Abstract
We report on the experimental search for the bound state of an η meson and He3 nucleus performed using the WASA-at-COSY detector setup. In order to search for the η-mesic nucleus decay, the pd→3He2γ and pd→3He6γ channels have been analysed. These reactions manifest the direct decay of the η meson bound in a He3 nucleus. This non-mesonic decay channel has been considered for the first time. When taking into account only statistical errors, the obtained excitation functions reveal a slight indication for a possible bound state signal corresponding to a 3He-η nucleus width Γ above 20 MeV and binding energy Bs between 0 and 15 MeV. However, the determined cross sections are consistent with zero in the range of the systematic uncertainty. Therefore, as final result we estimate only the upper limit for the cross section of the η-mesic He3 nucleus formation followed by the η meson decay which varies between 2 nb and 15 nb depending on possible bound state parameters.
Highlights
Strong attractive interactions between the η meson and nucleons mean that there is a chance to form η meson bound states in nuclei [1]
An off-shell η meson produced in nuclear reactions such as the pd → 3He2γ and pd → 3He6γ below the η production threshold may form a bound state with the nucleus within which it is produced
The range of possible bound state production cross section obtained based on statistical uncertainty corresponding to 90% confidence level is shown by blue lines
Summary
Strong attractive interactions between the η meson and nucleons mean that there is a chance to form η meson bound states in nuclei [1]. Strong interaction bound states are formed in a different way as compared to exotic atoms which involve binding of electrically charged mesons with nuclei. An off-shell η meson produced in nuclear reactions such as the pd → 3He2γ and pd → 3He6γ below the η production threshold may form a bound state with the nucleus within which it is produced. One finds a sharp rise in the cross section at threshold for η production in both photoproduction from 3He [2,30] and in the proton-deuteron reaction dp → 3Heη [31] These observations may hint at a reduced η effective mass in the nuclear medium. The data analysis is followed by the interpretation of the achieved excitation functions in view of the possible signal from the η-mesic 3He
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
