1. 1 Gamma-gamma Physics Group Report A.De Roeck CERN

2. 2 This meeting Sessions Gamma gamma session (3 talks) (including a Report from LCWS02 by M Krawczyk) Common session with QCD (1 talk) Common session with Higgs (6 talks) Common session with EW ( 2 talks) Jeju Photon Collider option discussion (Higgs group) –Physics case for PC has confirmed/strengthened (Higgs properties measurements/Heavy Higgs production) –Must do appropriate R&D to keep the possibility of a PC

3. 3 Studies Reach Maturity Aim: Level of detail in  as good or better than in e+e- –SIMDET simulation (~e+e- detector/ see K. Moenig). Brahms? –Real Luminosity spectra/polarization used –B search using ZVTOP –Adding overlap events –QCD backgrounds in NLO –QCD Monte Carlo tuning to existing data –Cross checks for key processes (Higgs production) –Direct contact & exchange with the NLC studies/exchange tools More work still needed on –Luminosity/polarisation measurement (& corresponding syst.) –Final design of IP/vertex detectors (  backgrounds)

4. 4 AMEGIC++ for  S. Schumann, F. Kraus Resolved Direct Event generator AMEGIC++

5. 5 AMEGIC++ for  Matching ME to parton showers NLO Underlying event structure Hadronization and fragmentation Specific for  : Photon decomposition & structure Expect first version (for lepton final states) next month/ Hadrons early next year. !Useful for background studies to Higgs!

6. 6 Monte Carlo Tuning JetWeb hep-ph/0210404 http://jetweb.hep.ucl.ac.uk J Butterworth et al M.Wing ‘fit’ MC parameters to data from LEP, HERA & Tevatron

7. 7 MC Tuning  have to check effects on our backgrounds

8. 8

9. 9 Update:Use SIMDET + ZVTOP B finder SM Higgs analyses P. Niezurawski 81% 1.8%

10. 10 Using NLO backgrounds (Jikia…) Fragmentation questions? Systematics…?? SM Higgs analyses 1 year/84 fb -1

11. 11 SM Higgs analyses Pythia reweighted with NLO cross sections ZVTOP Tagging optimization still ongoing (presently lower than prev. analysis) A. Rosca

12. 12 Overlap events 1.5 central high energy  events for L  (z > 0.8z max ) ~ 1.1.10 34 cm -2 s -1 Files for TESLA have been prepared/SIMDET adapted to use overlays e+e- and  files So far catalogued on the CLIC page //clicphysics.web.cern.ch/CLICphysics 200 & 500 GeV files available  file contains 5000 events Selection events: W 2 > 5 GeV 2, tracks: Pt> 150 MeV,  > 80 mrad photon polarization not taken into account Effect on the measurement? Work in progress…

13. 13 SM Higgs analyses

14. 14 H/A Higgs D. Asner/J. Gunion (LCWS02) Need few years to Close the wedge Need also European study

15. 15 Low Mass Charged Higgs V. Martin Using H  decays Full simulation Relative low efficiency after cuts: 2.5 % What can a PC contribute?

16. 16 2HDM model M. Krawczyk

17. 17 M. Krawczyk R. Godbole Invitation Upcoming initiative…

18. 18 CP studies via  tt R. Godbole et al. hep-ph/021136 & LCWS02 Construct combined asymmetries from intial lepton polarization and decay lepton charge Done with realistic spectra etc., but needs study with simulation

19. 19 Trilinear Gauge couplings in e  D. Anipko Analyse d 2  /dp dcos   e CompHEP

20. 20 Fitting results of the fit of   and  for ± 1 photon polarization state – single and two parameter fit for real (e  ) mode  Fitting results of the fit of   and  for ± 1 photon polarization state – single and two parameter fit for real (e  ) mode REAL MODE 1 par. fit E CM = 450 GeV, L = 110 fb -1 J  = +1J  = -1 LL1%0.1%accur.1%0.1%accur.   ·10 -3 3.41.00.59.71.10.5   ·10 -3 1.61.5 4.64.43.8 2 par. fit   ·10 -3 5.11.10.59.71.10.6   ·10 -3 2.31.6 4.6  REAL MODE - pure e  -mode, known beam directions Trilinear Gauge couplings in e  e   W, hadronic decay channel/total and differential cross sections J Sekaric & K. Moenig

21. 21 comparison of the single parameter fit for e ,  comparison of the single parameter fit for e ,  -, and e - e + - colliders E e  = 450 GeV L=110 fb -1 E  = 400 GeV L=110 fb -1 E ee = 500 GeV L=500 fb -1 LL0.1%   ·10 -4 10 / 9.86.73.1   ·10 -4 15 / 5.86.04.3  sensitivity to  WW only! -  ,   ~ 10 -3

22. 22 Most important processes hep-ph/0103090 Added since then: Non-commutative measurements, e  for ED’s, Light gravitinos, Radions, H  ?, H  H+H-?… Higgs Susy Tril/quart. Top QCD J Any Volunteers?? J Being done/ready J promised

23. 23 Plans Finalize current analyses, particularly higgs sector –If IP studies in near future will require changes  need to know this asap High priority to start H/A & SUSY particle analysis, CP studies Use synergy with NLC group/exchange of tools Indian group starts studying ED’s in  and e  (R. Godbole et al.). Expect first results by Amsterdam Additional meeting before Amsterdam: February 13 @ CERN Plan to write up summary of the PC studies for Amsterdam At Amsterdam: Plan a panel discussion on a PC collider

24. 24 NLC studies overview

25. 25 D. Miller Determining the Spin of the H in  collisions

26. 26 H/A higgs Can a photon collider close the wedge? Cross section gets small For M(H/A) > 600 GeV J.Gunion: 2-4 years needed CP studies Expect need to run of photon collider for several years if the physics scenario warrants it!

27. 27 Luminosity and spectra Usable in event simulation (Telnov/Ohl/Zarnecki) Pandora For TESLA… Z=W  /2E bea m

28. 28 Cross sections

29. 29 B-tagging IP B D Primary vertex Secondary vertex Tertiary vertex Reconstruction of the vertex using a topological vertex technique (ZVTOP).

30. 30 The photon collider case Advantages –Large cross sections (e.g. WW production cactor 20-40 times) –Large circular polarization e-e- beams (~80%)   (90-95% in peak) –Linear polarization (CP filter) –Extended kinematic range for some new particles S-channel production for H,… /association e.g. slepton  lepton+  0 –Sometimes different couplings probed (no “Z” effects) Issues –Luminosity spectrum spread (not monochromatic, but much better than LHC). How precise can we measure the spectrum/luminosity? –Luminosity typically factor 3 lower compared to e+e-(but yet not at limit) –Needs R&D to proof it works as expected.  plans –More complicated IR –Debate of backgrounds and its implication on detector not yet finalized –Only few processes so far studied in (almost) all experimental details, most important one   Higgs

31. 31 The light Higgs “State of the art”” (M. Krawczyk) All background under control? B-tagging different in  ?

32. 32 Background studies Frequently asked question: same b-tagging efficiency as in e+e- case? K. Moenig et al.: backgrounds studied for TESLA IP layout Study beam related background # of hits in the layers of the pixel Detector per bunch crossing Incoherent pair production: essentially the same as for e+e- Coherent pair production: under study Neutrons? Will be able to answer this question soon

33. 33 Is a photon collider a hadron collider? The QCD background in a  collider can be large Eg. for L geom ~ 10 35 cm -2 s -1, 400 nb  cross section  3  events/bunch crossing –Many events boosted and/or low mass: no problems –V. Telnov (TESLA TDR appendix): 1.5 central high energy  events for L  (z > 0.8z max ) ~ 1.1.10 34 cm -2 s -1 # of jets (Et > 5 GeV)  > 80 mrad  > 250 mrad 10-20 tracks/event few GeV, tails up to 20-30 GeV Looks not so bad! ( ADR, ST Malo meeting ) Common study with theorists and NLC groups starting NO !

34. 34 R&D program Europe: R&D for lasers in IP (10% size prototype cavity planned) US: Laser development at LLNL Plan for SLC photon collider testbed at SLAC (means reactiviating SLC/ Workshop at SLAC Nov 21-23 ‘02 Conclusion: Photon collider will enrich the program of an e+e- machine We cannot afford NOT to study it !