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CMS – B Physics Reach

CMS – B Physics Reach. V. Ciulli INFN Firenze on behalf of CMS collaboration IV INTERNATIONAL SYMPOSIUM ON LHC PHYSICS AND DETECTORS FERMILAB, MAY 1-3 2003. B-decays program Rare decays CP violation B 0 s Mixing b production at LHC

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CMS – B Physics Reach

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  1. CMS – B Physics Reach V. Ciulli INFN Firenze on behalf of CMS collaboration IV INTERNATIONAL SYMPOSIUM ON LHC PHYSICS AND DETECTORSFERMILAB, MAY 1-3 2003

  2. B-decays program Rare decays CP violation B0s Mixing b production atLHC peak luminosity: 2x1033 cm-2s-1 -> 1034 cm-2s-1 s = 0.5 mb  O(105-106) b pairs/sec only 100 ev/sec on tape for ALL interesting physics channels The main challenge is the trigger strategy Some benchmark channels analysed BS BSJ/ KK BSDS(KK)  Results from DAQ-TDR (CERN/LHCC 2002-26) B Physics at LHC CMS - b Physics Reach

  3. Trigger & DAQ architecture Two level trigger: Lvl-1 and HLT 40 MHZ 100 KHz 100 Hz Several staging scenarios possible. Each slice allows 12.5 KHz CMS - b Physics Reach

  4. Trigger & DAQ architecture Two level trigger: Lvl-1 and HLT 40 MHZ 50 KHz 100 Hz Several staging scenarios possible. Each slice allows 12.5 KHz 4 DAQ slices at start-up => 50 KHZ CMS - b Physics Reach

  5. A closer look to Lvl-1 trigger Total output rate: 50 kHz x 1/3 “safety” => 16 kHz allocated Low luminosity table => • Lvl-1 thresholds optimized for a wide physics discovery program • high-pt processes are selected b-jets are selected mainly by 1m and 2m trigger CMS - b Physics Reach

  6. Lvl-1 Trigger: Muon Stream Integrated muon rates above threshold Low Lumi 16 kHz DAQ3.6 kHz for m, mm h < 2.1 h < 2.1 14 ; 3,32.7+0.9=3.6 kHzeW =90%eZ =99%eBsmm =15% Muon rate dominated by ,K decays up to 4 GeV, then by b-, c-quark decays up to 25 GeV CMS - b Physics Reach

  7. • • • • • • • • • • • • • • High Level Trigger 40 MHZ Implemented on a PC farm: 300 msec/ev on 1GHz PIII (±50% uncertainty) Same software as for offline 50 KHz 100 Hz Low lumi A total of 30 Hz are allocated to muons 25 Hz single 5 Hz di-muons In addition non-isolated muons are rejected 30 Hz CMS - b Physics Reach

  8. HLT single muon stream content W 25 Hz b/c Only ~5 Hz are b/c events: 1 Hz -> 107 ev/year at low lumi Not enough for decays with BR<10-4 and selection efficiency <10% CMS - b Physics Reach

  9. HLT Tracking • Previous results can be improved by using Tracking in the High Level Trigger • HLT reconstruction has to be fast but not as global and precise as the offline one • HLT Tracking can therefore be: • Regional • Restricted to some phase-space region defined from external Lvl-1 information (e.g. a cone around muon/jet direction or the set of tracks coming from a vertex or above a PT threshold ) • Partial • Stopped after a number of hits have been assigned to the track • Conditional • Stopped when enough resolution is reached or on other condition CMS - b Physics Reach

  10. 10-30 7cm 4cm x z0 z Primary vertex reconstruction • Hit pairing with a straight line in rz • IP1 mm • PT>1 GeV • Matching with 3rd layer  track candidate • PV candidate if  3 track cross z-axis • Signal vertex from PT and Ntracks y y s = 26 mm PV efficiency >95% in high luminosity events Track candidates pointing to the PV used in the following reconstruction Average time:50msec/1 GHz CMS - b Physics Reach

  11. Partial reconstruction • Good track parameters resolution with 4-5 hits •  half the time for full reconstruction needed IP Time vs hits in 100 GeV b-jets Pt Full tracker performance CMS - b Physics Reach

  12. Benchmark channels • Di-muons Lvl-1 Trigger: • BS • BSJ/ KK • Single muon Lvl-1 Trigger (second B+X) • BSDS(KK)  CMS - b Physics Reach

  13. Bsmm • Lvl-1: 2 PT>3GeV, =15.2% • HLT strategy: • Select pixel seeds with PT > 4 GeV in - region around trigger ’s • Conditional tracking: • stop if pt<4 GeV/c @ 5σ or Nhit=6 or σ(pt)/pt<0.02 • Bs reconstruction if only 2 track candidates with opposite charge in 150 MeV window • Vertex: c2 < 20 and drf > 150 mm • Average CPU Time = 240 msec / 1GHz CPU FCNC b->s or b->d only at loop-level in SM => BR(Bsmm)=(3.5±1.0)x10-9 CMS - b Physics Reach

  14. Bsmm Mass resolution Full Tracker HLT s = 46 MeV s = 74 MeV Offline analysis results (hep-ph/9907256), using SM BR=3.5x10-9 (Lvl-1 trigger in |h|<2.4 instead of |h|< 2.1) 10 fb-1 => 7 signal events with <1 background 5s observation with 30 fb-1 and analysis could be perfomed at high lumi too CMS - b Physics Reach

  15. BsJ/ BR(BsJ/ )=(9.3±3.3)x10-4 J/ℓ+ℓ-(BR≈6%) K+K-(BR≈49%) CP violation weak phase s= 2dg= 22 SM predicts s~O(0.03) • HLT strategy: • Lvl-2: reconstruct muons as for Bs  mm • 100MeV window around J/ mass, c2 < 20 and drf > 200 mm • Rate = 15 Hz, <t>~260ms • 90% of Lvl-2 J/ are from b’s • Lvl-3: reconstruct f and Bs • Regional tracking around J/ direction • <t>~800ms CMS - b Physics Reach

  16. BsJ/ HLT mass resolutions s = 46.5 MeV s = 2.2 MeV s = 22.4 MeV J/  Bs CMS - b Physics Reach

  17. BsJ/ CERN-2000-04 ℓ+ Angular analysis of Bs->J/yf->mmKK on a sample of 600 x 103eventsyields: K+ ℓ- K- Error on ΔΓs vs stats 30 fb-1 dΔΓs /ΔΓs ~ 15 % ds(xs=20) ~ 0.025 rad ds(xs=40) ~ 0.05 rad CMS - b Physics Reach

  18. BsDs(KK)  BS-BS mixing: DmS 14.4 ps-1 @95%CL P(b  Bs) x Br(Bs DS f   K K  ) ~ 5 x 10-5 • L1 1 trigger: PT>14GeV, R=3.2KHz • HLT strategy: • pixel seeds in full acceptance and Primary Vertex • Partial tracking: 2 pixel and 1 strip hits • Topological cuts: DR(KK)<0.3, DR(p)<1.2, DR(DSp)<2.0, Df(BS,m)>0.6 • Kinematical cuts: PT()>2GeV, PT(DS)>4GeV, PT(BS)>5GeV • Mass reconstruction: DM<15MeV, DMDs<75MeV, DMBs<270MeV • HLT efficiency 9% • <t> = 640 msec CMS - b Physics Reach

  19. Can not be run on full Lvl-1 2.7 KHz because of large output rate: still room to improve BsDs(KK)  Mass resolutions (only 3 hits are used)  Ds Bs s = 25 MeV s = 95 MeV s = 5 MeV 1 year low luminosity (20 fb-1): Lvl-1 1KHz HLT 5Hz 300-400 signal events =>DmS up to 20 ps-1 1000 events are needed to test allowed SM range: DmS 26 ps-1 @99%CL CMS - b Physics Reach

  20. B-triggers in HLT table • Bandwith for B-physics at LHC start-up will depend on: • Luminosity • Lower lumi => higher B-bandwith • Background conditions • If good factor 3 for safety may have been overestimate • In addition a possible strategy is introducing B-triggers as the luminosity drops during the fill CMS - b Physics Reach

  21. Conclusions • CMS is a competitive detector for B-physics, even if it is not designed specifically for it • A key point is B-decay selection in the High Level Trigger thanks to fast tracking • A proof of concept has been given on few benchmark channels in the DAQ TDR • Much will depend on LHC starting conditions: Low lumi for a while  lot of B physics • Computing and Physics TDR’s will address in more details the CMS B-physics potential CMS - b Physics Reach

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