Laurence Carson, Beauty Charmless Hadronic B Decays at LHCb Laurence Carson, University of Glasgow (on behalf of the LHCb collaboration) 12 th International Conference on B Physics at Hadron Machines Heidelberg, 7 th – 11 th September 2009

Laurence Carson, Beauty Outline Overview of LHCb detector Physics opportunities in charmless hadronic B decays at LHCb –Measurement of γ in decays involving penguins Using B d → π + π - and B s → K + K - Using B +/- →K +/- π + π - and B d →K S π + π - –Search for rare decay modes –Many other analyses not covered here e.g. α measurement with B d → ρπ, ρρ and ππ

Laurence Carson, Beauty Take advantage of B production at LHC – pairs in 2fb -1 (nominal 2*10 32 cm -2 s -1 ) –Produce all B species: B +,B d,B s,B c,Λ b,… Use trigger ( * ) to cope with high event rate –Level 0: hardware trigger on high p T /E T leptons or hadrons –High Level Trigger: matches L0 object to track with displaced vertex, then runs inclusive & exclusive selections The LHCb Detector Unique angular coverage: 1.9 < η < 4.9 Single forward arm spectrometer (*) see talk on Friday by L. de Paula

Laurence Carson, Beauty bkg Hadronic Modes at LHCb Vertex Locator (VeLo): Si strip detector giving σ τ ≈ 40fs; allows displaced vertex trigger and time-dependent B s studies Cherenkov Counters (RICH): Excellent p/K/ π separation for 2<p<100GeV; can separate out final states Without RICH PID With RICH PID PID example: B s → K + K - B d → π + π - τ residual B s →K + K - oscillations with 2fb -1 width = 39fs Mass resoln ≈ 17MeV

Laurence Carson, Beauty Current Status of γ Least well constrained parameter of the “db” unitarity triangle. Indirect measurement from fit to apex gives γ = ( )°. Direct measurements from time-independent analyses of B +/- → D 0( * ) K +/-( * ) (“tree-only” decays) give γ = ( )° –Analysis method (ADS/GLW/GGSZ) depends on D decay mode. Such tree-only decays expected to give SM value for γ. Following talk (S. Ricciardi) will discuss how LHCb can improve on current γ measurements using tree-only decays.

Laurence Carson, Beauty LHCb γ Strategy Measurements of γ from decays involving both tree and penguin amplitudes are sensitive to New Physics effects –Compare to SM “standard candle” γ value from tree-only decays. –Significant disagreement would be unambiguous sign of NP. Prospects for two such measurements have been studied by LHCb –Measurement of time-dependent CP asymmetries in B d → π + π - and B s → K + K - (method: R. Fleischer, Phys. Lett. B 459 (306) 1999). –Combined Dalitz analysis of B +/- → K +/- π + π - and B d → K S π + π - (method: I. Bediaga et al, Phys. Rev. D 76 (073011) 2007). Gluonic penguin in SM Gluonic penguin in MSSM

Laurence Carson, Beauty Measuring γ with B d → π + π - and B s → K + K - Method first proposed by R. Fleischer, Phys. Lett. B 459 (306) 1999

Laurence Carson, Beauty ε geo acceptance ~21%, ε selection(no PID) ~18%, ε trigger ~36% ε total ~1.4% B→hh at LHCb Studies of two-body charmless hadronic (“B→hh”) decays at LHCb summarised as part of forthcoming “physics book”. –Including selection/bkg studies, calibration/systematics, and γ extraction. Expected total mass distribution ( ππ hypothesis) with 0.2fb -1 Channel2fb -1 Yield (no PID) B d → π + π - 59k B d → K + π - 217k B s → K - π + 15k B s → K + K - 72k Λ b → pπ - 7k Λ b → pK - 11k 3-body C.L. Combinatorial C.L.

Laurence Carson, Beauty Some Calibrations for B→hh Proper time resolution model is Gaussian with mean and width depending on per- event proper time error σ τ – Model can be determined on data using B s → K - π + (if mistag is known). Proper time acceptance distorted by IP cuts in trigger and selection –Can be determined on data by “swimming” the B to build up event-by-event acceptance (top hat). mean = GM.σ τ width = GS.σ τ swim B→hh acceptance after: offline selection offline selection + trigger PID likelihood calibrated using D* + → D 0 (→K - π + ) π + and Λ → p π -.

Laurence Carson, Beauty γ from B d → π + π -, B s → K + K - Direct and mixing induced CP asymmetries measured using tagged, time- dependent analysis: Have 4 asymmetries depending on 7 physics parameters:,,,. Assume U-Spin (d↔s) symmetry d=d’ and θ=θ’ Take φ d from J/ψK S system becomes soluble. d (d’) is related to the ratio of the magnitudes of the penguin and tree contributions for the B d (B s ) decay, while θ (θ’) is related to the difference in their strong phases.

Laurence Carson, Beauty LHCb B→hh Fit Approach Fit for branching ratios, lifetimes, CP asymmetries, and detector parameters is made in all B→hh channels simultaneously (68 free parameters) –Mass and PID likelihoods used to separate modes. With 2fb -1 of data, each of the four CP asymmetries from B d → π + π - and B s →K + K - will be measured with a statistical uncertainty of ≈ For the extraction of γ, A dir (KK) can be replaced with A CP (B d →K + π - ), since they are expected to be equal given U-spin symmetry, and the uncertainty on A CP (B d →K + π - ) with 2fb -1 will be <0.01 (systematics dominated). Fit to B s →K + K - mass distribution under ππ hypothesis (full MC) PID distribution for 0.2fb -1 toy MC sample π K p

Laurence Carson, Beauty LHCb Sensitivity to γ Extraction of γ allows for some U-spin breaking, with 0.8 < d’/d < 1.2 and -20° < θ’ - θ < 20°. SM solution for γ is isolated by imposing the condition θ>90°. 68% C.L. 95% C.L. γ (input 70°) φ s (input rad) With 2fb -1, find σ γ = 7°, σ φ s = 0.05 rad, σ d = 0.13 and σ θ = 7°. Contours in (d, γ ) plane without imposing θ >90° Alternative strategy would be to constrain φ s (expect σ φ s ≈ 0.03 rad from B s →J/ψφ with 2fb -1 ) and release one of the U-spin constraints d=d’ or θ=θ’.

Laurence Carson, Beauty Measuring γ with B +/- →K +/- π + π - and B d →K S π + π - Method first proposed by I. Bediaga et al, Phys. Rev. D 76 (073011) 2007

Laurence Carson, Beauty B +/- →K* 0 π +/- penguin only; B d →K* + π - penguin and tree –Extract penguin amplitude (V tb V* ts P) via standard Dalitz analysis of B +/- →K +/- π + π - –Use this as input to untagged Dalitz analysis of B d →K S π + π - to extract tree amplitude (V ub V* us T) –Tagging not required as resonance interference regions for B d and B d are distinct –Parameters extracted relative to contribution from χ c0 K (common contribution to B d and B +/- ) γ from B +/- →K +/- π + π -, B d →K S π + π - Combined: two distinct regions of resonance interference B d →K S π + π - Tree amplitudes in three-body charmless hadronic decays involve V ub –Probe γ using interference between intermediate resonances Resonances: K*(892) +/-, K*(1430) +/-, ρ (770) 0, f 0 (980), χ c0 m 2 (K S π + ) m 2 (K S π - )

Laurence Carson, Beauty B +/- →K +/- π + π -, B d →K S π + π - at LHCb Lower efficiency for B d →K S π + π - due to lower K S reconstruction efficiency –25% decay in VeLo good efficiency/resolution –50% decay between VeLo and TT Stations poorer efficiency/resolution –25% decay downstream of TT Stations track lost ChannelB.R.ε selection 2fb -1 yield (no HLT) B + →K + π + π - 5.5* %494k B d →K S π + π - 2.2* %90k Selection: want to avoid tight cuts on p T as this lowers efficiency in corner of Dalitz plot, where some of the resonances lie –Trade-off between minimising bias and reducing combinatoric bkg B + →K + π + π - with p T >200 MeV for all daughters Sensitivity to γ : idealised toy MC study (no background or detector effects) estimates σ γ ~5° (stat. only) with 2fb -1.

Laurence Carson, Beauty Baryonic mode B d → pp unobserved SM predictions close to being ruled out –If true B.R. close to current limit (1.1*10 -7 ), expect evidence with ~0.2fb -1 (2010 run) –Also expect to observe B d → K + K - and B s → π + π - (penguin annihilation and W exchange only) with ~1fb -1 (if SM B.R.s). Rare Hadronic B Decays at LHCb Specific bkgs to B d →pp suppressed by RICH PID B + → K - π + π + and B + → K + K + π - highly suppressed in SM –B.R.s O( ) and O( ) respectively. Can be strongly enhanced by NP effects –e.g. B.R.(B + →K - π + π + )~10 -6 (≈ current B.R. limit) with Z’. If such enhancements are present, LHCb may be able to make an observation.

Laurence Carson, Beauty Search for undiscovered rare decays –Expect to observe B s → π + π -, B d → K + K - and B d → pp with early data, whether SM branching ratio or not –Can observe B + → K - π + π +, B + → K + K + π - if B.R. strongly enhanced by NP. Measure α using B d → ρπ, ρρ, and ππ –Expect σ α (stat) ~ 5° after 2fb -1 (dominated by ρπ ). Conclusions LHCb has a rich physics programme using charmless hadronic decays: Measure γ from decays with penguins and compare to SM value from tree- only decays –Expect σ γ = 7° after 2fb -1 from analysis using B d → π + π -, B s → K + K - –Measurement with B +/- → K +/- π + π - and B d → K S π + π - should be competitive (effect We are awaiting the first collisions… of backgrounds and systematics to be checked).

Laurence Carson, Beauty Backup Slides

Laurence Carson, Beauty More Calibrations for B→hh PID calibrated using PID-unbiased samples of D* + → D 0 (→K - π + ) π + and Λ → p π - –Dedicated stream in trigger –Re-weight likelihood distribution for B using p and p T distributions. Tagging performance for B d measured using flavour-specific B d → K + π - –For B s tagging, B s → K - π + has less statistics and is sensitive to proper time resolution –Can study B d -B s difference in other modes (e.g. B d → D - π + and B s → D s π + ) –Can also calibrate using per-event mistag. DLL distributions: B d → π + π -, π from D → K π before reweighting, π from D → K π after reweighting. Per-event mistag for B d → K + π -

Laurence Carson, Beauty Measuring α with B d → π + π - π 0 α can be measured via a tagged Dalitz analysis of B d → π + π - π 0 –Dominant submodes are ρ + π -, ρ - π + and ρ 0 π 0 –Isospin symmetry used to extract α, tree/penguin amplitudes and strong phases. Multivariate selection used, ε total ~0.07%. Expected 2fb -1 yield is 14k, with B/S~1. Resolved π 0 Merged π 0 2fb -1 toy experiment gives α = ( )° (stat. only) Sum of Dalitz coords Effect of E T cut on π 0 Time evolution of tagged Dalitz plots before after