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Advancements in B Physics at CMS: Inclusive B Production and Rare Decays

This document discusses the latest progress in B physics at the CMS detector, focusing on inclusive B production and the study of rare decays. It highlights technical aspects of the CMS setup, including the integrated 4 Tesla solenoid and muon systems. Key benchmarks for B physics, such as B0s mixing and CP violation, are emphasized alongside the experimental strategies implemented for signal extraction and background suppression. The challenges faced in triggering and data acquisition at low luminosity are outlined, alongside ongoing research into important decay channels like Bs → J/ψφ and their implications for particle physics.

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Advancements in B Physics at CMS: Inclusive B Production and Rare Decays

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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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