Physics at a photon collider Page: 2 of 3
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b-tagging is therefore required to suppress the
charm background. The need to minimize the
radius of the beam pipe is one of the main chal-
lenges for a Photon Collider, since the beam pipe
has to accomodate the optical system for produc-
ing back-scattered photons.
The analyses presented here have assumed that
bb events are tagged with 70% efficiency and ci-
events with 3.5% efficiency. For a luminosity cor-
responding to roughly one year of running, a sta-
tistical uncertainty of about 2% for a Higgs mass
of 120-140 GeV for the two photon width mea-
surement can be achieved. The uncertainty in-
creases to about 10% for a Higgs mass of 160 GeV.
At Higgs boson masses above 160 GeV de-
cays into WW and ZZ pairs become important.
In this case the interference between signal and
yy - WW background needs to be taken into
account. The interference gives access to an ad-
ditional observable, the phase Pqq of the yy - H
amplitude. The combined precision of phase and
partial width determination gives sufficient preci-
sion to distinguish the SM from SM-like 2HDM
(II) scenarios . The results of a detector simu-
lation are shown in Fig. 2.
o simula n
-- no Hlggs
--- no Hlggs
Figure 2. Reconstructed invariant mass for yy -
WW events with a SM Higgs mass of 180 GeV
(left) and for 'y - ZZ events with a SM Higgs
mass of 300 GeV (right) .
The neutral MSSM Higgs Boson H,A for
masses above 200 GeV and for moderate tan B
7 might escape detection at the LHC. In this pa-
rameter region, where decays into bb are the dom-
inant SM decays up to Higgs masses around 550
GeV, the Photon Collider can discover the neutral
MSSM Higgs Bosons . In contrast to the e+e-
option of the LC, the Photon Collider can pro-
duce these Higgs Boson with masses up to about
80% of fee. Cross-sections for signal and back-
ground are shown in Fig. 3.
200 300 400 500
Figure 3. Cross-section for the process yy -
A - bb and for the background yy - bb. A
mass window of t3 GeV has been applied, 100%
polarisation is assumed, and only the two-jet con-
figuration is considered .
Many other Higgs scenarios have been studied
for the Photon Collider option, adding to the dis-
covery potential: For example, the measurement
of CP properties of the Higgs bosons A,H in tt de-
cays  or the production of charged Higgs bosons
in the process yy H+H- .
3. Non-Commutative Field Theories
One of many other interesting topics which
can be studied at a -m or at an ey collider are
non-commutative quantum field theories (NC-
QFT) with non-commuting (NC) space-time op-
erators . The additional cubic coupling (yy)
contributing to the process yy - ff is shown in
The parameter ANC characterises the threshold
where NC effects become relevant. The current
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Soldner-Rembold, Stefan. Physics at a photon collider, article, September 30, 2002; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc742520/m1/2/: accessed December 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.