Measurement of the I = 1 / 2 Kπ S - wave amplitude from Dalitz plot analyses of η c → KKπ in two - photon interactions

Measurement of the I = 1/2 Kπ S-wave amplitude from Dalitz plot analyses of η c →KKπ in two-photon interactions We study the processes γγ→K 0 S K ± π ∓ and γγ→K + K − π 0 using a data sample of 519 fb −1 recorded with the BABAR detector operating at the SLAC PEP-II asymmetric-energy e + e − collider at center-of-mass energies at and near the Υ (nS) (n = 2, 3, 4) resonances. We observe ηc decays to both final states and perform Dalitz plot analyses using a model-independent partial wave analysis technique. This allows a model-independent measurement of the mass-dependence of the I = 1/2 Kπ S-wave amplitude and phase. A comparison between the present measurement and those from previous experiments indicates similar behaviour for the phase up to a mass of 1.5 GeV/c 2. In contrast, the amplitudes show very marked differences. The data require the presence of a new a0(1950) resonance with parameters m = 1931 ± 14 ± 22 MeV/c 2 and Γ = 271 ± 22 ± 29 MeV.