Search for eta-mesic helium via deuteron-deuteron reactions with the WASA-at-COSY facility

TL;DR

This paper reports on the experimental search for eta-mesic helium nuclei using deuteron-deuteron reactions at the WASA-at-COSY facility, aiming to empirically confirm their existence and understand eta-nucleon interactions.

Contribution

It presents the first high-statistics experimental search for eta-mesic helium via specific decay channels using the WASA-at-COSY setup.

Findings

Data collected around eta production threshold

Analysis of decay channels dd->(4He-eta)bs->3He p pi- and dd->(4He-eta)bs->3He n pi0

Status of the experimental analysis and no definitive discovery yet

Abstract

The eta-mesic nuclei in which the eta meson is bound with nucleus via strong interaction was postulated already in 1986, however till now no experiment confirmed empirically its existence. The discovery of this new kind of an exotic nuclear matter would be very important for better understanding of the eta meson structure and its interaction with nucleons. The search for eta-mesic helium is carried out with high statistic and high acceptance with the WASA-at-COSY detection setup in the Forschungszentrum Julich. The search is conducted via the measurement of the excitation function for the chosen decay channels of the 4He-eta system. Untill now two reactions dd->(4He-eta)bs->3He p pi- and dd->(4He-eta)bs->3He n pi0 have been measured with the beam momentum ramped around the eta production threshold. This report includes the description of experimental method and status of the analysis.