Recent results on light hadron spectroscopy at BES 董燎原 (for BES Collaboration) 中国科学院高能物理研究所 中国物理学会高能物理分会 April 17-19 2010

Outline Introduction of BES at BEPC Introduction of Light hadron physics at BESIII Observation of charged  at BESII Confirmation of ppbar mass threshold structure at BESIII Confirmation of X(1835) at BESIII Summary 2 2010/4/18 2 2

Beijing Electron Positron Collider (BEPC) at IHEP BESI: Beijing Spectrometer I : 1989 -1998 BESII: 1999 - 2004 L ~ 5*1030cm-2s-1@ J/ Ebeam~ 1-2.5 GeV BESIII: 2008 (Physics run from March 2009)- , L~3.2*1032cm-2s-1@(3770)~30% of designed value 3

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Milestones of BESIII 5

Multi-quark State, Glueball and Hybrid Hadrons consist of 2 or 3 quarks： Naive Quark Model： New forms of hadrons: Multi-quark states ：Number of quarks >＝ 4 Hybrids ： qqg，qqqg … Glueballs ： gg， ggg … Meson（ q q ） Baryon（q q q） How quarks/gluons form a hadron is far from being well understood.

Light hadron physics Motivation: Establish spectrum of light hadrons Search for non-conventional hadrons Understand how hadrons are formed Study chiral symmetry in QCD Why at a tau-charm collider ? Gluon rich Larger phase space than at higher energies Clean environment, JPC filter Glueball spectrum from LQCD Y. Chen et al., PRD 73 (2006) 014516 Many results in BESII: ~ 50 publications Much more from BESIII: 100 statistics, 10 g resolution

Main contents in the study of the hadron spectroscopy Meson spectrum（qq) New forms of hadrons（glueballs,hybrid states, multi-quark states） Baryon sectrum (qqq)

Multi-quark states, glueballs and hybrids have been searched for experimentally for a very long time, but none is established. Searches for new forms of hadrons are of special importance at BES since J/psi decays are believed as an ideal factory to search and to study exotic hadrons. BES-III can also play a very important role in the study of excited nucleons and hyperons, i.e., the very poorly understood N*、*、*、* and *++ resonances.

Observation of charged  at BESII

Observation of charged  at BESII  was first found in K scattering data However, its phase shift is much less than 180o and it cannot be filled into any nonets of ordinary mesons. There have been hot debates on the existence of . In recent years: FNAL E791 found evidence of neutral  in D+ K-++. CLEO D0 K-+0 data find no evidence of . FOCUS data on D+K-++ require K*0 interfere with either a constant amplitude or a broad 0+ resonance in K. BESII observed neutral  in J/  K*0K  KK in 2006. neutral  pole: 12

The existence of charged  is expected ! CLEO reported the necessity of in . However, no charged  is needed in BABAR data. BESII studied charged  in . BESII Preliminary BESII Preliminary K*(1410), K*(1430)  (GeV/c2) again 13

Partial wave analysis results BESII Preliminary M(K) (GeV/c2) M(K*(892)) (GeV/c2) 14 M(K*(892)K) (GeV/c2) 14

Resonance parameters of charged  For reference, resonance parameters of neutral  Different parameterizations of  give consistent results on the pole of charged  . The pole position for charged  is consistent with that for neutral  within the error. arXiv:1002.0893 [hep-ex] 15 15

threshold structure at BESIII Confirmation of mass threshold structure at BESIII

Observation of an anomalous enhancement near the threshold of mass spectrum at BES II J/ygpp acceptance weighted BW +3 +5 -10 -25 X(1860) M=1859 MeV/c2 G < 30 MeV/c2 (90% CL) theoretical speculation: bound state FSI effects …… c2/dof=56/56 0.1 0.2 0.3 3-body phase space M(pp)-2mp (GeV) Phys. Rev. Lett. 91, 022001 (2003)    acceptance

The narrow threshold enhancement is NOT observed in those channels PR D73, 032001 (2006) EPJ C53 ,15 (2008) PRL 99, 011802 (2007) No significant narrow strong enhancement near threshold (~2 if fitted with X(1860)) 18 Mpp (GeV/c2) 18 18

Observation of an anomalous enhancement near the threshold of mass spectrum at BES III CPC(HEP & NP), 2010, 34(4): 421-426 Fitted with a S-wave BW, M=1861+6-13 (stat)+7-26 (syst) MeV/c2 G < 38 MeV/c2 (90% CL) 19 19

This narrow threshold enhancement is also observed in at BESIII BESIII preliminary

This narrow threshold enhancement is “NOT” observed in at BESIII No significant narrow strong enhancement near threshold Pure FSI interpretation disfavored 21 21 21

Confirmation of X(1835) at BESIII

Observation of X(1835) J/’+- at BESII PRL 95,262001(2005) Statistical Significance ~6  Statistical Significance ~5.1  To be confirmed with ~220M J/ data at BESIII 23 23 23 23

Mass spectrum of ’+- in J/’+-, ’ BESIII preliminary BESIII preliminary Significant peak at M~1835MeV Statistic significance of X(1835) is about 18σ 24

Mass spectrum of ’+- in J/’+-, ’+- BESIII preliminary BESIII preliminary Significant peak at M~1835MeV Statistic significance of X(1835) is about 9σ 25

??? Combined mass spectrum of the two decay modes Structures at higher mass region??? BESIII preliminary X(1835) is confirmed in BESIII and the significance increases as statistics increases BESII 26

Summary BEPCII/BESIII is a major upgrade of the BESII experiment at the BEPC accelerator for studies of hadron spectroscopy and -charm physics. BESIII has been in operation since 2008: ~110M ’ and ~220M J/ events have been collected Recent results at on light hadron BES are presented: Partial wave analysis of charged  at BESII Confirmation of ppbar mass threshold structure at BESIII Confirmation of X(1835) at BESIII More Exciting results are expected. 27

THANK YOU!

Data Accumulated @ BESIII Pb-1 Pb-1 Pb-1 29

Achieved Luminosity 30

Physics potential at BESIII The physics window is precision charm physics and the search for new physics. High statistics: high luminosity machine + high quality detector. Small systematic error: high quality detector. 31 2018/9/19