1. Leptonic Structure Functions of Photons
Klaus Dehmelt
Laszlo Baksay
Marcus Hohlmann

2. 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
SESAPS 2006
K. Dehmelt - November, 11th

3. 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
SESAPS 2006
K. Dehmelt - November, 11th

4. LEP-L3 Experiment at CERN
Large Electron Positron
Collider LEP
SESAPS 2006
K. Dehmelt - November, 11th

5. L3 – The Detector
SESAPS 2006
K. Dehmelt - November, 11th

6. 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

7. 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

8. 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

9. Two-Photon Interactions with Dimuon Events
SESAPS 2006
K. Dehmelt - November, 11th

10. Dilepton Formalism : density matrix : cross-sections
for different helicity
states of the photon
SESAPS 2006
K. Dehmelt - November, 11th

11. Dilepton Formalism Extraction of with GALUGA: SESAPS 2006
K. Dehmelt - November, 11th

12. Dilepton Formalism Extraction of with GALUGA: SESAPS 2006
K. Dehmelt - November, 11th

13. Cross-Section & Structure-Function VERMASEREN - GALUGA
SESAPS 2006
K. Dehmelt - November, 11th

14. Cross-Section & Structure-Function VERMASEREN - GALUGA
Limited x-range
due to small Q2
SESAPS 2006
K. Dehmelt - November, 11th

15. Summary Measurement of differential cross-section
and structure-function
in the kinematical range
Data suggest P2 > 0
SESAPS 2006
K. Dehmelt - November, 11th

16. Outlook Additional structure functions accessible: FA, FB
Interference terms
Modulated by and
SESAPS 2006
K. Dehmelt - November, 11th

17. SESAPS 2006
K. Dehmelt - November, 11th

18. SESAPS 2006
K. Dehmelt - November, 11th