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Study of Ds1(2460)+→D+sπ+π− in B→D¯(∗)D+sπ+π− decays
An amplitude analysis of the Ds1(2460)+→D+sπ+π− transition is performed simultaneously in B0→D−D+sπ+π−, B+→D¯0D+sπ+π−, and B0→D∗−D+sπ+π− decays. The study is based on a data sample of proton-proton collisions recorded with the LHCb detector at centre-of-mass energies of s√=7,8, and 13TeV, corresponding to a total integrated luminosity of 9fb−1. A clear double-peak structure is observed in the m(π+π−) spectrum of the Ds1(2460)+→D+sπ+π− decay. The data can be described either with a model including f0(500), f0(980) and f2(1270) resonances, in which the contributions of f0(980) and f2(1270) are unexpectedly large, or with a model including f0(500), a doubly charged open-charm tetraquark state T++cs¯ and its isospin partner T0cs¯. If the former is considered implausible, the Tcs¯ states are observed with high significance, and the data are consistent with isospin symmetry. When imposing isospin constraints between the two Tcs¯ states, their mass and width are determined to be 2327±13±13MeV and 96±16+170−23MeV, 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.