Bs hh LHCb Jacopo Nardulli NIKHEF On behalf
B(s) h+h’- @ LHCb Jacopo Nardulli NIKHEF (On behalf of the LHCb collaboration) Outline: • • • B(s) h+h’- (h, h’ = π, K) U-spin symmetry Extraction of the CKM angle γ Event Selection Sensitivity on direct and mixing induced CP violation parameters Jacopo Nardulli B hh @ LHCb / 17 Nagoya 15/12/2006 CKM 2006 Workshop
Why B(s) h+h’are interesting ? • Since CLEO measurement [BR(Bd K+ -)~4 BR(Bd + -)], penguin diagrams cannot be neglected in the two-body B-decay amplitude – Extraction of CKM phases gets more complicated – However unknown hadronic quantities can be eliminated relying on U-spin symmetry • The presence of penguins is an opportunity – New Physics might show up in loops of the penguin diagrams – CKM quantities from these modes can differ from the ones from tree-level modes, unaffected from NP Jacopo Nardulli B hh @ LHCb / 17 Nagoya 15/12/2006 CKM 2006 Workshop
Trees, Penguins and γ Sensitivity to from the interference of T and P amplitudes Where: • deiθ, d’eiθ’ : penguin-to-tree ratios • λ from CKM Matrix • C, C’ ~ CP-conserving factors Two amplitudes can be related by U-spin symmetry: d=d’ and = ’ Using method and parametrization from R. Fleischer, PLB 459 (1999) 306 Jacopo Nardulli B hh @ LHCb / 17 Nagoya 15/12/2006 CKM 2006 Workshop
U spin symmetry d s exchange Bd + T+P+PCEW+PA+E Bd + T+P+PCEW+PA+E Bs K+KT+P+PCEW+PA+E Bs +KT+P+PCEW Bd K+ T+P+PCEW • U-spin symmetry not exact for flavour specific decays: E and PA missing Where: T : tree P : penguin PCEW: colour suppressed electroweak penguin PA : penguin annihilation E: exchange • E and PA contributions very small can be seen in Bs + - and Bd K+K- (BR ~ 10 -8) Jacopo Nardulli B hh @ LHCb / 17 Nagoya 15/12/2006 CKM 2006 Workshop
Extraction of γ Where : Measure the direct and mixing-induced CP-violating terms 7 unknowns and 4 equations The mixing phase d ( s) can be measured from Bd J/ KS (Bs J/ ) 5 unknowns Finally, relying on U-spin symmetry it is possible to eliminate two further unknowns 3 unknowns, system over-constrained, can be extracted unambiguously Jacopo Nardulli B hh @ LHCb / 17 Nagoya 15/12/2006 CKM 2006 Workshop
B(s) h+h’- events at LHCb • Large b production at 14 Te. V p-p collisions. (All b mesons produced) - b Parton 2 Parton 1 p b p Boost • B hadrons are mostly produced in the forward direction (PYTHIA) LHCb is forward spectrometer 10 -300 mrad • At nominal luminosity about 1012 bb in 107 s (L=2 fb-1) bb correlation Millions of B(s) h+h’- per year (BR ~10 -5/10 -6) - / σinel ~ 0. 006 • σbb- ~ 500μb ; σinel ~ 80 mb σbb Many min-bias needed for background studies Main background comes from b events (min-bias cut at trigger level) In this study 300 k signal events and 27 M inclusive b events have been used Jacopo Nardulli B hh @ LHCb / 17 Nagoya 15/12/2006 CKM 2006 Workshop
B(s) h+h’- selection cuts For each pair of charged tracks we cut on – max (p. T 1, p. T 2) – min (p. T 1, p. T 2) – max (IP 1/ IP 1, IP 2/ IP 2) – min (IP 1/ IP 1, IP 2/ IP 2) – 2 of common vertex Then, the B candidate is selected with cuts on – p. T – IPB/ IP – L/ L Jacopo Nardulli B hh @ LHCb , K B 0(s) IP 1 IPB IP 2 , K L Parameters used for selection h, h Smallest pt Ge. V/c > 1 h, h largest pt Ge. V/c > 3 h, h smallest IP/ IP > 6 h, h largest IP/ IP > 12 h, h vertex fit 2 < 5 B pt > 1 B IP/ IP < 2. 5 B L/ L > 18 / 17 Ge. V/c Nagoya 15/12/2006 CKM 2006 Workshop
Particle identification through RICH system p/K/π separation Invariant mass (no PID) • Kinematic separation weak Efficient hadron PID crucial for B(s) h+h’ PID discriminant built as difference between log likelihoods of particle hypotheses K separation for B h+h’decays at LHCb Every Channel is potentially background of the others For true pions For true kaons K/π PID calibration will be done using decay chain: D*+ D 0π+, D 0 K+πDedicated D* trigger (300 Hz) for large “PID unbiased” sample Jacopo Nardulli B hh @ LHCb / 17 Nagoya 15/12/2006 CKM 2006 Workshop
PID performance Mass resolution performance B mass - Separation between Bd K-π+/Bs K-π + fully relies on the mass resolution ππ hypothesis • - Bd K-π+ is 16 times more abundant x 4 comes from the branching ratio x 4 comes from hadronization fraction B mass Clean samples through expected PID performance of RICH system Nominal mass resolution of 16 Me. V/c 2 allows clean separation between the two signals Jacopo Nardulli B hh @ LHCb / 17 πK hypothesis Nagoya 15/12/2006 CKM 2006 Workshop
Proper time resolution (from full GEANT 4 simulation) =~40 fs Excellent proper time resolution allows to resolve fast Bs oscillations t = ~40 fs TOY MC Decay rate for Bs K+K- events tagged as B at LHCb (integrated luminosity L=2 fb-1) Calibration of proper time resolution by disentangling prompt J/ + (affected by intrinsic resolution) from non-prompt component from B decays “Lifetime unbiased” prompt J/ events will be acquired with dedicated high-mass di-muon trigger (600 Hz bandwidth) Jacopo Nardulli B hh @ LHCb Bkg / 17 Δms 20 ps-1 in this simulation, a bit larger than the truth… Nagoya 15/12/2006 CKM 2006 Workshop
Selection summary Channel • • • Eff. (%) BR 10 -6 Yields are calculated for L= 2 fb-1 Limited background-to-signal ratios Both combinatorial and from the other B h+h’- modes (wrong particle ID) Hundreds of thousands of B h+h’decays triggered, reconstructed and selected per year with high purity Jacopo Nardulli B hh @ LHCb / 17 Yield B/S bb spec - K spectrum selected from a sample of 27 M bb MC events Partially reco B K*+ - Bd K+ - Nagoya 15/12/2006 CKM 2006 Workshop
Flavour tagging Opposite side • • • High p. T leptons K± from b → c → s Vertex charge B 0 opposite PV • : mistag probability K+ K K Tagging power in % Fragmentation K± accompanying Bs ± from B** → B(*) ± D 2= (1 -2 )2: tagging power : tagging efficiency D Qvertex, QJet K- Bs 0 signal Same side • e-, m- Opposite side Tag Bd Muon 1. 1 Electron 0. 39 Kaon opp. side 2. 1 Jet/ Vertex Charge 1. 0 Same side π / K 0. 73 (π) Combined 5. 1 Bs 3. 5 K 9. 5 Work in progress Jacopo Nardulli B hh @ LHCb / 17 Nagoya 15/12/2006 CKM 2006 Workshop
Fast MC Generation • Large Signal (S) and Background (B) samples through a TOY MC. To estimate sensitivity to CP Parameters • S generated simulating CP violation, proper time acceptance, proper time resolution and tagging For each event the toy MC generates mass, proper time, tagging and PID response from the full GEANT 4 simulations • Background mass and proper time spectra generated from the full GEANT 4 simulation Background proper time Proper time acceptance B 0 + - will be extracted from real data using mass sidebands will be calibrated on real data using event by event acceptance functions – studies going on in LHCb Jacopo Nardulli B hh @ LHCb / 17 Nagoya 15/12/2006 CKM 2006 Workshop
Sensitivity on CP asymmetries (for L=2 fb-1) • CP sensitivities are then estimated with an extended unbinned maximum likelihood fit to the toy MC sample – Likelihood fit simultaneously to all the B hh channels (both tagged and untagged samples) – Channels and background separated with PID observables and invariant mass • C and S coefficients for Bd + - and Bs K+K- events tagged as B (q=+1) or B (q=-1) are given by Fit results corresponding to L=2 fb-1 (C) LHCb can reach a sensitivity ~ 2 (S) times better than the current world average in 107 s of running (ACP) at nominal luminosity for the B 0 d system and can provide measurements in the B 0 s system with similar sensitivity Jacopo Nardulli B hh @ LHCb / 17 Bd + - Bs K+K- 0. 043 (0. 07*) 0. 042 0. 037 (0. 09*) Bd K+ - 0. 044 Bs +K- 0. 003 (0. 015*) 0. 02 *From current world average Nagoya 15/12/2006 CKM 2006 Workshop
Sensitivity on γ (for L=2 fb-1) Extraction of performed using UTfit bayesian approach and software tools in 3 different scenarios (in this exercise =65 o is assumed) (1) Perfect U-spin symmetry d=d’ - = ’ (2) Weaker assumption: perfect Uspin symmetry just for d, d’ d=d’ - no constraint on , ’ (3) Even weaker: given U-spin breaking for d, d’ d’/d =[0. 8, 1. 2] no constraint on , ’ : Sensitivity ~ 4 o • Perfect U-spin • Scenario (2) & (3) : Sensitivity ~ 7°-10° 1 2 3 (secondary fake solution appears) But sensitivity depends on the actual values of C and S… Jacopo Nardulli B hh @ LHCb / 17 Nagoya 15/12/2006 CKM 2006 Workshop
An exercise: using current world averages of Bd + and Bd K+ - (not using LHCb results) Using Bd K+ - instead of Bs K+K– Neglecting PA and E it just differs for the spectator quark – Assuming U-spin symmetry the direct asymmetry of Bs K+KCKK = AK , the charge asymmetry of Bd K+ – However SKK still missing We can solve the system for Using Current world averages from HFAG C = -0. 39 ± 0. 07 (Ba. Bar/Belle) S = -0. 59 ± 0. 09 (Ba. Bar/Belle) AK = -0. 093 ± 0. 015 (Ba. Bar/Belle/CLEO/CDF) p. d. f. for obtained allowing for a U-spin breaking: = ’- = ± 20 o d’/d = [0. 8, 1. 2] p. d. f. for = (75± 10)° Unitarity Triangle fits expectation Jacopo Nardulli B hh @ LHCb / 17 Nagoya 15/12/2006 CKM 2006 Workshop
Conclusion • LHCb will collect large samples of B h+h’- decays – Its excellent vertexing and PID capabilities will allow to collect several hundreds of thousands of B h+h’- events with very high purity • The CP sensitivity reachable (in 107 s at L = 2· 1032 cm-2 s-1 ) is about 2 times better than the current world averages from the bfactories and the Tevatron in the Bd sector, and will provide first measurements in the Bs sector with similar sensitivity • The B h+h’- modes can be used to constrain the angle with the U -spin flavour symmetry - Useful information on γ can be extracted, even if the U-spin symmetry will result to be broken to some extent - Testing on the breaking of the U-spin symmetry will be possible • New Physics inside the Penguin loops can be revealed by the extraction of – obtained from these decay modes might thus be different from tree level modes, such as B DK, which can be assumed to be basically free of New Physics contributions Jacopo Nardulli B hh @ LHCb / 17 Nagoya 15/12/2006 CKM 2006 Workshop
Backup Jacopo Nardulli B hh @ LHCb 18 / 17 Nagoya 15/12/2006 CKM 2006 Workshop
Some numbers Uncertainty phi_s 0. 06 in 2 fb-1; 0. 02 in phi_d 2 fb-1 Taken from Reopt TDR Taken from J. Piedra Talk FPCP 2006 Jacopo Nardulli B hh @ LHCb / 17 Nagoya 15/12/2006 CKM 2006 Workshop
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