1. SUSY small angle electron tagging requirements Philip Bambade LAL-Orsay MDI workshop - SLAC 6-8 January 2005 With M. Berggren, F. Richard, Z. Zhang + DESY colleagues

2. Philip BambadeSUSY small angle electron tagging requirements - SLAC 6-8/1/2005 2 Instrumentation in very forward region e.m. tagging down to ~ 5 mrad : - importance ? - feasibility ? ~ 3 GeV M. Büsser

3. Philip BambadeSUSY small angle electron tagging requirements - SLAC 6-8/1/2005 3 Dark Matter  SUSY  LHC + LC M. Battaglia et al. Eur.Phys.J.C33:273-296,2004  mSUGRA with WMAP constraint 0.094 <  DM h 2 < 0.129 (2 sigma) WMAP cosmic microwave background radiation measurement lead to :  total matter h 2  0.134  0.006 and  baryon h 2  0.023  0.001 PDG July 2004  for quasi mass-degenerate neutralino (  ) and slepton (  ), both  and  (co-)annihilations combine to regulate the amount of relic DM  N(  ) / N(  ) ~ exp(-20  m/m) ~ 1   m < 10 GeV and m < 400 GeV  attractive mechanisms also beyond mSUGRA D.Hooper et al. Phys.Lett.B562(2003)18

4. Philip BambadeSUSY small angle electron tagging requirements - SLAC 6-8/1/2005 4 Detection of l  ,  sleptons for small  m P.B. et al. hep-ph/0406010 signal major background :  ee  l  0 l  0 ee  (e)(e) l l  ~ 10 fb  ~ 10 6 fb Transverse view ~ Near threshold E l   (1   ) (m l 2 - m  2 ) / 2 m l ~  m  (1   )  background  must tag spectator electron (e.g. for  m  5 Gev):  ~  m  (1   ) / E beam  factor ~ 5-10 mrad ( factor  1 < 1 for   ) ~~ ~~~

5. Philip BambadeSUSY small angle electron tagging requirements - SLAC 6-8/1/2005 5 Preliminary  result benchmark point D’ with  m  -  = 12 GeV signal efficiency ~ 80% spectrum end-points preserved Mass extraction from endpoints :  m s  = 0.18 GeV and  m  = 0.17 GeV  m = 12 GeV  assumed tagging down to  ~ 25-30 mrad After requiring N  =2 Normalized for L=500fb -1 P.B. et al. hep-ph/0406010

6. Philip BambadeSUSY small angle electron tagging requirements - SLAC 6-8/1/2005 6 Preliminary  results benchmark point D’ with  m  -  = 5 GeV P.B. et al. hep-ph/0406010 H.-U. Martyn hep-ph/0408226 More difficult  Missing energies from neutrinos,  Very soft final state  electron tagging down to  ~ 5 mrad Two complementary strategies : i. For large signal cross section and 2m stau << E cm  end-point method ii. For small signal cross section and 2m stau ~ E cm  event counting method

7. Philip BambadeSUSY small angle electron tagging requirements - SLAC 6-8/1/2005 7 Main selection cuts for  1.Veto energetic forward electrons/photons 2.Number of charged tracks : 1 or 3 prongs, no 2 muons, charge conservation 3.15 o < q thrust < 165 o, acoplanarity angle < 160 o 4.P max 2.5 GeV 5.  T : P t sum w.r.t. the thrust axis in transverse plane to the beam > 2.75 (or 2) GeV (P Tmiss dependent) 6.Azimuthal cut on  T in the case of 20mrad crossing-angle Assumed ideal reconstruction in detector acceptance (modeled in SGV) Assumed ideal electron/photon veto down to 3.2mrad for P t > 0.8 GeV Z. Zhang

8. Philip BambadeSUSY small angle electron tagging requirements - SLAC 6-8/1/2005 8 Preliminary  result benchmark point D’ with  m  -  = 5 GeV Thrust axis angle in 3-dim  P T wrt thrust axis in the transverse plane Azimuthal dependence of the transverse momentum head-on crossing-angle efficiency ~ 11 % ~ 8 % Moderate effect of 2 nd hole after additional cut P.B. et al. hep-ph/0406010  c  20 mrad

9. Philip BambadeSUSY small angle electron tagging requirements - SLAC 6-8/1/2005 9 Luminosity, E CM and efficiency optimization benchmark point D’ with  m  -  = 5 GeV  mass precision wrt efficiency effect from 2 nd hole only Relative  mass precision from cross-section measurements near the production threshold with negligible background 8% 11%

10. Philip BambadeSUSY small angle electron tagging requirements - SLAC 6-8/1/2005 10 Mass measurement in case of background bkgd events 100 20 7 1 Mass precision degrades when background contribution increases Veto efficiency & analysis cut optimization essential High integrated luminosity will always help M. Berggren

11. Philip BambadeSUSY small angle electron tagging requirements - SLAC 6-8/1/2005 11 Tagging used & needed (preliminary examples) V. Drugakov angle [rad] rejection obtained (200 GeV) 10 -1 10 -2 10 -3 angle [rad]  /bin[fb] rejection needed for S/B ~ 1 ee  ee  after analysis cuts for  m  5GeV 0.005 0.010.02 0.010.02 10 -1 10 -2 10 -3 0.0050.010.02 algorithm Beamcal design  S/B ~ 1/2 Z. Zhang

12. Philip BambadeSUSY small angle electron tagging requirements - SLAC 6-8/1/2005 12 Simplifying assumptions, caveats  future work 1.Assumed 200 GeV electrons only  also low energy tail 2.Did not use all info  hard cases often accompanied by HE photon 3.Gain by specializing algorithm for HE electrons 4.Energy reconstruction and longitudinal distribution not fully used 5.Include (lower energy) em objects from Comptons in veto algorithm 6.Interpolation underestimates efficiency (limited statistical precision) 7.Muons/hadrons within the shower are not simulated 8. … Starting program to compare capabilities with respect to LC / MDI parameters ( besides BeamCAL itself ) Min.radius – L* – B field – crossing-angle ( + serpentine ) – N bunch – E CMS V. Drugakov, W. Lohmann rejection  f (angle) S/B in  with  m  5 GeV Criteria

13. Philip BambadeSUSY small angle electron tagging requirements - SLAC 6-8/1/2005 13 Summary and conclusions 1.Neutralinos and sleptons with small mass differences can be measured at the ILC 2.Important complementary to LHC 3.Link to cosmology : Planck constraints  2 % 4.reach (m,  m) / precision depend critically on very forward electron rejection :10 -1 - 10 -3  5-10 mrad 5.Program to compare capability wrt different LC and MDI parameters  Snowmass’05 6.Program to design, prototype and test BeamCAL 7.Check other ILC physics requiring forward veto