Performance studies of LHCb experiment

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Information about Performance studies of LHCb experiment

Published on June 15, 2007

Author: Abbott


Performance Studies for the LHCb Experiment:  Performance Studies for the LHCb Experiment Marcel Merk NIKHEF Representing the LHCb collaboration 19 th International Workshop on Weak Interactions and Neutrinos Oct 6-11, Geneva, Wisconsin, USA B Physics in 2007:  Direct Measurement of angles: s(sin(2b)) ≈ 0.03 from J/y Ks in B factories Other angles not precisely known Knowledge of the sides of unitary triangle: (Dominated by theoretical uncertainties) s(|Vcb|) ≈ few % error s(|Vub|) ≈ 5-10 % error s(|Vtd|/|Vts|) ≈ 5-10% error (assuming Dms andlt; 40 ps-1) In case new physics is present in mixing, independent measurement of g can reveal it… B Physics in 2007 B Physics @ LHC:  Large bottom production cross section: 1012 bb/year at 2x1032 cm-2s-1 Triggering is an issue All b hadrons are produced: Bu (40%), Bd(40%), Bs(10%), Bc and b-baryons (10%) Many tracks available for primary vertex Many particles not associated to b hadrons b hadrons are not coherent: mixing dilutes tagging B Physics @ LHC bb production: (forward) LHCb: Forward Spectrometer with: Efficient trigger and selection of many B decay final states Good tracking and Particle ID performance Excellent momentum and vertex resolution Adequate flavour tagging B Decay eg.: Bs-andgt;Dsh qb qb Simulation and Reconstruction:  Simulation and Reconstruction All trigger, reconstruction and selection studies are based on full Pythia+GEANT simulations including LHC 'pile-up' events and full pattern recognition (tracking, RICH, etc…) Sensitivity studies are based on fast simulations using efficiencies and resolutions and from the full simulation No true MC info used anywhere ! VELO RICH1 TT T1 T2 T3 Evolution since Technical Proposal:  Evolution since Technical Proposal Reduced material Improved level-1 trigger Track finding strategy:  Track finding strategy VELO seeds Long track (forward) Long track (matched) T seeds Upstream track Downstream track T track VELO track T tracks  useful for RICH2 pattern recognition Long tracks  highest quality for physics (good IP andamp; p resolution) Downstream tracks  needed for efficient KS finding (good p resolution) Upstream tracks  lower p, worse p resolution, but useful for RICH1 pattern recognition VELO tracks  useful for primary vertex reconstruction (good IP resolution) Result of track finding:  Result of track finding Typical event display: Red = measurements (hits) Blue = all reconstructed tracks Efficiency vs p : Ghost rate vs pT : Eff = 94% (p andgt; 10 GeV) Ghost rate = 3% (for pT andgt; 0.5 GeV) VELO TT T1 T2 T3 On average: 26 long tracks 11 upstream tracks 4 downstream tracks 5 T tracks 26 VELO tracks 2050 hits assigned to a long track: 98.7% correctly assigned Ghosts: Negligible effect on b decay reconstruction Experimental Resolution:  Experimental Resolution dp/p = 0.35% – 0.55% p spectrum B tracks sIP= 14m + 35 m/pT 1/pT spectrum B tracks Momentum resolution Impact parameter resolution Particle ID:  Particle ID B-andgt;hh decays: RICH 1 RICH 2 e (K-andgt;K) = 88% e (p-andgt;K) = 3% Example: Trigger:  Trigger 40 MHz 1 MHz 40 kHz 200 Hz output Level-1: Impact parameter Rough pT ~ 20% HLT: Final state reconstruction Calorimeter Muon system Pile-up system Vertex Locator Trigger Tracker Level 0 objects Full detector information L0 Level-0: pT of m, e, h, g ln pT ln pT ln IP/IP ln IP/IP L1 Signal Min. Bias B-andgt;pp Bs-andgt;DsK Flavour tag:  Flavour tag tagging strategy: opposite side lepton tag ( b → l ) opposite side kaon tag ( b → c → s ) (RICH, hadron trigger) same side kaon tag (for Bs) opposite B vertex charge tagging effective efficiency: eff = tag (1-2wtag )2 Efficiencies, event yields and Bbb/S ratios:  Efficiencies, event yields and Bbb/S ratios Nominal year = 1012 bb pairs produced (107 s at L=21032 cm2s1 with bb=500 b) Yields include factor 2 from CP-conjugated decays Branching ratios from PDG or SM predictions CP Sensitivity studies:  CP Sensitivity studies CP asymmetries due to interference of Tree, Mixing, Penguin, New Physics amplitudes: 1. Time dependent asymmetries in Bs-andgt;DsK decays. Interference between b-andgt;u and b-andgt;c tree diagrams due to Bs mixing Sensitive to g + fs (Aleksan et al) 2. Time dependent asymmetries in B-andgt;pp and Bs-andgt;KK decays. Interference between b-andgt;u tree and b-andgt;d(s) penguin diagrams Sensitive to g, fd, fs (Fleischer) 3. Time Integrated asymmetries in B-andgt; DK* decays. Interference between b-andgt;u and b-andgt;c tree diagrams due to D-D mixing Sensitive to g (Gronau-Wyler-Dunietz) Time dependent asymmetry in Bd-andgt;J/y Ks decays Sensitive to fd Time dependent asymmetry in Bs-andgt;J/y f decays Sensitive to fs Mixing phases: Measurements of Angle g: ftree fmix fpen fnew + + + Bs oscillation frequency: ms:  Bs oscillation frequency: ms Needed for the observation of CP asymmetries with Bs decays Use Bs Ds If ms= 20 ps1 Can observe andgt;5 oscillation signal if well beyond SM prediction (ms) = 0.011 ps1 ms andlt; 68 ps1 Proper-time resolution plays a crucial role Full MC Expected unmixed Bs Ds sample in one year of data taking. Mixing Phases:  Mixing Phases Bd mixing phase using B-andgt;J/y Ks Bs mixing phase using Bs-andgt;J/y f s(DGs/Gs) = 0.018 Background-subtracted BJ/()KS CP asymmetry after one year If ms= 20 ps1: (sin(fs)) = 0.058 NB: In the SM, s = 2 ~ 0.04 (sin(d)) = 0.022 Angular analysis to separate CP even and CP odd Time resolution is important: Proper time resolution (ps) st = 38 fs 1. Angle  from BsDsK:  1. Angle  from BsDsK Simultaneous fit of Bs-andgt;Dsp and Bs-andgt;DsK: Determination of mistag fraction Time dependence of background Time dependent asymmetries: Bs(Bs) -andgt;Ds-K+: → DT1/T2 + (g+fs) Bs(Bs) -andgt;Ds+K-: → DT1/T2 – (g+fs) ADs-K+ ADs+K- (2 Tree diagrams due to Bs mixing) 2. Angle  from B and BsKK:  Measure time-dependent CP asymmetries in B and BsKK decays: ACP(t)=Adir cos(m t) + Amix sin(m t) Method proposed by R. Fleischer: SM predictions: Adir (B0 ) = f1(d, , ) Amix(B0 ) = f2(d, , , d) Adir (BsKK ) = f3(d’, ’, ) Amix(BsKK ) = f4(d’, ’, , s) Assuming U-spin flavour symmetry (interchange of d and s quarks): d = d’ and  = ’ 4 measurements (CP asymmetries) and 3 unknown (, d and )  can solve for  2. Angle  from B and BsKK d exp(i) = function of tree and penguin amplitudes in B0  d’ exp(i’) = function of tree and penguin amplitudes in Bs  KK (b-andgt;u processes, with large b-andgt;d(s) penguin contributions) 2. Angle  from B and BsKK (cont.):  2. Angle  from B and BsKK (cont.) Extract mistags from BK and BsK Use expected LHCb precision on d and s pdf for  pdf for d 3. Angle  from B DK* and B DK* :  Application of Gronau-Wyler method to DK* (Dunietz): Measure six rates (following three + CP-conjugates): 1) B D(K)K*, 2) B DCP(KK)K* , 3) B D (K) K* No proper time measurement or tagging required Rates = 3.4k, 0.6k, 0.5k respectively (CP-conj. included), with B/S = 0.3, 1.4, 1.8, for =65 degrees and =0 3. Angle  from B DK* and B DK* (Interference between 2 tree diagrams due to D0 mixing) Measurement of angle g: New Physics?:  Measurement of angle g: New Physics? 1. Bs-andgt;DsK 2. B-andgt;pp, Bs-andgt;KK 3. B-andgt;DK* g not affected by new physics in loop diagrams g affected by possible new physics in penguin g affected by possible new physics in D-D mixing Determine the CKM parameters A,r,h independent of new physics Extract the contribution of new physics to the oscillations and penguins Systematic Effects:  Possible sources of systematic uncertainty in CP measurement: Asymmetry in b-b production rate Charge dependent detector efficiencies… can bias tagging efficiencies can fake CP asymmetries CP asymmetries in background process Experimental handles: Use of control samples: Calibrate b-b production rate Determine tagging dilution from the data: e.g. Bs-andgt;Dsp for Bs-andgt;DsK, B-andgt;Kp for B-andgt;pp, B-andgt;J/yK* for B-andgt;J/yKs, etc Reversible B field in alternate runs Charge dependent efficiencies cancel in most B/B asymmetries Study CP asymmetry of backgrounds in B mass 'sidebands' Perform simultaneous fits for specific background signals: e.g. Bs-andgt;Dsp in Bs-andgt;DsK , Bs-andgt;Kp andamp; Bs-andgt;KK, … Systematic Effects Conclusions:  Conclusions LHC offers great potential for B physics from 'day 1' LHC luminosity LHCb experiment has been reoptimized: Less material in tracking volume Improved Level1 trigger Realistic trigger simulation and full pattern recognition in place Promising potential for studying new physics

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