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Investigation of leptonic structure functions with lepton pairs produced in single tagged 2g events. Klaus Dehmelt Laszlo Baksay Marcus Hohlmann 69th Annual Meeting March 18, 2005 LEP-L3 Experiment at CERN Large Electron Positron Collider LEP FAS 2005 – K. Dehmelt – March, 18th Why studying leptonic structure function ? • QED test up to O ( 4 ) experimental check for procedures adopted in the study of hadronic structure function • Calibration of accelerators with colliding pp beams (LHC) • Measurement of transverse and longitudinal leptonic structure functions with two-photon helicity consideration FAS 2005 – K. Dehmelt – March, 18th L3 – The Detector FAS 2005 – K. Dehmelt – March, 18th Physics at LEP and L3 e+e- - collisions FAS 2005 – K. Dehmelt – March, 18th Two-Photon Interactions with Dilepton Events e e e e gg e e l l * l : lepton, i.e. or e Event Signature: • Single Tagged Electron, High Energy Deposition in Electromagnetic Calorimeters • Two tracks, at least one to be identified as a lepton (,e) • Compare Data to Monte Carlo generated events (DIAG36) FAS 2005 – K. Dehmelt – March, 18th Dilepton Kinematics Q 2 2 p i 1 T ,i 2 FAS 2005 – K. Dehmelt – March, 18th L3 Tagging Subdetectors Very Small Angle Tagger – VSAT Luminosity Monitor – LUMI Active Lead Ring – ALR Electromagnetic Calorimeter Endcaps – BGO Endcaps Tagging detectors used to identify scattered electron VSAT: huge background due to proximity to beam pipe FAS 2005 – K. Dehmelt – March, 18th Study of VSAT VSAT is moved for beam filling Alignment Studies Huge VSAT background due to scattered beam electrons FAS 2005 – K. Dehmelt – March, 18th Study of VSAT with Acoplanarity of selected two track events Cut FAS 2005 – K. Dehmelt – March, 18th Study of VSAT with Invariant mass distribution of di-lepton events () for 1998-2000, selected with HCAL FAS 2005 – K. Dehmelt – March, 18th Study of VSAT with Invariant mass distribution of di-lepton events () for 1998-2000, selected with MUCH FAS 2005 – K. Dehmelt – March, 18th Outlook • Determine p contamination Neural Network Method • Determine t background • Selection of LUMI- , ALR- , and ENDCAP- tagged events • Determine Cross-section FAS 2005 – K. Dehmelt – March, 18th The Cross-Section FAS 2005 – K. Dehmelt – March, 18th