Total and differential cross sections of $\eta$-production in proton-deuteron fusion for excess energies between $Q_\eta=13\;\text{MeV}$ and $Q_\eta=81\;\text{MeV}$

TL;DR

This study provides new measurements of total and differential cross sections for $ ext{eta}$ meson production in proton-deuteron fusion, revealing structure in the energy dependence and the evolution of angular distributions over a broad energy range.

Contribution

It offers the first detailed analysis of angular distribution development with increasing excess energy in $ ext{eta}$ production from proton-deuteron fusion.

Findings

Significant structure observed in total cross section between 20 and 60 MeV excess energy.

No confirmation of previously reported sharp variation around 50 MeV.

Angular distributions exhibit forward-peaking and evolve with excess energy.

Abstract

New data on both total and differential cross sections of the production of $\eta$ mesons in proton-deuteron fusion to ${}^3\text{He}\,\eta$ in the excess energy region $13.6\;\text{MeV}\leq Q_\eta \leq 80.9\;\text{MeV}$ are presented. These data have been obtained with the WASA-at-COSY detector setup located at the Forschungszentrum J\"ulich, using a proton beam at 15 different beam momenta between $p_p = 1.60\;\text{GeV}/c$ and $p_p = 1.74\;\text{GeV}/c$. While significant structure of the total cross section is observed in the energy region $20\;\text{MeV}\lesssim Q_\eta \lesssim 60\;\text{MeV}$, a previously reported sharp variation around $Q_\eta\approx 50\;\text{MeV}$ cannot be confirmed. Angular distributions show the typical forward-peaking that was reported elsewhere. For the first time, it is possible to study the development of these angular distributions with rising excess energy over a large interval.