Low-energy scattering and photoproduction ofηmesons on three-body nuclei

Abstract

The optical potential approach for low-energy scattering of mesons on three-body nuclei is compared to an exact treatment of the 3N system using four-body scattering theory with separable interactions in s waves only. The higher-order terms including the interaction of the struck nucleon with the surrounding nuclear medium and virtual target excitations in between successive scatterings are found to cause important corrections. Effects of final state interaction in photoproduction on 3 H and 3 He are also studied and sizable contributions beyond the optical model approach are found.

Coherentπ0π0photoproduction on lightest nuclei

“…For example, direct calculations within impulse approximation as described in Refs. [18] and [20], give for the ratio σ γ 3 He→η 3 He /σ γd→ηd in the region of S 11 (1535) the value about 20. The experimental results for the γd → ηd and γ 3 He→ η 3 He cross sections [16,21] indicate, that this ratio is likely to be essentially smaller, about 4.…”

“…It is also interesting to note one special property of photoproduction of two neutral pions on 3 He which is well seen in Eq. (20). Namely, within the approximation, in which only the spherically symmetric spatial part of the 3 He nuclear wave function is taken into account, the protons form a correlated pair with total spin S = 0.…”

Erratum: η-nucleon scattering length and effective range uncertainties [Phys. Rev. C 71, 014001 (2005)]

“…[32]. On the other hand, a refined four-body calculation, [33], based on a Nη scattering amplitude dominated by the N(1535) and fixed to a(f m) = 0.50+i0.32 fm finds A( 3 He η) = 1.82 + i2.75 fm. This difference in ImA( 3 He η) indicates an uncertainty in the absorbtive, subthreshold, Nη scattering amplitude.…”

Photoproduction of mesons off nuclei

“…Previous data from Pfeiffer et al [96]. Theory curves: (blue) dotted and dashed from Shevchenko et al [181] for two different versions of elastic ηN scattering, (red) solid (dash-dotted): Fix and Arenhövel [182] full model (plane wave), (black) long dash-dotted: Tiator et al [183]. Right hand side: excitation functions of π 0 −p back-to-back pairs for different ranges of the opening angle Ψπp after removal of the overall energy dependence ∝ E The left hand side of the figure shows the total cross section for the coherent γ 3 He → η 3 He reaction extracted from the two-photon and three-pion decays of the η-meson.…”

“…In the figure, the data are also compared to the results of different models. The plane-wave models (Tiator and co-workers [183], Fix and Arenhövel [182]) have a completely different energy dependence in the threshold region. The model of Fix and Arenhövel, including final state interactions, reproduces a very steep slope at threshold, but does not agree with the magnitude of the cross section in that region.…”