Leading Modes of the 3pi0 production in proton-proton collisions at incident proton momentum 3.35GeV/c

TL;DR

This study investigates the dynamics of the pp-->pp3pi0 reaction at 3.35GeV/c, revealing the dominant decay mode of N*(1440) and providing new measurements of resonance decay ratios and spectral line shapes.

Contribution

First direct measurement of the decay ratio R for N*(1440) and detailed analysis of the reaction mechanisms using Dalitz and Nyborg plots at this energy.

Findings

N*(1440)->Δ(1232)π is the leading decay mode for 3pi0 production.

The decay ratio R=0.039±0.011(stat)±0.008(sys) is measured for the first time.

The spectral line shape of N*(1440) and resonance interactions are highly sensitive to the missing mass distributions.

Abstract

This work deals with the prompt pp-->pp3pi0 reaction where the 3pi0 do not origin from the decay of narrow resonances like \eta(547), \omega(782), \eta'(958). The reaction was measured for the proton beam momentum of 3.35GeV/c with the WASA-at-COSY detector setup. The dynamics of the reaction is investigated by Dalitz and Nyborg plots studies. The reaction is described by the model assuming simultaneous excitation of two baryon resonances \Delta(1232) and N*(1440) where resonances are identified by their unique decays topology on the missing mass of two protons MMpp dependent Dalitz and Nyborg plots. The ratio R=\Gamma(N*(1440)->N\pi\pi)/\Gamma(N*(1440)->\Delta(1232)\pi->N\pi\pi)= 0.039 +- 0.011(stat.) +- 0.008(sys.) is measured for the first time in a direct way. It shows that the {N*(1440)->\Delta(1232)\pi->N\pi\pi} decay is a leading mode of 3pi0 production. It is also shown that the MMpp is very sensitive to the structure of the spectral line shape of the N*(1440) resonance as well as on the interaction between the \Delta(1232) and N*(1440) resonances. The multipion spectroscopy - a precision tool to directly access the properties of baryon resonances is considered. The pp-->pp\eta(3pi0) reaction was also measured simultaneously. It is shown that the {\eta} production mechanism via N*(1535) is 43.4 +- 0.8(stat.) +- 2.0(sys.) of the total production, for the {\eta} momentum in the CM system q_\eta^CM=0.45-0.7GeV/c. First time momentum dependence of the {\eta} angular distribution is seen, the strongest effect is observed for the cos(\theta_\eta^CM) distribution.