{a_1^+}}
\def\aonem   {\ensuremath{a_1^-}}

% Common B decay modes
\newcommand{\btodspi}{\ensuremath{\Bz\ra\Dstarm\pi^+}}
\newcommand{\btodsrho}{\ensuremath{\Bz\ra\Dstarm\rho^+}}
\newcommand{\btodsa}{\ensuremath{\Bz\ra\Dstarm a_1^+}}
\newcommand{\btodpi}{\ensuremath{\Bz\ra\Dm\pi^+}}
\newcommand{\btodrho}{\ensuremath{\Bz\ra\Dm\rho^+}}
\newcommand{\btoda}{\ensuremath{\Bz\ra\Dm a_1^+ }}
\newcommand{\btodsds}{\ensuremath{\Bz\ra\Dstarp\Dstarm}}

\newcommand{\btodzpi}{\ensuremath{B^+\ra\Dzb\pi^+}}
\newcommand{\btodzrho}{\ensuremath{B^+\ra\Dzb\rho^+}}
\newcommand{\btodza}{\ensuremath{B^+\ra\Dzb a_1^+}}

\newcommand{\btodzspi}{\ensuremath{B^+\ra\Dstarzb\pi^+}}
\newcommand{\btodzsrho}{\ensuremath{B^+\ra\Dstarzb\rho^+}}
\newcommand{\btodzsa}{\ensuremath{B^+\ra\Dstarzb a_1^+}}

% Common D decay modes
\newcommand{\dspi}{\ensuremath{\Dstarm\pip}}
\newcommand{\dsrho}{\ensuremath{\Dstarm\rho^+}}
\newcommand{\dkpi}{\ensuremath{\Dz\ra K^-\pi^+}}
\newcommand{\dkpipiz}{\ensuremath{\Dz\ra K^-\pi^+\pi^0}}
\newcommand{\dkpipipi}{\ensuremath{\Dz\ra K^-\pi^+\pi^-\pi^+}}
\newcommand{\dkpipipipiz}{\ensuremath{\Dz\ra K^-\pi^+\pi^-\pi^+\pi^0}}
\newcommand{\dkspipi}{\ensuremath{\Dz\ra \KS\pi^+\pi^-}}
\newcommand{\dkspipipiz}{\ensuremath{\Dz\ra \KS\pi^+\pi^-\pi^0}}
\newcommand{\dkspiz} {\ensuremath{\Kstarzb\piz}}
\newcommand{\dksmpi} {\ensuremath{\Kstarm\pi^+}}
\newcommand{\dkrhp}  {\ensuremath{\Km\rho^+}}
\newcommand{\dkspi}{\ensuremath{\Dp\ra \KS\pi^+}}
\newcommand{\dkpipi}{\ensuremath{\Dp\ra K^-\pi^+\pi^+}}


\newcommand{\etal}{{\it et al.}}






hep-ex0107068.extracted_bib
\begin{thebibliography}{99}
\bibitem{b0gammagammaSUSY}
  G. G. Devidze and G. R. Jibuti, \plb{\bf 429}, 48 (1998).

\bibitem{b0gammagamma2Higgs}
  T. M. Aliev and  G. Turan, \prd{\bf 48}, 1176 (1993).

\bibitem{L3} 
  L3 Collaboration, M. Acciarri \etal, \plb{\bf 363}, 137 (1995).

\bibitem{detector}
  \babar\ Collaboration, B.\ Aubert \etal,
  hep-ex/0105044,
  submitted to Nucl.\ Instr.\ Methods A.
  
\bibitem{pep}
  PEPII -- An Asymmetric $B$ Factory,
  Conceptual Design Report SLAC-0418.
  
\bibitem{geant}
  GEANT -- Detector Description and Simulation Tool,
  CERN Program Library Long Writeup W5013, 1994.
  
\bibitem{FoxWolfram}
  G. C. Fox and S. Wolfram, \prl{\bf 41}, 1581 (1978).
  
% \bibitem{definitionOfSecondMoment}
%   The second moment of a cluster is defined as
%   $
%   \frac{1}{\sum_{i=1}^n E_i} \times \sum_{i=1}^{n} E_i \, (\Delta \theta_i^2 + \Delta \phi_i^2);
%   $
%   $\Delta \theta_i$ and $\Delta \phi_i$ are the angular distances between the center of crystal $i$
%   and the cluster centroid in $\theta$ and $\phi$,
%   $E_i$ is the energy deposited in crystal $i$, where $i$ runs from 1 to $n$, the total number
%   of crystals contained in the EMC cluster.

\bibitem{PDG} 
  Particle Data Group, D. E. Groom \etal, \epjc{15}, 1 (2000).
  
\bibitem{CrystalBall} 
   For signal Monte Carlo events the $\Delta E$ and \mes\ distribution are fitted with the Crystal Ball function
   $$
   f(x) = N \cdot 
   \begin{cases}
     \exp (-\frac{(x - \bar {x})^2}{2 \; \sigma^2})  &; \;\;  ( x - \bar {x})/\sigma >   \alpha \\
     A \times (B - \frac{x - \bar {x}}{\sigma})^{-n} &; \;\;  ( x - \bar {x})/\sigma \leq \alpha \\
   \end{cases}
   $$
   where $A \equiv \left ( \frac{n}{|\alpha|} \right ) ^n \times \exp(-|\alpha|^2/2)$ and
   $B \equiv \frac{n}{|\alpha|} - |\alpha|$.
   $N$ is a normalization factor, $\bar x$ and $\sigma$ are the fitted peak position and width
   of the Gaussian portion of the function, and $\alpha$ and $n$ are the fitted point at which the function
   transitions to the power function and the exponent of the power function, respectively.
%   $A$ and $B$ are defined such as to maintain the continuity of the function and it first 
%   derivative at $\alpha$.
%   More details can be found in 
  D. Antreasyan, Crystal Ball Note 321 (1983).

\bibitem{JETSET}
  T. Sj\"ostrand, \cpc{\bf 82}, 74 (1994).  

\bibitem{Argus} 
  %%%%We parameterize the $\Delta E$ distribution with a first order polynomial.
%  The \mes\ distribution is parameterized using the ARGUS function
%  $f(x) = N \, x \, \sqrt{1-x^2} \, \exp(-\zeta \, (1-x^2) ) $ with $x = 2 \, m_{ES}/\sqrt{s}$
%  and $\sqrt{s}$ the center of mass energy. $N$ is a normalization factor and $\zeta$ a fit parameter.
%  More details can be found in Argus Collaboration, 
   H. Albrecht \etal, Z. Phys. {\bf C48}, 543 (1990).
  
\bibitem{Cousins} R. D. Cousins and  V. L. Highland, \nima{\bf 320}, 331 (1992).
\end{thebibliography}