Study Of ψ(3686)→ P(?) At BesⅢ

Most known hadrons can be described by the quark model.Quantum chromodynamics（QCD）,as the fundamental theory of strong interaction,has successfully explained many strong interaction phenomena.However,non-perturbative QCD in the low-energy region still requires further study.QCD also allows for new forms of hadrons beyond the quark model,such as glueballs,hybrids,and multi-quark states.The quark model predicts many states of baryons,but the number observed experimentally is smaller than expected,a phenomenon known as the“missing baryons”problem.Exploring the“missing baryons”and new forms of hadrons has become an important topic in hadron spectroscopy and is crucial for the testing and development of QCD.The hidden-charmed pentaquark states candidates,P_c（4380）and P_c（4450）,are situated close to the thresholds ofΣ_c^*D and Σ_cD^*,respectively.Similarly,two N^*resonances,N（1875）and N（2120）,with J^P=₂^3-,located near the thresholds ofΣ^*K andΣK^*,respectively,are also possible candidates for pentaquark states.The charmoniums decay has advantages such as high statistics,low background,simple isospin in the final state,and a gluon-rich environment,making it a convenient venue to search for these hadronic states.Based on a dataset of 2.71×10⁹ψ（3686）events collected with the BESⅢ detector,this paper presents a partial-wave analysis of theψ（3686）→p（?）process.A resonance N（2120）with spin-parity₂^3-is observed in the p（?）invariant mass spectrum with a statistical sig-nificance of 9.7σ.The mass and width of N（2120）are measured to be （?） and （?）,respectively.The branching fraction of theψ（3686）→p（?）process is measured to be （5.34±0.16（stat.）±0.34（syst.））×10^-6,and the branching fraction of the ψ（3686）→N（2120）（?）+c.c.→p（?）process is measured for the first time to be （?）.This is the first experimental observation of the decay N^*→（?）N.