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.
ABSTRACT We report extragalactic observations of two fluorine-bearing species, hydrogen fluoride (HF) and fluoronium (H2F+), in the z = 0.89 absorber in front of the lensed blazar PKS 1830−211 with ...the Atacama Large Millimeter/submillimeter Array. HF was detected toward both southwest and northeast images of the blazar, with column densities >3.4 × 1014 cm−2 and 0.18 × 1014 cm−2, respectively. H2F+ was not detected, down to an upper limit (3 ) of 8.8 × 1011 cm−2 and an abundance ratio of H2F+/HF 1/386. We also searched for H2F+ toward the Galactic sources NGC 6334 I and W51C, and toward Galactic center clouds with the Herschel HIFI spectrometer.6 The upper limit on the column density was derived to be 2.5 × 1011 cm−2 in NGC 6334 I, which is 1/68 of that for H2Cl+. In constrast, the ortho transition of H2Cl+ is detected toward PKS 1830-211. To understand the small abundance of interstellar H2F+, we carried out laboratory experiments to determine the rate constants for the ion-electron recombination reaction by infrared time-resolved spectroscopy. The constants determined are ke(209 K) = cm3 s−1 and cm3 s−1 for H2F+ and H2Cl+, respectively. The difference in the dissociative recombination rates between H2F+ and H2Cl+ by a factor ∼2 and the cosmic abundance ratio F/Cl 1/6 are not enough to explain the much smaller abundance of H2F+. The difference in the formation mechanism of H2F+ and H2Cl+ in interstellar space would be a major factor in the small abundance of H2F+.
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 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.
PDF
