Constraining the optical potential in the search for eta-mesic 4He

TL;DR

This paper refines the constraints on the eta-4He optical potential by comparing theoretical models with experimental data, narrowing down the parameter space for possible eta-mesic helium states.

Contribution

It provides new constraints on the eta-4He optical potential parameters using experimental excitation functions, excluding most previous optical model predictions.

Findings

Allowed potential parameters are |V_0| < ~60 MeV and |W_0| < ~7 MeV.

Most optical model predictions are excluded, except for some loosely bound narrow states.

The study enhances understanding of eta-mesic helium formation possibilities.

Abstract

A consistent description of the $ d d \rightarrow$ $^{4}\hspace{-0.03cm}\mbox{He} \eta$ and $ d d \rightarrow$ ($^4$He$\eta$)$_{bound} \rightarrow X $ cross sections was recently proposed with a broad range of real ($V_{0}$) and imaginary (W0), $\eta$-$^4$He optical potential parameters leading to a good agreement with the d d -> 4He eta data. Here we compare the predictions of the model below the $\eta$ production threshold, with the WASA-at-COSY excitation functions for the dd -> 3He N pi reactions to put stronger constraints on (V0, W0). The allowed parameter space (with |V_0| < \sim 60 MeV and |W_0| < \sim 7 MeV estimated at 90% CL ) excludes most optical model predictions of eta-4He nuclei except for some loosely bound narrow states.