Establishing the heavy quark spin and light flavor molecular multiplets of the X (3872), Zc (3900), and X (3960)

Recently, the LHCb Collaboration reported a near-threshold enhancement X(3960) in the Ds+Ds- invariant mass distribution. We show that the data can be well described by either a bound or a virtual state below the Ds+Ds- threshold. The mass given by the pole position is (3928±3) MeV. Using this mass and the existing information on the X(3872) and Zc(3900) resonances, a complete spectrum of the S-wave hadronic molecules formed by a pair of ground state charmed and anticharmed mesons is established. Thus, pole positions of the partners of the X(3872), Zc(3900), and the newly observed Ds+Ds- state are predicted. Calculations have been carried out at the leading order of nonrelativistic effective field theory and considering both heavy quark spin and light flavor SU(3) symmetries, though conservative errors from the breaking of these symmetries are provided.This research has been supported by the Spanish Ministerio de Ciencia e Innovación (MICINN) and the European Regional Development Fund (ERDF) under Contract No. PID2020–112777 GB-I00, by the EU STRONG- 2020 Project under Program H2020-INFRAIA-2018-1 with Grant Agreement No. 824093, by Generalitat Valenciana under Contract No. PROMETEO/2020/023, by the Chinese Academy of Sciences under Grant No. XDB34030000, by the National Natural Science Foundation of China (NSFC) under Grants No. 12125507, No. 11835015, No. 12047503, and No. 11961141012, and by the NSFC and the Deutsche Forschungsgemeinschaft (DFG) through the funds provided to the Sino-German Collaborative Research Center TRR110 “Symmetries and the Emergence of Structure in QCD” (NSFC Grant No. 12070131001, DFG Project-ID 196253076). M. A. is supported by Generalitat Valenciana under Grant No. CIDEGENT/2020/002

Determination of the number of J/ψ events with inclusive J/ψ decays

A measurement of the number of J/ψ events collected with the BESIII detector in 2009 and 2012 is performed using inclusive decays of the J/ψ. The number of J/ψ events taken in 2009 is recalculated to be (223.7 ± 1.4) × 106, which is in good agreement with the previous measurement, but with significantly improved precision due to improvements in the BESIII software. The number of J/ψ events taken in 2012 is determined to be (1086.9 ± 6.0) × 106. In total, the number of J/ψ events collected with the BESIII detector is measured to be (1310.6 ± 7.0) × 106, where the uncertainty is dominated by systematic effects and the statistical uncertainty is negligible