Hadronic interaction of the eta meson with two nucleons

TL;DR

This paper reports precise experimental measurements of eta meson production in proton-proton collisions near threshold, revealing deviations from uniform phase-space distribution and providing insights into proton-eta interactions.

Contribution

It presents new high-resolution data on eta meson production close to threshold, enabling model-independent analysis of proton-eta interactions and phase-space population deviations.

Findings

Observed deviations from homogeneous phase-space population.

Identified influence of proton-eta interaction on excitation function shape.

Compared eta and eta-prime production to distinguish interaction effects.

Abstract

The COSY-11 collaboration has conducted experiments aiming at the determination of the excitation function and phase-space population of the p p --> p p eta reaction close to the kinematical threshold. The precise data obtained with the stochastically cooled proton beam of the cooler synchrotron COSY and the high resolution zero-degree magnetic spectrometer allowed for the observation of the significant deviations - in the shape of the excitation function and two-particle invariant masses - from the predictions based on the assumption that the reaction phase space is homogenously populated. Comparison of the shape of the excitation function for the p p --> p p eta and p p --> p p eta-prime reaction allows to distinquish in the model independent way an influence originating from the proton-proton and proton-eta interaction. For the comparison the full data set from experiments performed at COSY and other laboratories is used.