New Results and Prospects of Light Hadron Spectroscopy Shan JIN Institute of High Energy Physics (IHEP) Presented by Yi-Fang Wang Charm 2007 Ithaca, August 7, 2007

Outline  New results on 0 -+ mesons  New results on 0 ++ mesons  New results on 1 -- mesons  New results on baryons at BESII  Prospects of glueball searches at BESIII

New results on 0 -+ mesons

 (1760) in at BESII

M(  +  -  0 )(GeV/c 2 )    sideband  signal after best candidate selection (best w masses)  signal with multiple entries Phys. Rev. D 73 (2006)

Eff. curve Phase Space Side-band M(  )

 (1760) f 0 (1710) f 0 (1790) f 0 (1810) PWA analysis M(  ) Total f2(1910) f2(160) BG Using observed mass and width for f 0 (1810) in J/    f 0 (1710) f 2 (1910) f 2 (1640) BG  (1760) > 10  f 0 M(  ) (GeV/c 2 )

 The existence of  (1760) is confirmed  Its mass and width were first correctly measured with PWA. Phys. Rev. D 73 (2006)

Candidate of 0 -+ baryonium

Observation of X(1835) in at BESII The  +  -  mass spectrum for  decaying into  +  -  and   Statistical Significance 7.7  Phys. Rev. Lett. 95, (2005)

Observation of an anomalous enhancement near the threshold of mass spectrum at BES II M=1859 MeV/c 2  < 30 MeV/c 2 (90% CL) J/    pp M(pp)-2m p (GeV) body phase space acceptance  2 /dof=56/56 acceptance weighted BW  10  25 BES II Phys. Rev. Lett. 91, (2003)

Re-fit to J/    p pbar including FSI Include FSI curve from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005 ) in the fit (I=0) M =  6.7 MeV  < 153 In good agreement with X(1835)

Candidate of 0 -+ ppbar Bound State  X(1835) could be the same structure as ppbar mass threshold enhancement X(1860)/X(1830).  It could be a ppbar bound state since it dominantly decays to ppbar when its mass is above ppbar mass threshold.  Its spin-parity should be 0 -+ : this would be an important test. There is already an  (1760) nearby, so that  X(1835) is very likely to be an unconventional 0 -+ meson.

 This result cannot be explained by pure FSI effect, since FSI is a universal effect. FSI interpretation of the narrow and strong ppbar threshold enhancement is disfavored.  This indicates that X(1860) has a production property similar to  ’ meson. c.f. : This strong threshold enhancement is NOT observed in at CLEO No enhancement near threshold Phys.Rev.D73, (2006)

 FSI interpretation of the narrow and strong ppbar threshold enhancement is disfavored.  This again indicates that X(1860) has a production property similar to  ’ meson. c.f. : No strong threshold enhancement is observed in at BESII No significant narrow strong enhancement near threshold (2.0  if fitted with X(1860)) Phys.Rev.Lett.99, (2007)

 This again disfavors FSI and indicates that X(1860) has a production property similar to  ’ meson. c.f. :  This also indicates X(1860) may have strong coupling to gluons as  ’ meson. This strong threshold enhancement is NOT observed in at BESII No narrow strong enhancement near threshold BESII Preliminary

Summary of new studies on ppbar mass threshold structure X(1860)  Pure FSI effect cannot explain X(1860) structure.  X(1860) has production properties similar to  ’ meson  Why a baryonium (candidate) has a production properties similar to  ’ meson?  ’ excitation? Why an  ’ excitation dominantly decays into ppbar above ppbar mass threshold?

New results on 0 ++ mesons

Observation of  mass threshold enhancement at BESII Phys. Rev. Lett. 96, (2006)

 We studied DOZI process: J/    +  +    +  -  0 K + K -    recoiling against 

A clear mass threshold enhancement is observed Acceptance Side-bands

 The radiative decay of J/  has been observed in the 58M J/  data.  A significant structure of  has been found near the mass threshold.  PWA shows the structure favors 0 ++, with a mass, width 105  20  28 MeV, and the corresponding branch ration is (2.61  0.27  0.65)x  It could be a multiquark/hybrid/glueball state.  Its relation with f 0 (1710),f 0 (1790)?

PWA of J/    +  - and  0  0 at BESII Phys. Lett. B 642 (2006) 441

PWA of J/    +  - and  0  0 M(  +  - ) M(  0  0 ) The channels fitted in PWA:

all 0 ++ all 2 ++ PWA components:

PWA results  Lower 0 ++ : 0 ++ is strongly preferred over 2 ++  f 0 (1370) cannot be excluded.  Higher 0 ++ : f 0 (1710) or f 0 (1790)

Phys. Lett. B 642 (2006) 441

About f0(1500)  It is first clearly observed in J/psi radiative decays.  Its production rate in J/psi radiative decays:  The production rate of f0(1500) in J/psi radiative decays is lower than f0(1710):  It indicates f0(1710) has stronger coupling to gluons than f0(1500)  which one contains more glueball content?

New results on 1 -- mesons

New observation of a broad 1 -- resonance in J/   K + K -  0 at BESII Phys. Rev. Lett. 97 (2006)

J/  K + K -  0 00 background  0 sideband ? K*(892) K * (1410) X(1580) PID and kinematic fit can significantly reduce the dominant background from J/    +  -  0.

 Four decay modes are included :  Amplitudes are defined by Covariant tensor formalism B.S. Zhou and D.V. Bugg, Eur. Phys. J. A16, 537(2003)  BW with energy-dependent width J.H. Kuhn, A. Satamaria, Z. Phys. C48, 445 (1990). Partial Wave Analysis of J/   K + K -  0 events

 Parity conservations in J/   K + K -  0 requires that spin-parity of K + K - should be 1 --,3 --,…  PWA fit with and phase space (PS) gives:  ( can be ruled out by much worse likelihood )  X pole position   big destructive interference among and PS Partial Wave Analysis of J/   K + K -  0 events

Broad X cannot be fit with known mesons or their interference  It is unlikely to be  (1450), because: The parameters of the X is incompatible with  (1450).  (1450) has very small fraction to KK. From PDG:  It cannot be fit with the interference of  (770),  (1900) and  (2150): The log-likelihood value worsens by 85 (  2 =170).

How to understand broad X(1580)?  Search of a similar structure in J/   K S K  will help to determine its isospin.  X(1580) could have different nature from conventional mesons: There are already many 1- - mesons nearby. Width is much broader than other mesons. Broad width is expected for a multiquark state.

 A structure at 2175MeV was observed in e + e -   f 0 (980), via initial- state radiation at BABAR. Evidence of a new 1 -- resonance Y(2175) at BaBar Phys. Rev. D 74 (2006) (R)

What is Y(2175)?  A conventional state?  An analog of Y(4260) ( )?  An 4-quark state?  More experimental information needed, especially we can search for it in J/psi decays at BESII and BESIII.

New results on baryons at BESII

N* in. at BESII M  00  M 2 (p  0 )

N* in. Resonances used in the PWA The best results to now

N* in.  data  Fit results The comparison between data and PWA fit results. Fit results agree with data reasonably, especially in the low mass region.

N* in.

K  mass threshold enhancement

PS, eff. corrected Observation of a strong enhancement near the threshold of mass spectrum at BES II (Arbitrary normalization) BES II NX*NX*

 A strong enhancement is observed near the mass threshold of M K  at BES II.  Preliminary PWA with various combinations of possible N* and Λ* in the fits —— The structure N x *has: Mass 1500~1650MeV Width 70~110MeV J P favors 1/2 - The most important is: It has large BR(J/ψ  pN X *) BR(N X *  KΛ)  2 X 10 -4, suggesting N X * has strong coupling to KΛ.

N x * is N(1535)?  From: If N x * is N(1535), we would have Then N(1535) would have very large ssbar component (a 5-quark system).

Such a big coupling to K  of N(1535) is NOT observed in process at SAPHIR Phase Space shape

A ΛK resonance predicted by chiral SU(3) quark model  Based on a coupled- channel study of ΛK and ΣK states in the chiral SU(3) quark model, the phase shift shows the existence of a ΛK resonance between ΛK and ΣK mass threshold. ( F. Huang, Z.Y. Zhang et al. Phys. Rev. C71: , 2005 ) E cm – ( M Λ +M K ) (MeV)

 The KΛ mass threshold enhancement N X (1610) could be a KΛ bound/resonant state.  Whether N X (1610) is N(1535) needs further study.

 No obvious N* in Dalitz plot.  We measured: Study of at BESII

Prospects of glueball searches at BESIII

J/  decays are an ideal factory to search for and study light exotic hadrons:  The production cross section of J/  is high.  The production BR of hadrons in J/  decays are one order higher than  ’ decays (“12% rule”).  The phase space to 1-3 GeV hadrons in J/  decays are larger than  decays.  Exotic hadrons are naively expected to have larger or similar production BR to conventional hadrons in J/  decays.  Clean background environment compared with hadron collision experiments, e.g., “J P, I” filter.

One Important Physics Goal of BESIII With J/psi events, we hope to answer:  Whether glueballs exist or not? Naively, we estimate in each exclusive decay mode: If the eff. is about 20%, we would have events for each decay mode  we should observe a relative narrow (width: 50~200MeV) glueball if it exists.

About scalar glueball  Many scalar mesons in the mass range 1.4~1.8 GeV, where a scalar glueball is predicted to be. More studies will be performed at BESIII.  More theoretical studies are also needed: Not only glueball mass, but also width Decay patterns Production rate in J/psi radiative decays Mixing mechanism

2 ++ glueball candidates  Lattice QCD predicts the 2 ++ glueball mass in the range of 2.2~2.4 GeV   (2230) was a candidate of 2 ++ glueball: It was first observed at MARKIII in J/  KK It was observed at BES I in J/  KK, ,  ppbar It was not observed at DM2.

BES-I  (2230) Result  (2230)

The situation at BESII  The mass plots shows no evident  (2230) peaks in J/  KK, ,  ppbar, which is different from BESI.  However, it is difficult to exclude its existence since we may still need a small signal at the 4.5  level in the PWA based on our preliminary study. Its mass, width and BR are consistent with BESI and MARKIII results  Difficult to draw firm conclusion at present. We hope to give a final answer at BESIII on  (2230)

Other 2 ++ glueball candidates  No other obvious good candidates have been observed in J/psi radiative decays in the mass range predicted by LQCD.  What does it mean: LQCD prediction might not be very reliable, or BR(J/    G)xBR(G  hh) is small ( <10 -4 ) so that we don’t have the sensitivity to observe it ( quite possible ), or, The width of a glueball is very large ( ~1GeV, E.Klepmt ).

Where to search for the 0 -+ glueball?  Lattice QCD predicts the 0 -+ glueball mass in the range of 2.3~2.6 GeV.   (1440) and X(1835) were suggested being possible candidates, but their masses are much lower than LQCD predictions.

No 0 -+ glueball candidate observed in the mass range 2.3~2.6 GeV  No evidence for a relatively narrow state ( 100 ~ 200 MeV width ) above 2GeV in  Again: LQCD reliable? Production rate could be very low. Glueball width could be very large.

Summary  New results on light 0 -+,0 ++ and 1 -- mesons as well as excited baryons were briefly reviewed.  We would expect more new observations on light hadron spectroscopy at BESIII and we hope to answer whether glueballs exist or not at that time.

谢 谢！ Thank You!

Discussion on KΛ mass threshold enhancement N X (1610)  N X (1610) has strong coupling to KΛ: From (S&D-wave decay) and is a P-wave decay, we can estimate From BESII, The phase space of N X to KΛ is very small, so such a big BR shows N X has very strong coupling to KΛ, indicating it has a big hidden ssbar component. (5-quark system)

Non-observation of N X in suggests an evidence of new baryon :  It is unlikely to be N*(1535). If N X were N*(1535), it should be observed in process, since: From PDG, for the N* in the mass range 1535~1750 MeV, N*(1535) has the largest, and from previous estimation, N X would also have almost the largest BR to KΛ.  Also, the EM transition rate of N X to proton is very low.