Status and perspectives of the search for Eta-Mesic nuclei

Abstract

Abstract.In this report the search for η-mesic nuclei is reviewed. The brief description of the experimental studies is presented with a focus on the possible production of the η-nucleus bound states for light nuclei like He.

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

“…In the case of η-mesic nuclei, the ηN interaction happens at subthreshold energies and F ηN should be evaluated at an energy shifted by an amount δ below threshold. The importance of taking such a downward shift into account has been discussed with different points of view in literature [59,60,61,62]. The authors in [59,60] (and references therein) provide a detailed analysis of this topic and derive an expression for δ which depends on the nuclear binding energy per nucleon as well as the real part of the optical potential itself.…”

“…Refs. [61,62], however, provide a simpler method with δ given by the average binding of the target nucleons.…”

Recent Results from WASA-at-COSY

“…In 2008 and 2010 we performed the measurements dedicated to search for the 4 He-η bound states in deuteron-deuteron fusion reaction [47,49]. The η-mesic nuclei were searched via studying of excitation function for the dd → 3 Hepπ − (2008 and 2010) [5,50,51] and dd → 3 Henπ 0 [50,52] (2010) reactions in the vicinity of the 4 Heη threshold.…”

“…Also another international collaborations perform experimental searches for η and η ′ -mesic nuclei [49] in hadro-and photo-production reactions [57,58]. The Eta-prime/Super-FRS collaboration for the first time have performed the search for η ′ -mesic bound statess in inclusive measurement of the 12 C(p,d) process [59,60] while, at J-PARC the search for η-mesic nuclei is planned in pion induced reaction [61].…”

Search for the η-mesic bound states with the WASA-at-COSY detector

“…However, despite many experiments performed, there is still no clear evidence of their existence [35][36][37][38][39][40][41][42]. The interested reader can find recent reviews on the η mesic bound state searches in Refs [6,7,16,18,30,[45][46][47][48][49].…”