Kai Zhu on behalf of BESIII collaboration Institute of High Energy Physics, Beijing March, Moriond QCD 2015

Transcription

1 Kai Zhu on behalf of BESIII collaboration Institute of High Energy Physics, Beijing March, Moriond QCD 2015

2 Introduction Charmonium & Exotics states BESIII experiment and BEPCII Exotic charmonium-like states at BESIII Z states X & Y states (fast review) Summary & Outlook 2

3 c c Simple image of charmonium Known charmonium states and candidates, with selected decay modes and transitions. See Yanbiao s talk for details. 3

4 Exotic candidates because of self-coupling of gluons in QCD Bound gluons (glueball) qq-pair with an excited gluon (hybrids) Multi-quark color singlet states qqqq (tetra-quark and molecular) qqqqq (penta-quark) qqqqqq (six-quark and baryonium) Dibaryon figures from arxiv: , S. Olsen 4

5 BEPCII BESIII s = 2~4.6 GeV, rich physics potential. Light hadron, charmonium, charm, R & QCD. 5

6 B ψ(3686) events 24 CLEO-c 1.3 B J/ψ events 21 BESII 2.9fb 1 ψ(3770) 11 CLEO-c others including scan and continuum data, etc. 5/fb collected above 4 GeV. Mainly for XYZ states! 6

7 At 4.26 GeV: PRL. 110, ISR: PRL 110, M = MeV = MeV events >8 M = MeV = MeV events >5.2 7

8 At 4.17 GeV: PLB M = MeV = MeV events 6.1 Couples to cc Has electric charge At least 4-quarks DD * molecule? Tetra-quark? Cusp? Threshold effect? More decay modes? Neutral partner? Excited states? Searched at BESIII 8

9 Fit to π 0 J/ψ spectrum. BESIII preliminary A simultaneous fit for three subsamples Mass = ±2.3 MeV Width = 29.6±8.2 MeV Significance = 10.4 exotic charmonium-like at BESIII 2015/3/23 9

10 e + e π ± DD at 4.26 GeV Phys. Rev. Lett. 112, s=4.26gev 525pb 1 Favor J P =

11 e + e π + D 0 D e + e π + D D pb 827 pb 1090 pb 827 pb The mass, width, branching fraction are consistent with previous results very well. BESIII preliminary And angular analysis favors J P =

12 Phys. Rev. Lett. 111, e + e π + π h c from 3.90 to 4.42 GeV (13 ) M = ( ± 0.8 ± 2.7) MeV/c 2 Γ = (7.9 ± 2.7 ± 2.6) MeV 12

13 Phys. Rev. Lett. 113, e + e π 0 π 0 h 4.23, 4.26, 4.36 GeV M = ( ± 2.2 ± 3.8) MeV/c 2 Consistent with its charged partner 13

14 e + e π ± D D at 4.26 GeV Phys. Rev. Lett. 112, s = 4.26 GeV 827 pb 1 M= (4026.3±2.6±3.7)MeV Γ = (24.8±5.6±7.7)MeV 14

15 1094 pb GeV 827 pb GeV : σ(e + e - Z c π, Z c ω π ) <0.27 GeV: σ(e + e - Z c π, Z c ω π ) <0.18 pb exotic charmonium-like at BESIII 2015/3/23 15

16 Red: not seen Blue: searching Z C ± Z C 0 Z S π J/ψ DD πh c πψ ωπ π J/ψ DD πh c πψ ωπ Z b (10610) πυ(ns) BB πh b (mp) Z C ± Z C 0 Z c 4200 πj/ψ Z c (4430) πj/ψ πψ π J/ψ D D πh c πψ D D π J/ψ D D πh c πψ D D Z b (10650) πυ(ns) BB, B B πh b (mp) 16

17 e + e γ(π + π J/ψ), new production mode of X(3872) observed. Phys. Rev. Lett. 112, y(1 3 D 2 ) candidate X(3823) is observed via e + e π + π X 3823 π + π γχ C1 ψ X(3823) ψ ψ ψ 17

18 π + π J/ψ Not BESIII publication Combined BESIII & CLEOc data preliminary η J/ψ η J/ψ π + π h C ωχ c0 π 0 π 0 π J/ψ + π X(3823) Obvious structures, limited statistics. Interference must be considered? 18

19 A relatively systematic study on exotic charmonium-like states, XYZ particles, has been performed at BESIII, abundant and interesting results are obtained. However The nature of them is mysterious. The relations between XYZ states are unclear. PWA is needed to clarify J PC. Some expected states and decay modes are missing. Future More results will come up soon with some analysis are on going. A finer scan from 3.8 to 4.6 GeV at BESIII may be helpful. 19

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22 Greek Alphabet α (helium nucleus) β (radioactively emitted electron or positron) ψ (charmonium) π (pion meson) ω (light un-flavored meson) Ω (baryon) English Letters e (electron) p (proton or positron) H (the Higgs particle) W & Z (bosons propagating weak interaction) X(3872), Y(4260), Z c (3900), etc. (unknown nature) 22

23 Due to their similar masses and width, we assume Z c 3900 and Z c 3885 are a same state Z c Z c 4020 and Z c 4025 are a same state Z c Higher Z c excited states? Belle observed Z c (4200) and Z c (4430) via B decay (π J/ψ & π ψ ). LHCb observed Z c (4430) via B decay (π ψ ) Z cs? Belle update K + K J/ψ to Dalitz Plot, no evident structure in K ± J/ψ mass distribution. Z b? Belle also observed charged Z b 10610, Z b (10650). 23

24 Structures from π + π h c Phys. Rev. Lett. 111, Cross sections of e + e ωχ c0 is measured. No signal of ωχ c1 or ωχ c2 found. Disfavor Y(4260) is a ωχ c1 molecule. Cross section of e + e η J/ψ [preliminary] Cross section of e + e π 0 π 0 J/ψ [preliminary] Cross section of e + e J/ψηπ 0, no observation, only upper limit report. [preliminary] Cross section of e + e π + π X 3823 π + π γχ c1 [preliminary] Cross section of e + e η J/ψ [preliminary] e + e γφ J/ψ, No significant Y(4140) signal. [preliminary] Cross section of e + e γχ cj, no observation, only upper limit report. [preliminary] 24