Starting from a recent model of the η′N interaction, we evaluate the η′-nucleus optical potential, including the contribution of lowest order in density, tρ/2mη′, together with the second-order terms ...accounting for η′ absorption by two nucleons. We also calculate the formation cross section of the η′ bound states from (π+,p) reactions on nuclei. The η′-nucleus potential suffers from uncertainties tied to the poorly known η′N interaction, which can be partially constrained by the experimental modulus of the η′N scattering length and/or the recently measured transparency ratios in η′ nuclear photoproduction. Assuming an attractive interaction and taking the claimed experimental value |aη′N|=0.1 fm, we obtain an η′ optical potential in nuclear matter at saturation density of Vη′=−(8.7+1.8i) MeV, not attractive enough to produce η′ bound states in light nuclei. Larger values of the scattering length give rise to deeper optical potentials, with moderate enough imaginary parts. For a value |aη′N|=0.3 fm, which can still be considered to lie within the uncertainties of the experimental constraints, the spectra of light and medium nuclei show clear structures associated to η′-nuclear bound states and to threshold enhancements in the unbound region.
.
The
η
mesic nucleus is considered to be one of the interesting exotic many-body systems and has been studied since the 1980s theoretically and experimentally. Recently, the formation of the
η
mesic ...nucleus in the fusion reactions of the light nuclei such as
d
+
d
→
(
η
+
α
)
→
X
has been proposed and the experiments have been performed by WASA-at-COSY. We develop a theoretical model to evaluate the formation rate of the
η
mesic nucleus in the fusion reactions and show the calculated results. We find that the
η
bound states could be observed in the reactions in cases with the strong attractive and small absorptive
η
-nucleus interactions. We compare our results with existing data of the
d
+
d
→
η
+
α
and the
d
+
d
→
3
H
e
+
N
+
π
reactions. We find that the analyses by our theoretical model with the existing data can provide new information on the
η
-nucleus interaction.
A consistent description of the dd→4Heη and dd→ (4Heη)→boundX cross sections was recently proposed with a broad range of real (V0) and imaginary (W0), η−4He optical potential parameters leading to a ...good agreement with the dd→4Heη data. Here we compare the predictions of the model below the η production threshold, with the WASA-at-COSY excitation functions for the dd→3HeNπ reactions to put stronger constraints on (V0,W0). The allowed parameter space (with |V0|<∼ 60 MeV and |W0|<∼7 MeV estimated at 90% CL) excludes most optical model predictions of η−4He nuclei except for some loosely bound narrow states.
We study eta-meson properties in the infinite nuclear matter and in atomic nuclei with an emphasis on effects of the eta coupling to
N
∗
(
1535
)
-nucleon–hole modes. The
N
∗
(
1535
)
resonance, ...which dominates the low-energy eta-nucleon scattering, can be seen as a chiral partner of the nucleon. The change of the chiral mass gap between the
N
∗
and the nucleon in a nuclear medium has an impact on the properties of the eta-nucleus system. If the
N
∗
-nucleon mass gap decreases with a density increase (chiral symmetry restoration) the calculations show the existence of the resonance state at the energy about
60
MeV
and two bound eta-nucleus states with the binding energies about
−
80
MeV
. These states can have strong effect on predicted cross sections of the
12C
(
γ
,
p
)
11B reaction with eta-meson production.
We report on the experimental search for the bound state of an η meson and He3 nucleus performed using the WASA-at-COSY detector setup. In order to search for the η-mesic nucleus decay, the pd→3He2γ ...and pd→3He6γ channels have been analysed. These reactions manifest the direct decay of the η meson bound in a He3 nucleus. This non-mesonic decay channel has been considered for the first time. When taking into account only statistical errors, the obtained excitation functions reveal a slight indication for a possible bound state signal corresponding to a 3He-η nucleus width Γ above 20 MeV and binding energy Bs between 0 and 15 MeV. However, the determined cross sections are consistent with zero in the range of the systematic uncertainty. Therefore, as final result we estimate only the upper limit for the cross section of the η-mesic He3 nucleus formation followed by the η meson decay which varies between 2 nb and 15 nb depending on possible bound state parameters.
We study the formation of deeply bound pionic atoms in the (
d
,
3
He) reactions theoretically and show the energy spectra of the emitted
3
He at finite angles, which are expected to be observed ...experimentally. We find that the different combinations of the pion-bound and neutron-hole states dominate the spectra at different scattering angles because of the matching condition of the reaction. We conclude that the observation of the (
d
,
3
He) reaction at finite angles will provide the systematic information of the pionic bound states in each nucleus and will help to develop the study of the pion properties and the partial restoration of chiral symmetry in nuclei.
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.
In a search for ω mesic states, the production of ω-mesons in coincidence with forward going protons has been studied in photon induced reactions on 12C for incident photon energies of 1250–3100 MeV. ...The π0γ pairs from decays of bound or quasi-free ω-mesons have been measured with the CBELSA/TAPS detector system in coincidence with protons registered in the MiniTAPS forward array. Structures in the total energy distribution of the π0γ pairs, which would indicate the population and decay of bound ω11B states, are not observed. The π0γ cross section of 0.3 nb MeV−1 sr−1 observed in the bound state energy regime between −100 and 0 MeV may be accounted for by yield leaking into the bound state regime because of the large in-medium width of the ω-meson. A comparison of the measured total energy distribution with calculations suggests the real part V0 of the ω11B potential to be small and only weakly attractive with V0(ρ=ρ0)=−15±35(stat)±20(syst) MeV in contrast to some theoretical predictions of attractive potentials with a depth of 100–150 MeV.
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