Evidence of a $J/\psi K_S^0$ structure in $B^0\to J/\psi \varphi K_S^0$ decays

Abstract

An amplitude analysis of $B^0\to J/\psi \varphi K_S^0$ decays is performed using proton-proton collision data corresponding to an integrated luminosity of 9 ${\mathrm{fb}}^{-1}$, collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 TeV. Evidence with a significance of $4.0$ standard deviations of a structure in the $J/\psi K_S^0$ system, named $T_{\psi s1}^{\theta }(4000{)}^0$, is seen, with its mass and width measured to be $3991{}_{-10}^{+12}{}_{-17}^{+9}$ MeV and $105{}_{-25}^{+29}{}_{-23}^{+17}$ MeV, respectively, where the first uncertainty is statistical and the second systematic. The $T_{\psi s1}^{\theta }(4000{)}^0$ state is likely to be the isospin partner of the $T_{\psi s1}^{\theta }(4000{)}^{+}$ state, previously observed in the $J/\psi K^{+}$ system of the $B^{+}\to J/\psi \varphi K^{+}$ decay. When isospin symmetry for the charged and neutral $T_{\psi s1}^{\theta }(4000)$ states, is assumed, the signal significance increases to $5.4$ standard deviations.

All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-040.html (LHCb public pages)

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