Evidence for a Neutral Near-Threshold Structure in the K0S Recoil-Mass Spectra in e+e− → K0SD+sD*− and e+e− → K0SD*s+D−

• We study the processes e+e− → K0SD+sD*− and e+e− → K0SD*s+D−, as well as their charge conjugated processes, at five center-of-mass energies between 4.628 and 4.699 GeV, using data samples corresponding to an integrated luminosity of 3.8  fb−1 collected by the BESIII detector at the BEPCII storage ring. Based on a partial reconstruction technique, we find evidence of a structure near the thresholds for D+sD*− and D*s+D− production in the K0S recoil-mass spectrum, which we refer to as the Zcs(3985)0. Fitting with a Breit-Wigner line shape, we find the mass of the structure to be (3992.2±1.7±1.6)  MeV/c2 and the width to be (7.7+4.1−3.8±4.3)  MeV, where the first uncertainties are statistical and the second are systematic. The significance of the Zcs(3985)0 signal is found to be 4.6σ including both the statistical and systematic uncertainty. We report the Born cross section multiplied by the branching fraction at different energy points. The mass of the Zcs(3985)0 is close to that of the Zcs(3985)+. Assuming SU(3) symmetry, the cross section of the neutral channel is consistent with that of the charged one. Hence, we conclude that the Zcs(3985)0 is the isospin partner of the Zcs(3985)+.

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NATURVETENSKAP  -- Fysik -- Subatomär fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Subatomic Physics (hsv//eng)

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