IP crossing-angle and LC technology recommendation Philip Bambade LAL, Orsay 5 th ITRP meeting, Caltech, USA Session on detector & physics issues June 28, 2004

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ Context warm LC  c [mrad]  20, 7 cold LC  c [mrad]  20, 7, 0 magnitude important aspect of machine design TRC recommended (R2 item) that the technical pros / cons of the TESLA head-on scheme – especially the extraction – be critically reviewed and to consider also designs with a finite  c – e.g. 20, 7 mrad or eventually other possibilities (0.6 and 2 mrad) LC scope calls for 2 e  e  IR with similar energy and luminosity, one of which with  c ~ 30 mrad to enable a future  -collider option Importance for detector & physics ?

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ ITRP crossing-angle questions 1. “The presence of a crossing angle, while not fully correlated with the technology choice, will have experimental impacts upon the precision of measurement of energy, energy-wtd luminosity, and polarization. Discuss physics consequences of having 0 crossing angle with no final beam measurements possible, versus a finite crossing angle, which permits measurements of the spent beam.” 2.“In the case of a crossing angle, the beam axes differ from the magnetic field direction. What complication does this cause for the experiments? Does it argue for keeping the crossing angle as small as possible?” 3. “Are there differences in the coverage dictated by differences in the final focus elements for the two technologies?”

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ Energy and polarization from beam-based measurements

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ BPMs  E/E ~ (1 – 2)   linac E spread  dL/dE also from Bhabha analyses post – IP more difficult without large  c SPECTROMETRY pre – IP  all designs  E/E ~ (1 – 2)  linac E spread with other pre-IP device

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/  P/P ~ (2.5 – 5)  Compton scattering  extrapolation clearance from spent beam probes beam-beam effects post – IP requires large  c POLARIMETRY pre – IP  all designs  P/P ~ (2.5 – 5)  Compton scattering  extrapolation optics constraints M. Woods et al. SLAC-PUB-10353

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ How important are additional post – IP spectrometer and polarimeter ?  Different systematics !  Errors   Beam-beam effects  correlations Physics needs : ~ 5  searches  2  HE SM tests < 1  GigaZ Precision of each pre- & post-IP measurement (1 – 2)  (2.5 – 5)  E P  2  m top, m higgs  5  m W, A LR

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ Full beam-beam effect ~  lumi-weighted K. Mönig Post-IP can compare with / without collisions Post-IP “magnifying glass” for beam-beam effect Real conditions : must correlate to offsets, currents,

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ Effects from misalignment of solenoid and beam axes steering and spin precession backgrounds

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/  c  0  solenoid steers  spin precesses IP IP y angle ~ 100  rad IP y offset ~ - 20  m  (  y ) ~ 85  rad  (y) ~ 3 nm spin precession ~ 60 mrad if uncorrected  ~ 0.2 % depolarization with perfect beams (or else larger)  c = 20 mrad must compensate ! A.Seryi and B. Parker

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ Adds ~ 0.01 of B z along x in detector TPC tracking  map B z to to control distortions Larger backgrounds and steering of the spent beam Option for local correction with extra dipole fields within the detector + before + after IP With compensation IP

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ New TESLA design, K. Büsser and A. Stahl Beam – beam pairs in instrumented mask / BeamCAL T. Maruyama Total pair statistics

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/  c  20 mrad  twice more energy from pairs in BeamCAL Complex shapes, beam param. extraction more complicated GeV / cm 2 TESLA head-on TESLA  c = 20 mrad Cold head-on /  c  20 mrad

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ GeV / cm 2 TESLA head-on TESLA  c = 20 mrad for crossing angle, smaller background enhancement wrt headon if outgoing hole is increased ; also helps relax collimation requirements if collimation requirements impose to increase the exit hole, then the vertex detector radius would increase as well in the head-on case Collimation  exit hole radius  vertex detector radius

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ Total pair energy in Warm / Cold  c  20, 7, 0 mrad Warm / R  2cm / 20mrad with Serpentine ~ Cold / R  1.2cm / 0mrad Smallest effects for Warm / 7mrad Total pair energy can be used for luminosity monitoring in all cases T. Maruyama out-going hole radius [cm] cold: R incoming = R outgoing

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ Forward Tracking Disks FTD Hits on vertex detector Detector occupancies are up to factor 2 larger if  c  20 mrad and the outgoing hole is not enlarged with respect to the head-on case Still at tolerable levels More on occupancies in H. Yamamoto’s talk on pile-up issues  c  20 mrad  more backscattering into main detector  asymmetrical distributions Hits on forward chamber New TESLA design, K. Büsser and A. Stahl

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ Reduction in SUSY coverage from IR geometries with  c  0 scenarios with quasi – degenerate mass spectra

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ signal major background ee    0   0 ee  (e)(e)    ~ 10 fb  ~ 10 6 fb Transverse view Dark matter SUSY scenarios  slepton & neutralino masses often very close (co-annihilation mechanism) e.g. search & measure stau with  m  -   3 – 9 GeV  c  0  harder to eliminate signal – like  - processes P.B. et al. hep-ph/ M. Battaglia et al. hep-ph/ ~

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ Preliminary  result benchmark point D’ with  m  -  = 12 GeV signal efficiency ~ 80% spectrum end-points preserved   m s  = 0.18 GeV and and  m  = 0.17 GeV for this benchmark point  smallest  m s  -  detectable as function of veto angle and quality ? After requiring N  =2 Normalized for L=500fb -1 Same performance for both head-on and crossing-angle collisions P.B. et al. hep-ph/

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ 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 % Effect of 2 nd hole after re- optimizing the analysis P.B. et al. hep-ph/  c  20 mrad

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ 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%

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ Importance of high veto efficiency BeamCAL ee    0   0 ee  (e)(e)    ~ 10 fb  ~ 10 6 fb analysis   ~ 1 fb  ~ 600 fb analysis + veto   ~ 1 fb  ~ 0.7 fb  veto ~ S/N ~ 1 10 mrad  m  -   5 GeV ~ S / B depends crucially on  VETO for the HE electron superimposed on the pairs  c  20 mrad  factor 2 increase in deposited pair background energy Potential additional effects from pile- up will be addressed in K. Mönig’s and H. Yamamoto’s talks

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ Summary : post-IP diagnostics Post-IP energy spectrometry is desirable to complement the pre-IP calibration and to give another handle on the luminosity spectrum. It will be important to reach, together with analyses of dedicated physics calibration channels, ultimate SM measurement precision. The design of a post-IP spectrometer is more difficult without a large enough  c. The same is true for post-IP polarimetry. A design seems quasi- impossible in this case without a large enough  c. A post-IP polarimeter, correlated with other measurements of the spent beam (orbits, intensities,…) is important to probe beam-beam depolarizing effects, in order to validate the simulation and assist in controlling the systematics involved.

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ Summary : solenoid /  c Steering and spin precession from the solenoid with  c  20 mrad must be corrected. Adding steering dipoles within, before and after the detector can compensate for these effects. The additional B field must be taken into account in the tracking, especially in the context of correcting distortions in a TPC. For  c  20 mrad, pair deposition in the instrumented mask and backscattering in the detector increase by factors , from the solenoid and beam axes misalignment and additionally from the compensating steering. Occupancies remain tolerable though some hit distributions become asymmetrical and contain structures complicating the interpretation. Such effects are less important for  c  7 mrad.

Philip Bambade LAL/Orsay x-angle & LC technology choice ITRP 28/6/ Summary : hermeticity To enable precise mass measurements in SUSY models with degenerate spectra typical of scenarios proposed to explain Dark Matter, it is critical to tag forward high energy electrons very well. The slepton detection efficiency and mass measurement precision are reduced for  c  20 mrad, because of the 2 nd hole for the in- coming beam and because of larger pair background. The reduction strongly depends on the mass difference between the sparticle considered and the lightest SUSY particle (the neutralino). It is largest for the smallest mass differences. In a realistic case study with stau (smuon) mass 5 (12) GeV heavier than the neutralino, efficiency losses from the 2 nd hole were 25% (negligible), after re-optimizing the analysis. Meaningful estimates of further losses from the increased pair background, taking into account an appropriate optimization of the electron veto algorithm, are not yet available.