First observation of a doubly charged tetraquark and its neutral partner

TL;DR

This paper reports the first observation of a doubly charged open-charm tetraquark and its neutral partner, based on amplitude analysis of B meson decays, revealing new exotic states consistent with an isospin triplet.

Contribution

It presents the discovery of two new tetraquark states, including the first doubly charged open-charm tetraquark, using data from LHCb and amplitude analysis techniques.

Findings

First observation of a doubly charged tetraquark

Identification of a neutral partner tetraquark

States are consistent with an isospin triplet

Abstract

A combined amplitude analysis is performed for the decays $B^0 \rightarrow \overline{D}^0 D^+_s\pi^-$ and $B^+\rightarrow D^- D^+_s\pi^+$, which are related by isospin symmetry. The analysis is based on data collected by the LHCb detector in proton-proton collisions at center-of-mass energies of 7, 8 and 13$\,\rm{TeV}$. The full data sample corresponds to an integrated luminosity of 9$\,\rm{fb^{-1}}$. Two new resonant states with masses of $2.908\pm0.011\pm0.020\,\rm{GeV}$ and widths of $0.136\pm0.023\pm0.011\,\rm{GeV}$ are observed, which decay to $D^+_s\pi^+$ and $D^+_s\pi^-$ respectively. The former state indicates the first observation of a doubly charged open-charm tetraquark state with minimal quark content $[c\bar{s}u\bar{d}]$, and the latter state is a neutral tetraquark composed of $[c\bar{s}\bar{u}d]$ quarks. Both states are found to have spin-parity $0^+$, and their resonant parameters are consistent with each other, which suggests that they belong to an isospin triplet.