Mutual entrainment effects in cold neutron-proton mixtures are studied in the framework of the self-consistent nuclear energy-density functional theory. Exact expressions for the mass currents, valid for both homogeneous and inhomogeneous systems, are directly derived from the time-dependent Hartree-Fock equations with no further approximation. The equivalence with the Fermi-liquid expression is also demonstrated. Focusing on neutron-star cores, a convenient and simple analytical formulation of the entrainment matrix in terms of the isovector effective mass is found, thus allowing one to relate entrainment phenomena in neutron stars to isovector giant dipole resonances in finite nuclei. Results obtained with different functionals are presented. These include the Brussels-Montreal functionals, for which unified equations of state of neutron stars have been recently calculated.

We report first precision mass measurements of the $1/2^{-}$ isomeric and $9/2^{+}$ ground states of ${}^{101}\mathrm{In}$. The determined isomeric excitation energy continues a smooth trend of odd-$A$ indium isotopes up to the immediate vicinity of $N=50$ magic number. This trend can be confirmed by dedicated shell-model calculations only if the neutron configuration mixing is considered. We find that the single-particle energies are different for different states of the same isotope. The presented configuration-dependent shell evolution, type-II shell evolution, in odd-$A$ nuclei is discussed for the first time. Our results will facilitate future studies of single-particle neutron states.

We report on the measurement of the beam asymmetry $\mathrm{\Sigma }$ for the reactions $\vec{\gamma }p\to p\eta$ and $\vec{\gamma }p\to p{\eta }^{\prime }$ from the GlueX experiment using an 8.2–8.8-GeV linearly polarized tagged photon beam incident on a liquid hydrogen target in Hall D at Jefferson Laboratory. These measurements are made as a function of momentum transfer $-t$ with significantly higher statistical precision than our earlier $\eta$ measurements and are the first measurements of ${\eta }^{\prime }$ in this energy range. We compare the results to theoretical predictions based on $t$-channel quasiparticle exchange. We also compare the ratio of ${\mathrm{\Sigma }}_{\eta }$ to ${\mathrm{\Sigma }}_{{\eta }^{\prime }}$ to these models as this ratio is predicted to be sensitive to the amount of $s\overline{s}$ exchange in the production. We find that photoproduction of both $\eta$ and ${\eta }^{\prime }$ is dominated by natural parity exchange with little dependence on $-t$.

We study the properties of hot $\beta$-stable nuclear matter using equations of state derived within the Brueckner-Hartree-Fock approach at finite temperature including consistent three-body forces. Simple and accurate parametrizations of the finite-temperature equations of state are provided. The adiabatic index is analyzed in some detail. The properties of hot neutron stars are then investigated within this framework, in particular, the temperature dependence of the maximum mass. We find very small temperature effects and analyze the interplay of the different contributions.

We perform a quantitative study of the microscopic effective shell-model interactions in the valence $sd$ shell, obtained from modern nucleon-nucleon potentials, chiral N3LO, JISP16, and Daejeon16, using no-core shell-model wave functions and the Okubo-Lee-Suzuki transformation. We investigate the monopole properties of those interactions in comparison with the phenomenological universal $sd$-shell interaction, USDB. Theoretical binding energies and low-energy spectra of O isotopes and of selected $sd$-shell nuclei, are presented. We conclude that there is a noticeable improvement in the quality of the effective interaction when it is derived from the Daejeon16 potential. We show that its proton-neutron centroids are consistent with those from USDB. We then propose monopole modifications of the Daejeon16 centroids in order to provide an adjusted interaction yielding significantly improved agreement with the experiment. A spin-tensor decomposition of two-body effective interactions is applied in order to extract more information on the structure of the centroids and to understand the reason for deficiencies arising from our current theoretical approximations. The issue of the possible role of the three-nucleon forces is addressed.

Background: The nuclear shape is a macroscopic feature of an atomic nucleus that is sensitive to the underlying nuclear structure in terms of collectivity and the interaction between nucleons. Therefore, the evolution of nuclear shapes has attracted many theoretical and experimental nuclear structure studies. The structure of the $A\approx 70, N\approx Z$ nuclei, lying far from the stability line, is interesting because a particularly strong proton-neutron correlation may occur here due to the occupation of the same orbits by nucleons of both types. In this region, different particle configurations drive a nucleus towards various deformed shapes: prolate, oblate, octupole, or nonaxial. These nuclear shapes change rapidly with nucleon number and also with angular momentum. This is reflected by a presence of different structures (bands) of excited states which exhibit a broad range of lifetimes.

Purpose: The aim of this paper is to determine lifetimes of some high-spin excited states in ${}^{69}\mathrm{As}$ and ${}^{66}\mathrm{Ge}$ nuclei to examine the shape evolution in these neutron-deficient nuclei.

Methods: Lifetimes of high-spin states in ${}^{69}\mathrm{As}$ and ${}^{66}\mathrm{Ge}$ have been measured by using the Doppler-shift attenuation technique with the GASP and recoil filter detector setup at the Laboratori Nazionali di Legnaro. The nuclei of interest were produced in the ${}^{32}\mathrm{S}\left(95\text{MeV}\right)+0.8{\mathrm{mg}/\mathrm{cm}}^2 {}^{40}\mathrm{Ca}$ fusion-evaporation reaction. The strongest reaction channels $3p$ and $\alpha 2p$ led to the ${}^{69}\mathrm{As}$ and ${}^{66}\mathrm{Ge}$ final nuclei, respectively. Using $\gamma -\gamma$-recoil coincidences we were able to determine very short lifetimes (in the femtosecond range) in the residual nuclei of interest.

Results: In ${}^{69}\mathrm{As}$, the extracted lifetimes are $\tau =72$ ($-32, +45$) fs for the $33/2^{+}$ state at 7897 keV and $\tau <85$ fs for the $37/2^{+}$ state at 9820 keV. For the ${}^{66}\mathrm{Ge}$ case, the lifetime of the ${11}^{-}$ state at 7130 keV is $\tau =122(\pm 41)$ fs. Lifetimes in ${}^{69}\mathrm{As}$ and ${}^{66}\mathrm{Ge}$ reported in this paper have been measured for the first time in the present experiment.

Conclusions: The results are discussed in the terms of deformation and shape evolution in ${}^{69}\mathrm{As}$ and ${}^{66}\mathrm{Ge}$. The quadrupole moments deduced from the measured lifetimes were compared with the cranked Woods-Saxon-Strutinsky calculations by means of the total Routhian surface method. It turns out that Band 3 in ${}^{69}\mathrm{As}$ shows an oblate-prolate shape transition, and above spin $33/2^{+}$ it corresponds to a prolate collective structure with ${\beta }_2\approx 0.27$ and $\gamma \approx {20}^{\circ }$. In turn, in ${}^{66}\mathrm{Ge}$ the negative-parity band built on the $7^{-}$ state at 4205 keV corresponds to a triaxial shape with ${\beta }_2=0.33$ and $\gamma ={31}^{\circ }$. Analysis of the transitional quadrupole moments derived from the experimental and theoretical ones points to a significant change of deformation in the ${}^{69}\mathrm{As}$ and ${}^{66}\mathrm{Ge}$ nuclei with increasing rotational frequency.

Excited levels in ${}^{87}\mathrm{Br}$, populated in $\beta$ decay of ${}^{87}\mathrm{Se}$, have been studied by means of $\gamma$-ray spectroscopy using an array of broad energy Ge detectors. ${}^{87}\mathrm{Se}$ nuclei were produced by irradiating a natural Th target with 25-MeV protons. Fission products were extracted from the target chamber using the IGISOL technique, then separated on a dipole magnet and Penning trap (JYFLTRAP) setup. The scheme of excited levels of ${}^{87}\mathrm{Br}$ has been significantly extended. 114 new transitions and 51 new levels were established. $\beta$ feedings and $log\left(ft\right)$ values of levels were determined. The upper limit for $\beta$ feeding to the ground state of ${}^{87}\mathrm{Br}$ was determined to be 23(5)%. Ground state spin and parity $5/2^{-}$ was confirmed, as suggested by previous studies. We also confirm the low-energy excited state at 6.02 keV. The ground state and two lowest excited states in ${}^{87}\mathrm{Br}$ were interpreted as the ${\left(\pi f_{5/2}\right)}_{j,j-1,j-2}^3$ triplet produced by the so-called anomalous coupling. The 333.61- and 699.26-keV levels were interpreted as $\pi p_{3/2}$ and $\pi p_{1/2}$ single-particle excitations. The $9/2^{+}$ level reported previously as corresponding to the $\pi g_{9/2}$ single-particle excitation is proposed to be an isomer with half-life 20 ns. Large-scale shell-model calculations performed in this work are in good agreement with experimental results.

A hybrid model is proposed which combines the nuclear structure part from configuration-interaction (CI) calculations and the emission dynamics from a three-body approach. By normalizing the partial half-lives from the three-body model with CI amplitudes, we can reasonably well reproduce all known experimental two-proton ($2p$) emission half-lives, except for ${}^{67}\mathrm{Kr}$. For the purpose of the present paper, the full body of experimental $2p$ radioactivity data for nuclei for which the half-life and the $2p$ emission branching ratio are experimentally known has been analyzed in our hybrid model.

An upgraded ion-guide system for the production of neutron-deficient isotopes with heavy-ion beams has been commissioned at the IGISOL facility with an ${}^{36}\mathrm{Ar}$ beam on a ${}^{\mathrm{nat}}\mathrm{Ni}$ target. It was used together with the JYFLTRAP double Penning trap to measure the masses of ${}^{82}\mathrm{Zr}, {}^{84}\mathrm{Nb}, {}^{86}\mathrm{Mo}, {}^{88}\mathrm{Tc}$, and ${}^{89}\mathrm{Ru}$ ground states and the isomeric state ${}^{88}\mathrm{Tc}^m$. Of these, ${}^{89}\mathrm{Ru}$ and ${}^{88}\mathrm{Tc}^m$ were measured for the first time. The precision of measurements of ${}^{82}\mathrm{Zr}, {}^{84}\mathrm{Nb}$, and ${}^{88}\mathrm{Tc}$ was significantly improved. The literature value for ${}^{86}\mathrm{Mo}$ was verified. The measured states in ${}^{88}\mathrm{Tc}$ were compared to shell-model calculations and additional constraints on the spins and level scheme were obtained. The masses of ${}^{82}\mathrm{Mo}$ and ${}^{86}\mathrm{Ru}$ have been predicted using the measured masses of their mirror partners and theoretical mirror displacement energies, resulting in more tightly bound nuclei with smaller atomic mass uncertainties than reported in the literature.

Effects of quantum statistics for nuclear matter equation of state are analyzed in terms of the recently proposed quantum van der Waals model. The system pressure is expanded over a small parameter $\delta \propto n{\left(mT\right)}^{-3/2}{\left[g(1-bn)\right]}^{-1}$, where $n$ and $T$ are, respectively, the particle number density and temperature, $m$ and $g$ the particle mass and degeneracy factor. The parameter $b$ corresponds to the van der Waals excluded volume. The corrections due to quantum statistics for the critical point values of $T_c, n_c$, and the critical pressure $P_c$ are found within the linear and quadratic orders over $\delta$. These approximate analytical results appear to be in a good agreement with exact numerical calculations in the quantum van der Waals model for interacting Fermi particles: the symmetric nuclear matter ($g=4$) and the pure neutron matter ($g=2$). They can be also applied to the system of interacting Bose particles like the matter composed of $\alpha$ nuclei.

Herein, we present a theoretical study of how Fermi-surface distortion affects symmetric nuclear matter, pure neutron matter, and neutron-star matter. The results indicate that, for the binding energy of symmetric nuclear matter, the generally accepted value extracted from the Bethe-Weizäcker mass formula for nuclei can constrain the degree of anisotropy because of Fermi-surface deformation $\delta \lesssim 0.05$. The value of $\delta$ starts to affect the stiffness of the equation of state for symmetric nuclear matter and pure neutron matter when $\delta \gtrsim 0.01$. Moreover, if the Fermi surface is distorted, the results indicate that neutron stars can be deformed into an oblate shape. This deformation depends on two factors: the stiffness of the corresponding equation of state and value of $\delta$. The corresponding deformation near the maximum neutron-star mass comes from the anisotropic pressure within these stars, which is caused by the distortion of Fermi surface predicted by the equation of state of the models.

Thanks to Schwinger [Phys. Rev. 73, 407 (1948)], the process of elastic scattering of neutrons by nuclei is known to depend on the interference between a nuclear amplitude and an electromagnetic one for small scattering angles, resulting in spin asymmetries of a cross section or in polarization of the scattered neutrons. Although this interference depends on the neutron's transverse polarization and on an imaginary part of the nuclear amplitude, this conclusion holds only for the incident plane-wave neutrons with a definite momentum. Here, we show that this scattering is altered when the twisted neutrons, recently obtained experimentally, are used instead—that is, neutrons with an orbital angular momentum. For bulk targets, the angular distributions of the scattered neutrons get modified, whereas scattering of a superposition of states with the different angular momenta also reveals dependence on the longitudinal polarization. For well-localized targets, the observables develop dependence on the neutron's helicity and on a real part of the nuclear amplitude, providing full access to its phase already in the Born approximation. We argue that the corresponding spin asymmetries are measurable at existing neutron facilities. Thus, scattering of the twisted neutrons by nuclei can provide means for quantum tomography of the neutron states and become a useful tool for hadronic studies, low-energy nuclear physics, tests of fundamental symmetries, and neutron optics.

We report on high-statistics data from the ${\beta }^{-}$ decay of the ${}^{46}\mathrm{K}{J}^{\pi }=2^{-}$ ground state taken with the GRIFFIN spectrometer located at the TRIUMF-ISAC facility. In total, 199 $\gamma$ rays and 42 excited states were placed in the level scheme, and from the observed $\beta$ feeding and angular correlations of pairs of cascading $\gamma$ rays, it was possible to assign spins and parities to excited states and determine mixing ratios for selected $\gamma$ rays. The level structure of ${}^{46}\mathrm{Ca}$ is compared to theoretical predictions from a microscopic valence-space Hamiltonian derived from two- and three-nucleon forces. These calculations are in reasonable agreement with the experimental data and indicate that the protons in this region are not as inert as would be expected for semimagic nuclei.

In a recent work [Phys. Rev. C 97, 044619 (2018)], a universal odd-even staggering (OES) has been observed in isotopic cross sections of neutron-rich nuclei produced by various fragmentation and spallation reactions. However, the universality of this OES is not clear for neutron-deficient nuclei, and thus more quantitative studies of this OES effect are required for these nuclei from different reactions. For neutron-deficient nuclei with ($N-Z$) from 0 to $-4$, the OES magnitudes are calculated by a third-order difference formula using cross sections measured in various fragmentation and spallation systems and they are applied to derive the evaluation values of the OES magnitudes. The evaluated OES magnitudes for both neutron- and proton-rich nuclei are benchmarked with some additional experimental data from fragmentation as well as spallation reactions. Furthermore, the OES factors predicted by two recent fragmentation and spallation models are checked by comparing with the OES magnitudes evaluated from extensive experimental data. This comparison suggests that the OES factors in these fragmentation and spallation models should be improved to reproduce measured cross sections.

Background: High-momentum nucleons in a nuclear environment can be associated with short-range correlations (SRC) that primarily occur between nucleon pairs. Observations and theoretical developments have indicated that the SRC properties can be captured by general quantitative principles that are subject to model dependence upon quantification. The variations in the aggregated effect of SRC across nuclei, however, can be quantified in an approximately model-independent fashion in terms of the so-called SRC scaling factors that capture the aggregated effect of SRC for a specific nucleus $A$ relative to the deuteron ($A$-to-$d$).

Purpose: We aim to provide predictions for the SRC scaling factors across the nuclear periodic table and determine the relative contribution of the different nucleon pair combinations to this quantity. We will also determine the SRC scaling factors for both bound protons and bound neutrons and study how these quantities evolve with the neutron-to-proton ($\frac{N}{Z}$) ratio in asymmetric nuclei.

Methods: We employ the low-order correlation operator approximation (LCA) to compute the SRC contribution to the single-nucleon momentum distribution and ratios of $A$-to-$d$ momentum distributions. We do this for a sample of fifteen nuclei from He to Pb, thereby gaining access to the evolution of the SRC scaling factor with the nuclear mass $4\le A\le 208$ and the neutron-to-proton ratio $1.0\le \frac{N}{Z}\le 1.54$.

Results: We provide evidence for approximate $A$-to-$d$ scaling of the single-nucleon momentum distribution at nucleon momenta exceeding about $4{\mathrm{fm}}^{-1}$. For the studied sample of fifteen nuclei, the total SRC scaling factor is in the range 4.05–5.14, of which roughly 3 can be attributed to proton-neutron ($pn$) correlations. The SRC scaling factors receive sizable contributions from $pp$ and $nn$ correlations. They depend on the $\left(\frac{N}{Z}\right)$ ratio reflecting the fact that the minority species (protons) becomes increasingly more short-range correlated with increasing $\left(\frac{N}{Z}\right)$. We compare the computed SRC scaling factors in the LCA with those of ab initio calculations and with measured quantities from SRC-sensitive inclusive electron-scattering data.

Conclusions: It is shown that the LCA provides predictions for the SRC scaling factors across the nuclear table that are in line with measured values. In asymmetric nuclei there are sizable differences between the SRC scaling factors for protons and neutrons. It is suggested that this phenomenon may impact the variations of the magnitude of the European Muon Collaboration (EMC) effect across nuclei. Our results corroborate the finding that SRC physics can be qualitatively understood by universal principles that build on local modifications of mean-field wave functions of nucleon pairs.

The system-size dependence of hadrochemistry at vanishing baryon density is considered within the canonical statistical model (CSM) with local exact conservation of three conserved charges, allowing for a possibility of strangeness undersaturation, i.e., ${\gamma }_S\le 1$. Exact baryon number conservation is found to be even more important than that of strangeness in the canonical suppression picture at the CERN Large Hadron Collider, in contrast to intermediate and low collision energies. The model is applied to $p\text{−}p$, $p$-Pb, and Pb-Pb data of the ALICE Collaboration. A chemical equilibrium CSM with a fixed $T_{\mathrm{ch}}=155$ MeV describes the trends seen in most yield ratios. However, this “vanilla” version of CSM predicts an enhancement of the $\varphi /\pi$ ratio at smaller multiplicities, in stark contrast to the suppression seen in the data. The data are described with a 15% relative accuracy level whence a multiplicity dependence of both the temperature and the strangeness saturation parameter ${\gamma }_S\le 1$ is accepted. Both the canonical suppression and the strangeness undersaturation effects are small at $d{N}_{\mathrm{ch}}/d\eta \gtrsim 100$, but they do improve substantially the description of hadron yields in $p\text{−}p$ collisions, in particular the $\mathrm{\Omega }$ yields. A possibility to constrain the rapidity correlation volume using net-proton fluctuation measurements is pointed out.

We use a thermal model with single freeze-out to determine longitudinal polarization of $\mathrm{\Lambda }$ hyperons emitted from a hot and rotating hadronic medium. We consider the top RHIC energies and use the model parameters determined in the previous analyses of particle spectra and elliptic flow. Using a direct connection between the spin polarization tensor and thermal vorticity, we reproduce earlier results which indicate a quadrupole structure of the longitudinal component of the polarization three-vector with an opposite sign compared to that found in the experiment. We further use only the spatial components of the thermal vorticity in the laboratory system to define polarization and show that this leads to the correct sign and magnitude of the quadrupole structure. This procedure resembles a non-relativistic connection between the polarization three-vector and vorticity employed in other works. In general, our results bring further evidence that the spin polarization dynamics in heavy-ion collisions may be not directly related to the thermal vorticity. The additional material explains the construction of the hydrodynamically consistent gradients of fluid velocity and temperature in thermal models with the help of the perfect-fluid equations of motion.

The process at the heart of neutrinoless double-$\beta$ decay, $nn\to pp{e}^{-}{e}^{-}$ induced by a light Majorana neutrino, is investigated in pionless and chiral effective field theory. We show in various regularization schemes the need to introduce a short-range lepton-number-violating operator at leading order, confirming earlier findings. We demonstrate that such a short-range operator is only needed in spin-singlet $S$-wave transitions, while leading-order transitions involving higher partial waves depend solely on long-range currents. Calculations are extended to include next-to-leading-order corrections in perturbation theory, where to this order no additional undetermined parameters appear. We establish a connection based on chiral symmetry between neutrinoless double-$\beta$ decay and nuclear charge-independence breaking induced by electromagnetism. Data on the latter confirm the need for a leading-order short-range operator but do not allow for a full determination of the corresponding lepton-number-violating coupling. Using a crude estimate of this coupling, we perform ab initio calculations of the matrix elements for neutrinoless double-$\beta$ decay for ${}^6\mathrm{He}$ and ${}^{12}\mathrm{Be}$. We speculate on the phenomenological impact of the leading short-range operator on the basis of these results.

I have compared the proton closed-shell ($Z=50$) nucleus ${}^{116}\mathrm{Sn}$ with its neighbor ${}^{114}\mathrm{Cd}$, which has $Z=48$. In both energies and $E2$ strengths, both large similarities and major differences are pointed out. I have estimated mixing of the lowest $0^{+}$ and $2^{+}$ states with the sum of second and third states of each $J^{\pi }$. Mixing is much larger in ${}^{114}\mathrm{Cd}$ than in ${}^{116}\mathrm{Sn}$.

Nucleon momentum distributions at various densities and isospin asymmetries for nuclear matter are investigated systematically within the extended Brueckner-Hartree-Fock approach. The shapes of the normalized momentum distributions varying with $k/k_F$ are practically identical, while the density- and isospin-dependent magnitude of the distribution is directly related to the depletion of the Fermi sea. Based on these properties, a parametrized formula is proposed with the parameters calibrated to the calculated result.