Abstract
Using the production reactions pd→He3ω and pp→ppω, the Dalitz plot distribution for the ω→π+π−π0 decay is studied with the WASA detector at COSY, based on a combined data sample of (4.408±0.042)×104 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 ϕ. For the first time, a deviation from pure P-wave phase space is observed with a significance of 4.1σ. The deviation is parametrised by a linear term 1+2αZ, with α determined to be +0.147±0.036, consistent with the expectations of ρ-meson-type final-state interactions of the P-wave pion pairs.
Highlights
The present work and foreseeable follow-ups are based on two motivations: 1. To check and improve on our understanding of the importance of hadronic final-state interactions for the structure and decays of hadrons.2
Using the production reactions pd → 3He ω and pp → ppω, the Dalitz plot distribution for the ω → π +π −π 0 decay is studied with the WASA detector at Cooler Synchrotron (COSY), based on a combined data sample of (4.408 ± 0.042) × 104 events
The combination of Bose, isospin, and parity symmetry of the strong interaction demands that for the decay ω → π +π −π 0 every pion pair is in a state of odd relative orbital angular momentum
Summary
The present work and foreseeable follow-ups are based on two motivations: 1. To check and improve on our understanding of the importance of hadronic final-state interactions for the structure and decays of hadrons. Pion P -wave phase shift is dominated by the appearance of the ρ-meson resonance; an experimental result pointing to a negative value of α would be spectacular in the sense that it would be at odds with the universality of the final-state interactions. Demonstrated that a once-subtracted dispersive representation describes such very-high-accuracy data well, but not perfectly, leading to the need to introduce a second subtraction [4] With such a second free parameter used in the ω → π +π −π 0 decay amplitude, the energy dependence in principle cannot be entirely predicted any more. Estimating the size of such a second constant from the φ → π +π −π 0 data analysis, it was found that the uncertainty range for the theoretical prediction of the Dalitz plot parameters is only moderately increased [4]. Additional interaction terms have been neglected therein, which were considered to be small, but it is not clear yet how small they are
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