Study of muon-tagged $D_{s1}(2460{)}^{+}$ and $D_{s1}(2536{)}^{+}$ decays to the $D_s^{+}{\pi }^{+}{\pi }^{-}$ final state

Abstract

Decays of the pseudovector $D_{s1}(2460{)}^{+}$ and $D_{s1}(2536{)}^{+}$ mesons to the three-body $D_s^{+}{\pi }^{+}{\pi }^{-}$ final state are studied. The data sample is based on decays of beauty hadrons into $D_{s1}^{+}$ states accompanied by a muon from the $b$-hadron decay chain collected by the LHCb detector during 2016--2018, corresponding to an integrated luminosity of 5.4 fb${}^{-1}$. The \mbox{$D_{s1}(2536{)}^{+}\to D_s^{+}{\pi }^{+}{\pi }^{-}$} branching fraction is measured for the first time, with the $D_{s1}(2536{)}^{+}\to D^{+}{K}^{+}{\pi }^{-}$ decay used as a reference. A simultaneous amplitude analysis of the $D_{s1}(2460{)}^{+}$ and $D_{s1}(2536{)}^{+}\to D_s^{+}{\pi }^{+}{\pi }^{-}$ decays is performed. The Dalitz-plot distributions of the two decays are found to be significantly different, suggesting differences in the internal structure of the two states, with evidence of exotic contributions to the $D_s^{+}{\pi }^{\pm }$ channel with the pole below the $DK$ threshold. Measurements of the masses of the $D_{s1}(2460{)}^{+}$ and $D_{s1}(2536{)}^{+}$ states are performed, and an upper limit on the $D_{s1}(2460{)}^{+}$ width is set.

All figures and tables, along with any supplementary material and additional information, are available at https://lhcb-glance.cern.ch/alcm/public/analysis/full-details/3761 (LHCb public pages)