Meson–nucleus potentials and the search for meson–nucleus bound states

Abstract

Recent experiments studying the meson-nucleus interaction to extract meson-nucleus potentials are reviewed. The real part of the potentials quantifies whether the interaction is attractive or repulsive while the imaginary part describes the meson absorption in nuclei. The review is focused on mesons which are sufficiently long-lived to potentially form meson-nucleus quasi-bound states. The presentation is confined to meson production off nuclei in photon-, pion-, proton-, and lightion induced reactions and heavy-ion collisions at energies near the production threshold. Tools to extract the potential parameters are presented. In most cases, the real part of the potential is determined by comparing measured meson momentum distributions or excitation functions with collision model or transport model calculations. The imaginary part is extracted from transparency ratio measurements. Results on K + , K 0 , K − , η, η , ω, and φ mesons are presented and compared with theoretical predictions. The interaction of K + and K 0 mesons with nuclei is found to be weakly repulsive, while the K − , η, η , ω and φ meson-nucleus potentials are attractive, however, with widely different strengths. Because of meson absorption in the nuclear medium the imaginary parts of the meson-nucleus potentials are all negative, again with a large spread. An outlook on planned experiments in the charm sector is given. In view of the determined potential parameters, the criteria and chances for experimentally observing meson-nucleus quasi-bound states are discussed. The most promising candidates appear to be the η and η mesons.

η′ and η mesons with connection to anomalous glue

“…Early experiments with low statistics using photon (Baskov et al, 2012;Pheron et al, 2012), pion (Chrien et al, 1988), proton (Budzanowski et al, 2009b) or deuteron (Afanasiev et al, 2011;Moskal and Smyrski, 2010) beams gave hints for possible η mesic bound states but no clear signal (Kelkar et al, 2013;Metag et al, 2017). New COSY searches have focused on possible η bound states in 3 He and 4 He (Adlarson et al, 2013(Adlarson et al, , 2017b.…”

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

“…They provide only signals which might be interpreted as indications of the η-mesic nuclei. The interested reader can find recent reviews on the η mesic bound states searches in Refs [4,5,14,16,39,40,41,42,43,44].…”

Mass Modifications of Light Mesons in Nuclear Matter with the Three Flavor Extended Linear Sigma Model

“…The figures clearly show that the mass reduction of the η meson is sensitive to the value ofk 1 . Experimentally, while the η-nucleus interaction is known to be attractive, its binding energy has not been determined well [27]. Our results suggestk 1 ≈ 0 is preferable so as to get an appropriate mass reduction at finite density.…”