  This thesis concerns the observation of a new particle and the measurements
of its properties, from the search of the Higgs boson through its decay into
two photons at the CMS experiment at CERN's Large Hadron Collider (LHC), on the
full LHC "Run I" data collected by the CMS detector during 2011 and 2012,
consisting of proton-proton collision events at $\sqrt{s}$ $=$ $7~\mathrm{TeV}$
with $L$ $=$ $5.1~\mathrm{fb^{-1}}$ and at $\sqrt{s}$ $=$ $8~\mathrm{TeV}$ with
$L$ $=$ $19.7~\mathrm{fb^{-1}}$, with the final calibration. In particular, an
excess of events above the background expectation is observed, with a local
significance of 5.7 standard deviations at a mass of 124.7 GeV, which
constitutes the observation of a new particle through the two photon decay
channel. A further measurement provides the precise mass of this new particle
as $124.72_{-0.36}^{+0.35}$ GeV =
124.72$_{-0.32}^{+0.31}$(stat)$_{-0.16}^{+0.16}$(syst) GeV. Its total
production cross section times two photon decay branching ratio relative to
that of the Standard Model Higgs boson is determined as $1.12_{-0.23}^{+0.26}$
= 1.12$_{-0.21}^{+0.21}$(stat)$_{-0.09}^{+0.15}$(syst), compatible with the
Higgs boson expectation. Further extractions of its properties relative to the
Higgs boson, including the production cross section times decay branching
ratios for separate Higgs production processes, couplings to bosons and to
fermions, and effective couplings to the photon and to the gluon, are all
compatible with the expectations for the Standard Model Higgs boson.
