1. Laurence Carson, Beauty 20091 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

2. Laurence Carson, Beauty 20092 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

3. Laurence Carson, Beauty 20093 Take advantage of B production at LHC – pairs in 2fb -1 (nominal year @ 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

4. Laurence Carson, Beauty 20094 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

5. Laurence Carson, Beauty 20095 Current Status of γ Least well constrained parameter of the “db” unitarity triangle. Indirect measurement from fit to apex gives γ = (66.8 +5.4 -3.8 )°. Direct measurements from time-independent analyses of B +/- → D 0( * ) K +/-( * ) (“tree-only” decays) give γ = (70 +27 -29 )° –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.

6. Laurence Carson, Beauty 20096 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

7. Laurence Carson, Beauty 20097 Measuring γ with B d → π + π - and B s → K + K - Method first proposed by R. Fleischer, Phys. Lett. B 459 (306) 1999

8. Laurence Carson, Beauty 20098 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 bkg[76k,186k]@68% C.L. Combinatorial bkg[106k,226k]@68% C.L.

9. Laurence Carson, Beauty 20099 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 -.

10. Laurence Carson, Beauty 200910 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.

11. Laurence Carson, Beauty 200911 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 ≈ 0.04. 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

12. Laurence Carson, Beauty 200912 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 -0.04 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’.

13. Laurence Carson, Beauty 200913 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

14. Laurence Carson, Beauty 200914 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 - )

15. Laurence Carson, Beauty 200915 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*10 -5 1.1%494k B d →K S π + π - 2.2*10 -5 0.5%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.

16. Laurence Carson, Beauty 200916 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(10 -14 ) and O(10 -11 ) 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.

17. Laurence Carson, Beauty 200917 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).

18. Laurence Carson, Beauty 200918 Backup Slides

19. Laurence Carson, Beauty 200919 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 -

20. Laurence Carson, Beauty 200920 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 = (97 +9 -4 )° (stat. only) Sum of Dalitz coords Effect of E T cut on π 0 Time evolution of tagged Dalitz plots before after