Charmless b-meson and b-baryon decays at LHCb. Adam Morris

Transcription

1 Charmless b-meson and b-baryon decays at Adam Morris University of Edinburgh on behalf of the Collaboration 13 th International Conference on Heavy Quarks and Leptons 6 th May 16 A. Morris (Edinburgh Charmless b decays at HQL 16 1

2 Introduction Charmless b-hadron decays Penguin b d or b s Sensitive to new particles in the loop b W u, c, t d, s q q Tree-level b u suppressed by V ub Similar magnitude of tree & penguin contributions Tree & penguin have relative weak phase γ Interference CP violation b W u ū d, s B c annihilation diagrams Sensitive to BSM charged propagators b W d, s c ū A. Morris (Edinburgh Charmless b decays at HQL 16

3 Introduction Outline 1 Observations of Λ b ΛK + π and Λ b ΛK + K and searches for other Λ b and Ξ b decays to Λh+ h -PAPER-16-4 arxiv: JHEP 5 (16 81 Observation of the Λ b Λφ decay -PAPER-16- arxiv: Submitted to PLB 3 Search for B + c decays to the p pπ + final state -PAPER-16-1 arxiv: Submitted to PLB A. Morris (Edinburgh Charmless b decays at HQL 16 3

4 Introduction Track types at Long tracks pass through all tracking stations Downstream tracks pass through the TT and T Λ and K S can decay outside VELO Performance paper: -DP-14- A. Morris (Edinburgh Charmless b decays at HQL 16 4

5 Introduction Event selection Full Run 1 dataset: 3 fb 1 of pp collisions at s = 7 and 8 TeV Pre-selection using track quality, vertex quality, isolation criteria and kinematic information Multivariate Analysis to reduce combinatorial background Hadron PID requirements to suppress misidentified backgrounds A. Morris (Edinburgh Charmless b decays at HQL 16 5

6 Λ b /Ξ b Λh+ h Λ b /Ξ b Λh+ h A. Morris (Edinburgh Charmless b decays at HQL 16 6

7 Λ b /Ξ b Λh+ h -PAPER-16-4 Introduction Motivation: Only a handful of observed charmless b-baryon decay modes Λ b pπ and Λ b pk Λ b K S pπ Some evidence for Λ b Λη No charmless decays of the Ξ b have been observed Can be used to study hadronisation in b-baryons Complement CP violation studies performed in b-mesons This analysis: Search for charmless Λ b and Ξ b decays to Λπ+ π, ΛK ± π and ΛK + K Veto open charm Λ + c Λh +, Ξ + c Λh + and D h + h Normalise to Λ b Λ + c ( Λπ + π Measure branching fractions and CP asymmetries of observed modes A. Morris (Edinburgh Charmless b decays at HQL 16 7

8 Λ b /Ξ b Λh+ h -PAPER-16-4 Branching fractions The Λ b branching fractions are calculated as: B(Λ b Λh + h B(Λ b Λ + c ( Λπ + π = N Λb Λh+ h N Λb Λ + c ( Λπ + π ε Λb Λ Since f Ξ is not known, we measure: b f Ξ b B(Ξ b Λh+ h f Λb B(Λ b Λ + c ( Λπ + π = NΞ b Λh+ h ε Λb Λ N Λb Λ + c ( Λπ + π Yields are obtained by fitting mass distributions Efficiencies are found from simulation Data-driven corrections + c ( Λπ + π ε Λb Λh + h + c ( Λπ + π ε Ξb Λh + h A. Morris (Edinburgh Charmless b decays at HQL 16 8

9 Λ b /Ξ b Λh+ h -PAPER-16-4 Fits to mass distributions Components for Λ b /Ξ b Λh+ h signal, cross-feed, partially reconstructed backgrounds (missing π and missing γ and combinatorial background partial recon. Candidates / ( MeV/c Λ b Λ + c ( Λπ + π comb. Λ b Normalisation cross-feed m(λπ π [MeV/c ] N Λb = 471 ± Candidates / ( MeV/c partial recon. Λ b /Ξ b Λπ + π comb. Λ b Ξ b cross-feed m(λπ π [MeV/c ] N Λb = 65 ± 14 N Ξ b = 19 ± 8 A. Morris (Edinburgh Charmless b decays at HQL 16 9

10 Λ b /Ξ b Λh+ h -PAPER-16-4 Fits to mass distributions Components for Λ b /Ξ b Λh+ h signal, cross-feed, partially reconstructed backgrounds (missing π and missing γ and combinatorial background Λ b /Ξ b ΛK + π Λ b /Ξ b ΛK + K Candidates / ( MeV/c partial recon. comb. Λ b Ξ b ± cross-feed m(λk π [MeV/c ] ± Candidates / ( MeV/c partial recon. comb. Λ b Ξ b cross-feed m(λk K [MeV/c ] N Λb = 97 ± 14 N Ξ b = 4 ± 7 N Λb = 185 ± 15 N Ξ b = 4 ± 4 A. Morris (Edinburgh Charmless b decays at HQL 16

11 Λ b /Ξ b Λh+ h -PAPER-16-4 Branching fraction results Observation of Λ b ΛK + K with significance 15.8σ Observation of Λ b ΛK + π with significance 8.1σ Evidence for Λ b Λπ + π at 4.7σ B(Λ b Λπ + π = (4.6 ± 1. ± 1.4 ±.6 6 B(Λ b ΛK + π = (5.6 ±.8 ±.8 ±.7 6 B(Λ b ΛK + K = (15.9 ± 1. ± 1. ±. 6 Order of uncertainties: ± stat. ± syst. ± norm. No observation of any of the Ξ b decays f Ξ b f Λb B(Ξ b Λπ+ π < at 9 % CL f Ξ b f Λb B(Ξ b ΛK π + <.8 6 at 9 % CL f Ξ b f Λb B(Ξ b ΛK+ K <.3 6 at 9 % CL A. Morris (Edinburgh Charmless b decays at HQL 16 11

12 Λ b /Ξ b Λh+ h -PAPER-16-4 CP asymmetries Fit separately for Λ b and Λ b in the ΛK + π and ΛK + K samples Calculate efficiency-corrected yields, N corr, using Dalitz plots A raw CP = Ncorr f Nf corr N corr f + N corr f Λ b Λ + c ( Λπ + π has the same b-hadron production asymmetry and similar detection asymmetry, therefore: A CP (Λ b Λh + h = A raw CP (Λ b Λh + h A raw CP (Λ b Λ + c ( Λπ + π A CP (Λ b ΛK + π =.53 ±.3 ±.11 A CP (Λ b ΛK + K =.8 ±. ±.7 Both consistent with zero A. Morris (Edinburgh Charmless b decays at HQL 16 1

13 Λ b Λφ Λ b Λφ A. Morris (Edinburgh Charmless b decays at HQL 16 13

14 Λ b Λφ -PAPER-16- Introduction Motivation: Λ b ΛK + K 31 proceeds via a b! ßs penguin process. should contain significant Λ b Λφ component 33 b s ss FCNC transition penguin34loop sensitive to new particles 35 Of particular interest is non-sm CP violation 36 Previously studied in B φks, B φk and Bs sss 37 of the phase has provided a value of 38 φφ CP violation []. For the case of the B Results so far consistent with SM 39 s! 4 41 Measurements with Λ b look for direct 4 CP violation CP asymmetries T-odd observables This analysis: Measure Λ b Λφ branching fraction Normalise to B φk S Measure T-odd triple-product asymmetries φ K + K, Λ pπ, K S π+ π Introduction In the Standard Model (SM, the flavour-changing neutral current (FCNC deca A Feynman diagram of the gluon process that contributes to this decay is given in Figure 1. This is therefor as the Bs! decay, which is a golden mode for the upgrade. Ne entering the penguin loop could induce non-sm CP violation. In the Bs! is tested through the measurement of CP violation in the interference betw sss and decay, characterised through the CP -violating phase, s. An me s =.17 ±.15(stat ±.3(syst ra SM can also be tested with triple product asymmetries, which also provide a decay, which is a pseudo-scala vector transition, the triple product asymmetries exploit the helicity angles o to isolate the interference terms between the CP -even and CP -odd polarisation CP -even polarisations therefore allow for two triple product asymmetries, deno and AV. An measurement of these triple product asymmetries has prov of AU =.3 ±.17(stat ±.6(syst and AV =.17 ±.17(stat ±. that are currently limited by statistical uncertainties. b b ud W u, c, t ud s s s Figure 1: Gluonic penguin Feynman diagram contributing to the b! A. Morris (Edinburgh Charmless b decays at HQL 16 14

15 Λ b Λφ -PAPER-16- Fits to mass distributions for Λ b Λφ Components for Λ b Λφ signal, non-resonant Λ b ΛK + K, Λ + random φ and pure combinatorial background m(λφ m(k + K m(pπ Long Events / (7 MeV/c 1 (a Long Λ Events / (1 MeV/c 16 (c 14 Long Λ Events / (1 MeV/c 1 (e Long Λ Downstream Pull Events / (7 MeV/c M [MeV/c KKpπ ] 5 (b Downstream Λ 15 5 Pull Events / (1 MeV/c - 3 M [MeV/c KK ] 18 (d 16 Downstream Λ Pull Events / (1 MeV/c M pπ [MeV/c ] 5 (f 15 5 Downstream Λ N = 89 ± 13 Pull M [MeV/c KKpπ ] Pull - 3 M [MeV/c KK ] Pull M pπ [MeV/c ] A. Morris (Edinburgh Charmless b decays at HQL 16 15

16 Λ b Λφ -PAPER-16- Fits to mass distributions for B φk S Components for B φk S signal, non-resonant B K + K K S, K S + random K+ K pair and pure combinatorial background m(φk S m(k + K m(π + π Long Events / (8 MeV/c 4 (a Long K 35 S Events / (1 MeV/c 5 (c Long K S 15 5 Events / (1 MeV/c 5 (e 15 5 Long K S Downstream Pull Events / (8 MeV/c M [MeV/c ] KKππ 6 (b 5 Downstream K S 4 3 Pull Events / (1 MeV/c - 3 M [MeV/c KK ] 45 (d 4 Downstream K S Pull Events / (1 MeV/c M ππ [MeV/c ] 35 (f Downstream K S N = 35±4 Pull M [MeV/c ] KKππ Pull - 3 M [MeV/c KK ] Pull M ππ [MeV/c ] A. Morris (Edinburgh Charmless b decays at HQL 16 16

17 Λ b Λφ -PAPER-16- Branching fraction result Λ b Λφ is observed with a significance of 5.9σ Branching fraction calculated as: Result: B(Λ b Λφ = f d f Λb N Λb Λφ ε B φks N B φks ε Λb Λφ B(B φk B(KS π+ π B(Λ pπ B(Λ b Λφ = (5.18 ± 1.4 ± ±.44 6 Order of uncertainties: ± stat. ± syst. ± norm. ± f d /f Λb A. Morris (Edinburgh Charmless b decays at HQL 16 17

18 Λ b Λφ -PAPER-16- T-odd observables 5 angles needed to describe the angular distribution of Λ b Λφ T-odd observables: cos(φ Λ sin(φ Λ cos(φ φ sin(φ φ DOI:.16/j.nuclphysbps A. Morris (Edinburgh Charmless b decays at HQL 16 18

19 Λ b Λφ -PAPER-16- T-odd observables results Datasets split by sign of observables mass fits to obtain N ±,O D D is daughter: Λ or φ O is observable: cos Φ D or sin Φ D ± denotes sign of O Asymmetries calculated as: Results: A O D = N+,O D N +,O D N,O D + N,O D A c Λ =. ±.1 ±.6 A s Λ = +.13 ±.1 ±.5 A c φ =.1 ±.1 ±.3 A s φ =.7 ±.1 ±.1 All consistent with zero A. Morris (Edinburgh Charmless b decays at HQL 16 19

20 B + c p pπ + B + c p pπ + A. Morris (Edinburgh Charmless b decays at HQL 16

21 B + c p pπ + -PAPER-16-1 Introduction Motivation: Charmless B c + decays proceed via annihilation diagrams Probe BSM physics such as charged Higgs A( bc W + qu V cb V uq where q = d, s Cabibbo suppression final states with zero strangeness dominate In B decays to states containing baryons, often enhancement at threshold Poorly understood This analysis: Search for B + c p pπ + Normalise to B + p pπ + Focus on B + c p pπ + with m(p p <.85 GeV/c Below c c threshold Cross-check with B + c (J/ψ p pπ + b c W d, s ū A. Morris (Edinburgh Charmless b decays at HQL 16 1

22 B + c p pπ + -PAPER-16-1 Analysis strategy Since f c is unknown, the measured quantites are: R p f c f u B(B + c p pπ + = N + Bc p pπ + ε u B(B + p pπ + N B+ p pπ + ε c R J/ψ p f c f u B(B + c J/ψπ + = N + Bc J/ψ( p pπ + ε u B(B + p pπ + N B + p pπ + ε J/ψ B(J/ψ p p c A. Morris (Edinburgh Charmless b decays at HQL 16

23 B + c p pπ + -PAPER-16-1 Mass fits: B + c p pπ + signal Fits to m(p pπ + with components for B + (c signal, combinatorial background and partially reconstructed B + (c p pρ+ ( π + π Simultaneous fit to 3 bins in multivariate classifier output for B c + region Candidates/(.1 GeV/c m(ppπ (GeV/c m(p p <.85 GeV/c Candidates/(.1 GeV/c m(ppπ (GeV/c.85 < m(p p < 3.15 GeV/c N B + c p pπ + =.7 ± 6.3 (stat N B + c J/ψ( p pπ + =.1 ± 3. (stat A. Morris (Edinburgh Charmless b decays at HQL 16 3

24 B + c p pπ + -PAPER-16-1 Mass fits: normalisation mode Fits to m(p pπ + with components for B + (c signal, combinatorial background and partially reconstructed B + (c p pρ+ ( π + π Candidates/(.8 GeV/c B m(ppπ (GeV/c N B+ p pπ + m(p p <.85 GeV/c = 1644 ± 83(stat Candidates/(.8 GeV/c B m(ppπ (GeV/c.85 < m(p p < 3.15 GeV/c A. Morris (Edinburgh Charmless b decays at HQL 16 4

25 B + c p pπ + -PAPER-16-1 Upper limits Profile likelihood ratio scans for S+B and B-only hypotheses Signal p-value profiles calculated by dividing S+B by B p value 1 p value R p J/ψ R p R p <.8 8 (9% CL R J/ψ p < (9% CL A. Morris (Edinburgh Charmless b decays at HQL 16 5

26 Summary Summary Λ b /Ξ b Λh+ h Observations of Λ b ΛK + K and Λ b ΛK + π Branching fractions: (15.9 ±.6 6 and (5.6 ± CP asymmetries consistent with zero Evidence for Λ b Λπ + π at 4.7σ New upper limits on Ξ b Λh+ h branching fractions Λ b Λφ Observation of Λ b Λφ Branching fraction: (5. ± T-odd triple product asymmetries consistent with zero B + c p pπ + No evidence for this decay upper limits on fc f u B(B + c p pπ + Many more analyses in progress with Run I data and soon with Run II data. Stay tuned... A. Morris (Edinburgh Charmless b decays at HQL 16 6

27 Backup slides Backup slides A. Morris (Edinburgh Charmless b decays at HQL 16 7

28 Backup slides Λ b /Ξ b Λh+ h Λ b ΛK + h Dalitz plots m (ΛK + [GeV /c 4 ] m (ΛK + [GeV /c 4 ] m (K + π [GeV /c 4 ] 5 15 m (K + K [GeV /c 4 ] A. Morris (Edinburgh Charmless b decays at HQL 16 8

29 Backup slides Λ b /Ξ b Λh+ h Λ b /Ξ b Λh+ h signal yields Mode Run period Yield Λ b downstream long downstream long 11. ± ± ± ± 3. Λπ + π 1a 9.1 ± ± ± ±.6 1b 17. ± ± ± ±.7 Total 65 ± ± ± ± ± ±.4 ΛK + π 1a 9.3 ± ± ± ± 1.5 1b 39.7 ± ± ± ± 1.5 Total 97 ± 14 4 ± ± ± ±.3. ±.6 ΛK + K 1a. ± ± 4..5 ±.4. ±.5 1b 6.5 ± ± ±.7. ±.6 Total 185 ± 15 4 ± ± ± 9. ( Λπ + Λ + c π 1a 45. ± ± 8.3 1b ± ± 9.8 Total 471 ± A. Morris (Edinburgh Charmless b decays at HQL 16 9 Ξ b

30 Backup slides Λ b /Ξ b Λh+ h Λ b /Ξ b Λh+ h systematics Systematic uncertainties ( 3 Fit Eff. Ph. sp. PID Vetoes N Λ + c π Total Λ b Λπ + π Λ b ΛK + π Λ b ΛK + K Ξ b Λπ+ π Ξ b Λπ+ K Ξ b ΛK+ K A. Morris (Edinburgh Charmless b decays at HQL 16 3

31 Backup slides Λ b /Ξ b Λh+ h Λ b /Ξ b Λh+ h CP asymmetries Systematic uncertainties ( 3 A CP (Λ b ΛK + π A CP (Λ b ΛK + K Control mode PID asymmetry Fit model 7 3 Fit bias 14 4 Efficiency uncertainty 8 8 Total 1 71 A. Morris (Edinburgh Charmless b decays at HQL 16 31

32 Backup slides Λ b Λφ Λ b Λφ efficiencies Combination of efficiencies for reconstruction, offline selection, trigger requirements and detector acceptance, ε tot, taken from simulation. Difference in detector-material interaction cross section determined from simulation Data-driven corrections applied where necessary Hardware-level hadron trigger corrected with calibration samples from charm decays Reconstruction efficiency for long tracks corrected with tag-and-probe method with J/ψ calibration samples D φks samples used to correct vertexing efficiency A. Morris (Edinburgh Charmless b decays at HQL 16 3

33 Backup slides Λ b Λφ Λ b Λφ branching fraction systematics Source Uncertainty (% Mass model 3. Simulation sample size. Tracking efficiency.5 Vertex efficiency.6 Hardware trigger.8 Selection efficiency 4.1 Peaking background.1 Total 6.7 A. Morris (Edinburgh Charmless b decays at HQL 16 33

34 Backup slides Λ b Λφ Λ b Λφ T-odd observables Events /.7 5 (a sinφ nλ Events /.7 16 (b cosφ nλ Events /.7 (c sinφ nφ Events /.7 (d cosφ nφ A. Morris (Edinburgh Charmless b decays at HQL 16 34

35 Backup slides Λ b Λφ Λ b Λφ T-odd observables Systematic uncertainties Source A c Λ A s Λ A c φ A s φ Mass model Angular acceptance.... Angular resolution Total A. Morris (Edinburgh Charmless b decays at HQL 16 35

36 Backup slides B + c p pπ + B + c p pπ + mass fits: signal Simultaneous fit to 3 bins in BDT output for B c + region Candidates/(.1 GeV/c m(ppπ (GeV/c Candidates/(.1 GeV/c m(ppπ (GeV/c Arbitrary units Signal Background Candidates/(.1 GeV/c m(ppπ (GeV/c Candidates/(.1 GeV/c m(ppπ (GeV/c BDT output Candidates/(.1 GeV/c m(ppπ (GeV/c Candidates/(.1 GeV/c m(ppπ (GeV/c m(p p <.85 GeV/c.85 < m(p p < 3.15 GeV/c N B + c p pπ + N B + c J/ψ( p pπ + =.7 ± 6.3 (stat =.1 ± 3. (stat A. Morris (Edinburgh Charmless b decays at HQL 16 36

37 Backup slides B + c p pπ + B + c p pπ + efficiencies Detector acceptance efficiency, ε acc, taken from simulation. Selection efficiency, ε sel : Acceptance maps in the m (p p vs m (pπ plane Account for reconstruction, triggers, preselection, BDT, PID All but PID calculated from simulation PID part calculated using calibration samples from charm decays Use s-weights to calculate average ε sel for B + No B c + signal simple average over phase space region large systematic Ratio ε sel u /ε sel c corrected for differences in data and simulation ε sel u ε sel =.495 ±.8 c ε acc u ε acc = ±.7 c ε sel u =.513 ±.3 ε J/ψ,sel c ε acc u = ±.7 ε J/ψ,acc c A. Morris (Edinburgh Charmless b decays at HQL 16 37

38 Backup slides B + c p pπ + B + c p pπ + efficiencies ] [(GeV/c p m π [(GeV/c ] m pp Efficiency ] [(GeV/c p m π [(GeV/c ] m pp Efficiency Acceptance map for B + c p pπ + Acceptance map for B + p pπ + A. Morris (Edinburgh Charmless b decays at HQL 16 38

39 Backup slides B + c p pπ + B + c p pπ + systematics Relative systematic uncertainties on ε u /ε c and input Bs Source m(p p <.85 GeV/c B c + J/ψ( p pπ + PID 3. % 3. % B c + lifetime. %. % Simulation.8 %.9 % Detector acceptance.6 %.6 % BDT shape 1.5 % 1.5 % Hardware trigger correction.8 %.9 % Fiducial cut.1 %.1 % Modelling 15 % B(B + p pπ + 15 % 15 % B(J/ψ p p 1.4 % PID uncertainty dominated by proton calibration sample size B c + lifetime =.57 ±.9 ps Modelling : variation in efficiency over phase space B(B + p pπ + = (1.7 ±.16 6 B(J/ψ p p = (. ±.9 3 A. Morris (Edinburgh Charmless b decays at HQL 16 39