Light Meson Decays at BESIII

Transcription

1 Light Meson Decays at BESIII Liqing QIN (for the Collaboration ) Shandong University XVI International Conference on Hadron Spectroscopy Sep , 2015, Newport News, VA

2 OUTLINE n Introduction n Recent results l First observation of η(1405) f 0 (980)π 0 in J/ψ γ3π l Study of Y(2175)/f 1 (1285)/η(1405) in J/ψ ηφπ + π - l Hadronic and radiative decays of η/η n Summary 2

3 Introduction Bird view of BEPCII Linac Storage ring τ charm physics Ø Charmonium decays transitions Ø Light hadron spectroscopy l l Light meson decays Ø Charm physics 5/31/12 Meson2012 Ø τ physics 3

4 The BESIII Detector DriO Chamber (MDC) σp/p ( 0 / 0 ) = 0.5%(1GeV) σ de/dx ( 0 / 0 ) = 6% Super- conduc\ng magnet (1.0 tesla) Time Of Flight (TOF) σ T : 90 ps Barrel 110 ps endcap EMC: σe/ E( 0 / 0 ) = 2.5 % (1 GeV) (CsI) σ z,φ (cm) = cm/ E μcounter 8-9 layers RPC δrφ=1.4 cm~1.7 cm BESIII accumulated billion J/ψ events in 2009 and 2012: Clean and rich source for light hadrons 4

5 Observation of η(1405) f 0 (980)π 0 in J/ψ γ3π based on billion J/ψ events Ø First observation of an isospin- violate process: η(1405) f 0 (980)π 0 - B(η(1405) f 0 (980)π 0 π + π - π 0 )= (1.50± 0.11 ± 0.11) B(η(1405) f 0 (980)π 0 π 0 π 0 π 0 )= (7.10± 0.82 ± 0.72) B(η(1405) è a 0 (980)π 0 è ηπ 0 π 0 ) - Much larger than a0- f0 mixing rate (< 1%) PRD 83, (2011) Ø Narrow f 0 (980) - Charged channel: Γ= 9.5 ± 1.1 MeV - Neutral channel: Γ= 4.6 ± 5.1 MeV C.L.) - Much smaller than PDG value: MeV Ø Theoretical explanation: triangle singularity? PRL 108, (2012) charged PRL 108, (2012) neutral Ø Evidence of f 1 (1285)/η(1295) around 1.3 GeV: - B(f 1 (1285)/η(1295) f 0 (980)π 0 π + π - π 0 ) = (9.99 ± 3.00 ± 1.03) σ - B(f 1 (1285)/η(1295) f 0 (980)π 0 π 0 π 0 π 0 ) < at 90% C.L. 1.2σ 5

6 Study of J/ψ ηφπ + π - based on billion J/ψ events PRD 91, (2015) Ø Y(2175) was observed by BABAR, then confirmed by BESII, BELLE and BABAR; Ø Different interpretations have been proposed: ss - gluon hybrid? excited φ state? tetraquark state? ΛΛ bound state? an ordinary φf 0 (980) resonance produced by FSI? Ø Confirmation and study of the Y(2175) with a large data sample is necessary for clarifying its nature. Product branching fraction of J/ψ ηy(2175), Y(2175) φf 0 (980), f 0 (980) ππ is measured to be: (1.20 ± 0.14 ± 0.37) 10-4 Y(2175) > 10σ triangle: 2D- sideband events Mass and width are in agreement with previous measurements 6

7 Study of J/ψ ηφπ + π - PRD 91, (2015) Ø Offer a unique opportunity to investigate the properties of the f 1 (1285), η(1295), and η(1405)/η(1475) resonances. f 1 (1285) Ø Search for the new production in different J/ψ decays for a better understand of X(1835) and X(1870): η(1405) Via the M(ηπ + π - ) spectrum recoiling against the φ in J/ψ decays B= product branching fraction of J/ψ φ Res with Res ηπ + π - Res N obs (up) eff. (%) Sign. B (up limit) [10-4 ] f 1 (1285) 1154± ± ± 0.06 ± 0.14 η(1405) 172±50 (<345) 19.75± σ (2.01 ± 0.58 ± 0.82) 10-1 (< ) X(1835) 394±360 (<1522) 13.85± σ <2.80 X(1870) 25±73 (<330) 13.73± σ < ü f 1 (1285) is observed significantly: M=1281.7±0.6 MeV, Γ=21.0±1.7 MeV in good agreement with that of PDG. ü A small structure around 1.4 GeV seems to be present (3.6σ for η(1405) ): It imply the u- d account for more of the quark content in the η(1405) than s quark. ü No evidence of X(1835) and X(1870), upper limits at 90% C.L. are set. 7

8 η/η :a rich physics field l Listed in many facilities physics program: ( VES, Gams (- 4π), CLEO, CLAS, Crystal Ball at MAINZ, WASA- at- COSY, KLOE- 2, GlueX, BESIII) l l Unique place to test fundamental symmetries in QCD at low energy Probe physics beyond the Standard Model (SM): η/η 2γ η/η π+π-π 0 η γπ+πη/η ππ η/η µ + µ - π 0, e + e - π 0 η/η µ e chiral anomaly quark masses box anomaly CP violation C violation LF violation l η and η events at BESIII - B(J/ψ γη) ~ η events; - B(J/ψ γη ) ~ η events; l Results of η/η presented in this talk are based on all the data sample of J/ψ events. 8

9 Matrix Element for the Decays η π + π - π 0, η/η π 0 π 0 π 0 PRD92, (2015) ² Investigate the fundamental symmetries; ² Measure the u- d quark mass difference; ² Comparison to the theoretical calculations with the effective ChPT; ² Previous measurements (KLOE, WASA- at- COSY, ) where T π denotes the energy of a given pion in the η rest frame. 9

10 η π + π - π 0 Flat, seems no dynamics is involved 10

11 A comparison of experimental and theoretical results η π + π - π 0 Assume charge conjugation invariance Inclusion of the possibility of charge conjugation violation - agree with the two most recent measurements; - consist with the predictions of the dispersive approach and ChPT at NNLO c and e parameters are consistent with zero within 1σ; We found no significant charge- parity violation (0.65σ) 11

12 η π 0 π 0 π 0 A(Z) 2 = N (1 + 2αZ + ) Comparison of experimental and theoretical results α= ±0.014±0.004 η π 0 π 0 π 0 α= ±0.046±0.047 Ø Ø In agreement with previous measurements; α for η π 0 π 0 π 0 significantly deviates from zero 12

13 Observation of η π + π - π + π -, π + π - π 0 π 0 PRL 112, (2014) Upper C.L. by CLEO (PRL102, (2009)): Β(η π + π - π + π - ) < Β(η π + π - π 0 π 0 ) < η π + π - π + π - 18σ Prediction by ChPT and VMD (PRD85, (2012)): Β(η π + π - π + π - ) = (1.0 ± 0.3) 10-4 Β(η π + π - π 0 π 0 ) = (2.4 ± 0.7) 10-4 Β(η π + π - π + π - )=[8.53±0.69±0.64] 10-5 Β(η π + π - π 0 π 0 )=[1.82±0.35±0.18] 10-4 background free for η π + π - π + π - η π + π - π 0 π 0 5σ 13

14 Observation of η ωe + e - Ø Decay of η Ve + e - proceeds via a two- body radiative decay into a vector meson and an off- shell photon. Ø M(ee) provide information about the intrinsic structure of η and the transition F(q). Ø Theoretical predictions from VMD * : B(η ωe + e - ) ~ * PRC 61, (2000); EPJ A48, 190 (2012) Ø First measurement of η ωe + e - : 8σ Accepted by PRD, arxiv: ) 2 ) (GeV/c - M( M( 0 + ) (GeV/c ) B(η γω) = (2.55 ± 0.03 ± 0.16) 10-2 Good agreement with PDG; B(η ωe + e - )= (1.97 ± 0.34 ± 0.17) 10-4 Consist with prediction = (7.71 ± 1.34 ± 0.54)

15 Observation of Dalitz Decay η γe + e - Ø Reveal the inner structure of the meson; Ø Study the transition form factor providing information for study of the muon anomalous magnetic moment. PRD 92, (2015) QED(q 2 ) represents the calculable QED part for a point- like meson. 15

16 Form-Factor Measurement with acceptance correction Single- pole form factor Pointlike case Discrepancy between QED and data observed. Ø In agreement with the result of η γµ + µ - from CELLO: b = (1.7 ± 0.4) GeV - 2 Λ=(0.79 ± 0.04 ± 0.02) GeV/c 2 γ=(0.13 ± 0.06 ± 0.03) GeV/c 2 b=(1.60 ± 0.17 ± 0.08) GeV - 2 Ø Theoretical predictions: b = 1.45 GeV - 2 VMD model b = 1.60 GeV - 2 ChPT b = GeV- 2 Dispersion 16

17 Study on η γπ + π - : model-dependent fit Events / 5 MeV pull ). fit with ρ(770)-ω ( ) = ± M( ) = ± arg = ± = ndf = 28.7 & ± M( + ) 0.8 (GeV/c 0.9 ) Events / 5 MeV pull ). fit with ρ(770)-ω- ρ(1450) 3). fit with ρ(770)-ω-box anomaly (1450) & & (1450) & (1450) χ 2 /ndf= M( + ) 0.8 (GeV/c 0.9 ) Events / 5 MeV pull & box & box & box χ 2 /ndf= M( ) 0.8 (GeV/c 0.9 ) ü Besides ρ(770) resonance, the presence of ω is needed significantly; ü ρ(770)-ω cannot describe data well; ü Extra contribution (maybe ρ(1450) or box-anomaly, maybe both of them) is also necessary to provide a good description of data; ü Box anomaly contribution and the ρ(1450) contribution cannot clearly be distinguished.

18 Model-independent fit Based on a combination of ChPT and a dispersive analysis*; * Physics Letters B 707 (2012) Cross section of π + π : 2 ) (s F V 10 F V (s ππ ) 2 Events / 5 MeV P(s ππ ) = 1+ α s ππ + β Ο(s 2 ππ ) = ± = ± ndf = 12.3 Events / 5 MeV P(s ππ ) = 1+ α s ππ + β Ο(s 2 ππ ) + δ BW ω = ± = ± = ± ndf = (GeV s 2 ) pull M( + ) 0.8 (GeV/c 0.9 ) pull M( + ) 0.8 (GeV/c 0.9 ) Inspecting data of Crystal barrel: α = (1.80 ± 0.49 ± 0.04) GeV -2 β = (0.04 ± 0.36 ± 0.03) GeV -4 GAMS-200: α = (2.7 ± 1.0) GeV -2 Our results without ω with ω ü ω is significantly needed (34σ) ü Linear polynomial is insufficient.

19 Summary n Many interesting physics results of light meson from BESIII are presented: ü First observation of η(1405) f 0 (980)π 0. ü Confirmation of the Y(2175); ü Evidence of f 1 (1285)/η(1405) in M(ηπ + π - ); ü Recent results of η/η decays are presented. n More results are expected to come soon! 19

20 Thanks for your attention 20

21 back up 21

22 BESIII status on η/η decays - η π + π - η, PRD 83, (2011) - η/η π + π -, π 0 π 0, PRD 83, (2011) - η π + π - π 0, π + π - π 0, PRL 108, (2012) - η/ηʹ invisible, PRD 87, (2013) - η/ηʹ π - e + ν+c.c., PRD 87, (2013) - η π + π - l + l -, PRD 87, (2013) - η 3(π + π - ), PRD 88, (2013) - η 2(π + π - ), π + π - π 0 π 0, PRL 112, (2014) - η γe + e -, PRD 92, (2015) - η π + π - π 0, η/η π 0 π 0 π 0, PRD92, (2015) - η ωe + e -, Accepted by PRD, arxiv: η γπ + π -, Preliminary result - η γγπ 0, Preliminary result 22

23 η γπ + π - : model-independent fit, where E η /F η is the box anomaly constant. 23