Observation of X(2370) and search for X(2120) in J/ ψ→ γKK¯ η′ : BESIII Collaboration

Abstract

Using a sample of 1.31×109J/ψ events collected with the BESIII detector, we perform a study of J/ ψ→ γKK¯ η′. X(2370) is observed in the KK¯ η′ invariant-mass distribution with a statistical significance of 8.3 σ. Its resonance parameters are measured to be M=2341.6±6.5(stat.)±5.7(syst.)MeV/c2 and Γ=117±10(stat.)±8(syst.)MeV. The product branching fractions for J/ ψ→ γX(2370) , X(2370) → K+K-η′ and J/ψ→γX(2370),X(2370)→KS0KS0η′ are determined to be (1.79±0.23(stat.)±0.65(syst.))×10-5 and (1.18±0.32(stat.)±0.39(syst.))×10-5, respectively. No evident signal for X(2120) is observed in the KK¯ η′ invariant-mass distribution. The upper limits for the product branching fractions of B(J/ ψ→ γX(2120) → γK+K-η′) and B(J/ψ→γX(2120)→γKS0KS0η′) are determined to be 1.49 × 10 - 5 and 6.38 × 10 - 6 at the 90% confidence level, respectively.