Chengping Shen: Beihang University, Beijing XVI International Conference on Hadron Spectroscopy (Hadron 2015) September, 2015, JLab, USA

Transcription

1 Chengping Shen: Beihang University, Beijing XVI International Conference on Hadron Spectroscopy (Hadron 2015) September, 2015, JLab, USA

2 Hadrons: normal & exotic Quark model: hadrons are composed from 2 (meson) quarks or 3 (baryon) quarks Normal vs. Exotic QCD does not forbid hadrons with N quarks 2, 3 Glueball: N quarks = 0 (gg, ggg, ) Hybrid: N quarks = 2 (or more) + excited gluon Multiquark state: N quarks > 3 Molecule: bound state of more than 2 hadrons 2 1

3 XYZ particles X(3823) X(3872) X(3915) X(4350) Y(4008) Y(4260) Y(4140) Y(4360) Y(4660) Y(4630) XYZ(3940) Z c (3900) Z c (4020) Z(4430) Z(4250) Z(4050) m(d+d) XYZ or charmonium-like particles Not an obvious charmonium But charmonium in the final state h c (2005) Hybrids ~ GeV Tetraquarks ~ GeV DD*/D*D*/D* s D* s /DD 1 molecule ~ GeV Godfrey & Isgur, PRD32, 189 (1985) 3 2

4 Variety of recorded reactions Υ decay B decay Continuum J PC =0 -+, 1, 1 ++ in factorization limit. gg collision Double chamonia production C=+1. Initial state radiation J PC =0 -+, J PC =1. 3

5 Thanks B-factories! Discovery of X(3872) and other many XYZ states etc. Unexpected bonus of the B-factories 4

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8 Outline The X states The Y states The Z states BelleII perspective Summary & Outlook Due to the time limitation, it is impossible to cover all of these XYZ states in this report. I select some typical/recent results. 7

9 The X states 8

10 What is the X(3872)? Mass: Very close to D 0 D *0 threshold Width: Very narrow, < 1.2 MeV Belle, /fb J PC =1 ++ Production in pp/pp collison rate similar to charmonia M( J/ ) M(J/ ) [GeV] In B decays KX similar to cc, K*X smaller than cc Y(4260) g+x(3872) Decay BR: open charm ~ 50%, charmonium~o(%) Nature (very likely exotic) Loosely D 0 D *0 bound state (like deuteron?)? Mixture of excited c1 and D 0 D *0 bound state? Many other possibilities (if it is not c1, where is c1?) 9

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12 PRD91,051101(R) (2015) 11

13 K + π - mass spectrum study We do not consider the interference between the them. 12

14 Search for X b in e + e - ɣπ + π - π 0 Y(1S) at GeV The X(3872) counterpart in the bottomonium sector X b, NOT observed decay channel π + π - ϒ(1S). As X b is above ωy(1s) threshold, this Isospin-conserving process should be a more promising decay mode. [PRD88, ]. 12σ 118 fb σ PLB 727, 57 (2013). Large Brs of Y(5S) to π + π - π 0 χ b1/b2, ωχ b1/b2 are observed for the first time and their ratios are measured: hadronic loop effect? arxiv: PRL 113, (2014) Assuming X b is narrow, the upper limit on the product branching fraction was given. 13

15 The Y states (vectors) 14

16 The Y states Belle: PRL99,142002, 670/fb BaBar: PRD89,111103, 520/fb PRL110, /fb do not confirm Y(4008) BESIII can measure e + e - π + π - J/ cross section line shape precisely, which can solve Y(4008) puzzle soon. 15

17 Updated e + e - π + π - (2S) Phys. Rev. D 91, (2015) 16

18 Fit M(π + π - (2S)) with three resonances Phys. Rev. D 91, (2015) 17

19 Updated e + e - K + K - J/ PRD 89,072015(2014) Event selections are almost the same as in Phys. Rev. D 77, (R) (2008) Shaded hist.: J/ mass sidebands 980fb -1 +one resonance. Fit with (4415) Y(4260) 2 /ndf=30/11 M= MeV = MeV 4-6 GeV: 213 events 35 bkg, signal 7.8% sys. error was not included. 18

20 Phys. Rev. D 92, (2015) 19

21 The Z c states For Z b states, please see C.Z.Yuan s report 20

22 Discovery of Z c (4430) ± PRL 112, (2014) 21

23 Z c (3900) and Z c (4050) BESIII: PRL 110, (2013) A 4-quark particle?! Belle with ISR data (PRD 91, 12007(2015)) Belle with ISR data (PRL 110, ) Y(4360) region 22

24 Search for Z cs KJ/ states in e + e - K + K - J/ PRD 89,072015(2014) No evident structure in K +- J/ mass distribution under current statistics 23

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26 BelleII perspective 25

27 BelleII will take data in 2018 and the total luminosity will reach 50 ab -1 in

28 Some new XYZ states? e + e X(3823) PRL 115, (2015) Open circles: Belle e + e J/ Solid dots: BESIII e + e h c Broad structure at high energy region? PRL 112, (2014) e + e - gx(3872) e + e - w c0 PRL114, (2015) 27

29 BelleII is very promising with ISR method BESIII level 28

30 Search for more XYZ states with higher energy point data 29

31 Summary Belle still made progress in study of XYZ states We still have more questions to answer BelleII will take data in Huge data sample is very promising. Exciting times ahead Thanks a lot! 30

32 Thanks a lot! 谢谢!

33 We found more questions to answer In the X sector Where the X(3872) & X(3823) come from? Resonance decays or continuum production? May other X states be produced and where? In the Y/ sector Is the Y(4260) a single resonance? Is Y(4008) a real structure? Does the Y(4360) decay only to? Not to J/? What is hidden behind h c? Large coupling to spin-singlet, is a hybrid state observed? Correlation between charm production & charmonium transitions? May we observe the charmonium 3 3 D 1 state at ~4.5 GeV? In the Z sector Are the Z c and Z c from resonance decays or continuum prod.? Are there excited Z c states and Z cs states [D*D s or DD s *]? In the C sector Charm spectroscopy: D*, D 0, D 1, D 2, D s0, D s1, D s2,... Charm decays: D s and c samples are too small