B-Physics Potential of ATLAS, CMS, LHCb and BTeV

Transcription

1 B-Physics Potential of ATLAS, CMS, LHCb and BTeV Neville Harnew University of Oxford 8th International Symposium on Heavy Flavour Physics N.Harnew 29th July

2 Outline Introduction The 2nd Generation experiments : LHCb,B-TeV,ATLAS,CMS. Precision measurements : CP-violation, rare B decays. Performance summary N.Harnew 29th July

3 Introduction Before 2005 various experiments will explore the unitarity triangle : Im V ud V ub + V cd V cb + V td V tb = 0 sin 2β well measured by BaBar/Belle/ HERA-B/CDF/D0 perhaps to ~ Side opposite γ : known assuming B s mixing is measured by (SLD/LEP?) CDF/D0 Side opposite β : significant hadronic error sin 2α measured - but with poor statistical precision and significant theoretical uncertainties η(1 λ 2 /2) η 0 λ V cb (1 λ 2 /2)V ub Im V ub λ V cb γ α ρ(1 λ 2 /2) V td λ V cb V tb V ub + V ts V us + V td V ud = 0 β (1 λ 2 /2)V td λ V cb 1 Re γ no good or direct measurement ηλ 2 0 γ ρ δγ V ts V cb (1 λ 2 /2+ρλ 2 ) Re N.Harnew 29th July

4 Decay modes to measure triangle parameters High statistics B d D nπ ππ ρπ γ detection V ub Good πk separation α V td B s mixing Good decay time resolution B s D S K Good πk separation V ub V td γ V cb β γ V ts B d DK High statistics B d J/ψK S δγ B s J/ψφ N.Harnew 29th July

5 Either : Inconsistency in gold plated measurements (eg. β and mixing side) Or : Hint of inconsistency, or inconsistency with less precise data (eg. α,kaon asymmetries) Or : Measurements consistent with SM interpretation In all cases, next generation experiments at LHC/Tevatron will need to make precise investigation of CP violation Precision measurements : same parameters in previously measured channels Different channels (theoretically clean but not necessarily easiest experimentally) : cross checks of same parameters New parameters : eg. What is γ? B s sector : relatively unexplored by Phase 1 N.Harnew 29th July

6 Comparison of the LHC and the Tevatron experiments Tevatron LHC Energy / collision mode 2.0 TeV pp 14.0 TeV pp bb cross section ~100µb ~ 500 µb Inelastic cross section ~50mb ~80mb Ratio bb / inelastic 0.2% 0.6% Bunch spacing 132 ns 25 ns BTeV LHCb ATLAS / CMS Detector configuration Two-arm forward Single-arm forward Central detector Running luminosity 2x10 32 cm -2 s -1 2x10 32 cm -2 s -1 1x10 33 cm -2 s -1 bb events per 10 7 sec 2x10 11 x accept. 1 x xaccept. 5x10 12 xaccept. <Interactions/crossings> ~ (~30% single int.) ~ 2.3 N.Harnew 29th July

7 Advantages of forward detector geometry bb production sharply peaked forward-backward At LHC, low luminosity is sufficient (2.0x10 32 cm -2 s -1 ) Less radiation >80% triggered events single interactions Vertex detector close to interaction region. <p B > Accepted ~80GeV/catLHC Mean flight path of B s ~7mm Open geometry allows for easy installation and maintenance Disadvantages Minimum bias also peaks forward High occupancy, high track density 3 θb [rad] B 0 π π + d in 4π with π π + measured 3 θ b [rad] B 0 decay length [cm] N.Harnew 29th July

8 The BTeV Detector Key design features Forward double arm spectrometer Precision pixel vertex detector inside dipole B field ( B.dL=5.2 Tm) Vertex trigger at first level Single RICH detector for particle ID Lead tungstate EM calorimeter for γ and π 0 reconstruction N.Harnew 29th July

9 The LHCb Detector Key design features Forward single arm spectrometer Precision Si-strip vertex detector Efficient 4 Level trigger incl. L1 vertex trigger Two RICH detectors for particle ID Hadron & EM calorimetry Designed to run at low LHC lumi (2x10 32 cm -2 s -1 ) N.Harnew 29th July

10 The ATLAS/CMS Detectors Central general-purpose detectors : Tracking up to η <2.5 Specialist B triggers operating at lumi 1x10 33 cm -2 s -1 N.Harnew 29th July

11 Importance of efficient triggering BTeV Three levels :- L1: Pioneering pixel vertex trigger (132ns pipelined) L2,L3: Software triggers LHCb Four levels :- L0: High p T µ,e,hadron (p T ~1-2 GeV/c) L1: Vertex trigger L2, L3: Software triggers ATLAS/CMS Three levels :- L1: Highp T µ,&cal (p T ~5-6GeV/c) L2,L3: Software triggers No vertex trigger Level-1 vertex-trigger efficiencies BTeV LHCb B 0 J/ψ K 0 s (µµ µµ) 50% 50% B 0 π + π 55% 48% B 0 s D s K + 70% 56% Tagging efficiencies typically 40% Wrong tag fractions typically 30% Total trigger efficiency (L0-L3) typically 30%, for reconstructable evnts. N.Harnew 29th July

12 V V BTeV Pixel Detector Why pixels? Good signal to noise Good spatial resolution, 5-10µm Low occupancy Radiation hard Special Features Used in the Level-1 trigger Located in the B field The BTeV Baseline Pixel Detector µ 400µ + Pixel Orientation in Triplet 4mm 4mm 5cm Beams Triplet position along beam v v 5cm 6mm X + -6mm Beam hole B π + π - event in the vertex detector + - Disadvantage Large radiation length (~1X 0 ) N.Harnew 29th July

13 Importance of Particle ID (RICH detectors) RICH2 RICH-1 Tracking chamber Gas (C 4 F 10 ) Photodetectors 300 mrad RICH-1 C 4 F 10 & aerogel rings Interaction point Aerogel (n = 1.03) Mirror (R = 190 cm) 120 mrad Window (Mylar) Beam pipe 330 mrad Mirrors Photodetectors 0 1 (m) 2 Gas (CF 4 ) RICH-2 CF 4 rings Aerogel C4F10 CF4 π threshold 0.6 GeV/c 2.6 GeV/c 4.4 GeV/c K threshold 2.0 GeV/c 9.3 GeV/c 15.6 GeV/c N.Harnew 29th July

14 Reducing background in B d π + π B d π + π ~ , K ± π = B s K + K = , K ± π = σ separation for 1<p<150GeV/c Without RICH All combinations Background With RICH eff. = 85% σ m = 17 MeV/c 2 BTeV : One RICH 3<p<70GeV/c Softer B momentum spectrum m(π + π ) m(π + π ) N.Harnew 29th July

15 B d J/Ψ K s decay Events ATLAS Pure mixing: B d ->J/yK s Mass (GeV) Here the General Purpose Detectors compare quite well with the forward detectors (high p T muon triggers). Sensitivities per year : σ(sin 2β) BTeV LHCb to ATLAS CMS N.Harnew 29th July

16 Entries per 0.05 ps tagged tagged as having oscillated tagged as having oscillated (background only) x s = 15 Xs Reach B s D s - π +,B s D s+ π Entries per 0.02 ps x s = Proper time (ps) Xs reach (10 7 s/year) BTeV 60 ATLAS 46 CMS 48 LHCb 75 -Log Likelihood N.Harnew 29th July

17 B d0 D 0 K * 0 decay Determination of γ from the measurement of 6 time-integrated decay rates : B d D 0 K * 0, B d D 0 K * 0,B d D 0 CP=+1 K* 0 B d D 0 K * 0, B d D 0 K * 0,B d D 0 CP=+1 K* B d D 0 K *0 signal Without RICH K + π - K - π + K + Κ -, π + π - Visible BR s Measurement only possible with forward detector with particle ID (LHCb, BTeV) B - D 0 K - decay With RICH m(k + π K + π ) [GeV/c 2 ] LHCb sensitivity per year : σ(γ) =10 O Determination of γ from the measurement of 9 time-integrated decay rates : Interference of the decays B - D 0 K -, B - D 0 K - where D 0,D 0 same final state BTeV sensitivity per year : σ(γ) =13 O N.Harnew 29th July

18 ( ) B s0 D s - K +,D s+ K - decays Measurement of (γ -2δγ) from the measurement of 4 time-dependent decay rates : arbitrary scale Without RICH arbitrary scale With RICH B s D s K (σ m = 11 MeV/c 2 ) B s D s π B s D s K B s D s π GeV/c 2 Sensitivities per year : GeV/c 2 m(d s K) m(d s K) σ(γ 2δγ γ 2δγ) BTeV 11 O Depends on γ 2δγ LHCb 6-13 O and strong phase diff. N.Harnew 29th July

19 Fitting γ in B s0 D s - K + (BTeV) 1000 experiments Input values : ρ = 0.5 ; sin (γ γ + δ) = ; sin (γ γ δ γ δ) = ; γ = 45 O Result of fit : +11 Ο 9 γ = 46 9 Ο Estimated error on γ N.Harnew 29th July

20 Extraction of (2β+γ) B d D π +,D + + π 4 Time-dependent decay rates Relies on efficient hadron trigger Need large statistics (CP asymmetry very small) - Inclusive D* reconstruction ~ 270 k events/year with S/B~7 -AddD*a 1 channels ~ 320 k events/year (2β + γ) in degrees σ (2β + γ) in degrees 1year σ(γ) ~4 O 5years No strong phase difference assumed N.Harnew 29th July

21 B d ρπ reconstruction Measurement of the angle α BTeV mass resolution B d0 π + π π tagged B d0 ρ + π events per year obtained BTeV : lead tungstate calorimetry : LHCb : Shashlik EM calorimetry : ~2% / sqrt(e) + 0.6% vs. 10% / sqrt(e) + 1.5% N.Harnew 29th July

22 Rare decays B s µ + µ Standard Model BR ~ 3.5x10-9 Here the General Purpose Detectors have an advantage : high p T di-muon triggering at high (1x10 34 ) luminosity. Muon trigger : 2 µ s withp T >4.3GeV η < 2.4 CMS : 100 fb -1 (10 7 sat10 34 cm -2 s -1 ): 26 signal events 6.4 events background N.Harnew 29th July

23 Performance summary Sensitivities per year : Measurement Channel BTeV LHCb ATLAS CMS sin(2β) B 0 0 J/ψ K s to sin(2α) B 0 π + π (assuming no penguin) B 0 ρπ π + π π β + γ B 0 D* + π 9 O γ -2δγ B 0 s D s K + 11 O 6 O to13 O γ B d 0 D 0 K* 10 O γ B D 0 K 13 O δγ B 0 s J/ψ Φ 0.6 O 0.9 O X S B s 0 D s π + <60 <75 <46 <48 Rare decays B 0 s µ + µ - 4.4σ SM 4.3σ SM 10σ SM (SM. BR. ~3.5x10-9 ) signal signal signal B 0 d K* γ 24k evts. 26k evts N.Harnew 29th July

24 Summary The 2nd Generation CP-violation experiments will provide massive statistics : ~10 12 bb pairs per year. LHCb/BTeV will provide : Efficient B triggers Excellent proper time resolution (σ t ~40-50fs) Particle ID. The experiments will measure precisely the angles and the sides of the Unitarity Triangle. A unique opportunity to understand origin of CP violation in framework of SM and BEYOND! N.Harnew 29th July