Observation of a Near-Threshold Structure in the K+ Recoil-Mass Spectra in e+ e- ? K+ (Ds- D*0 + Ds* - D0)

Abstract

We report a study of the processes of e(+)e(-) -> K+Ds- D*(0) and K+Ds* D-0 based on e(+)e(-) annihilation samples collected with the BESIII detector operating at BEPCII at five center-of-mass energies ranging from 4.628 to 4.698 GeV with a total integrated luminosity of 3.7 fb(-1). An excess of events over the known contributions of the conventional charmed mesons is observed near the D-s(-) D*(0) and D-s*(-) D-0 mass thresholds in the K+ recoil-mass spectrum for events collected at root s = 4.681 GeV. The structure matches a mass-dependent-width Breit-Wigner line shape, whose pole mass and width are determined as (3982.5(-2.6)(+1.8) +/- 2.1) MeV/c(2) and (12.8(-4.4)(+5.3) +/- 3.0) MeV, respectively. The first uncertainties are statistical and the second are systematic. The significance of the resonance hypothesis is estimated to be 5.3 sigma over the contributions only from the conventional charmed mesons. This is the first candidate for a charged hidden-charm tetraquark with strangeness, decaying into D-s(-) D*(0) and D-s*(-) D-0. However, the properties of the excess need further exploration with more statistics.