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Fisica del b in CMS

Fisica del b in CMS. N. Magini Università & INFN Firenze Parma, 19 Gennaio 2006. The CMS detector. 4 Tesla Solenoid. Muon system in return yoke. Tracker (Pixel + Silicon Microstrip) |h| < 2.4. ECAL & HCAL inside solenoid. Staged Scenario for start-up

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Fisica del b in CMS

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  1. Fisica del b in CMS N. Magini Università & INFN Firenze Parma, 19 Gennaio 2006

  2. The CMS detector 4 Tesla Solenoid Muon system in return yoke Tracker (Pixel + Silicon Microstrip) |h| < 2.4 ECAL & HCAL inside solenoid Staged Scenario for start-up 1. 3rd forward pixel disks missing 2. RPC up to |h| < 1.6 3. Single muon trigger up to |h| < 2.1, dimuon up to |h| < 2.4 22 m long, 15 m diameter, 14.000 ton Detector Fisica del B in CMS

  3. B-decays program Inclusive b production CP violation B0s Mixing Rare decays Bc b production atLHC Starting luminosity  1033 cm-2s-1 s = 0.5 mb  about 0.5 x106 b pairs/s only 100 ev/s on tape for ALL interesting physics channels The trigger strategy is a great challenge B Physics at CMS Fisica del B in CMS

  4. Inclusive b production bb differential cross section (from b m X) Expected CMS reach – up to pT~ 1 TeV/c b c b m X rate extracted from total m rate fitting the distributions of m pTw.r.t. the closest B jet udsg 120 < pT < 170 GeV/c Valery Andreev, David B. Cline, Stan Otwinowski Fisica del B in CMS

  5. Benchmark channels • Decays into muons (di-muon Lvl-1 Trigger) : • BS J/  KK (Bs mixing, CPV) • BS(d)  (rare decays) • Fully hadronic channel • (Single muon Lvl-1 Trigger from other B   + X ) : • BS DS (KK)  (Bs mixing) Fisica del B in CMS

  6. B0s oscillations s B0s B0s s s • Bs are too heavy to be produced at B factories • studied at hadron colliders Standard Model predictions DmS < 22.2 x 1012 s-1 @ 95% CL, DGs/Gs ~ 0.12 • PDG Experimental limits @ 95% CL DmS > 14.4 x 1012 s-1,DGs/Gs < 0.59 Latest result by CDF : DGs/Gs = 0.65 D0 : DGs/Gs = (25+14-15)% Fisica del B in CMS

  7. ℓ+ K+ ℓ- K- p p Bs  J/ Main ongoing activity: benchmark channel for B Physics studies in CMS Physics TDR – Vol. 2 • Angular distributions of decay products depend onGs,DGs,DMs(B0s mixing) and fs (CP Violation) 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) N. Magini, V. Ciulli, T. Speer, K. Prokofiev, L. Wilke, S. Shulga, T. Ilicheva Fisica del B in CMS

  8. Main backgrounds s at LHC • Signal B0s J/y f  m+m-K+K- 167 fb • Exclusive bkg B0d J/y K* m+m-Kp 900 fb • Inclusive backgrounds : • b  J/y X 51.4 nb • Prompt pp  J/y X 310 nb • In all samples : pT m > 2 GeV/c • In signal + Bd bkg : pT m > 0.5 GeV/c Fisica del B in CMS

  9. B0s J/y f  m+m-K+K- • Selection strategy • Trigger • L1 : double muon trigger • L2 : regional J/y reco with fast tracking • L3 : regional f + B0sreco with fast tracking • Offline • Kinematic fitting Optimization performed vs. the following backgrounds: Prompt pp  J/y X • Inclusive b  J/y X • B0d J/y K* Fisica del B in CMS

  10. CMS Trigger & DAQ Two level trigger: Lvl-1 and HLT 40 MHZ HW 50 kHz SW 100 Hz 4 DAQ slices at start-up  50 kHZ Fisica del B in CMS

  11. Level 1 Muon Trigger rates Low Lumi 16 kHz DAQ3.6 kHz for m, mm Lvl-1 thresholds optimized for discovery physics High - pT processes are selected b-jets are selected mainly by 1m and 2m trigger h < 2.1 14 ; 3,32.7+0.9=3.6 kHzeW =90%eZ =99%eBsmm =15% Bs  J/yf efficiency 33.3% Fisica del B in CMS

  12. Using the Tracker at HLT • Muon HLT stream optimized for high pT isolated muons  use the Silicon Tracker instead to reconstruct the decay chain at HLT • HLT track reconstruction has to be fast but does not need to be global as the offline one, therefore it can 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 pT Full tracker performance Fisica del B in CMS

  13. Bs  J/ • HLT L2 strategy Signal x 103 b  J/y X prompt J/y • Transverse decay length resolution ~ 100 mm • c2 < 10 and LT/s(LT)> 3  Rate = 10 Hz, <t> ~ 190 ms ~ 80% of L2 J/ are from b •  150 MeV/c2 around J/ mass Tracks reconstructed with 5 hits around L1 muons - |Dh| < 0.15 , |Df| < 0.5 Fisica del B in CMS

  14. Bs  J/ • HLT L3 strategy Regional tracking around J/ direction |Dh| < 0.9, |Df| < 0.9 f mass  20 MeV/c2 B0s mass  190 MeV/c2 Fisica del B in CMS

  15. Bs  J/ • Offline selection strategy • Combinatorial decay chain reconstruction • Kinematic fitting – application of constraints from decay kinematics • J/y mass constraint DM(f)<12 MeV/c2, DM(B0s) < 67 MeV/c2 Fisica del B in CMS

  16. Bs  J/ Proper time resolution Fisica del B in CMS

  17. Event selection • Events selected per 10 fb-1 • Estimated S/B ~ 6, but very limited statistics for backgrounds  larger MC sample produced • Vertex pointing (cos a > 0.9) • Dm f < 12 MeV/c2 • Dm B0s< 67 MeV/c2 Fisica del B in CMS

  18. Bs J/ Analysis Two methods may be used to extract parameters of interest from angular distributions • Unbinned maximum Likelihood fit Fisica del B in CMS

  19. Angular moments method Time evolution is a function of the transversity amplitudesA0(t), A||(t), A(t) which contain the parameters of interest  A set of 6 weighting functions wi(1,2,) is defined to separate the 6 bi(t)components Known functions of the three helicity angles1,2,describing decay product kinematics Fisica del B in CMS

  20. Angular moments method • Statistical error with 64k generator level events • Sources of systematics: • Background contamination • Detector resolution • effect shown to be negligible • Selection efficiency bias • Taking into account these effects, after 3 years at low luminosity (60 fb-1): error on ΔΓs /Γs < 0.018 Fisica del B in CMS

  21. Bs(d)mm • Lvl-1: 2 pT> 3 GeV/c, =15.2% • HLT strategy: • Select pixel seeds with pT > 4 GeV/c 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/c2window • Vertex: c2 < 20 and drf > 150 mm FCNC bs or bd only at loop-level in SM  BR(Bsmm) = (3.5±1.0)x10-9 MSSM enhancement (high tanβ) probe for new physicsBR(Bsμμ)=3x10-6(tanβ/50)6(200 GeV/c2 / mA)4 U. Langenegger, A. Starodumov, P. Trüb Fisica del B in CMS

  22. Bsmm Mass resolution Full Tracker HLT s = 50 MeV/c2 s = 74 MeV/c2 Offline analysis (hep-ph/9907256) based on SV cuts (decay length and direction) + Tk/Calo Isolation: with SM BR=3.5x10-9 10 fb-1  7 signal events with < 1 background 5s observation with 30 fb-1 and analysis could be perfomed at high lumi too Fisica del B in CMS

  23. 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/c , R=3.2 kHz • 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/c, pT(DS) > 4 GeV/c, pT(BS) > 5 GeV/c • Mass reconstruction: DM<15 MeV/c2, DMDs<75 MeV /c2, DMBs<270 MeV/c2 • HLT efficiency 9% Fisica del B in CMS

  24. 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) s = 95 MeV /c2  Ds Bs s = 25 MeV/c2 s = 5 MeV/c2 1 year low luminosity (20 fb-1): Lvl-1 1 kHz HLT 5 Hz 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 Fisica del B in CMS

  25. Bc Physics M = 6287.0 ± 4.8 ± 1.1 MeV/c2 t = 0.46+0.18−0.16± 0.03 ps Bc→J/ψµν (J/ψ→µµ) Bc→J/ψπ(J/ψ →µµ) 258 evts after 1 fb-1 (+156 for e chan) 70 evts after 1 fb-1, Mass RMS 76 MeV But still need to study bkg rejection Decay length residual RMS 25 mm J.Q. Tao, G.M. Chen, C.H. Jiang Fisica del B in CMS

  26. High Level Trigger table for low lumi • Allocation of additional 50 Hz to “Standard” Physics ? In this case we would like to trigger on the full 10 Hz bJ/yX rate • Bandwith for B-physics at LHC start-up will also depend on actual luminosity • Lower luminosity at startup  higher B-bandwith Where is B – physics ? Table optimized in DAQ-TDR for discovery physics From DAQ-TDR (CERN/LHCC 2002-26) Fisica del B in CMS

  27. Conclusions • CMS is a competitive detector for B-physics, even if it is not designed specifically for it • Low-pT dimuon L1 Trigger and use of Fast Tracking at HLT are fundamental for B-decay selection • We should profit from LHC starting conditions: Low luminosity for a while  lots of B physics • In only a few months: the Physics TDR Vol. 2 will address in deeper detail the CMS B-physics potential,with a chapter dedicated to the full analysis for theB0s J/y fbenchmarkchannel and sections on the other topics Fisica del B in CMS

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