Jacopo Nardulli NIKHEF (On behalf of the LHCb collaboration) 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

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

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

U spin symmetry d  s exchange Bd+- BsK+K- T+P+PCEW+PA+E T+P+PCEW+PA+E Bd +- Bs+K- T+P+PCEW+PA+E T+P+PCEW BsK+K- Bd K+- Where: T : tree P : penguin PCEW: colour suppressed electroweak penguin PA : penguin annihilation E: exchange U-spin symmetry not exact for flavour specific decays: E and PA missing E and PA contributions very small  can be seen in Bs+- and BdK+K- (BR ~ 10-8)

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

B(s) h+h’- events at LHCb Large b production at 14TeV p-p collisions. (All b mesons produced) B hadrons are mostly produced in the forward direction  LHCb is forward spectrometer 10-300mrad At nominal luminosity about 1012 bb in 107 s (L=2fb-1)  Millions of B(s) h+h’- per year (BR ~10-5/10-6) σbb ~ 500μb ; σinel ~ 80mb  σbb / σinel ~ 0.006 Many min-bias needed for background studies  Main background comes from b events (min-bias cut at trigger level) In this study 300k signal events and 27M inclusive b events have been used - b Parton 2 Parton 1 p p b Boost (PYTHIA) - - bb correlation - -

B(s) h+h’- selection cuts , K , K IP1 IP2 IPB L For each pair of charged tracks we cut on max (pT1, pT2) min (pT1, pT2) max (IP1/IP1, IP2/IP2) min (IP1/IP1, IP2/IP2) 2 of common vertex Then, the B candidate is selected with cuts on pT IPB/IP L/L Parameters used for selection h,h Smallest pt GeV/c > 1 largest pt 3 smallest IP/IP 6 largest IP/IP 12 h, h vertex fit 2 < 5 B pt IP/IP 2.5 L/L 18

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*+ D0π+, D0K+π-Dedicated D* trigger (300Hz) for large “PID unbiased” sample

Mass resolution performance allows clean separation PID performance Mass resolution performance B mass - Separation between Bd K-π+/Bs  K-π + fully relies on the mass resolution Bd K-π+ is 16 times more abundant  x 4 comes from the branching ratio  x 4 comes from hadronization fraction ππ hypothesis - B mass Clean samples through expected PID performance of RICH system Nominal mass resolution of 16 MeV/c2 allows clean separation between the two signals πK hypothesis

Proper time resolution Excellent proper time resolution allows to resolve fast Bs oscillations t = ~40 fs Proper time resolution (from full GEANT4 simulation) =~40 fs TOY MC Decay rate for BsK+K- events tagged as B at LHCb (integrated luminosity L=2fb-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) Δms 20 ps-1 in this simulation, a bit larger than the truth… Bkg

Selection summary - Yields are calculated for L= 2 fb-1 BR 10-6 Yield B/S bb B/S spec Channel Eff. (%) - 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 K spectrum selected from a sample of 27M bb MC events Partially reco BK*+- BdK+-

Flavour tagging Same side e-, m- Qvertex, QJet Opposite side High pT leptons K± from b → c → s Vertex charge B0opposite K- D PV Bs0signal K- Same side K + K+ Same side Fragmentation K± accompanying Bs ± from B** → B(*)± Tagging power in % 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 D2=(1-2)2: tagging power : tagging efficiency : mistag probability 3.5 K 9.5 Work in progress

Background proper time Proper time acceptance 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 GEANT4 simulations Background mass and proper time spectra generated from the full GEANT4 simulation Background proper time Proper time acceptance B0  +- B0  +- 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

Sensitivity on CP asymmetries (for L=2fb-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 LHCb can reach a sensitivity ~ 2 times better than the current world average in 107 s of running at nominal luminosity for the B0d system and can provide measurements in the B0s system with similar sensitivity Fit results corresponding to L=2fb-1 Bd+- BsK+K- (C) 0.043 (0.07*) 0.042 (S) 0.037 (0.09*) 0.044 BdK+- Bs+K- (ACP) 0.003 (0.015*) 0.02 *From current world average

Sensitivity on γ (for L=2fb-1) (secondary fake solution appears) Extraction of  performed using UTfit bayesian approach and software tools in 3 different scenarios (in this exercise =65o is assumed) (1) Perfect U-spin symmetry d=d’ -  = ’ (2) Weaker assumption: perfect U- spin 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 , ’ Perfect U-spin : Sensitivity ~ 4o Scenario (2) & (3) : Sensitivity ~ 7°-10° (secondary fake solution appears) 2 3 But sensitivity depends on the actual values of C and S…

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+K- CKK = 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 (BaBar/Belle) S = -0.59 ± 0.09 (BaBar/Belle) AK = -0.093 ± 0.015 (BaBar/Belle/CLEO/CDF) p.d.f. for  obtained allowing for a U-spin breaking:  = ’-  = ±20o d’/d = [0.8, 1.2] p.d.f. for   = (75±10)° Unitarity Triangle fits expectation

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-2s-1 ) is about 2 times better than the current world averages from the b-factories 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  from tree level modes, such as BDK, which can be assumed to be basically free of New Physics contributions

Backup

Some numbers Uncertainty phi_s 0.06 in 2 fb-1; 0.02 in phi_d 2fb-1 Taken from Reopt TDR Taken from J. Piedra Talk FPCP 2006