2 nd 2 nd Super-B Factory Workshop Super-B Factory Workshop April 20-22, 2005 April 20-22, 2005 Hawaii Hawaii The expected LHCb Physics Performance The expected LHCb Physics Performance R. Le Gac R. Le Gac on behalf of the LHCb Collaboration on behalf of the LHCb Collaboration CPPM, Marseille CPPM, Marseille 1
LHCb Reoptimized Detector, LHCb TDR 9, CERN/LHCC 2003-030 Monte-Carlo Monte-Carlo Detailed simulation of the detector: Detailed simulation of the detector: Data samples end '03: Data samples end '03: Event generation with PYTHIA 6.2 GEANT 3 Event generation with PYTHIA 6.2 GEANT 3 s = 14TeV tuned to ; tuned to ; 32× 32 ×10 10 6 6 m minimum bias; inimum bias; Tracking of the particle though the Tracking of the particle though the 11× 11 ×10 10 6 6 i inclusive events nclusive events b b detector with GEANT; detector with GEANT; Many specific signal B decays: Many specific signal B decays: Simulation of the detector response Simulation of the detector response 50k to 200k per decay channel. 50k to 200k per decay channel. including spillover and pile-up; including spillover and pile-up; Simulation of the trigger decision. Simulation of the trigger decision. Data samples end '04: Data samples end '04: Object oriented software processes Object oriented software processes GEANT 4; GEANT 4; simulated events as real data: simulated events as real data: 110× 110 ×10 10 6 6 m minimum bias; inimum bias; Track finding; Track finding; 61×10 61× 10 6 6 i inclusive events; nclusive events; b b Particle identification; Particle identification; Many specific signal B decays. Many specific signal B decays. Selection of B-meson final states. Selection of B-meson final states. All results quoted in this talk are based on 2003 samples 2
b hadrons production at LHC b hadrons production at LHC All b hadrons species are produced in All b hadrons species are produced in proton-proton collisions at 14 TeV: proton-proton collisions at 14 TeV: B d B d , B , B s s , B , B c c , B , B ± ± , Λ , Λ b b , ...: , ...: B d per second 27×10 3 B s per second 7×10 3 in the LHCb acceptance; in the LHCb acceptance; B/S ~ 160. B/S ~ 160. The huge statistics of B The huge statistics of B s s meson meson opens new approaches to study the CP opens new approaches to study the CP symmetry in the beauty sector. symmetry in the beauty sector. 3
B B s s system system Mass and lifetime: Mass and lifetime: m B s = 5369.6 ± 2.4 MeV s = 1.461 ± 0.057 ps Most of observables are not yet measured: Most of observables are not yet measured: SM Expectation Δ m s Oscillation frequency ~ 20ps -1 Φ s Weak mixing phase –2λ 2 η ~ –0.04 ΔΓ s /Γ s Relative decay width difference ~ 0.1 Time dependent decay rate asymmetries: Time dependent decay rate asymmetries: dir cos m s t A f R B s f t − R B s f t mix sin m s t R B s f t R B s f t = A f CP t = A f cosh s sinh s t − A f t 2 2 = 2Re f 2 A f dir =− 1 −∣ f ∣ mix = 2Im f f = q where: A f A f A f p A f 2 2 2 1 ∣ f ∣ 1 ∣ f ∣ 1 ∣ f ∣ 4
Time dependent asymmetry at LHCb Time dependent asymmetry at LHCb ~10 mm b b The proper time of the signal B decay is measured via: The proper time of the signal B decay is measured via: the position of the primary and secondary vertexes; the position of the primary and secondary vertexes; the momentum of the signal B state from its decay products. the momentum of the signal B state from its decay products. 5
Event selection: (1) Event selection: (1) ± K ∓ K K − ± K ∓ B s D s T1 T2 T3 ? Trigger Tracker Vertex Locator Reconstructed event: ~72 tracks 6
Event selection: (2) Event selection: (2) ± K ∓ K K − ± K ∓ B s D s Summary of the cuts. 1) Primary vertex. Primary vertex. 2) D D s s meson by using identified kaon and meson by using identified kaon and pion and a vertex constrained to the D s pion and a vertex constrained to the D s mass. mass. 3) B B s s meson by combining a D meson by combining a D s s with a with a kaon forming a vertex (no mass kaon forming a vertex (no mass constraint). constraint). 4) Select B Select B s s with an impact parameter ~0 with an impact parameter ~0 and and an invariant mass in the window an invariant mass in the window 2 m B s ± 50MeV / c 7
Resolution: Resolution: B s D s ± K ∓ K K − ± K ∓ Primary vertex: 47µm Bs vertex: 144µm Bs mass: 14 MeV/ c 2 8
Flavour Tagging Flavour Tagging } Tagging B Opposite side } Signal B d,s Same side Several algorithm to determine the flavour Several algorithm to determine the flavour of the signal B meson at production: of the signal B meson at production: Opposite side: Opposite side: — e, µ from semileptonic b decays; e, µ from semileptonic b decays; — K K ± ± from b decays chain; from b decays chain; — Inclusive vertex charge. Inclusive vertex charge. Same side: Same side: — K K ± from fragmentation accompanying B s meson. ± from fragmentation accompanying B s meson. 9
Performance of Flavour Tagging Performance of Flavour Tagging After passing trigger and offline cuts After passing trigger and offline cuts Breakdown for B d,s h + h – { Effective tagging efficiencies vary where: Effective tagging efficiencies vary where: R W tag = between 3 and 9% depending on the between 3 and 9% depending on the R W U final state. final state. W = In real physics analysis, the wrong tag In real physics analysis, the wrong tag R W fraction will be measured using control fraction will be measured using control 2 eff = tag 1 − 2 channels with similar topology, e.g. channels with similar topology, e.g. * 0 for B d J / K S B d J / K 10
Estimation of Background Estimation of Background Sources of background: Sources of background: Exclusive B-decays mimicking the Exclusive B-decays mimicking the signal decay; signal decay; Combinatorial background in Combinatorial background in bb inclusive events. inclusive events. Difficult to estimate the combinatorial Difficult to estimate the combinatorial contribution since the available contribution since the available statistics of events is limited. statistics of events is limited. bb Method: Method: 2 Open the B Open the B d,s d,s mass window mass window ± 500MeV / c Scale down the obtained number to Scale down the obtained number to 2 the tight mass window ± 50MeV / c the tight mass window using linear extrapolation. using linear extrapolation. { B Exclusive / S = 0.04 B Comb. / S 0.51 11
Evaluation of Sensitivity Evaluation of Sensitivity Acceptance − h B s D s Sensitivities to CP violating observables are Sensitivities to CP violating observables are determined with a toy Monte-Carlo. determined with a toy Monte-Carlo. Inputs come from the full simulation: Inputs come from the full simulation: Number of signals/background events after Number of signals/background events after trigger, off-line selection and tagging; trigger, off-line selection and tagging; Wrong tag fraction; Wrong tag fraction; Acceptances as a function of proper time; Acceptances as a function of proper time; Resolutions. Resolutions. Proper time resolution: 33fs Many sets of events are generated. Many sets of events are generated. − h B s D s For each of them, decay rates are fitted with For each of them, decay rates are fitted with an unbinned likelihood where an unbinned likelihood where Re f , Im f , m d , s , d , s , d , s , f are free parameters. The fit also takes into are free parameters. The fit also takes into account backgrounds and resolution. account backgrounds and resolution. 12
Branching Ratio Branching Ratio Performances were evaluated through Performances were evaluated through few benchmark channels. few benchmark channels. Visible Branching ratio B d J / − K S − − 5 1.98 × 10 − K − − 4 B s D s K − 1.2 × 10 − K K − − 5 B s J / 3.1 × 10 − 6 − B d 4.8 × 10 − 5 K − B s K 1.85 × 10 − 5 ± K ± K − K ∓ B s D s 1.0 × 10 0 K *0 K − 6 − K − B d D 1.2 × 10 0 K *0 K − 7 K − K − B d D CP 1.9 × 10 − 5 B d 2 × 10 13
The phase ) ... ... The phase β (Φ β (Φ 1 1 ) 14
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