Leptonic Structure Functions of Photons

73rd Annual Meeting

November 9-11, 2006

Leptonic Structure Functions of Photons

Klaus DehmeltLaszlo Baksay

Marcus Hohlmann

SESAPS 2006K. Dehmelt - November, 11th

The Concept of the“Structure of the Photon”

Dual nature of photons: uncertainty principle allows photon to fluctuate into various states (leptons, quarks, …)

Lifetime of virtual particles:

Photon is ideal tool for probing structure of objects

tE

m pa ir

2

2


Why studying leptonic structure function ?

• QED test up to

• Measurement of leptonic structure function check for experimental procedures adopted for QCD

• Background to many processes

• Calibration process for pp colliders

O ( ) 4


LEP-L3 Experiment at CERNLarge Electron Positron

Collider LEP


L3 – The Detector


Two-Photon Interactions withDimuon 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 ()• VERMASEREN Monte Carlo generator



Data Sample:Ec.m.s. = 189 … 206 GeV

Int. Luminosity = 600 pb-1

(*) (*)


L3 Tagging SubdetectorsVery Small Angle Tagger – VSATLuminosity Monitor – LUMIActive Lead Ring – ALRElectromagnetic Calorimeter Endcaps – BGO Endcaps

Tagging detectors used to identify scattered electron

VSAT: huge background due to proximity to beam pipe


Dilepton Formalism

iM N

PQ PQ,

: density matrix

: cross-sectionsfor different helicitystates of the photon


Dilepton Formalism

Extraction of with GALUGA: F QED2 ,


Cross-Section & Structure-FunctionVERMASEREN - GALUGA


Cross-Section & Structure-FunctionVERMASEREN - GALUGA

Limited x-rangedue to small Q2


Summary

Measurement ofdifferential cross-sectionand structure-functionin the kinematical range

Data suggest P2 > 0


Outlook

• Additional structure functions accessible: FA, FB

Interference terms

• Modulated by and

Leptonic Structure Functions of Photons

Documents

Transcript of Leptonic Structure Functions of Photons