2 Lepton 2 Quark Production in 2 Photon
- Slides: 8
2 Lepton 2 Quark Production in 2 Photon Collisions W. da Silva *, F. Kapusta LPNHE, Paris Introduction ( computation : why, how, hypothesis ) Results (numerical, signal and background simulation) Outlook ECFA@Durham 1 -4 september 2004
●Introduction ●Experimental Motivation ●The cross-section of 4 fermion production ●has a large value at high energy ●( use leptons for luminosity measurement, . . . ) ●Study background generated by leptons ●(luminosity, b and c physics ●– don't forget LEP results- , ●W physics. . . ) ●Source of leptons at very low angle ●(i. e. study the forward region instrumentation) ●Theoretical Motivation ●Study of theoretical approximations ● and methods to compute the cross section ●( range of validity, test of numerical approximations, . . )
●Introduction ●Theoretical calculation ●Our Computation ( and Generator) ●Computation of space-like photon diagrams only ( including masses) ●Use factorisation i. e. Impact factor method ●( cf Lipatov-Frolov, Serbo(1985), ●Cheng-Wu) ●Use semi-analytic computation ●without approximation ●(cf PHOTON 2000/2001 proceedings) ●Test with GRACE ●( for the channel) ●Numerical computation including ●space-like and time-like photon
●Numerical Results ●(2 muon 2 up quark channel) ●“Huge” cross section at high energy (55 pb) ●Space like terms are dominant ●as expected long time ago. ● Good agreement between ●our computation and GRACE ●The Impact factor approx. ●Fails slightly at low energy ●(cf electron collider using ●quasi real photon fluxes) ●Test OK with modified GRACE ●(using quasi real photon fluxes) Cross-section pb
●Simulation Results : ●the hadronic background ●Photon fluxes ( cf Telnov) ●+ Pythia 6. 161 ( VDM + DIRect + RESolved terms) ●Huge events at low Pt and low Wvis (VDM terms. . . ) ●Opportunity to study the total ●cross-section and help to measure the luminosity ( absolute or relative) ? ● Using LEP 2 result ? ●Example of selected events : ●very loose cuts + ● 2 jets with same energy back to back ●Usual problem : computation time + easy rejected events
●Simulation Results : ●The leptons + jets signal ●Generator level ● 2 muon 2 up quark production ●Huge cross section but t-channel ●( low angle production) ●Topology of back to back pairs ●helps to select signal events ●(loose cut + angle(muons, jets)> 90 deg. ) ●Other lepton sources : beauty, charm, . . . ●( viewed as signal or as background ) ●Luminosity measurement : ●need more study ● to cancel the background !
●Simulation Results : a photon collider LEP-like plot ●Do not forget the 2 lepton 2 quark channel in inclusive lepton analyses
●Outlook ●Theoretical point of view ●more comparisons needed : space and time like terms, ●with and without impact factor approximation , . . . ●Experimental point of view ●Simulation with huge statistics ( signal and background ) ●in order to explore the high visible invariant mass ●and get some numerical results for the luminosity measurement ● using the 2 lepton 2 quark channel ●And. .
