Systematic few-body analysis of ηd, ηHe3 , and ηH

Abstract

The Alt-Grassberger-Sandhas N -body theory is used to study interaction of η-mesons with d, 3 He, and 4 He. Separable expansion of the subamplitudes is adopted to convert the integral equations into the quasi-two-body form. The resulting formalism is applied to fit the existing data for low-energy η production on few-nucleon targets. On the basis of this fitting procedure the scattering lengths a ηd , a η 3 He , a η 4 He as well as the subthreshold behaviour of the elementary ηN scattering amplitude are obtained.

Resonance-like structure near the $ηd$ threshold in the $γ{d}${$\to$}$π^0η{d}$ reaction

“…for production of an ηd system at low relative momentum p η , where a ηd denotes the ηd scattering length. Using a ηd = 2.16 + i1.25 fm [56] extracted from pn → ηd [28,29], the M ηd distributions are expected as shown in the long-dashed curves (black) in Fig. 2(left), and similar to the decomposed D ηd contributions.…”

“…The solid curve (magenta) shows the fitted function that includes S-wave (blue dashed) and D-wave (cyan twodot-dashed) decay contributions of a BW resonance in the ηd channel with (M, Γ) = (2.425, 0.034) GeV, as well as a contribution from a BW resonance in the π 0 d channel with (M, Γ) = (2.155, 0.110) GeV (red dot-dashed). The longdashed curves (black) are the predicted M ηd distributions with arbitrary normalization using an ηd scattering length of 2.16 + i1.25 fm [56].…”