Recent Results On Light Hadron Spectroscopy at BESIII

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1 Recent Results On Light Hadron Spectroscopy at BESIII CHEN Ye (for BESIII Collaboration) Institute of High Energy Physics, Beijing 0 The 4th International Workshop on Charm Physics, Oct. 23, 2010, Beijing

2 Outline Introduction Recent results on Light Hadron Spectroscopy from BESIII Summary

3 Motivation: Study of the spectroscopy a way of understanding the internal structure Establish spectrum of light hadrons Search for non-conventional hadrons Understand how hadrons are formed Why at a τ-charm collider? Gluon rich Clean environment J PC filter, isospin filter glueball spectrum from LQCD 3 PRD 73 (2006)

4 Results from BESIII Confirm BESII results threshold enhancement in γpp, X(1835), New improved measurements h c, η c, χ cj,, New observations χ cj decays h c decays Light hadrons, J/ψ ψ(2s)

5 pp mass threshold study at BES J / ψ γ pp BESII theoretical speculation: p p bound state (baryonium) FSI effect M pp -2m p (GeV) Observation of an anomalous enhancement near the threshold of p p mass spectrum PRL 91 (2003)

6 pp mass spectrum and Dalitz plot at BESIII ψ(2s) ππ J/ψ, J/ψ γpp BESII J / ψ γ pp M0. pp -2m 0. p (GeV) 2 3 M= MeV/c Γ < 30 MeV/c 2 (90% CL) PRL 91 (2003) M= MeV/c 2 Γ < 38 MeV/c 2 (90% CL) Chinese Physics C 34, 421 (2010) 6

7 J/ψ γpp BESIII preliminary BESII BESIII preliminary M= MeV/c Γ < 30 MeV/c 2 (90% CL) Fit result: Mass= ± 0.8 M ev / Γ< 8 MeV(90% CL) c 2 7

8 Confirmation of X(1835) and observation of two new structures in J ψ γ π + π η

9 X(1835) observed at BESII in J ψ γ π + π η BESII result(stat. sig. ~ 7.7 σ ) : M = ± 6.1( stat) ± 2.7( syst) MeV Γ= 67.7 ± 20.3(stat) ± 7.7(syst)MeV PRL 95,262001(2005) Confirmation of X(1835) is necessary at BESIII. LQCD predicts the 0 + glueball mass is ~2.3GeV. + Important and interesting to study J / ψ γπ π η 9

10 J ψ γ π + π η γρ η ππη BES III Preliminary BES III Preliminary X(1835) and η c are observed. Combination of η to π + π - η and γρ BES III Preliminary Two additional structures at M~2.1GeV and 2.3GeV observed f 1 (1510). 10

11 Fitting with four resonances (acceptance weighted BW gauss) Three background components: ) 2 Events/(0.02GeV/c Contribution from non η events estimated by η mass sideband Contribution from Combined mass spectrum fitting 0 / ψ πππη + '( η' γρ) Contribution from PS background J f ( ) ( ) ( ) ( ), 2 bkg x = x m + a x m + a x m m = m + m BES III Preliminary M 2.2 ππη (GeV/c ) 1/2 3/2 5/ π η Red line: estimated contribution of 1+ 2 Black line: total background 11

12 X(1835) resonance is confirmed at BESIII, but the width is significantly larger than that measured at BESII with one resonance in the fit. Two new resonances, X(2120) and X(2370), are observed with significances larger than 7.2σ and 6.7σ, respectively. PWA is needed not only to determine the spinparities of above three resonances, but also to make more precise measurements on masses, widths and BRs by considering possible interferences among them. 12

13 Observation of X (1870) a (980) π 0 J + ψ ωπ π η in at BESIII

14 J ψ ωπ + π With a 0 (980): Veto a 0 (980): a 0 (980) f 1 (1285) X(1870) η(1405) η BES III Preliminary BES III Preliminary BES III Preliminary The f 1 (1285), η(1410) and X(1870) primarily decay via a 0 (980)π ± 14

15 Mass spectrum fitting Fitting with three resonances (acceptance weighted BW Gauss) Background component described by Polynomial function BES III Preliminary Fit result ( stat. sig.~7.7σ ) M = 1873 ± 11MeV Γ= 82 ± 19MeV Whether the X(1870) is the X(1835) or η 2 (1870), or a new resonance, further study is needed. 15

16 a 0 (980) f 0 (980) mixing a 0 / f 0 : qq, four quarks, KK molecule, hybrids, Study of the mixing of a 0 and f 0 will shed new light on the enigmatic light scalars. No firm experimental determination. A narrow peak (8MeV) between the charged and neutral kaon thresholds (987~995 MeV). J.Wu, Q.Zhao, B.Zou PRD , C. Hanhart etc. PRD , etc. φ J/ψ η J.Wu, B.Zou PRD χ c1 π 0 π + f 0 a 0 π 0 a 0 f 0 π - 16

17 a 0 (980) f 0 (980) mixing: f 0 a 0 transition J/ψ φf 0 φa 0 φηπ 0 BESIII Preliminary Significance: 3.3 σ. Mixing signal --- a 0 (980) contribution from J/ψ γ*/k*k φa 0 (980) --- Background polynomial N(mixing)=24.7 ± 8.6 C.L) 0 Br(J/ ψ φ f0 φa0 φηπ ) =(3.1± 1.1± 0.8) (<5.5 90% C.L.) Mixing intensity: ψ φ φ φηπ ξf a = Br(J/ ) 0 Br(J/ f0 a0 ) [BESII] ψ φ f0 φππ = (0.6 ± 0.2 ± 0.2)% 90% C.L.) 17

18 a 0 (980) f 0 (980) mixing: a 0 f 0 transition ψ γχ c1, χ c1 a 0 π 0 f 0 π 0 π + π - π 0 BESIII Preliminary Significance: 2.0 σ. Mixing signal --- f 0 (980) contribution from other processes --- Background polynomial N(mixing)=6.5 ± 3.2 C.L) Br( ψ γχc 1 )Br( χc 1 a 0π f 0π π π π ) =(2.8 ± 1.4 ± 0.5) (<5.5 90% C.L.) Mixing intensity: ξ Br( χ aπ f π π π π ) c1 0 0 af = [PDG] Br( χc 1 π a0 ηπ π ) = (0.3 ± 0.2 ± 0.1)% 90% C.L.) 18

19 Models of a 0 /f 0 give different resonance parameters Comparison with ξ fa /ξ af from those parameters a 0 f 0 mixing: a sensitive probe BESIII Preliminary Zoomed in shaded region: BES3 measurements red line: BES3 upper limit 19 dots: various predictions

20 Matrix Element Measurement of the decay η' ηππ 3 m X = ( T + + T ) and Y = π π Q General parametrization : M Linear parametrization : M 2 2 = A(1 + ay + by = A(1 + αy cx + dx + cx + dx 2 ) η + 2m m 2 π ) π Tη 1 Q 20

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22 Summary Nice results are obtained Important BESII results have been confirmed, new improved measurements have been carried out and BESIII have new observations More results will come soon