WASA-at-COSY

Decay studies of the $\omega$, a light vector meson, covers a span of interesting physics including $3\pi$ decay dynamics, the $\rho - \omega$ mixing and the $\omega-\pi^0$ transition form factor. The ongoing study presented by this poster covers the first two mentioned topics through measurements of the $\omega\to\pi^+\pi^-\pi^0$ and $\omega\to\pi^+\pi^-$ channels where the $\omega$ was produced in the $p\ +\ d\ \to\ {}^3He\ +\ \omega$ reaction and measured with the experimental setup of WASA-at-COSY. A high statistics study of the $\omega\to\pi^+\pi^-\pi^0$ dynamics can provide quantitative experimental verification of the predicted onset of the $\rho$ in the decay process as well as the impact of $\pi - \pi$ interactions. This study has the goal of providing experimental values of a parametrisation of the Dalitz plot for a comparison with current theoretical predictions, [1,2]. The isospin breaking $\omega\to\pi^+\pi^-$ decay can give insight into the behaviour of the $\rho - \omega$ mixing. This channel has already been widely studied in $e^+e^-$ collisions where the interference has been conclusively shown as destructive [3]. Only a few measurements with limited statistics have been performed for hadronic production of the $\omega$ meson with hints of a possible constructive interference 4]. The aim of this study is to investigate the structure of the $\omega\to\pi^+\pi^-$ signal in proton on deuteron collisions.

[1] C.Terschlüsen, B.Strandberg, S.Leupold and F.Eichstädt, arXiv:1305.1181 [hep-ph] [2] F.Niecknig, B.Kubis and S.P.Schneider, Eur.Phys. J. C72 (2012) 2014 [3] R.R.Akhmetshin et al., Phys. Lett. B527 (2002) 161 [4] B.N.Ratcliff et al., Phys. Lett. B38 (1972) 345