Mechanism of the close-to-threshold production of the eta meson

TL;DR

This study investigates eta meson production near threshold energies in proton-proton collisions, showing it occurs mainly via s-wave and likely involves pi meson exchange during nucleon excitation.

Contribution

It provides new experimental data on analyzing power at specific energies and suggests the dominant exchange mechanism for eta meson production in nucleon collisions.

Findings

Analyzing power is consistent with zero, indicating s-wave dominance.

Evidence suggests pi meson exchange mediates nucleon excitation.

Results support pi exchange as the primary mechanism for eta production.

Abstract

Measurements of the analysing power for the p(pol)p --> ppeta reaction have been performed in the close-to-threshold energy region at beam momenta of p_{beam}=2.010 and 2.085 GeV/c, corresponding to excess energies of Q=10 and 36 MeV, respectively. The determined analysing power is essentially consistent with zero implying that the eta meson is produced predominantly in the s-wave at both excess energies. The angular dependence of the analysing power, combined with the hitherto determined isospin dependence of the total cross section for the eta meson production in nucleon-nucleon collisions, reveal a statistically significant indication that the excitation of the nucleon to the S_{11}(1535) resonance, the process which intermediates the production of the eta meson, is predominantly due to the exchange of the pi meson between the colliding nucleons.