Amplitude analysis of the D_s⁺ → π⁻π⁺π⁺ decay

A Dalitz plot analysis of the D_s⁺ → π⁻π⁺π⁺ decay is presented. The analysis is based on proton-proton collision data recorded by the LHCb experiment at a centre-of-mass energy of 8 TeV and corresponding to an integrated luminosity of 1.5 fb ⁻¹. The resonant structure of the decay is obtained using a quasi-model-independent partial-wave analysis, in which the π⁺π⁻ S-wave amplitude is parameterised as a generic complex function determined by a fit to the data. The S-wave component is found to be dominant, followed by the contribution from spin-2 resonances and a small contribution from spin-1 resonances. The latter includes the first observation of the D_s⁺ → ω(782)π⁺ channel in the D_s⁺ → π⁻π⁺π⁺ decay. The resonant structures of the D_s⁺ → π⁻π⁺π⁺ and D⁺ → π⁻π⁺π⁺ decays are compared, providing information about the mechanisms for the hadron formation in these decays.