Absolute Branching Fractions of Λ + c at BESIII

Transcription

1 Absolute Branching Fractions of Λ + c at BESIII Decays Zhang Yu On Behalf of the BESIII Collaboration Uversity of Chinese Academy of Sciences zhangyu13@mails.ucas.ac.cn November 3, 17

2 Overview 1 Introduction L1 Λ + c Physics and Λ + Λ c c Production u d L Analysis Techque Hadroc decays c Measurement of Hadroc Λ + c Branching Fractions Measurement of Singly Cabbibo Suppressed Decays of Λ + c pπ + π and Λ + c pk + K Observation of Λ + c nks π+ Measurement of Λ + c Σ π + π + π and Λ + c Σ π + π + Evidence for the SCS Decay Λ + c pη and Search for Λ + c pπ 3 Semileptoc decays Measurement of the Branching Fractions of Λ + c Λl + ν l (l = e, µ 4 Inclusive decays Measurement of the branching fractions of Λ + c Summary ΛX Zhang Yu (UCAS Charm Physics November 3, 17 / 16

3 Discovery of the Λ + c Baryon BNL (hint νp µλπ + π π + π + Fermi Lab (evidence MARKII (observation Λ + c pk π + PRL 34, 11 (197 PRL 37, 88 (197 PRL 44, 1 (198 Its decays are important to probe the quark structure when a heavy quark exists As a dominant final state particle in bottom decays, its decays are essential to test QCD in b-factories Zhang Yu (UCAS Charm Physics November 3, 17 3 / 16

4 Singly Charmed Baryon Spectroscopy u L1 c L d Quark structure: a heavy quark (c with an ground state spin zero diquark (ud The lightest charmed baryon (m Λ + c = MeV, most of the charmed baryon would decay to it Only weak decays for Λ + c, but its total measured B is much less than 1 for PDG, so many channels are to be discovered Zhang Yu (UCAS Charm Physics November 3, 17 4 / 16

5 Λ + c Λ c Production at 4.99 GeV σ(nb.6 PRL 11, 171 (8 [Belle Collaboration].67fb 1 Λ + c Λ GeV collected with BESIII M(Λ + c Λ c GeV/c Λ + Λ c c pair production provides a uque laboratory for precision measurements allows to determine the absolute branching fractions (B Zhang Yu (UCAS Charm Physics November 3, 17 / 16

6 Analysis Techque Tag side: 1 Single Tag(ST M BC = Ebeam /c4 p /c Double Tag(DT for semi-leptoc decays: U miss = E miss c p miss 3 B = N sig N tag ε sig /ε tag,sig Tag the Λ c events via hadroc decays with large branching fractions, thus could suppress background effectively; Signal side: Hadroc decays (fully reconstructed; Semi-leptoc decays (neutrino missed and Inclusive decays (partially reconstructed Zhang Yu (UCAS Charm Physics November 3, 17 6 / 16

7 Measurement of Hadroc Λ + c Single Tag Λ + c Events Branching Fractions [PhysRevLett.116.1] Events/. MeV/c 3 pk S Λπ 4 3 pk π S 1 1 pk π + π S pk π Λπ π 6 + Σ π + π Λπ + π π + 3 Σ π Σ π Σ + ω M BC (GeV/c Dominated by pk π + pk π + π single tag events Mode pks 143 ± 37 pk π ± 88 pks π 8 ± 33 pks π + π 48 ± 9 pk π + π 1849 ± 71 Λπ + 76 ± 7 Λπ + π 1497 ± Λπ + π π + 69 ± 31 Σ π + ± 7 Σ + π 39 ± 4 Σ + π + π 116 ± 49 Σ + ω 17 ± N ST Zhang Yu (UCAS Charm Physics November 3, 17 7 / 16

8 Measurement of Hadroc Λ + c Branching Fractions [PhysRevLett.116.1] Background free double tags Events/1. MeV/c 1 1 pk S + Λπ pk π 1 S pk π + π S 1 pk π + + Λπ π Λπ + π π + Σ π Σ + π + 1 Σ ω 1 pk π + π Σ π + π Msig_mBC_6 BC (GeV/c sig_mbc_64 1 Mode pks 97 ± 1 pk π + 4 ± pks π 47 ± 8 pks π + π 34 ± 6 pk π + π 176 ± 14 Λπ + 6 ± 8 Λπ + π 11 ± 13 Λπ + π π + 3 ± 7 Σ π + 38 ± 6 Σ + π ± Σ + π + π 8 ± 9 Σ + ω 13 ± 3 N DT i A least square global fitter: N DT i + j = N Λ + c Λ B ib j ɛ DT c i + j simultaneous fit to all the tag modes, while constraing the total Λ c Λ c pair number, taking into account the correlations. Zhang Yu (UCAS Charm Physics November 3, 17 8 / 16

9 Measurement of Hadroc Λ + c Cabbibo favored decays Branching Fractions [PhysRevLett.116.1] Mode This work (% PDG (% BELLE (% pks 1. ±.8 ± ±.3 pk π +.84 ±.7 ±.3. ± ± pks π 1.87 ±.13 ±. 1.6 ±. (PhysRevLett pks π + π 1.3 ±.11 ± ±.3 pk π + π 4.3 ±.3 ± ± 1. Λπ ±.7 ± ±.8 Λπ + π 7.1 ±.37 ± ± 1.3 Λπ + π π ±.4 ±.18.6 ±.7 Σ π ±.8 ±.3 1. ±.8 Σ + π 1.18 ±.1 ±.3 1. ±.34 Σ + π + π 4. ±.4 ±. 3.6 ± 1. Σ + ω 1.6 ±. ±.7.7 ± 1. 1 Absolute Bs are measured with improved precision; The V ub measurement suffers large uncertainty from B Λ + c pk π +. Zhang Yu (UCAS Charm Physics November 3, 17 9 / 16

10 Measurement of Singly Cabbibo Suppressed Decays of Λ + c pπ + π and Λ + c pk + K Single Tag method [PhysRevLett.117.3] nonfactorizable contributions from W-exchange diagrams only internal W-emission diagram in Λ + c pφ Events/(1. MeV/c 1 Events/(3. MeV/c M π + π (GeV/c Λ + c M BC (GeV/c.6 Reference mode: Λ + c pk π + M BC (GeV/c pπ+ π Events/(1. MeV/c 1 Λ + c pk + K Events/(. MeV/c 3 1 Λ + c pφ Λ + c pk + K (non-φ 1 1. M 1.1 (GeV/c K + K Decay modes B (This work B (PDG average Λ + c pπ+ π (3.91 ±.8 ±.1 ± (3. ±. 1 3 Λ + c pφ (1.6 ±.19 ±.8 ± (8. ± Λ + c pk + K (non-φ (.47 ± 1.3 ±.41 ± (3. ± the first observation of the SCS decay Λ + c pπ + π Zhang Yu (UCAS Charm Physics November 3, 17 1 / 16

11 4 Observation of Λ + c nk S π+ A test to the isospin symmetry [PhysRevLett ] /c Events/.1 GeV 3 (a 1 1 (c M (GeV /c miss Events/. MeV/c 3 (b 1 1 M distri (d M π + π (GeV/c Mmiss = Emiss /c4 p miss /c Peaking backgrounds: Λ + c Σ + π + π Λ + c Σ π + π + (Σ ± nπ ± B(Λ + c nk S π+ = (1.8 ±.3 ±.11% B(Λ + c n K π + /B(Λ + c pk π + = (.6 ±.9% B(Λ + c n K π + /B(Λ + c p K π = (.97 ±.16% confirms the isospin symmetry and helps to understand the final state interactions Zhang Yu (UCAS Charm Physics November 3, / 16

12 Measurement of Λ + c Σ π + π + π and Λ + c Σ π + π + first observation of Λ + c Σ π + π + π [PLB.77 ( ] Mn (GeV/c Events/. GeV/c Λ + c Σ π + π + Λ + c Σ π + π + π E n = (E beam E 3πs(π p n = p Λ + c p 3πs(π M n = E n p n M nπ (GeV/c M nπ M n (GeV/c B(Λ + c Σ π + π + = (1.81 ±.17 ±.9% B(Λ + c Σ π + π + π = (.11 ±.33 ±.14% the first observation of Λ + c Σ π + π + π and improvement on the B(Λ + c Σ π + π + Zhang Yu (UCAS Charm Physics November 3, 17 1 / 16

13 + Evidence for the SCS Decay Λ + c pη and Search for Λ + c pπ [PhysRevD ] Events / (.MeV/c Λ + c pη η γγ set constraint on the theoretical calculations test SU(3 flavor symmetry and understand the underlying dynamics Events / (.MeV/c 1 data signal curve background curve η π + π π total curve 1 data in E sideband data in M π + sideband π π M BC (GeV/c data signal curve background curve total curve data in E sideband N(Λ c pπ Λ + c pπ M BC (GeV/c Normalized likehood value < 7.9@ 9% C.L. Λ + c pη Λ+ c pπ B Λ + c pπ B Λ + c pη This work 1.4 ±.8 ±.1 <.7 <.4 Sharma et al[1]. a (1.7 b. 1. a (.1 b Uppal et al[] S. L. Chen et al[3] Cai-Dian Lü et al[4] assume positive (a and negative sign (b of p-wave amplitude of Λ + c Ξ K + [1]PRD,767 []PRD 49,3417 [3]Commun. Theor. Phys. 4, 63 [4]PRD 93, 68 B Λ + c pη is consistent with one theoretical expectation[3] within σ, but much higher than the other Upper limit on B Λ + c pπ is compatible with expected values Zhang Yu (UCAS Charm Physics November 3, / 16

14 B of Λ + c Λl + ν l (l = e, µ [ PRL and PLB ] U miss = E miss c p miss background: Λ + c Λπ + π Events/.1 GeV 3 1 Λ + c Λe + ν e U miss (GeV Events/.1 GeV 3 1 Λ + c Λµ + ν µ U miss (GeV 1 the first absolute measurement, with B Λ + c Λe + ν e = (3.63 ±.38 ±.% and B Λ + c Λµ + ν µ = (3.49 ±.46 ±.7% a good test to non-perturbative models and LQCD calculations Zhang Yu (UCAS Charm Physics November 3, / 16

15 B of Λ + c ΛX proceed via c s and dominates the rates of Λ + c decay help to understand the Λ + c quark structure and decay dynamics essential input for Λ b decays BESIII Preliminary Two tag modes: Λ c pk S, pk + π N sig = N S NA +N B f (N D NC +N E B Λ + c ΛX = ( ±.6% A CP = ( ± 1.1% The total known B involving Λ is (4. ±.1%, indicates many unknown decay channels from this measurement BESIII Preliminary No CP asymmetry effect is observed in current precision Zhang Yu (UCAS Charm Physics November 3, 17 1 / 16

16 Summary 1 Λ + Λ c c pair production at BESIII allows to determine the absolute Bs of Λ + c decays; The semileptoc decays improve the understanding of non-perturbative QCD, and provide good test to theoretical calculations; 3 The hadroc and inclusive decays are good channels to understand the decay dynamics and quark structure; 4 Λ + c decays serve as essential inputs in Λ b precision measurement and V ub determination; More data is expected at BESIII in the near future to explore more channels and improve the existing results. The End Zhang Yu (UCAS Charm Physics November 3, / 16