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Early physics of LHCb Malcolm John On behalf of the LHCb collaboration

Early physics of LHCb Malcolm John On behalf of the LHCb collaboration. Very brief introduction Status of LHCb A selection of the most promising results. ( r , h ). *. V ud V td. *. V cd V cb. a. (1- l 2 /2)( r , h ). *. V ub V tb. b + c. *. V cd V cb. *. *. V td V tb.

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Early physics of LHCb Malcolm John On behalf of the LHCb collaboration

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  1. Early physics of LHCb Malcolm John On behalf of the LHCb collaboration • Very brief introduction • Status of LHCb • A selection of the most promising results

  2. (r,h) * Vud Vtd * Vcd Vcb a (1-l2/2)(r,h) * Vub Vtb b+c * Vcd Vcb * * Vtd Vtb Vtd Vtb * * Vub Vud Vub Vud a g-c * * Vcd Vcb Vcd Vcb Vcd Vcb Vcd Vcb (1-l2+rl2,hl2) * Vus Vts 2 * g Vcd Vcb b (0,0) (0,0) (0,1) At LHCb terms up to l5 must be considered (r,h) a g c b Major LHCb goals: Weak phase,,g Bs mixing phase fs = -2c  -2arg(Vts) B(Bs  ) (0,0) (0,1)

  3. bb produced into forward region • spp→bb(s=14TeV)  500mb • operate at ℒ = 2x1032 cm-2s-1 • 1012 b-hadrons a [107s] year • <momentum>  80 GeV/c • <d.o.f.(B)> = 7mm The LHCb detector status in a nut-shell • All major sub-detector intrastructure is installed and instrumentation is well underway • LHCb will be ready to [space and time] -align during the 2007 LHC engineering run • 2008: Calibrate the complete detector and trigger for s =14TeV Expect 0.5fb-1 (50 billion b-quarks) • 2009: Full physics data-taking Expect 2fb-1/year

  4. LHCb at LHC - P8 Inset: retracted HCAL & muon filter

  5. VErtex LOcator • 170 000 channels • 8.1mm from beam • (40<pitch<100)mm • sZ(PV) < 50mm • st(Bs) < 40fs Beam’s eye view

  6. Simulation • Expectations are evaluated using the LHCb MC simulation software: Pythia, EvtGen, GEANT4 and Gaudi-based reconstruction (2004 MC data) • Detailed detector and material description (GEANT) • Pattern recognition, trigger simulation and offline event selection • Implemented detector inefficiencies, noise hits, effects of events from the previous bunch crossings Slide by Peter Vankov

  7. (1-l2/2)(r,h) a * * Vub Vud Vtd Vtb * * Vcd Vcb Vcd Vcb b (0,0) (0,1) Bs→ Ds K B→ D0K(*) g = (82±20)°(current direct measurements)

  8. g from Bs →DsK • Study sensitivity by generating toy-experiments with experimental inputs derived from full MC (Decay time and mass resolution, reconstruction efficiency, tagging…) • Sensitivity with 2 fb-1 : σ(g) ~ 13° + ch.c. diagrams • Two tree decays (bc and bu), which interfere via Bs mixing: • can determine (s + ), hence in a very clean way • Fit 4 tagged, time-dependent rates • Extract s + , strong phase difference , amplitude ratio • Bs Ds also used in the fit to constrain other parameters (w, ms,s) Expect 140 000 Dsp 98% suppression achieved with RICH PID system in the analysis Used to measure Dms 2 fb–1: s(Dms)  0.012ps–1 Expect 6200 DsK events in 2 fb–1 B/S < 0.5

  9. g from Bu,d →D0K • Interplay of Bu and D0 decays where interferes with • charged Bs only (time-independent, direct CPV) • choose decay hierarchies in which large CP asymmetry is possible • “tree-level” dominates. No penguins pollution Colourfavoured bcamplitude Colour suppressed bu amplitude → X  → X Benefit from CLEO-c … • A similar analyses possible with B0→D0K*0decays • The b→c transition is also colour suppressed. Expect large CP-asymmetries • self-tagging (i.e. the b-quark flavour is given by the sign of the prompt signal kaon) † favoured decay (not sensitive to g)

  10. (r,h) a * * * Vub Vtb Vus Vts b+c Vud Vtd * * * Vcd Vcb Vcd Vcb Vcd Vcb g-c (1-l2+rl2,hl2) 2 (0,0) fs = -2c  -2arg(Vts) Bs→ J/yf …etc… and Bs→ ff c

  11. Illustration of CPV: toy-modeling LHCb data with s = -0.2 (i.e. 5SM) events tagged as Bs events tagged as Bs Bs mixing phase: fs • The equivalent of “sin2b“ for Bsmesons • In the standard model, fs is small: = -2arg(Vts)  0.0360.003 • Could be larger if New Physics is present in the box diagram • Recent D0 result s= –0.79 ±0.56(stat) +0.14–0.01(syst) with 1.1 fb–1 • To resolve Bs oscillations, excellent proper time resolution is required • Modes sensitive tofs : • CP-odd & even: Bs→ J/y f • CP-even only: Bs→ hc f Bs→ J/yh Bs→ Ds Ds • Control channel (Dms): Bs→ Ds p

  12. Current, including first measurement of ms With (s)= ±0.03 (~ 2 fb–1) (different x-scale) ss ss >90% CL >32% CL >5% CL from hep-ph/0604112 0.5 hs hs Precision on a measurement of fs = 0.04 0.020 2fb-1 0.044 0.5fb-1 0.5 Arbtrary new physics parameterisation: MNP = MSM (1+hseis)

  13. Bs →ff • FCNC gluonic penguin decay. Analogue of B0→fKsfor the Bs • Dependence on Vtsin both the decay and Bs mixing amplitudes, phase cancels and leads to the SM CP-violation expectation < 1% • Large CP asymmetry would be a signature of New Physics • The PVV decay requires a full angular, time-dependent CP analysis • Expect 4000 events/2 fb-1 (based on a CDF B.F. measurement: 1.40.9 x10-5) • Early feasibility studies suggest LHCb statistical precision on a New Physics phase (defined at 0.2 for the purposes of this work) in 2fb-1 is: ~0.10 • Current combined, B-factory measurement of sin 2β in B0 →K0S : 0.39 ± 0.18 • For comparison, the 2 fb-1 LHCb sensitivity in this mode is 0.32

  14. New Physics enhancement of very b m t Z0 b m Bs W H0/A0 c t Bs m W b s m b m t s Bs t nm s m B.F.(Bsmm)MSSMtan6b W B.F.(Bsmm)SM3.5x10-9 Bs→ mm and Bs→ K*0mm rare B-decays

  15. LHCb sensitivity (signal+bkg is observed) LHCb limit on BR at 90% CL (only bkg is observed) BF (x10–9) BF (x10–9) 5 observation Expected final CDF+D0 limit SM Uncertainty in bkg prediction 3 evidence SM “early” period Integrated luminosity (fb–1) Bsmm expected sensitivity • Very exciting possibility of sensitivity to New Physics enhancement in the early period • Current upper limit from the Tevatron is around 20 x SM prediction • The dominate background is b , b. • Background analysis is currently limited by Monte Carlo statistics (generation) • LHCb’s superior Bs invariant mass resolution is crucial in the background rejection

  16. AFB(s), theory + B0 q K* – AFB(s), fast MC, 2 fb–1 s = (m)2 [GeV2] s = (m)2 [GeV2] NP model descrimination possible with B0 K*0m+m- • Suppressed loop decay, BR ~1.210–6 • Forward-backward asymmetry AFB(s) in the  rest-frame is sensitive probe of New Physics: • Sensitivity (ignoring non-resonant K evts for the time being) • 7.2k signal events/2fb–1, Bbb/S = 0.2 ± 0.1 • After 2 fb–1: zero of AFB(s) located to ±0.52 GeV2 • Other sensitive observables based on transversity angles accessible (under study)

  17. Conclusion • LHCb is a spectrometer experiment at the LHC which instruments the forward region of the LHC hadron collision • The final assembly and commissioning is on schedule: ready to take calibration and alignment data this autumn • LHCb has a rich physics program and most analyses expect good results in the early period (<2fb-1): • Observation of Bs→mm • s(g)LHCb 5 degrees • s(fs)LHCb 0.02 radians • Sensitivity to New Physics phase in Bs →ff • In addition, • (Dms)  0.012ps–1 • (sin(2))  0.02 (2x105/2fb–1) [final B-factory result: σ(sin(2))  ± 0.017stat] • ()  10 degrees • ACP(K*) measured at % level (ACP < 1% in SM) • Charm physics: • D0 mixing (expect ~ 45k D0 candidates in final fit sample… 5x B-factories’ combined yield) • direct CPV in D0K+K– • D0+– • and I’m sure I’ve under-represented someone…`

  18. (r,h) a * * * Vus Vts Vub Vtb b+c Vud Vtd * * * Vcd Vcb Vcd Vcb Vcd Vcb g-c (1-l2+rl2,hl2) 2 (0,0) Supplementary Slides c

  19. Dz/bgc = Dt K+ u u s s b b K - l + (e+, m+) Same-side tag l - (e-, m-) Uses flavour conservation in the hadronization around the Brec eD2  1% (B0) , 3% (Bs) eD2  5% Opposite side tag Assume: Time-dependent analysis requires B flavour tagging • We need to know the flavour of the B at a reference t=0 (at the primary vertex) • Tag (give best estimate of) the flavour by examining the rest of the event Bs0 rec t =0 Dt picoseconds after leaving the primary vertex, the reconstructed Bdecays. b-hadron PV

  20. Aerogel 22 tiles RICH systems • Particle ID: p~1-100 GeV provided by 2 RICH detectors RICH2 Slide by Val Gibson

  21. A successful trigger is crucial in LHCb • Only ~1% of inelastic collisions produces b-quarks. • Branching fractions of interesting B decays are <10-4 • Properties of minimum bias events ate similar to those containing B decays • First Level Trigger (L0) • Hardware (custom boards, 4ms latency) • Largest ET hadron, e(g) and (di-)m • Pile-up system (not for m trigger) • Reduces 10 MHz inelastic rate to 1MHz • High Level Triggers • Software trigger run on CPU farm (1800 nodes) • Access to all detector data • Full event reconstruction; inclusive and exclusive selections tuned to specific final states • Output rate 2 kHz, 35 kB per event Slide by Olivier Schneider

  22. PYTHIA+GEANT full simulation RICH1 VELO TT Magnet RICH2 T1 T2 T3 Expected tracking performance • High multiplicity environment: • In a bb event, ~30 charged particles traverse the whole spectrometer • Track finding: • efficiency > 95% for long tracks from B decays(~ 4% ghosts for pT > 0.5 GeV/c) • KS+– reconstruction 75% efficient for decay in the VELO, lower otherwise • Average B-decay track resolutions: • Impact parameter: ~30 m • Momentum: ~0.4% • Typical B resolutions: • Proper time: ~40 fs (essential for Bs physics) • Mass: 8–18 MeV/c2 * * with J/ mass constraint Slide by Olivier Schneider

  23.  invariant mass With PID With PID  invariant mass K invariant mass Particle ID performance • Average efficiency: • K id = 88% •  mis-id = 3% • Good K/ separation in 2–100 GeV/c range • Low momentum • kaon tagging • High momentum • clean separation of the different Bd,shh modes • will be best performance ever achieved at a hadron collider No PID Slide by Olivier Schneider

  24. * * Vtd Vtb Vub Vud * Vcd Vcb Vcd Vcb (1-l2+rl2,hl2) 2 At LHCb terms up to l5 must be considered * (r,h) Vud Vtd (1-l2/2)(r,h) * Vcd Vcb * a Vub Vtb * a Vcd Vcb b+c g-c g * b Vus Vts c * Vcd Vcb (0,0) (0,1) (0,0) Major LHCb goals :Weak phase,,g Bs mixing phase fs = -2c  2arg(Vts)

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