1 Recent Results on J/  Decays Shuangshi FANG Representing BES Collaboration Institute of High Energy Physics, CAS International Conference on QCD and Hadronic Physics June , 2005 Beijing, China

Introduction Measurements of some J/  decays Measurements of some  c decays Study of the excited baryon states Multiquark candidates Summary Outline

BESII Detector VC:  xy = 100  m TOF:  T = 180 ps MDC:  xy = 220  m BSC:  E/  E= 21 %  dE/dx = 8.5 %   = 7.9 mr  p/p=1.78  (1+p 2 )  z = 2.3 cm  counter:  r  = 3 cm B field: 0.4 T  z = 5.5 cm Introduction J/  World J/  Samples (×10 6 ) BESII 58M J/ 

Measurements of some J/  decays

Measurement of J/  →  +  -  0 Br(J/  →  +  -  0 ) = (21.84  0.05  2.01)  Absolute Measurement from BESII 58 million J/  Decays Phys. Rev. D 70, (2004)

Measurement of J/  →  +  -  0 Br(J/  →  +  -  0 ) = (20.9  0.2  1.1)  Phys. Rev. D 70, (2004) Relative Measurement from 14M  (2S) Decays

Measurement of J/  →  +  -   1.9)  BaBar: (21.8  1.9)  Phys.Rev.D70:072004,  1.1)  BES : (21.0  1.1)  Phys.Rev.D70:012005,2004 PDG: (15.0  2.0)  10 -3

Measurement of J/  decays to Vector + Pseudoscalar --- channels measured:

  00

  decays into  +  -  0

 

The measured branching fractions Phys. Rev. D 71 (2005)

First measurements of J/   2(  +  - )  and 3(  +  - )  J/   2(  +  - )  J/   3(  +  - )  Phys. Lett. B 610 (2005) 192 M(  ) GeV  

2 nd polynomial backgrounds  J/  f 2 f 2 f 2  background The invariant mass spectrum of  +  - with mass cut |M  +  |<0.185GeV for another  +  - pair is used to fit the signal. Four components are used in the fit. The branching ratio is measured for the first time to be: First measurement of J/   f2(1270)f2(1270)  4  Phys. Rev. D 70 (2004)

Measurements of some decays cc

First observation of  c  K + K - 2(  +  - ) Nobs= significance: Background from MC

Measurement of sidebands

Search for

Nobs= significance: Submitted to Phys. Lett. B (hep-ex/ ) First observation of  c  3(  +  - ) Background from MC

First observation of  c  f 2 (1270)f 2 (1270) Sidebands Nobs=91 20 Phys. Rev. D 70 (2004)

Study of Excited baryon states

The evidence of 2 new N* peaks Missing mass spectrum (GeV/c 2 ) N*(1440) N*(1520) N*(1535) N*(1650) N*(1675) N*(1680) ?

► Possible new N* resonance Add PWA part and resubmit to Phys. Rev. Lett. hep-ex/ PWA results: Nx(2065) favors 3/2 + ► N*(1440) resonance Usually obscured by the strong peak in and experiment

Multi-quark candidates  K  and mass threshold enhancement in. See Prof. Jin’s talk.  Observation of X(1835) in

Observation of X(1835) in

 A narrow enhancement is observed in. Assuming that the system is in an S-wave resulted in a resonance mass of MeV and a total width of MeV.  It can be interpreted as bound state. In such a case, it is desirable to observe such a state in other decay modes. M=1859 MeV/c 2  < 30 MeV/c 2 (90% CL)  10  25

Analysis of X(1835) 5.1  BESII Preliminary BESII Preliminary

Analysis of X(1835) 6.0  BESII Preliminary

Observation of X(1835) in The sum  +  -  mass spectrum for  decaying into  +  -  and   Statistical Significance 7.7  BESII Preliminary

Mass spectrum fitting 7.7  The sum  +  -  mass spectrum for  decaying into  +  -  and   BESII Preliminary

Mass Spectrum Fitting The  +  -  mass spectrum for  decaying into  +  -  5.1  BESII Preliminary

Mass Spectrum Fitting 6.0  The  +  -  mass spectrum for  decaying   BESII Preliminary

Results of mass spectrum fitting  Mass and width from m=  8.1MeV/c 2,  =54.2  34.5MeV/c 2  Mass and width from m=  7.9MeV/c 2,  =70.3  23.1MeV/c 2  The sum of mass spectrum for two decay modes m=  6.1  2.7MeV/c 2,  =67.7  20.3  7.7MeV/c 2   The sum of mass spectrum for two decay modes  The mass, width and branching fractions obtained from two different decay modes are consistent with each other.

X(1835) could be the same structure as what is indicated by pp mass threshold enhancement X(1835) mass is consistent with the mass of the s- wave resonance indicated by the ppbar mass threshold enhancement. Its width is 1.9  higher than the upper limit of the width obtained from ppbar mass threshold enhancement. On the other hand, if the FSI effect is included in the fit of the pp mass spectrum, the width of the resonance near pp mass threshold will become larger.

Fit to J/   pp including FSI Include FSI curve from A.Sirbirtsev et al.(hep-ph/ ) in the fit (I=0) M =  6.7 MeV  = 0  93 MeV In good agreement with X(1835)

Light Scalar Mesons: σ, κ, f 0 (980), f 0 (1370), f 0 (1500), f 0 (1710), f 0 (1790) See Prof. Jin’s talk   f 0 (980), f 0 (1370), f 0 (1500), f 0 (1710), f 0 (1790)

Summary Measurements of J/  decays are performed, some of the channels are first observation. First observation of  c  K + K - 2(  +  - ),3(  +  - ) and f 2 f 2 New N* peaks observed in X(1835) is observed in, It could be same structure as the pp mass threshold enhancement, i.e., it could be a pp bound state.

MARK-III & DM2 Results Threshold enhancement Claimed in Phys. Rep. 174(1989) Too small statistics to draw any conclusion on the threshold enhancement, e.g., cannot exclude known particles such as  (1760) MARK-III DM2

Final State Interaction ? —— Not favored Theoretical calculation might be unreliable, however, according to Watson’s theorem, we can use elastic scattering experiments to check the FSI effect, i.e., if the BES structure were from FSI, it should be the same as in elastic scattering : But it is NOT !  FSI cannot explain the BES structure. elastic scattering |M| 2 BES Both arbitrary normalization

Analysis of Phase space events  sidebands Background study MC data MC BESII Preliminary BESII Preliminary BESII Preliminary

Analysis of Phase space events  sidebands Background study data MC BESII Preliminary BESII Preliminary BESII Preliminary

BCK subtracted PS corrected

BCK subtracted PS corrected

Photon angular distributions in For Data – it is not inconsistent with statistics is too low. X(1835) region X(1835) sideband Sideband Subtracted & Eff. corrected

Mass plots with backgrounds Background components are different.  ’ sidebands 0+-’0+-’ Data

Efficiency curve MC

Why are light scalar mesons interesting? There have been hot debates on the existence of  and . Lattice QCD predicts the 0 ++ scalar glueball mass from GeV. f 0 (1500) and f 0 (1710) are good candidates.

The  pole in M(  +  - )   Pole position: MeV PLB598, 149 (2004)

BES II observed  in J/  K*   K  K . Preliminary PWA results Pole position:  at BES BES II Preliminary

Important parameters from PWA fit: Large coupling with KK indicates big component in f 0 (980) f 0 (980) at BES f 0 (980)

There has been some debate whether f 0 (1370) exists or not. f 0 (1370) clearly seen in J/   , but not seen in J/   . PWA 0 ++ components f 0 (1370) NO f 0 (1370) f 0 (1370) at BES

Clear f 0 (1710) peak in J/    KK. No f 0 (1710) observed in J/    ! f 0 (1710) at BES f 0 (1710) NO f 0 (1710)

A clear peak around 1790 MeV is observed in J/   . No evident peak in J/    KK. If f 0 (1790) were the same as f 0 (1710), we would have: Inconsistent with what we observed in J/   ,  KK New f 0 (1790)?? f 0 (1790) ?  f 0 (1790) is a new scalar ??

PWA analysis shows one scalar. Phys. Rev. D 68 (2003) f 0 (1710) in J/    KK

f 0 (1710) in J/    Two scalars in J/    :  One is around 1470 MeV, may be f 0 (1500)?  The other is around 1765 MeV, is it f 0 (1790) or f 0 (1710) or a mixture of f 0 (1710) and f 0 (1790)? BES II Preliminary

f 0 (1500) at BES One scalar with a mass = 1466  6  16 MeV is needed in J/   , is it f 0 (1500)? Why the mass is different from PDG? No peak directly seen in ,  KK, ,  KK.

OZI rule and flavor tagging in J/  hadronic decays In J/  hadronic decays, an  or  signal determines the or component, respectively.  OZI rule

Unusual properties of f 0 (1370) and f 0 (1710) f 0 (1710):  It dominantly decays to KK (not to  )   It is mainly produced together with  (not  )   What is it ? f 0 (1370)  It dominantly decays to  (not to KK)   It is mainly produced together with  (not  )   What is it ?  Scalar Puzzle