Search for η-mesic He4 in the dd→He

$\eta$ η -nucleus interaction from the d + d reaction around the $\eta$ η

“…From this figure, the upper limit reported in Ref. [35] is found to provide very valuable information on η-nucleus interaction and strongly suggests the small |V 0 | and |W 0 | values. However, it should be noted that the results in Fig.…”

“…17-20 can be compared to the shape of the experimental spectra on the background reported in Ref. [35], where the upper limit of the peak structure of the d + d → 3 He + n + π 0 is 3-6 nb. This implies that the experimental upper limit for the semi-inclusive conversion spectrum of d + d → (η + α) → 3 He + N + π including both n + π 0 and p + π − channel could be estimated to be 3-6 nb ×3 = 9-18 nb because of the isospin symmetry of the decay channel of the η-α system.…”

“…The shape of the observed spectra in Ref. [35] were smooth without any clear peak structures, and the upper limit of the η-nucleus formation cross section was reported to be around 3-6 nb for d + d → 3 He + n + π 0 reaction [35]. To evaluate these upper limits, the Fermi motion of N * in nucleus [36] is also taken int account.…”

“…Recently, the new experiments of the d+d → (η+α) → X reaction have been proposed and performed at WASAat-COSY [29,30,31,32,33,34,35]. In the experiments, the formation cross section of the η mesic nucleus in the α particle in the d + d fusion reaction is planned to be measured by observing the emitted particles from the decay of the η mesic nucleus below the η production threshold.…”

“…To evaluate these upper limits, the Fermi motion of N * in nucleus [36] is also taken int account. The upper limit for 3 He + p + π − final state is two times larger because of isospin [35]. There were also the data of η production reaction d + d → η + α above the threshold [37,38,39], which are expected to provide the valuable information on the reaction mechanism.…”