Observation of X(2370) and search for X(2120) in J/? ? ? K ¯K ?

Abstract

Using a sample of 1.31x109<mml:mspace width="3.33333pt"></mml:mspace>J/psi events collected with the BESIII detector, we perform a study of J/psi -> gamma KK<overbar></mml:mover>eta '. X(2370) is observed in the KK<overbar></mml:mover>eta ' invariant-mass distribution with a statistical significance of 8.3 sigma. Its resonance parameters are measured to be M=2341.6 +/- 6.5<mml:mspace width="0.166667em"></mml:mspace>(stat.)+/- 5.7<mml:mspace width="0.166667em"></mml:mspace>(syst.)<mml:mspace width="3.33333pt"></mml:mspace>MeV/c2 and Gamma =117 +/- 10<mml:mspace width="0.166667em"></mml:mspace>(stat.)+/- 8<mml:mspace width="0.166667em"></mml:mspace>(syst.)<mml:mspace width="3.33333pt"></mml:mspace>MeV. The product branching fractions for J/psi -> gamma X(2370),X(2370)-> K+K-eta ' and J/psi -> gamma X(2370),X(2370)-> KS0KS0 eta ' are determined to be (1.79 +/- 0.23<mml:mspace width="0.166667em"></mml:mspace>(stat.)+/- 0.65<mml:mspace width="0.166667em"></mml:mspace>(syst.))x10-5 and (1.18 +/- 0.32<mml:mspace width="0.166667em"></mml:mspace>(stat.)+/- 0.39<mml:mspace width="0.166667em"></mml:mspace>(syst.))x10-5, respectively. No evident signal for X(2120) is observed in the KK<overbar></mml:mover>eta ' invariant-mass distribution. The upper limits for the product branching fractions of B(J/psi -> gamma X(2120)-> gamma K+K-eta ') and B(J/psi -> gamma X(2120)-> gamma KS0KS0 eta ') are determined to be 1.49x10<mml:mo>-5 and 6.38<mml:mo>x10<mml:mo>-6 at the 90% confidence level, respectively.