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 1999 1
Outline Introduction The 2nd Generation experiments : LHCb,B-TeV,ATLAS,CMS. Precision measurements : CP-violation, rare B decays. Performance summary N.Harnew 29th July 1999 2
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 ~ 0.03-0.05 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 1999 3
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 1999 4
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 1999 5
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 10 12 xaccept. 5x10 12 xaccept. <Interactions/crossings> ~ 2.0 0.5 (~30% single int.) ~ 2.3 N.Harnew 29th July 1999 6
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] 10 4 10 3 10 2 10 2 1 0 1 2 B 0 π π + d in 4π with π π + measured 3 θ b [rad] 0 1 2 3 4 5 B 0 decay length [cm] N.Harnew 29th July 1999 7
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 1999 8
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 1999 9
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 1999 10
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 1999 11
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 + + 50µ 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 1999 12
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 ) 6 8 10 12 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 1999 13
Reducing background in B d π + π B d π + π ~ 0.8 10 5, K ± π = 1.5 10 5 B s K + K = 1.5 10 5, K ± π = 0.7 10 5 3σ 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 1999 14
B d J/Ψ K s decay Events 2000 1000 0 ATLAS Pure mixing: B d ->J/yK s 5 5.1 5.2 5.3 5.4 5.5 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 0.021 LHCb 0.011 to 0.017 ATLAS 0.021 CMS 0.025 N.Harnew 29th July 1999 15
Entries per 0.05 ps 800 600 400 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 - 200 Entries per 0.02 ps 0 200 150 100 50 0 x s = 46 0 1 2 3 4 5 Proper time (ps) Xs reach (10 7 s/year) BTeV 60 ATLAS 46 CMS 48 LHCb 75 -Log Likelihood N.Harnew 29th July 1999 16
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* 0 300 200 B d D 0 K *0 signal Without RICH K + π - K - π + K + Κ -, π + π - Visible BR s 10 10 Measurement only possible with forward detector with particle ID (LHCb, BTeV) B - D 0 K - decay 100 0 With RICH 4.55 5.56 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 1999 17
( ) B s0 D s - K +,D s+ K - decays Measurement of (γ -2δγ) from the measurement of 4 time-dependent decay rates : arbitrary scale 180 160 140 120 Without RICH arbitrary scale 45 40 35 30 With RICH B s D s K (σ m = 11 MeV/c 2 ) 100 80 B s D s π 25 20 60 40 20 B s D s K 15 10 5 B s D s π 0 5.2 5.3 5.4 5.5 5.6 5.7 GeV/c 2 Sensitivities per year : 0 5.2 5.3 5.4 5.5 5.6 5.7 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 1999 18
Fitting γ in B s0 D s - K + (BTeV) 1000 experiments Input values : ρ = 0.5 ; sin (γ γ + δ) = 0.771 ; sin (γ γ δ γ δ) = 0.629 ; γ = 45 O Result of fit : +11 Ο 9 γ = 46 9 Ο Estimated error on γ N.Harnew 29th July 1999 19
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 1999 20
B d ρπ reconstruction Measurement of the angle α BTeV mass resolution B d0 π + π π 0 2800 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 1999 21
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 1999 22
Performance summary Sensitivities per year : Measurement Channel BTeV LHCb ATLAS CMS sin(2β) B 0 0 J/ψ K s 0.021 0.011 to 0.021 0.025 0.017 sin(2α) B 0 π + π 0.06 0.05 0.10 0.17 (assuming no penguin) B 0 ρπ π + π π 0 -- -- 2β + 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 1999 23
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 1999 24