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Charmless Hadronic B Decays at LHCb

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. Outline. Overview of LHCb detector

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Charmless Hadronic B Decays at LHCb

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

  2. Outline • Overview of LHCb detector • Physics opportunities in charmless hadronic B decays at LHCb • Measurement ofγin decays involving penguins • Using Bd→π+π-andBs→K+K- • Using B+/-→K+/-π+π-andBd→KSπ+π- • Search for rare decay modes • Many other analyses not covered here • e.g. αmeasurement with Bd→ρπ, ρρandππ Laurence Carson, Beauty 2009

  3. The LHCb Detector Single forward arm spectrometer • Take advantage of B production at LHC • pairs in 2fb-1 (nominal year @ 2*1032cm-2s-1) • Produce all B species: B+,Bd,Bs,Bc,Λb,… • Use trigger(*) to cope with high event rate • Level 0: hardware trigger on high pT/ET leptons or hadrons • High Level Trigger: matches L0 object to track with displaced vertex, then runs inclusive & exclusive selections Unique angular coverage: 1.9 < η < 4.9 Laurence Carson, Beauty 2009 (*) see talk on Friday by L. de Paula

  4. Hadronic Modes at LHCb • Vertex Locator (VeLo): Si strip detector giving στ≈40fs; allows displaced vertex trigger and time-dependent Bs studies • Cherenkov Counters (RICH): Excellent p/K/π separation for 2<p<100GeV; can separate out final states Bd→π+π- τresidual Bs→K+K- oscillations with 2fb-1 width = 39fs bkg PID example: Bs→K+K- Without RICH PID With RICH PID Mass resoln ≈ 17MeV Laurence Carson, Beauty 2009

  5. 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+/-→ D0(*)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. Laurence Carson, Beauty 2009

  6. LHCbγ 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. Gluonic penguin in SM Gluonic penguin in MSSM • Prospects for two such measurements have been studied by LHCb • Measurement of time-dependent CP asymmetries in Bd→ π+π-and Bs→ K+K-(method: R. Fleischer, Phys. Lett.B 459 (306) 1999). • Combined Dalitz analysis of B+/-→ K+/-π+π-and Bd→ KSπ+π- (method: I. Bediaga et al, Phys. Rev.D 76 (073011) 2007). Laurence Carson, Beauty 2009

  7. Measuring γ with Bd→ π+π-and Bs→ K+K- Method first proposed by R. Fleischer, Phys. Lett.B 459 (306) 1999 Laurence Carson, Beauty 2009

  8. 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. • εgeo acceptance~21%, εselection(no PID)~18%, εtrigger~36% εtotal~1.4% Expected total mass distribution (ππ hypothesis) with 0.2fb-1 Laurence Carson, Beauty 2009

  9. Some Calibrations for B→hh mean = GM.στwidth = GS.στ • Proper time resolution model is Gaussian with mean and width depending on per-event proper time error στ • Model can be determined on data using Bs→ K-π+(if mistag is known). • PID likelihood calibrated using D*+→ D0(→K-π+)π+ and Λ → pπ-. • 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). B→hh acceptance after: offline selection offline selection + trigger swim Laurence Carson, Beauty 2009

  10. γ from Bd→ π+π-, Bs→ K+K- • Direct and mixing induced CP asymmetries measured using tagged, time-dependent analysis: • Have 4 asymmetries depending on 7 physics parameters: , , , . • d (d’) is related to the ratio of the magnitudes of the penguin and tree contributions for the Bd (Bs) decay, while θ (θ’) is related to the difference in their strong phases. • Assume U-Spin (d↔s) symmetry d=d’ and θ=θ’ • Take φd from J/ψKS system becomes soluble. Laurence Carson, Beauty 2009

  11. 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. Fit to Bs→K+K- mass distribution under ππhypothesis (full MC) PID distribution for 0.2fb-1 toy MC sample π K p • With 2fb-1 of data, each of the four CP asymmetries from Bd→π+π- and Bs→K+K- will be measured with a statistical uncertainty of ≈0.04. • For the extraction of γ, Adir(KK) can be replaced with ACP(Bd→K+π-), since they are expected to be equal given U-spin symmetry, and the uncertainty on ACP(Bd→K+π-) with 2fb-1 will be <0.01 (systematics dominated). Laurence Carson, Beauty 2009

  12. 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 γis isolated by imposing the condition θ>90°. • With 2fb-1, find σγ= 7°, σφs = 0.05rad, σd= 0.13 andσθ= 7°. Contours in (d,γ) plane without imposing θ >90° 68% C.L. 95% C.L. γ (input 70°) φs (input -0.04 rad) • Alternative strategy would be to constrain φs (expect σφs≈ 0.03 radfrom Bs→J/ψφwith 2fb-1) and release one of the U-spin constraints d=d’ or θ=θ’. Laurence Carson, Beauty 2009

  13. Measuring γ with B+/-→K+/-π+π- and Bd→KSπ+π- Method first proposed by I. Bediaga et al, Phys. Rev.D 76 (073011) 2007 Laurence Carson, Beauty 2009

  14. γfrom B+/-→K+/-π+π-, Bd→KSπ+π- • Tree amplitudes in three-body charmless hadronic decays involve Vub • Probe γ using interference between intermediate resonances • B+/-→K*0π+/- penguin only; Bd→K*+π- penguin and tree • Extract penguin amplitude (VtbV*tsP) via standard Dalitz analysis of B+/- →K+/-π+π- • Use this as input to untagged Dalitz analysis of Bd→KSπ+π- to extract tree amplitude (VubV*usT) • Tagging not required as resonance interference regions for Bd and Bd are distinct • Parameters extracted relative to contribution from χc0K (common contribution to Bd and B+/-) Combined: two distinct regions of resonance interference m2(KSπ-) Bd→KSπ+π- Bd→KSπ+π- m2(KSπ-) m2(KSπ-) m2(KSπ+) m2(KSπ+) m2(KSπ+) Resonances: K*(892)+/-, K*(1430)+/-, ρ(770)0, f0(980), χc0 Laurence Carson, Beauty 2009

  15. B+/-→K+/-π+π-, Bd→KSπ+π- at LHCb • Selection: want to avoid tight cuts on pT 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 pT >200 MeV for all daughters • Lower efficiency for Bd→KSπ+π- due to lower KS 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 • Sensitivity to γ: idealised toy MC study (no background or detector effects) estimates σγ ~5° (stat. only) with 2fb-1. Laurence Carson, Beauty 2009

  16. Rare Hadronic B Decays at LHCb • Baryonic mode Bd→ 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 Bd→ K+K- and Bs→π+π-(penguin annihilation and W exchange only) with ~1fb-1 (if SM B.R.s). • 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. Specific bkgs to Bd→ppsuppressed by RICH PID Laurence Carson, Beauty 2009

  17. 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 σγ= 7° after 2fb-1from analysis using Bd→ π+π-, Bs→ K+K- • Measurement with B+/-→ K+/-π+π- and Bd→ KSπ+π- should be competitive (effect of backgrounds and systematics to be checked). • Search for undiscovered rare decays • Expect to observe Bs→ π+π-, Bd→ K+K- and Bd→ 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 Bd→ ρπ, ρρ, andππ • Expect σα(stat)~ 5° after 2fb-1 (dominated by ρπ). • We are awaiting the first collisions… Laurence Carson, Beauty 2009

  18. Backup Slides Laurence Carson, Beauty 2009

  19. More Calibrations for B→hh DLL distributions: Bd →π+π-, πfrom D → Kπbefore reweighting,π from D → Kπ after reweighting. • PID calibrated using PID-unbiased samples of D*+→ D0(→K-π+)π+ and Λ → pπ- • Dedicated stream in trigger • Re-weight likelihood distribution for B using p and pT distributions. • Tagging performance for Bd measured using flavour-specific Bd→ K+π- • For Bs tagging, Bs→ K-π+ has less statistics and is sensitive to proper time resolution • Can study Bd-Bs difference in other modes (e.g. Bd → D-π+ and Bs → Dsπ+) • Can also calibrate using per-event mistag. Per-event mistag for Bd → K+π- Laurence Carson, Beauty 2009

  20. Measuring α with Bd→ π+π- π0 Resolved π0 Merged π0 • αcan be measured via a tagged Dalitz analysis of Bd→ π+π- π0 • Dominant submodes are ρ+π-, ρ-π+andρ0π0 • Isospin symmetry used to extract α, tree/penguin amplitudes and strong phases. • Multivariate selection used, εtotal~0.07%. Expected 2fb-1 yield is 14k, with B/S~1. • 2fb-1 toy experiment gives α= (97+9-4)° (stat. only) Effect of ET cut on π0 Time evolution of tagged Dalitz plots before after Sum of Dalitz coords Laurence Carson, Beauty 2009

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