  We have measured the azimuthal angular correlation of bottom anti-bottom
production, using 86.5 pb-1 of data collected by Collider Detector at Fermilab
(CDF) in proton anti-proton collisions at sqrt{s}=1.8 TeV during 1994-1995. In
high-energy p-pbar collisions, such as at the Tevatron, bottom anti-bottom
production can be schematically categorized into three mechanisms. The
leading-order (LO) process is ``flavor creation,'' where both the bottom and
anti-bottom quarks substantially participate in the hard scattering and result
in a distinct back-to-back signal in final state. The ``flavor excitation'' and
the ``gluon splitting'' processes, which appear at next-leading-order (NLO),
are known to make a comparable contribution to total bottom anti-bottom cross
section, while providing very different opening angle distributions from the LO
process. An azimuthal opening angle between bottom and anti-bottom, Delta phi,
has been used for the correlation measurement to probe the interaction creating
bottom anti-bottom pairs. The Delta phi distribution has been obtained from two
different methods. One method measures the Delta phi between bottom hadrons
using events with two reconstructed secondary vertex tags. The other method
uses b-bbar --> (J/psi X)(l X') events, where the charged lepton (l) is an
electron or a muon, to measure Delta phi between bottom quarks. The bottom
anti-bottom purity is determined as a function of Delta phi by fitting the
decay length of the J/psi and the impact parameter of the lepton. Both methods
quantify the contribution from higher-order production mechanisms by the
fraction of the b-bbar pairs produced in the same azimuthal hemisphere,
f_toward. The measured f_toward values are consistent with both parton shower
Monte Carlo and NLO QCD predictions.
