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 1 B Physics in 2007 Direct Measurement of angles: Knowledge of the sides of unitary triangle: (Dominated by theoretical uncertainties) s(sin(2b)) ≈ 0.03 from J/y Ks in B factories Other angles not precisely known s(|Vcb|) ≈ few % error s(|Vub|) ≈ 5-10 % error s(|Vtd|/|Vts|) ≈ 5-10% error (assuming Dms < 40 ps-1) In case new physics is present in mixing, independent measurement of g can reveal it… 2 B Physics @ LHC √s 14 TeV bb production: (forward) L (cm-2 s-2) 2x1032 cm-2 s-1 sbb 500 mb sinel / sbb 160 qb 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 qb B Decay eg.: Bs->Dsh Bs Ds ,K K K 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 3 Simulation and Reconstruction No true MC info used anywhere ! 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…) T1 T2 T3 TT RICH1 VELO Sensitivity studies are based on fast simulations using efficiencies and resolutions and from the full simulation 4 Evolution since Technical Proposal • Reduced material • Improved level-1 trigger 5 Track finding strategy T track Upstream track VELO seeds VELO track Long track (forward) Long track (matched) T seeds Downstream track Long tracks highest quality for physics (good IP & 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 T tracks useful for RICH2 pattern recognition VELO tracks useful for primary vertex reconstruction (good IP resolution) 6 On average: 26 long tracks 11 upstream tracks 4 downstream tracks 5 T tracks 26 VELO tracks Result of track finding Typical event display: Red = measurements (hits) Blue = all reconstructed tracks T1 T2 T3 TT VELO 2050 hits assigned to a long track: 98.7% correctly assigned Efficiency vs p : Ghost rate vs pT : Ghost rate = 3% (for pT > 0.5 GeV) Eff = 94% (p > 10 GeV) Ghosts: Negligible effect on b decay reconstruction 7 Experimental Resolution Momentum resolution Impact parameter resolution sIP= 14m + 35 m/pT dp/p = 0.35% – 0.55% p spectrum B tracks 1/pT spectrum B tracks 8 RICH 1 Particle ID RICH 2 e (K->K) = 88% e (p->K) = 3% Example: B->hh decays: 9 m, e, h, g Calorimeter Muon system Pile-up system 1 MHz Vertex Locator Trigger Tracker Level 0 objects 40 kHz HLT: Final state reconstruction 200 Hz output L1 B-> ln IP/sIP Level-1: Impact parameter Rough pT ~ 20% Bs->DsK ln IP/sIP Level-0: pT of Trigger pile-up 40 MHz L0 Full detector information Signal Min. Bias ln pT ln pT 10 Flavour tag Knowledge of flavour at birth is essential for the majority of CP measurements B0 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 B0 D K- l b b sources for wrong tags: Bd-Bd mixing (opposite side) b → c → l (lepton tag) conversions… Combining tags effective efficiency: eeff = etag (1-2wtag )2 Bd Bs K K tag Bs 0 s s + u K u Wtag [%] eff [%] 42 35 4 50 33 6 [%] 11 Efficiencies, event yields and Bbb/S ratios Det. eff. (%) B0 12.2 Bs K K 12.0 Bs Ds 5.4 Bs Ds+ K 5.4 B0 D~0 (K)K*0 5.3 B0 J/y(mm) K0S 6.5 B0 J/y(ee) K0S 5.8 Bs J/y(mm) 7.6 Bs J/y(ee) 6.7 B0 6.0 B0 K* g 9.5 Bs g 9.7 + few more channe ls in T DR Rec. eff. (%) 91.6 92.5 80.6 82.0 81.8 66.5 60.8 82.5 76.5 65.5 86.8 86.3 Sel. eff. (%) 18.3 28.6 25.0 20.6 22.9 53.5 17.7 41.6 22.0 2.0 5.0 7.6 Trig. eff. (%) 33.6 36.7 31.1 29.5 35.4 60.5 26.5 64.0 28.0 36.0 37.8 34.3 Tot. eff. (%) 0.69 0.99 0.34 0.27 0.35 1.39 0.16 1.67 0.32 0.03 0.16 0.22 Vis. Annual BR signal 6 (10 ) yield 4.8 26k 18.5 37k 120. 80k 10. 5.4k 1.2 3.4k 20. 216k 20. 26k 31. 100k 31. 20k 20. 4.4k 29. 35k 21. 9.3k B/S from bb bkg. < 0.7 0.3 0.3 < 1.0 < 0.5 0.8 1.0 < 0.3 0.7 < 7.1 < 0.7 < 2.4 Nominal year = 1012 bb pairs produced (107 s at L=21032 cm2s1 with sbb=500 mb) Yields include factor 2 from CP-conjugated decays Branching ratios from PDG or SM predictions 12 CP Sensitivity studies CP asymmetries due to interference of Tree, Mixing, Penguin, New Physics amplitudes: tree + mix + pe + new n Measurements of Angle g: Mixing phases: Time dependent asymmetry in Bd->J/y Ks decays Sensitive to d Time dependent asymmetry in Bs->J/y decays Sensitive to s 1. Time dependent asymmetries in Bs->DsK decays. Interference between b->u and b->c tree diagrams due to Bs mixing Sensitive to g + s (Aleksan et al) 2. Time dependent asymmetries in B-> and Bs->KK decays. Interference between b->u tree and b->d(s) penguin diagrams Sensitive to g, d, s (Fleischer) 3. Time Integrated asymmetries in B-> DK* decays. Interference between b->u and b->c tree diagrams due to D-D mixing Sensitive to g (Gronau-Wyler-Dunietz) 13 Bs oscillation frequency: Dms Needed for the observation of CP asymmetries with Bs decays Use Bs Ds If Dms= 20 ps1 Expected unmixed Bs Ds sample in one year of data taking. s(Dms) = 0.011 ps1 Full MC Can observe >5s oscillation signal if Dm < 68 ps1 s well beyond SM prediction Proper-time resolution plays a crucial role 14 Mixing Phases Bd mixing phase using B->J/y Ks Background-subtracted BJ/y(mm)KS CP asymmetry after one year Bs mixing phase using Bs->J/y Angular analysis to separate CP even and CP odd Time resolution is important: st = 38 fs Proper time resolution (ps) s(sin(d)) = 0.022 If Dms= 20 ps1: NB: In the SM, s = 2 ~ 0.04 s(DGs/Gs) = 0.018 s(sin(s)) = 0.058 15 1. Angle g from BsDsK (2 Tree diagrams due to Bs mixing) Simultaneous fit of Bs->Ds and Bs->DsK: Determination of mistag fraction Time dependence of background Time dependent asymmetries: Bs(Bs) ->Ds-K+: → DT1/T2 + (g+s) Bs(Bs) ->Ds+K-: → DT1/T2 – (g+s) ADs-K+ After one year, if Dms= 20 ps1, DGs/Gs = 0.1, 55 < g < 105 deg, 20 < DT1/T2 < 20 deg: s(g) = 1415 deg ADs+K- No theoretical uncertainty; insensitive to new physics in B mixing (after 5 years of data) 16 2. Angle g from B and BsKK (b->u processes, with large b->d(s) penguin contributions) Measure time-dependent CP asymmetries in B and BsKK decays: ACP(t)=Adir cos(Dm t) + Amix sin(Dm t) Method proposed by R. Fleischer: SM predictions: d exp(i) = function of tree and Adir (B0 ) = f1(d, , g) penguin amplitudes 0 Amix(B ) = f2(d, , g, d) in B0 d’ exp(i’) = function of tree and Adir (BsKK ) = f3(d’, ’, g) penguin amplitudes Amix(BsK K ) = f4(d’, ’, g, s) in Bs KK Assuming U-spin flavour symmetry (interchange of d and s quarks): d = d’ and = ’ 4 measurements (CP asymmetries) and 3 unknown (g, d and ) can solve for g 17 2. Angle g from B and BsKK (cont.) Extract mistags from BK and BsK Use expected LHCb precision on d and s blue bands from BsKK (95%CL) red bands from B (95%CL) ellipses are 68% and 95% CL regions (for ginput = 65 deg) pdf for g If Dms= 20 ps1, DGs/Gs=0.1, d =0.3, = 160 deg, 55 < g < 105 deg: “fake” solution pdf for d s(g) = 46 deg U-spin symmetry assumed; sensitive to new physics in penguins d vs g 18 3. Angle g from B DK* and B DK* (Interference between 2 tree diagrams due to D0 mixing) Application of Gronau-Wyler method to DK* (Dunietz): √2 A2 A3 √2 A2 2g A3 Dg A1 = A1 Measure six rates (following three + CP-conjugates): 1) B D(K)K*, 2) B DCP(KK)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 g=65 degrees and D=0 s(g) = 78 deg 55 < g < 105 deg 20 < D < 20 deg No theoretical uncertainty; sensitive to new physics in D mixing 19 Measurement of angle g: New Physics? 1. Bs->DsK g not affected by new physics in loop diagrams 2. B->, Bs->KK g affected by possible new physics in penguin Determine the CKM parameters A,,h independent of new physics 3. B->DK* g affected by possible new physics in D-D mixing Extract the contribution of new physics to the oscillations and penguins 20 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->Ds for Bs->DsK, B->K for B->, B->J/yK* for B->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->Ds in Bs->DsK , Bs->K & Bs->KK, … 21 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 22