Search for eta-mesic Helium with the WASA-at-COSY detector

TL;DR

This study conducted an experimental search for eta-mesic helium nuclei using the WASA-at-COSY detector, but found no evidence of such bound states within the examined energy range.

Contribution

First experimental search for eta-mesic helium using exclusive measurement at COSY with no observed bound state signal.

Findings

No eta-mesic helium bound state detected.

Excitation function showed no resonance signal.

Data constrains the possible existence of eta-mesic helium.

Abstract

A search for the 4He-eta bound state via exclusive measurement of the excitation function for the dd->3Heppi- reaction, was performed at the Cooler Synchrotron COSY-Juelich with the WASA-at-COSY detection system. The data were taken during a slow acceleration of the beam from 2.185 GeV/c to 2.400 GeV/c crossing the kinematic threshold for the eta production in the dd -> 4He-eta reaction at 2.336 GeV/c. The corresponding excess energy in the 4He-eta system varied from -51.4 MeV to 22 MeV. The shape of the excitation function for the dd -> 3Heppi- was examined. No signal of the 4He-eta bound state was observed in the excitation function.