# Measurement of the I=1/2 $K \pi$ $\mathcal{S}$-wave amplitude from Dalitz plot analyses of $\eta_c \to K \bar K \pi$ in two-photon interactions

Abstract : We study the processes $\gamma \gamma \to K^0_S K^{\pm}\pi^{\mp}$ and $\gamma \gamma \to K^+ K^- \pi^0$ 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 $\Upsilon(nS)$ ($n = 2,3,4$) resonances. We observe $\eta_c$ 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 $I=1/2$ $K \pi$ $\mathcal{S}$-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 $a_0(1950)$ resonance with parameters $m=1931 \pm 14 \pm 22 \ MeV/c^2$ and $\Gamma=271 \pm 22 \pm 29 \ MeV$.
Document type :
Journal articles

http://hal.in2p3.fr/in2p3-01226759
Contributor : Sabine Starita <>
Submitted on : Tuesday, November 10, 2015 - 10:07:23 AM
Last modification on : Friday, November 6, 2020 - 3:33:40 AM

### Citation

J. P. Lees, V. Poireau, V. Tisserand, N. Arnaud, M. Davier, et al.. Measurement of the I=1/2 $K \pi$ $\mathcal{S}$-wave amplitude from Dalitz plot analyses of $\eta_c \to K \bar K \pi$ in two-photon interactions. Physical Review D, American Physical Society, 2016, 93, pp.012005. ⟨10.1103/PhysRevD.93.012005⟩. ⟨in2p3-01226759⟩

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