Precision Study of theηHe3System Using thedp→He3η

Studies of Mesic Nuclei via Decay Reactions

“…The existence of such states has been elusive, however. At this moment, the experimental evidence is rather indirect, getting the most clear indication from the measurements of pd → η 3 He [3,4] and of dp → η 3 He [5,6], and from the realization [7] that the rapid slope of the cross section close to threshold may be a signal of a quasi-bound state. The same behavior of the total cross section was also confirmed in the photon induced reaction γ 3 He → η 3 He [8].…”

Investigation of the $^3$He--$\eta $ System with Polarised Beams at ANKE

“…which has the desired linear dependence on cos θ η observed in the data [1]. The scattering amplitudes |f | 2 extracted from the unpolarised data close to threshold as well as a fit to the data up to Q = 11.3 MeV, i.e.…”

“…Earlier high-precision measurements performed at the COSY-ANKE facility on the reaction dp → 3 He η resulted in a rich data set of differential cross sections as well as in 195 total cross sections for the first 11 MeV excess energy above threshold [1]. The very small relative systematic errors resulting from the measurement of the excitation function in a single experiment led to a robust data set for detailed analyses on the final state interaction of the η- 3 He system.…”

“…[1] considers s-and p-waves in the final state as well as a strong final state interaction. Here, it can be shown that there are two independent dp → 3 He η s-wave amplitudes (A and B) [3] and five p-wave amplitudes close to threshold.…”

Search for $\eta $-mesic Nuclei with WASA-at-COSY

“…expressed as η-nucleus scattering length. Although, such studies [19][20][21][22] provided important experimental indications in the case of 3 He and 4 He systems, where they showed the existence of an s-wave pole in the scattering matrix, they are not able to give the decisive answer whether the pole corresponds to a virtual or bound state as it was stated by [23]. The second category contains direct-search methods, which look for a subthreshold manifestation of a bound state in the excitation functions for chosen decay modes.…”