Eur. Phys. J. C (2007) 49: 731-736
https://doi.org/10.1140/epjc/s10052-006-0129-y

Regular Article - Theoretical Physics

Some properties of the newly observed X(1835) state at BES

¹ Department of Physics, Nankai University, Tianjin, P.R. China
² NCTS/TPE, Department of Physics, National Taiwan University, Taipei, Taiwan
³ Institute of Theoretical Physics, Academia Sinica, Beijing, P.R. China

^* e-mail: liuxiang726@mail.nankai.edu.cn

Received: 17 March 2006
Published online: 21 November 2006

Abstract

Recently the BES collaboration has announced the observation of a resonant state in the π⁺π^-η’ spectrum in J/ψ→γπ⁺π^-η’ decay. Fitting the data with a 0^-+ state, the mass is determined to be 1833.7 MeV with 7.7σ statistic significance. This state is consistent with the one extracted from previously reported pp̄ threshold enhancement data in J/ψ→γpp̄. We study the properties of this state using QCD anomaly and QCD sum rules, assuming X(1835) to be a pseudoscalar, and we show that it is consistent with the data. We find that this state has a sizeable matrix element , leading to branching ratios of (2.61–7.37)×10^-3 and (2.21–10.61)×10^-2 for J/ψ→γG_p and for G_p→π⁺π^-η^′, respectively. Combining the calculated branching ratio of J/ψ→γG_p and data on threshold enhancement in J/ψ→γpp̄, we determine the coupling for the G_p–p–p̄ interaction. We finally study the branching ratios of the other J/ψ→γ+three mesons decay modes. We find that J/ψ→γG_p→γ(π⁺π^-η,KKπ⁰) can provide useful tests for the mechanism proposed.