Observation of a near-threshold enhancement in  mass spectrum from J/    彭 海 平 中国科学技术大学 广西桂林（ 29/10/2006 ）

Outline  Introduction  BES Detector and Event Selections  Partial Wave Analysis  Results and Discussions  Summary

Introduction  QCD predicts a rich spectrum of glueballs, hybrids and four quark states in 1.0 to 2.5GeV/c 2 mass region. Radiative J/  decays provide an excellent laboratory to search for these states.  Enhancements near threshold in the invariant mass spectra of and were observed in the J/  decays by BESII experiment. These surprising observations stimulated many theoretical speculations. Therefore it is interesting to search for possible resonances in other final states. J/    pp M(pp)-2m p (GeV) PRL. 9(2003) PRL 93(2004),

 Systems of two vector particles, such as  and , can be produced in the J/  radiative decay with OZI suppressed process, and pseudoscalar enhancements have been seen in the  and  invariant mass threshold. Unlike  and  final states process, J/    is a DOZI suppressed process, and its production ratio should be suppressed by at least one order. Therefore the measurement of this decay and search for possible resonant states are interesting Introduction J/  DOZIJ/ ,  OZI

BES Detector & Event Selections  4 good tracks with |cos  |<0.8 in MDC;  The total charge is required to be 0;  PID: TOF and dE/Dx information;  3-6 good photon candidates from BSC;  Five-constraint energy-momentum conservation kinematic fit is made under the J/  K + K -  +  -  0 hypothesis with probability larger than 1%;  Cut |E  1 - E  2 |/|E  1 + E  2 |<0.90 is applied to the two photons from  0 to remove the background with false  0 ;

 K + K - &  +  -  0 mass spectra    Dalitz plot B.G. J/K * K

 Invariant Mass Clear Enhancement Acceptance Curve After Efficiency Correction Phase Space The enhancement on the threshold is not from the phase space !

B.G. From Sideband B.G. from sideband, no enhancement on threshold !

B.G. Check  60M Inclusive MC data, no enhancement on threshold !  Many possible exclusive MC samples are generated to check the background, no events peak on the threshold. The main background is from J/    K * K, but it peaks at the high mass region of .  About 2272nb -1 data with 3.07GeV center mass energy are used to check the continuum contribution, no events are survived.  As a check, the branching fraction of J/    is measured, the results is consistent with that from the J/    K + K - K + K -, but with a larger error. Inclusive B.G.J/  K*K  J/    0  and J/    are forbidden by C-invariance.

Partial Wave Analysis  Two body decay:  Decay amplitude:  Helicity coupling amplitude : Amplitude Construction : Covariant Helicity Coupling Amplitude J,S,  : The spin of particle. M,, : The helicity of particle. ,  : The polar and azimuthal angle. M. Jacob and G.C. Wick, Ann. Phys. (N.Y) 7, 404(1959); S.U.CHUNG, BNL-QGS94-21; S.U.Chung.Phy. Rev. D57, 1998; 431; S.U.Chung. Phy. Rev. D48, 1993; 1225; Ning Wu and Tu-Nan Ruan, Commun, Theor. phys. (Beijing China) 35(2001)547

Partial Wave Analysis  Sequential decay process amplitude:  The total differential cross section:  The probability density function p(  j,  ): Normalization Phase space

PWA Process  The normalization constant can be obtained by M.C integral from phase space M.C sample.  The likelihood function:  The task of PWA is to fit the unknown parameters, and get the minimum value of, CERNLIB MINUIT package is used.

PWA Results  The best fitting is that with both the  and  X systems being S-wave, which corresponds to a 0 ++ scalar state considering the C-parity of the .  Statistical significance is larger than 10  !  The mass and width:  The branching ratio:

PWA Results  If the system of  X is treated as D-wave, the mass and width of the resonance, as well as the log likelihood value do not change much. However, if the system of  is treated as D-wave, the log likelihood value gets worse by about 40.  If the resonance is fitted with 0 -+ spin-parity, the log likelihood value gets worse by about 58.  If the resonance is fitted with 2 -+ spin-parity, the log likelihood value gets worse by about 17.  If the resonance is fitted with 2 ++ spin-parity, the log likelihood value gets worse by about 4.7. Although the fit is not too much worse than 0 ++ case, but there is only one free parameter for 0 ++, while four free parameters for Also, D-wave is required for  system, if only S-wave is used in the fit, the log likelihood value get worse by about 13.

Discussions  The mass and width of this state are not compatible with any known scalars listed in PDG!  The decay is DOZI suppressed process, and the phase space of X(1810)  is small, so the branching ratio should be three order of magnitude weaker than the OZI suppressed process if the resonance is a ordinary q qbar meson (hep-ph/ ).  It could be a multiquark/hybrid/glueball state. hep-ph/ , , , , ,  Its relation with f 0 (1710),f 0 (1790)? Further look in , K*K*,  …. are desirable !

BESII J/  PRD73 (2006) w signal after best candidate selection   sideband

 PWA of helicity coupling amplitude is performed.  Dominated by  (1760):  A scalar is needed around 1.8GeV/c 2 with 6.5 . But the mass and width are very difficult to be determined due to dominant contribution of pseudoscalar. BESII J/  PRD73 (2006) Inclusive B.G. M = 1744  10  15 MeV/c 2  = 244  23  25 MeV/c 2 Br( J/    (1760)) Br(  (170)   ) = (1.98  0.08  0.32 ) x Br( J/    0 ++ ) Br( 0 ++   ) = (0.31  0.05  0.08 ) x 10 -3

Summary  The doublely OZI suppressed decay J/  is studied based on BESII 58M J/  data.  An enhancement near  threshold is observed with a statistical significance of more than 10 .  PWA with covariant helicity coupling amplitudes is performed, the 0 ++ spin-parity of the enhancement is favored.  The mass, width and product branching fraction are not compatible with any known scalars listed in PDG. It could be an unconventional state.

谢 谢谢 谢

Publications  PRL (2006) BES Collab.  Observation of a Near-Threshold Enhancement in the omega phi Mass Spectrum from the Doubly OZI-Suppressed Decay J/psi->gamma omega phi  Received 16 February 2006; published 27 April 2006  An enhancement near threshold is observed in the invariant mass spectrum from the doubly Okubo-Zweig-Iizuka – suppressed decays of J/Psi, based on a sample of 5.8×10^7 J/Psi events collected with the BESII detector. A partial wave analysis shows that this enhancement favors J^P=0^+, and its mass and width are M=1812 (stat)±18(syst) MeV/c^2 and =105±20(stat)±28(syst) MeV/c^2. The product branching fraction is determined to be B(J/Psi->Gamma X)B(X->omiga phi )=[2.61±0.27(stat)±0.65(syst)]×10-4.  SPIRES-HEP search( ) 14 times cited

Publications  PRD 73 (2006) BES Collab.  Pseudoscalar production at omegaomega threshold in J/psi-->gamma omega omega  Received 24 April 2006; published 14 June 2006)  The decay channel J/\psi->gamma omega omega, omega -> pi+ pi- pi0 is analyzed using a sample of 5.8x10^7 J/psi events collected with the BESII detector. The omega omega invariant mass distribution peaks at 1.76 GeV/c^2, just above the omega omega threshold. Analysis of angular correlations indicate that the omega omega system below 2 GeV/c^2 is predominantly pseudoscalar. A partial wave analysis confirms the predominant pseudoscalar structure, together with small 0^{++} and 2^{++} contributions, and yields a pseudoscalar mass M = 1744 \pm 10 (stat) \pm 15 (syst) MeV/c^2, a width Gamma = 244^{+24}_{- 21} (stat) \pm 25 (syst) MeV/c^2, and a product branching fraction Br(J/psi-> gamma eta(1760)) \cdot Br(\eta(1760)- >omega omega) = (1.98 \pm 0.08 (stat) \pm 0.32 (syst)) x 10^{-3}.