First Observation of a Doubly Charged Tetraquark and Its Neutral Partner

Abstract

A combined amplitude analysis is performed for the decays B0 → D0 Dþ s π− and Bþ → D−Dþ s πþ, which are related by isospin symmetry. The analysis is based on data collected by the LHCb detector in protonproton collisions at center-of-mass energies of 7, 8, and 13 TeV. The full data sample corresponds to an integrated luminosity of 9 fb−1. Two new resonant states with masses of 2.908 0.011 0.020 GeV and widths of 0.136 0.023 0.013 GeV are observed, which decay to Dþ s πþ and Dþ s π− respectively. The former state indicates the first observation of a doubly charged open-charm tetraquark state with minimal quark content ½csu¯ d¯, and the latter state is a neutral tetraquark composed of ½cs¯ u d¯ quarks. Both states are found to have spin-parity of 0þ, and their resonant parameters are consistent with each other, which suggests that they belong to an isospin triplet.