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Leptonic Structure Functions of Photons Klaus Dehmelt Laszlo Baksay Marcus Hohlmann 73rd Annual Meeting November 9-11, 2006 The Concept of the “Structure of the Photon” Dual nature of photons: uncertainty principle allows photon to fluctuate into various states (leptons, quarks, …) t 2 E Lifetime of virtual particles: Photon is ideal tool for probing structure of objects m2pair SESAPS 2006 K. Dehmelt - November, 11th Why studying leptonic structure function ? • QED test up to O( 4 ) • Measurement of leptonic structure function check for experimental procedures adopted for QCD • Background to many processes • Calibration process for pp colliders SESAPS 2006 K. Dehmelt - November, 11th LEP-L3 Experiment at CERN Large Electron Positron Collider LEP SESAPS 2006 K. Dehmelt - November, 11th L3 – The Detector SESAPS 2006 K. Dehmelt - November, 11th Two-Photon Interactions with Dimuon Events (*) (*) Data Sample: Ec.m.s. = 189 … 206 GeV Int. Luminosity = 600 pb-1 Event Signature: • Single Tagged Electron, High Energy Deposition in Electromagnetic Calorimeters • Two tracks, at least one to be identified as a lepton (m) • VERMASEREN Monte Carlo generator SESAPS 2006 K. Dehmelt - November, 11th Two-Photon Interactions with Dimuon Events (*) (*) Data Sample: Ec.m.s. = 189 … 206 GeV Int. Luminosity = 600 pb-1 SESAPS 2006 K. Dehmelt - November, 11th 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 SESAPS 2006 K. Dehmelt - November, 11th Two-Photon Interactions with Dimuon Events SESAPS 2006 K. Dehmelt - November, 11th Dilepton Formalism iMN : density matrix PQ , PQ : cross-sections for different helicity states of the photon SESAPS 2006 K. Dehmelt - November, 11th Dilepton Formalism Extraction of F2, QED with GALUGA: SESAPS 2006 K. Dehmelt - November, 11th Dilepton Formalism Extraction of F2, QED with GALUGA: SESAPS 2006 K. Dehmelt - November, 11th Cross-Section & Structure-Function VERMASEREN - GALUGA SESAPS 2006 K. Dehmelt - November, 11th Cross-Section & Structure-Function VERMASEREN - GALUGA Limited x-range due to small Q2 SESAPS 2006 K. Dehmelt - November, 11th Summary Measurement of differential cross-section and structure-function in the kinematical range Data suggest P2 > 0 SESAPS 2006 K. Dehmelt - November, 11th Outlook • Additional structure functions accessible: FA, FB Interference terms • Modulated by and SESAPS 2006 K. Dehmelt - November, 11th SESAPS 2006 K. Dehmelt - November, 11th SESAPS 2006 K. Dehmelt - November, 11th