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 ）

29/10/06 penghp@mail.ihep.ac.cn 2

Outline

Introduction BES Detector and Event

Selections Partial Wave Analysis Results and Discussions Summary

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Introduction

QCD predicts a rich spectrum of glueballs, hybrids and four quark states in 1.0 to 2.5GeV/c2 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.

pp p

J/pp

M(pp)-2mp (GeV)PRL. 9(2003) 022001

pKJ /

PRL 93(2004), 112002

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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

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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 |E1- E2|/|E1 + E2|<0.90 is applied to the two photons from

0 to remove the background with false 0;

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K+K- & +-0 mass spectra

MeVMMKK

15||

MeVMKKMMeV 30||15

Dalitz plot MeVMM

MeVMM KK

30||

15||

B.G. J/K*K

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Invariant MassClear Enhancement Acceptance

Curve

After Efficiency Correction

Phase Space

The enhancement on the threshold is not from the phase space !

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B.G. From SidebandMeVMMMeV

MeVMM KK

80||50

15||

MeVMM

MeVMMMeV KK

30||

35||20

MeVMMMeV

MeVMMMeV KK

80||50

35||20

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

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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.

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Partial Wave Analysis

Two body decay: Decay amplitude: Helicity coupling amplitude :

Amplitude Construction : Covariant Helicity Coupling AmplitudeJ,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

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Partial Wave Analysis Sequential decay process amplitude:

The total differential cross section:

The probability density function p(j,):

Normalization

Phase space

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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.

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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:

2

21926

MeV/c 2820105

MeV/c 181812

M

410)65.027.061.2()()/(

XBrXJBr

MeV 2820105MeV 181812 19

26

M

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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 2++. 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.

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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/0602072). It could be a multiquark/hybrid/glueball state. hep-ph/0602072, 0602172, 602190, 0603018, 0604141, 0606196 Its relation with f0(1710),f0(1790)?

Further look in , K*K*, …. are desirable !

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BESII J/ PRD73 (2006) 112007

w signal after best candidate selection

sideband

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PWA of helicity coupling amplitude is performed. Dominated by (1760):

A scalar is needed around 1.8GeV/c2 with 6.5. But the mass and width are very difficult to be determined due to dominant contribution of pseudoscalar.

BESII J/ PRD73 (2006) 112007

Inclusive B.G.

M = 1744 10 15 MeV/c2

= 244 23 25 MeV/c2

Br( J/ (1760)) Br( (170) ) = (1.98 0.08 0.32 ) x 10-3

Br( J/ 0++ ) Br( 0++ ) = (0.31 0.05 0.08 ) x 10-3

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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.

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谢 谢

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Publications PRL 96 162002(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(2006-10-23) 14 times cited

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Publications PRD 73 (2006) 112007 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}.