Decays at BESIII. Lei Li. For BESIII Collaboration. Beijing Institute of Petro-chemical Technology (BIPT)

Transcription

1 L c Decays at BESIII Lei Li For BESIII Collaboration Beijing Institute of Petro-chemical Technology (BIPT) 中国物理学会高能物理分会 / 第十二届全国粒子物理学术会议 Aug , 2016, Hefei, China 1

2 Outline Introduction L c decays L c semi-leptonic decays L c hadronic decays Summary 2

3 Discovery of L c L c was first observed of at Fermi Lab in 1976 and then established at Mark II experiment in Invariant mass distribution L c pk - p [PRL44(1980)10] L c- Lp - p p - [PRL37(1976)882] 3

4 L c cornerstone of charmed baryon spectroscopy Quark model picture: a heavy quark (c) with a unexcited spin-zero diquark (u-d) Heavy Quark Effective Theory: diquark correlation is enhanced by weak Color Magnetic Interaction with a heavy quark more reliable prediction of heavy-light quark transition without dealing with light degrees of freedom that have net spin or isospin. L c may provides more powerful test on internal dynamic than D/Ds does. 4

5 L c Measurements [PDG2015] DB/B 9.3% 5.8% 14.1% 22.9% 25.0% 10.5% 13.3% 23.5% 11.4% 13.0% 33.3% 18.0% 66.7% 45.4% 45.4% 53.2% 64.0% 36.4% 8.9% 26.0% 7.8% 20.0% 18.7% DB/B 42.8% 80.0% 36.0% 20.8% 30.2% 37.5% 20.3% 33.3% 10.0% 21.9% 33.3% 10.2% 17.4% 36.0% 27.4% 27.1% 15.8% 16.3% 26.2% 24.5% 11.4% 28.6% 20.3% 17.5% 30.4% 31.6% Total branching fraction small than 65%. Lots of unknown decay channels Quite large uncertainties, most larger than 20% Most BFs are measured relative to L c pk - p 17.2% 22.2% 5

6 Beijing Electron Positron Collider (BEPC) Linac South BESIII detector 2004: start BEPCII construction 2008: test run of BEPCII 2009: Start of BESIII data taking Beam energy: GeV Achieved Design Luminosity on Apr 5 th, 2016 : cm -2 s -1 6

7 BESIII Detector 7

8 Data samples at BESIII In 2014, BESIII collected data above L c pair threshold and run machine at GeV with excellent performance. Energy (GeV) Luminosity (pb -1 ) ~48 PRL101 (2008) BELLE ~ ~ ~567 In the future, it is possible that BESIII can collect L c data at high energies, for example 4.64 GeV or more high energies. It is time to systematically study the decay property of L c at BESIII.

9 Analysis Technique Example: DT Single Tags (ST) Double Tags (DT) Branching Fraction (BF) ST Clean sample of ST charmed baryons can be fully reconstructed by hadronic decays with large BFs. Based on this, one can access to absolute BFs and dynamics in the decays. 9

10 Singly Tagged L c - baryons The singly tagged L c - baryons are reconstructed by: with

11 Singly Tagged L c - baryons Summary of the BFs for 11 single tags: PDG2015 ~40% Currently, the total measured BFs for L c is less than 65%.

12 Singly Tagged L c - baryons M BC distributions for 11 single tags ST yields: 14415±159 events with 11 ST modes

13 L c Ll n l decays In 1991, ARGUS reported the first measurement of L c Ll n l with 477 pb -1 Ƴ(1S), Ƴ(2S) and Ƴ(4S) data Phys. Lett. B 269, 234 (1991). In 1994, CLEO performed same measurement with 1.6 fb -1 Ƴ(4S) data Phys. Lett. B 323, 219 (1994). Based on above two measurements, PDG extracts BF for L c Ll n l with t(l c ) and the assumption of form factors Not a direct measurement! 13

14 L c Le n e decays Theoretical calculations on the BF ranges from 1.4% to 9.2% PDG2014: ( )% Input B[L C pk - p ]=( )% PDG2015: ( )% by BELLE [PRL113,042002(2014)] PRL115(2015) ±11 DT B[L c Le v]=( )% First absolute measurement 14 Important for test and calibrate the LQCD calculations.

15 Model &Experiment Br exp [%] References SU(4) symmetry limit 9.2 M. Avila-Aoki et al [PRD40, 2944 (1989)] Non-relativistic quark model 2.6 Perez-Marcial et al [PRD40, 2955 (1989)] MIT bag model [MBM] 1.9 Perez-Marcial et al [PRD40, 2955 (1989)] Relativistic spectator Model 4.4 F. Hussain et al [ZPC51, 607 (1991)] Spectator quark model 1.96 Robert Singleton, Jr. [PRD43, 2939(1991)] Quark confinement Model 5.62 G. V. Efimov et al [ZPC52, 149 (1991)] Non-relativistic quark model 2.15 A. Garcia et al [PRD45, 3266 (1992)] Non-relativistic quark model 1.42 H. Y. Cheng et al [PRD53, 1457 (1995)] QCD Sum Rule 3.0±0.9 H. G. Dosch et al [PLB431, 173 (1998)] QCD Sum Rule 2.6±0.4 R. S. Marques de Carvalho et al QCD Sum Rule 5.8±1.5 [PRD60, (1999)] HOSR 4.72 M. Pervin et al [PRC72, (2005)] HONR 4.2 STSR 2.22 STNR 1.58 LCSRs 3.0±0.3 (CZ-type) 2.0±0.3(Ioffe-type) Y. L. Liu, M.Q. Huang and D. W. Wang [PRD80, (2009)] Convariant confined quark model 2.78 Thomas Gutsche et al [PRD93, (2016)] BESIII [First absolute measurement] 3.63±0.43 PRL 115, (2015)]

16 L c Lm n m decays Theoretical calculations on the BF ranges from 1.4% to 9.2% BESIII preliminary BESIII preliminary 79±11 DT Preliminary results: B[L c Lm n m ]=( )% First absolute measurement G[L c Lm n m ]/G[L c Le n e ]= 0.96±0.16±0.04 where the first error is statistical and the second systematic.

17 Search for L c L * l n l If L c is J=1/2, it favors the decay L c Ll n l. Searching for L c L * l n l is quite important. B[L c L * l n l ]<<B[L c Ll n l ]? suggestive of di-quark model L * pk - /Sp channel N. Ikeno et al. [PRD93, 14021] M. Pervin et al [PRC72, ] L c L(1405) e n e % L c L(1520) e n e % Some theories suggested that the weak decay processes are important to clarify the existence and the nature of L(1405). Thus, study of L 17 c L(1405)l n l is very important.

18 Absolute BFs for L c hadron decays Measurement using the threshold pair-productions via e e - annihilation is unique: the most simple and straightforward PRL116(2016) A global least-square fitter is utilized to improve the measured precision for 12 L c hadronic decay channels. Absolute BFs are improved significantly. BESIII BF for L c pk - p is smaller. Improved absolute BF of pk - p together with BELLE s result are key to calibrate other decays. 18

19 Observation of L c nk S0 p First observation of L C decays to final states involving the neutron. BESIII preliminary BESIII preliminary The missing neutron is detected by: 83±11 net signal events BESIII Preliminary results: B[L c nk S0 p ]=( )% Fit to M 2 miss and M pp spectra in (a,b) L c - signal region and (a,b ) L c - sideband region simultaneously. The relative BF of neutron-involved mode to proton-involved mode is essential to test the isospin symmetry and extract the strong phases of different final states. [PRD93 (2016) ] 19

20 Study of SCS Decays L c pp p - and L c pk K - L c pk - p L c pp p ±85 495±35 Two-dimensional unbinned maximum likelihood fit L c pk K - [non-f] 38±9 L c pk K - [via-f] 44±8 Submitted to PRL arxiv: Study of SCS decays can shed light on dynamics of L c decays B[L c pf] is of particular interest since it proceeds W- exchange only, which is essential to validate the theoretical models and test the application of large-n c factorization in charmed baryon. ST study, relative BFs to L c pk - p is measured. Input BESIII measurement: B[L c pk - p ]=(5.84±0.27±0.23)%

21 Summary BESIII provides important results on L c decays L C Semi-leptonic decys L C hadronic decays Important to understand the decay property of L c More fruitful results will come out! 21

22 Thanks! 22