Study of $D_{s1}(2460{)}^{+}\to D_s^{+}\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ in $B\to {\bar{D}}^{(\ast )}{D}_s^{+}\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ decays

Abstract

An amplitude analysis of the $D_{s1}(2460{)}^{+}\to D_s^{+}\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ transition is performed simultaneously in $B^0\to D^{-}{D}_s^{+}\ddot{I}{€}^{+}\ddot{I}{€}^{-}$, $B^{+}\to {\bar{D}}^0{D}_s^{+}\ddot{I}{€}^{+}\ddot{I}{€}^{-}$, and $B^0\to D^{\ast -}{D}_s^{+}\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ decays. The study is based on a data sample of proton-proton collisions recorded with the LHCb detector at centre-of-mass energies of $\sqrt{s}=7,8,$ and $13$TeV, corresponding to a total integrated luminosity of $9{\mathrm{fb}}^{-1}$. A clear double-peak structure is observed in the $m(\ddot{I}{€}^{+}\ddot{I}{€}^{-})$ spectrum of the $D_{s1}(2460{)}^{+}\to D_s^{+}\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ decay. The data can be described either with a model including $f_0(500)$, $f_0(980)$ and $f_2(1270)$ resonances, in which the contributions of $f_0(980)$ and $f_2(1270)$ are unexpectedly large, or with a model including $f_0(500)$, a doubly charged open-charm tetraquark state $T_{c\bar{s}}^{++}$ and its isospin partner $T_{c\bar{s}}^0$. If the former is considered implausible, the $T_{c\bar{s}}$ states are observed with high significance, and the data are consistent with isospin symmetry. When imposing isospin constraints between the two $T_{c\bar{s}}$ states, their mass and width are determined to be $2327\pm 13\pm 13$MeV and $96\pm 16{}_{-23}^{+170}$MeV, respectively, where the first uncertainty is statistical and the second is systematic. The mass is slightly below the $DK$ threshold, and a spin-parity of $0^{+}$ is favoured with high significance.

All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/3280 (LHCb public pages)