Formation of mesic nuclei by reactions

Abstract

We present a theoretical study on formation rates of η and ω meson-nucleus systems induced by (γ, p) reactions on nuclear targets at ideal recoilless condition. We find that the smaller distortion effect in the (γ, p) reaction enables us to investigate properties of the mesons created deeply inside nucleus more clearly. We also consider excitation of scalar-isoscalar (σ) mode in nucleus in order to investigate spectral enhancement around two-pion threshold caused by partial restoration of chiral symmetry. We conclude that valuable information of meson-nucleus interactions can be extracted from global structure of the missing mass spectra in the (γ, p) reaction.

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

“…21, where the acceptable region of V 0 , W 0 values can be easily understood for each value of the upper limit of the height of the structure in the conversion spectra such as shown in Figs. [17][18][19][20]. From this figure, the upper limit reported in Ref.…”

“…Stimulated by this theoretical result, there have been many studies of the structure and the formation reactions of the η mesic nucleus [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24]. Recently, the η-nucleon and η-nucleus interactions have been studied theoretically in the context of the chiral symmetry of the strong interaction and the η mesic nucleus can be considered as one of the interesting objects to investigate the aspects of the chiral symmetry at finite density [9,12,13,14,15,18,20,23]. As for the experimental studies, the first attempt to observe the η mesic nucleus was performed by the (π + , p) reaction with finite momentum transfer [2], and the interpretation of the data is still controversial [23].…”

Formation ofη′(958)-mesic nuclei by the (p,d) reaction

“…In contrast to the φ meson, we find that the ω meson production gives larger contribution to the η ′ bound region. Although it is still unknown whether the ω-nucleus interaction is attractive or repulsive, we consider the case that the ω-nucleus optical potential is repulsive as V ω = −(−42.8 + 19.5i)ρ(r)/ρ 0 MeV [34,40] because in the repulsive case the quasi-free ω contribution above the ω production threshold is enhanced and then it overlaps the η ′ bound region [15]. The elementary cross section of pn → dω in laboratory frame with T p = 2.6 GeV is estimated as 27 µb/sr by using the experimental data [41].…”

Experimental results on theω- andη′-nucleus potential - on the way to mesic states

“…the width of possible η mesic states is expected to be much smaller than the depth of the potential. Motivated by the present experimental results and earlier theoretical predictions [30][31][32], three experiments have been launched to search for η bound states using hadron and photon beams. At the Fragment Separator FRS at GSI the 12 C(p, d) reaction has been studied in a search for η mesic states by missing mass spectrometry with a resolution of 1.6 MeV/c 2 [33].…”