You are an expert at summarizing long articles. Proceed to summarize the following text: 
the central challenge for particle physics nowadays is the origin of mass . in the standard model both fermions and gauge boson masses are generated through interactions with the same scalar particle , the higgs boson , h. if it exists , the higgs boson will certainly be discovered by the time a photon collider is constructed . the aim of this machine will be then a precise measurement of the higgs properties . the photon scattering can be used to produce the higgs particles singly in the s - channel of the colliding photons . this facility permits a high precision measurement of the h @xmath4 partial width , which is sensitive to new charged particles . the measurement is significantly important . if we find a deviation of the two photon width from the standard model prediction it means that an additional contribution from unknown particles is present , and so it is a signature of physics beyond the sm . for example , the minimal extension of the sm predicts the ratio of the two photon width @xmath5/ @xmath6 1.2 @xcite for a higgs boson with a mass of 120 gev , assuming a supersymmetry scale of 1 tev and the chargino mass parameters @xmath7 and @xmath8 of 300 and 100 gev , respectively .    a photon collider can measure the product @xmath9@xmath10br@xmath11 . to obtain the two - photon partial width independent of the branching ratio one has to combine with an accurate measurement of the br(@xmath12 ) from another machine . this study investigates the accuracy of the measurement of the two photon decay width times the branching ratio for a higgs boson with the mass of 120 gev , the preferred mass region by recent electroweak data @xcite . the signal and background processes studied are specified in section 2 . event selection is described in section 3 . results are summarized in section 4 . the feasibility of the measurement of the two photon decay width of the higgs boson in this mass region has also been reported by @xcite . high energy photon beams can be produced at a high rate in compton backscattering of laser photons off high energy electrons @xcite . setting opposite helicities for the laser photons and the beam electrons the energy spectrum of the backscattered photons is peaked at  80@xmath2 of the @xmath13 beam energy . the backscattered photons are highly polarized in this high energy region . with an integrated luminosity of 80 fb@xmath3 per year for @xmath14 @xcite , about 20000 higgs bosons with standard model coupling and a mass of 120 gev can be produced in the @xmath0h process . in this mass region the higgs particle will decay dominantly into a b@xmath1 pair . the beam spectra at @xmath15 = 210 gev are simulated using the compaz @xcite , a fast parameterization which includes multiple interactions and non - linearity effects . the response of the detector has been simulated with simdet 4 @xcite , a parametric monte carlo for the tesla @xmath16 detector . it includes a tracking and calorimeter simulation and a reconstruction of energy - flow - objects ( efo ) . only efos with a polar angle above 7@xmath17 can be taken for the higgs reconstruction simulating the acceptance of the photon collider detector as the only deference to the @xmath16 detector @xcite . the considered backgrounds are the direct continuum @xmath18 and @xmath19 production . due to helicity conservation , the continuum background production proceeds mainly through states of opposite photon helicities , making the states @xmath20 . choosing equal helicity photon polarizations the cross section of the continuum background is suppressed by a factor @xmath21 , with @xmath22 being the quark mass . unfortunately , this suppression does not apply to the process @xmath23 , because after the gluon radiation the @xmath24 system is not necessarily in a @xmath25 state . the surviving background is large and overwhelms the signal . signal @xmath26 events are generated using pythia 6.2 @xcite . background processes @xmath27(g ) are generated with the sherpa ( the simulation for high energy reactions of particles ) @xcite generator . higher order qcd effects are simulated in pythia by evolving the hard process event using the parton shower , which allows partons to split into pairs of other partons . this technique is most effective when the emitted gluons are soft or collinear , while the region of high transverse momentum is poorly described . for a reliable background estimation correct nlo corrections are needed . combining the hard process with its higher order correction in pythia is not trivial . a fraction of @xmath28 events are included in the @xmath29 process via gluon radiation in the parton shower . combining the two processes without special procedures amounts in double counting of some phase space regions . sherpa @xcite is a generator which matches correctly the exact matrix elements with showering . a comparison between the distributions of jet multiplicity in the @xmath30 process obtained with pythia and sherpa is shown in figure [ fig_jets ] . however , since virtual diagrams are not included , to obtain the correct rates the sherpa results for the spin @xmath31 states have to be scaled by the correct nlo cross section . the cross sections at the nlo for the @xmath32 process have been calculated @xcite , @xcite . a cross section comparison is shown in figure [ fig_cs ] . .cross sections and the number of expected and generated events for the signal and background processes [ cols="<,^ " , ]     [ tab_cs ] the analysis aims to select events with two or three jets from the higgs boson decay . two of these jets contain bottom quarks . the invariant mass of the jets has to be consistent with the higgs mass . high multiplicity ( feo ) events are selected and their visible energy is required to be greater than 95 gev . events with longitudinal imbalance greater than 10@xmath2 of the visible energy are rejected . finally the cosine of the thrust angle has to be less than 0.7 .    in the remaining event sample jets are reconstructed using the durham clustering scheme @xcite with the resolution parameter y@xmath33=0.02 . the cross section for the continuum production of the charm quark is 16 times larger than for bottom quarks , therefore b - quark tagging is crucial for this analysis . the b - tagging algorithm combines several discriminating variables , as for example , the impact parameter joint probability tag introduced by aleph @xcite , the @xmath34 corrected vertex invariant mass obtained with the zvtop algorithm written for the sld experiment @xcite and a one - prong charm tag , into a feed forward neural network with 12 inputs and 3 output nodes , described in ref . @xcite .    the distribution of the neural network output @xmath35 to discriminate b - quark jets from u- , d- , s- and c - quark jets is presented in figure [ fig_btag]a . the performance of the neural network b - tag in z@xmath17 decays is shown in figure [ fig_btag]b . the b - tagging efficiency is 70@xmath2 and corresponds to a purity of 98@xmath2 . the b - quarks coming from the decay of the higgs boson are highly energetic , whereas in the case of the background processes the gluon and one b - quark jet are the most energetic . in order to reduce the background further we look at the two fastest jets in the event and require the @xmath35 to be greater than 0.95 for one jet and greater than 0.2 for the second one .      +    the expected number of signal and background events are summarized in table [ tab_cs ] . a total signal efficiency is estimated to be 36@xmath2 . the hadronic cross section for @xmath0hadrons events , within the energy range above 2 gev , is about 400 nb , so that about 1 such event is produced per bunch crossing ( pileup ) . these events obscure the interesting physics processes described in the previous sections . for this reason this class of events needs to be included in the pythia simulation for overlap in the next step of this analysis . the hades @xcite program will be used for this purpose . a large fraction of this background is distributed at small angles and we believe that it can be reduced cutting on the polar angle of the tracks @xcite . a careful study of this hadronic background is currently being performed . the reconstructed invariant mass for the selected signal and background events is shown in figure [ fig_mass ] . to enhance the signal a cut on the invariant mass is tuned such that the statistical significance of the signal over background is maximized . events in the mass region of 114 gev @xmath36 126 gev are selected . the number of estimated signal and background events in this window are 4505 and 1698 , respectively . the two photon decay width of the higgs boson is proportional to the event rates of the higgs signal . the statistical error of the number of signal events , @xmath37 , corresponds to the statistical error of this measurement . here @xmath38 is the number of observed events , while @xmath39 is the number of expected background events . we conclude that for a higgs boson with a mass @xmath41=120 gev we can measure the product @xmath42 with an accuracy of 1.7@xmath2 using an integrated luminosity corresponding to one year of data taking at the tesla photon collider . t. ohgaki , t. takahashi and i. watanabe , hep - ph/9703301 ; g. jikia and s. sldner - rembold , nucl . inst . and meth a472 ( 2001 ) 133 ; p. niezurawski , a.f . zarnecki and m. krawczyk , acta physica polonica b34 ( 2003 ) 177 . p. niezurawski , a.f . zarnecki and m. krawczyk , hep - ph/0307183 .
this study investigates the potential of a photon collider for measuring the two photon partial width times the branching ratio of a light higgs boson . 
 the analysis is based on the reconstruction of the higgs events produced in the @xmath0h process , followed by higgs decay into a b@xmath1 pair . a statistical error of the measurement of the two - photon width times the b@xmath1 branching ratio of the higgs boson 
 is found to be 1.7 @xmath2 with an integrated luminosity of 80 fb@xmath3 in the high energy part of the spectrum .