Measurement of the $\omega \to \pi^+ \pi^- \pi^0$ Dalitz plot distribution

TL;DR

This study measures the Dalitz plot distribution for the omega meson decay into three pions, revealing a significant deviation from pure phase space consistent with rho-meson interactions, using data from COSY with the WASA detector.

Contribution

First measurement of the omega decay Dalitz plot showing deviation from pure phase space, indicating rho-meson-like final-state interactions.

Findings

Observed a 4.1 sigma deviation from pure P-wave phase space.

Parametrized deviation with a linear term, alpha = +0.147 ± 0.036.

Results support rho-meson-type interactions in the decay process.

Abstract

Using the production reactions $pd\to {}^3\mbox{He}\,\omega$ and $pp\to pp\omega$, the Dalitz plot distribution for the $\omega \to \pi^+ \pi^- \pi^0$ decay is studied with the WASA detector at COSY, based on a combined data sample of $ (4.408\pm 0.042) \times 10^4$ events. The Dalitz plot density is parametrised by a product of the $P$-wave phase space and a polynomial expansion in the normalised polar Dalitz plot variables $Z$ and $\phi$. For the first time, a deviation from pure $P$-wave phase space is observed with a significance of $4.1\sigma$. The deviation is parametrised by a linear term $1+2\alpha Z$, with $\alpha$ determined to be $+0.147\pm0.036$, consistent with the expectations of $\rho$-meson-type final-state interactions of the $P$-wave pion pairs.