Upper limits for the production of the eta-mesic Helium in the dd ->3Henpi0 and dd -> 3Heppi- reactions

TL;DR

This study searched for eta-mesic helium bound states in dd reactions using high-statistics measurements but did not observe any signals, setting upper limits on production cross sections.

Contribution

First high-statistics search for eta-mesic helium in dd reactions with precise upper limit measurements.

Findings

No narrow structures observed near eta production threshold.

Upper limits on cross sections range from 21 to 36 nb for dd -> 3Henpi0.

Upper limits range from 5 to 9 nb for dd -> 3Heppi-.

Abstract

We performed a search for 4He-eta bound state in dd -> 3Henpi0 and dd -> 3Heppi- reactions with the WASA-at-COSY facility using a ramped beam technique. The measurement was carried out with high statistics and high acceptance. The signature of eta-mesic nuclei was searched for by the measurement of the excitation functions in the vicinity of the eta production threshold for each of the considered channels. We did not observe the narrow structure which could be interpreted as a bound state. The preliminary upper limits of the total cross sections for the bound state production and decay varies from 21 nb to 36 nb for the dd -> 3Henpi0 channel, and from 5 nb to 9 nb for the dd -> 3Heppi- channel for the bound state width ranging from 5 to 50 MeV.