1. P. Bambade, LAL/Orsay TESLA collaboration meeting APDG session 22/1/2004 1 Crossing-angle-or-not physics implications report from 19-01-04 phone-meeting cold crossing-angle head-on warm crossing-angle - physics issues evaluated more IP tuning optics design constraints crab-cavity req. beam(strahlung) extraction SC mini-quad. electrostatic separators backgrounds collimation  get worse at 1 TeV technical issues hermetic  veto post-IP diagnostics transverse boost for energy and B and P not polarisation no killer arguments either way - quantify physics impact consensually

2. P. Bambade, LAL/Orsay TESLA collaboration meeting APDG session 22/1/2004 2 1. Introduction, specification and context of study, meeting goals 10‘ P. Bambade/LAL 2. Smuon and stau searches with small slepton-neutralino mass differences Implications for dark matter interpretation in co-annihilation scenarios 25‘ Z. Zhang/LAL 3. Smuon and stau searches with small slepton-neutralino mass differences 20‘ U. Martyn/DESY Tentative conclusion & further work concerning impact on slepton search capabilities 4. Crossing angle and luminosity spectrum measurement 10‘ D. Miller/UCL 5. News from the ALPCG SLAC Workshop 20‘ E. Torrence/Oregon 6. Polarisation effects of the crossing angle 10’ K. Mönig/DESY 7. Review of arguments for upstream / downstream polarimetry 15‘ G. Mortgat-Pick/Durham P. Schüler/DESY Tentative conclusion & further work concerning impact on energy and polarisation 8. Status of the detector background simulations Comparison of recent beamstrahlung pair calculations 20‘ K. Büsser/DESY 9. Electron identification & veto in the LCAL / LumCAL Comparison with recent results from Takashi Maruyama 20‘ K. Kousnetzova/DESY 10. Update on gamma-gamma to hadrons calculation 20‘ T. Barklow/SLAC Tentative conclusion & further work concerning requirements on the background and very forward region meeting agenda of the physics evaluation http://www-flc.desy.de/bdir/BDIRmeetings.html Conclude by LCWS04 - strengthen international collaboration (GLC)

3. P. Bambade, LAL/Orsay TESLA collaboration meeting APDG session 22/1/2004 3 SUSY motivation for head-on mode Some popular dark matter SUSY explanations need the LSP  0 to be quasi mass-degenerate with the lightest sleptons , ,…  co-annihilation mechanism mSUGRA + new dark matter constraints from WMAP cosmic microwave background measurements point in this direction Scenario considered also relevant more generally in the MSSM M. Battaglia et al. hep-ph/0306219 co-annihilation example with g-2 constraint J. Ellis et al. hep-ph/0310356 Acceptable solutions in mSUGRA:

4. P. Bambade, LAL/Orsay TESLA collaboration meeting APDG session 22/1/2004 4 efficient / hermetic  veto crucial for  measurement Signal Main background ee    0   0 ee  (e)(e)    ~ 10 fb  ~ 10 4 fb Transverse view imperfect spectator electron veto ? R = 1.2 cm hole at 20 mrad  10 -3 background efficiency Important LC channel, complementary to LHC Precise slepton masses  DM  CMB constraints from Planck ( luminosity & energy strategy ) ( LC  cosmology )

5. P. Bambade, LAL/Orsay TESLA collaboration meeting APDG session 22/1/2004 5 Forward region geometries Specs for study l* = 4.1m  veto at 3.7m holes 1.2cm radius (2.1cm likely for x-angle) 1. head-on 1 bunch 2. x-angle 1 bunch 3. x-angle n bunches (pile-up)

6. P. Bambade, LAL/Orsay TESLA collaboration meeting APDG session 22/1/2004 6 Ideal vs. realistic veto and head-on vs. cross-angle  Low angle veto essential to reduce photon-photon background  Veto power is better in head-on collision mode r out =2.1cm instead of r out =1.2cm in-coming beam hole from Z. Zhang

7. P. Bambade, LAL/Orsay TESLA collaboration meeting APDG session 22/1/2004 7 Preliminary  result benchmark point D’ with  m  -  = 12 GeV signal efficiency ~ 80% spectrum end-points preserved  m s  and m LSP can be measured with precision for this benchmark point  more model-independent : smallest  m s  -  detectable wrt to veto angle and quality ? After requiring N  =2 Normalized for L=500fb -1 from Z. Zhang cuts valid for both head-on and crossing-angle collisions

8. P. Bambade, LAL/Orsay TESLA collaboration meeting APDG session 22/1/2004 8 Preliminary  result benchmark point D’ with  m  -  = 5 GeV Thrust axis angle in 3-dim  P T sum wrt thrust axis in the transverse plane Azimuthal dependance in the transverse momentum head-on crossing-angle signal efficiency ~ 11 % ~ 8 % S/B ratio 3.1  1.3 2.4  1.1 Caveat 1 : TESLA  electron veto efficiencies with beamstrahlung pairs from single bunch crossing ; warm LC will need fast read-out (R&D?) to avoid pile-up Caveat 2 : some physics backgrounds still need to be fully included in the analysis from Z. Zhang degradation visible but not huge

9. P. Bambade, LAL/Orsay TESLA collaboration meeting APDG session 22/1/2004 9 Preliminary slepton study by H.U. Martyn

10. P. Bambade, LAL/Orsay TESLA collaboration meeting APDG session 22/1/2004 10 Effect of crossing-angle on cms energy calibration Acollinearity angle of Bhabha events monitor the luminosity-weighted centre-of-mass spectrum in the presence of ISR and beamstrahlung radiation = 0  changes in angles from the 0.01*E CMS transverse boost in a 20 mrad crossing-angle are corrected perfectly radiation > 1%  use calorimetric information radiation < 1%  use approximate correction ( : “very good for symmetrical radiation”)  simulation exercise started to check magnitude of potential bias Desired precision ~ few 10 -4 - 5 10 -5 for top & W masses (10 -5 - 10 -6 to improve M Z measurement) S. Boogart D. Miller T. Barklow

11. P. Bambade, LAL/Orsay TESLA collaboration meeting APDG session 22/1/2004 11 Steering and depolarisation from the solenoid with a 10 mrad crossing-angle Solenoid B field not aligned to momentum  deflection ~ 0.4 mrad (assumes total length = 8 m, B = 4 T, E b = 250 GeV) 100 % longitudinal polarisation  spin precession to IP ~ 115 mrad is known and can be corrected   P = 1- cos(0.115) = 0.7 % If measurement error of polarimeter  P ~ 0.5 %  additional spin misalignment ~ 100 mrad   P = cos(0.115) – cos(0.215) = 1.6 % ! Must include effects from fringe fields   P = 0.7 % K. Mönig (+ M. Woods) Physics requirement new physics searches SM tests @ HE SM tests @ GigaZ  P ~ 0.5 %  P ~ 0.2 - 0.1 %  P < 0.1 %  extra vertical bends ( + some tuning ) required to correct for both effects ( M. Woods et al. are working on this ) G. Mortgat-Pick

12. P. Bambade, LAL/Orsay TESLA collaboration meeting APDG session 22/1/2004 12 1.Physics channels (Bhabhas, radiative Z returns, WW, We ) give the relevant luminosity-weighted information  but need statistics 2.pre-IP calibration needed to monitor incoming changes in E and P 3.post-IP very desirable to measure beam-beam effects and validate simulated predictions and biases; they provide important redundancy and can also be used in single-beam mode Energy and polarisation calibration strategies Head-on collisions  post-IP diagnostics quasi-impossible how essential are they ? P. SchülerE. Torrence Beam-beam depolarisation 1. spin precession in the magnetic field 2. spin-flip probability in beamstrahlung total depolarisation ~ 4  lumi - weighted

13. P. Bambade, LAL/Orsay TESLA collaboration meeting APDG session 22/1/2004 13 Bottom-line on crossing-angle-or-not physics implications (preliminary) Head-on is quantifiably better for some topics while crossing-angle is preferable for some others Both are acceptable for physics  With TESLA one can in principle choose one or the other ? Proposed intermediate solution : 0.3 mrad x-angle Comparison and optimisation of cold/warm very forward veto capability and more comprehensive background studies seem more important

14. P. Bambade, LAL/Orsay TESLA collaboration meeting APDG session 22/1/2004 14 1 2 3 4 5 6 X (cm) Y (cm) BG SiLayers Deposited Energy (arb. Units) 250 GeV e - K. Büsser E. Kousnetzova T. Maruyama K. Mönig A. Stahl Pair deposition and electron ID in the BeamCAL/LumCAL Large fake-rate if more than 3 bunch crossings pile-up

15. P. Bambade, LAL/Orsay TESLA collaboration meeting APDG session 22/1/2004 15 Ecm (GeV) Assume constant for T. Barklow background calculation

16. P. Bambade, LAL/Orsay TESLA collaboration meeting APDG session 22/1/2004 16 Tracker Occupancy = (# hits / train) / # channels T. Barklow