Glauber models based on nucleon-nucleon interactions are commonly used to characterize the initial state in high-energy nuclear collisions and the dependence of its properties on impact parameter or number of participating nucleons. In this paper, an extension to the Glauber model is presented, which accounts for an arbitrary number of effective subnucleon degrees of freedom, or active constituents, in the nucleons. Properties of the initial state, such as the number of constituent participants and collisions, as well as eccentricity and triangularity, are calculated and systematically compared for different assumptions of how to distribute the subnuclear degrees of freedom and for various collision systems. It is demonstrated that at high collision energy the number of produced particles scales with an average number of subnucleon degrees of freedom of between 3 and 5. The source codes for the constituent Monte Carlo Glauber extension, as well as for the calculation of the overlap area and participant density in a standard Glauber model, are made publicly available.

Recent measurements of jet production rates at large transverse momentum ($p_T$) in the collisions of small projectiles with large nuclei at the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider indicate that they have an unexpected relationship with estimates of the collision centrality. One compelling interpretation of the data is that they capture an $x_p$-dependent decrease in the average interaction strength of the nucleon in the projectile undergoing a hard scattering. A weakly interacting or “shrinking” nucleon in the projectile strikes fewer nucleons in the nucleus, resulting in a particular pattern of centrality-dependent modifications to high-$p_T$ processes. We describe a simple one-parameter geometric implementation of this picture within a modified Monte Carlo Glauber model tuned to $d+\mathrm{Au}$ jet data, and explore two of its major consequences. First, the model predicts a particular projectile-species effect on the centrality dependence at high $x_p$, opposite to that expected from a final state energy loss effect. Second, we find that some of the large centrality dependence observed for forward dihadron production in $d+\mathrm{Au}$ collisions at RHIC may arise from the physics of the “shrinking” projectile nucleon, in addition to impact parameter dependent shadowing or saturation effects at low nuclear $x$. We conclude that analogous measurements in recently collected $p+\mathrm{Au}$ and ${}^3\mathrm{He}+\mathrm{Au}$ collision data at RHIC can provide a unique test of these predictions.

We investigate the possibility of ultracold neutron (UCN) storage in quantum states defined by the combined potentials of the Earth's gravity and the neutron optical repulsion by a horizontal surface of liquid helium. We analyze the stability of the lowest quantum state, which is most susceptible to perturbations due to surface excitations, against scattering by helium atoms in the vapor and by excitations of the liquid, comprised of ripplons, phonons, and surfons. This is an unusual scattering problem since the kinetic energy of the neutron parallel to the surface may be much greater than the binding energies perpendicular. The total scattering time of these UCNs at $0.7$ K is found to exceed 1 h, and rapidly increases with decreasing temperature. Such low scattering rates should enable high-precision measurements of the sequence of discrete energy levels, thus providing improved tests of short-range gravity. The system might also be useful for neutron $\beta$-decay experiments. We also sketch new experimental propositions for level population and trapping of ultracold neutrons above a flat horizontal mirror.

One of the greatest questions for modern physics to address is how elements heavier than iron are created in extreme astrophysical environments. A particularly challenging part of that question is the creation of the so-called $p$-nuclei, which are believed to be mainly produced in some types of supernovae. The lack of needed nuclear data presents an obstacle in nailing down the precise site and astrophysical conditions. In this work, we present for the first time measurements on the nuclear level density and average $\gamma$ strength function of ${}^{92}\mathrm{Mo}$. State-of-the-art $p$-process calculations systematically underestimate the observed solar abundance of this isotope. Our data provide stringent constraints on the ${}^{91}\mathrm{Nb}(p,\gamma ){}^{92}\mathrm{Mo}$ reaction rate, which is the last unmeasured reaction in the nucleosynthesis puzzle of ${}^{92}\mathrm{Mo}$. Based on our results, we conclude that the ${}^{92}\mathrm{Mo}$ abundance anomaly is not due to the nuclear physics input to astrophysical model calculations.

The Lippmann-Schwinger equation for the nucleon-nucleon $t$ matrix as well as the corresponding Bethe-Goldstone equation to determine the Brueckner reaction matrix in nuclear matter are reformulated in terms of the resolvents for the total two-nucleon Hamiltonians defined in free space and in medium correspondingly. This allows one to find solutions at many energies simultaneously by using the respective Hamiltonian matrix diagonalization in the stationary wave-packet basis. Among other important advantages, this approach simplifies greatly the whole computation procedures both for the coupled-channel $t$ matrix and the Brueckner reaction matrix. Therefore this principally novel scheme is expected to be especially useful for self-consistent nuclear matter calculations because it allows one to accelerate in a high degree single-particle potential iterations. Furthermore the method provides direct access to the properties of possible two-nucleon bound states in the nuclear medium. The comparison between reaction matrices found via the numerical solution of the Bethe-Goldstone integral equation and the straightforward Hamiltonian diagonalization shows a high accuracy of the method suggested. The proposed fully discrete approach opens a new way to an accurate treatment of two- and three-particle correlations in nuclear matter on the basis of the three-particle Bethe-Faddeev equation by an effective Hamiltonian diagonalization procedure.

Background: The fission processes of thermal excited nuclei are conventionally studied by statistical models which rely on inputs of phenomenological level densities and potential barriers. Therefore the microscopic descriptions of spontaneous fission and induced fission are very desirable for a unified understanding of various fission processes.

Purpose: We propose to study the fission rates, at both low and high temperatures, with microscopically calculated temperature-dependent fission barriers and collective mass parameters.

Methods: The fission barriers are calculated by the finite-temperature Skyrme-Hartree-Fock+BCS method. The mass parameters are calculated by the temperature-dependent cranking approximation. The thermal fission rates can be obtained by the imaginary free energy approach at all temperatures, in which fission barriers are naturally temperature dependent. The fission at low temperatures can be described mainly as a barrier-tunneling process. While the fission at high temperatures has to incorporate the reflection above barriers.

Results: Our results of spontaneous fission rates reasonably agree with other studies and experiments. The temperature dependencies of fission barrier heights and curvatures have been discussed. The temperature dependent behaviors of mass parameters have also been discussed. The thermal fission rates from low to high temperatures with a smooth connection have been given by different approaches.

Conclusions: Since the temperature dependencies of fission barrier heights and curvatures, and the mass parameters can vary rapidly for different nuclei, the microscopic descriptions of thermal fission rates are very valuable. Our studies without free parameters provide a consistent picture to study various fissions such as that in fast-neutron reactors, astrophysical environments, and fusion reactions for superheavy nuclei.

We investigated the ${}^{238}\mathrm{U}\left(d,p\right)$ reaction as a surrogate for the $n+{}^{238}\mathrm{U}$ reaction. For this purpose we measured for the first time the $\gamma$-decay and fission probabilities of ${}^{239}\mathrm{U}^{*}$ simultaneously and compared them to the corresponding neutron-induced data. We present the details of the procedure to infer the decay probabilities, as well as a thorough uncertainty analysis, including parameter correlations. Calculations based on the continuum-discretized coupled-channels method and the distorted-wave Born approximation (DWBA) were used to correct our data from detected protons originating from elastic and inelastic deuteron breakup. In the region where fission and $\gamma$ emission compete, the corrected fission probability is in agreement with neutron-induced data, whereas the $\gamma$-decay probability is much higher than the neutron-induced data. We have performed calculations of the decay probabilities with the statistical model and of the average angular momentum populated in the ${}^{238}\mathrm{U}\left(d,p\right)$ reaction with the DWBA to interpret these results.

We evaluate the Fermi and Gamow-Teller (GT) matrix elements in tritium $\beta$ decay by including in the charge-changing weak current the corrections up to one loop recently derived in nuclear chiral effective field theory ($\chi \mathrm{EFT}$). The trinucleon wave functions are obtained from hyperspherical-harmonics solutions of the Schrödinger equation with two- and three-nucleon potentials corresponding to either $\chi \mathrm{EFT}$ (the N3LO/N2LO combination) or meson-exchange phenomenology (the AV18/UIX combination). We find that contributions due to loop corrections in the axial current are, in relative terms, as large as (and in some cases, dominate) those from one-pion exchange, which nominally occur at lower order in the power counting. We also provide values for the low-energy constants multiplying the contact axial current and three-nucleon potential, required to reproduce the experimental GT matrix element and trinucleon binding energies in the N3LO/N2LO and AV18/UIX calculations.

Isoscalar monopole transitions from the ground states to cluster states in ${}^{10}\mathrm{Be}$ and ${}^9\mathrm{Li}$ are investigated using ${}^6\mathrm{He}+\alpha$ and ${}^6\mathrm{He}+t$ cluster models, respectively. In ${}^{10}\mathrm{Be}$, significant monopole strengths are obtained for ${}^6\mathrm{He}+\alpha$ cluster resonances of ${}^{10}\mathrm{Be}\left(0_{3,4}^{+}\right)$ above the $\alpha$-decay threshold, whereas the strengths for ${}^6\mathrm{He}+t$ cluster resonances in ${}^9\mathrm{Li}$ are not enhanced because of the large fragmentation of strengths in the corresponding energy region. The monopole transition to ${}^{10}\mathrm{Be}\left(0_2^{+}\right)$ with the molecular orbital structure is relatively weak compared with those to ${}^6\mathrm{He}+\alpha$ cluster resonances. Monopole strength distributions do not directly correspond to distributions of ${}^6\mathrm{He}\left(0^{+}\right)+\alpha$ and ${}^6\mathrm{He}\left(0^{+}\right)+t$ components but reflect the component of the deformed ${}^6\mathrm{He}$ cluster with a specific orientation, which is originally embedded in the ground state.

In high-energy heavy-ion collisions, the directed flow of particles is conventionally measured with respect to that of the projectile spectators, which is defined as positive $x$ direction, but it is not known if the spectators deflect in the outward or inward directions—outward or toward the center line of the collision. In this Communication we discuss how the measurements of the directed flow at midrapidity, especially in asymmetric collision such as $\mathrm{Cu}+\mathrm{Au}$, can be used to answer this question. We show that the existing data strongly favor the case that the spectators, in the ultrarelativistic collisions, on average deflect outward.

By using local central Yukawa-type interactions that reproduce the low-energy parameters of the latest updates of the Nijmegen ESC08c potentials, we show that the $N\mathrm{\Xi }, NN\mathrm{\Xi }, N\mathrm{\Xi }\mathrm{\Xi }$, and $NN\mathrm{\Xi }\mathrm{\Xi }$ systems with maximal isospin are bound. Since in these states the strong decay $N\mathrm{\Xi }\to \mathrm{\Lambda }\mathrm{\Lambda }$ is forbidden by isospin conservation, these strange few-body systems will be stable under the strong interaction. These results may suggest that other states with different number of $N\mathrm{s}$ and $\mathrm{\Xi }\mathrm{s}$ in the maximal isospin channel could also be bound.

The time dependent local isospin density approximation (TDLIDA) has been extended to the study of the transverse isospin response function in nuclear matter with an arbitrary neutron-proton asymmetry parameter $\xi$. The energy density functional has been chosen in order to fit existing accurate quantum Monte Carlo calculations with a density dependent potential. The evolution of the response with $\xi$ in the $\mathrm{\Delta }{T}_z=\pm 1$ channels is quite different. While the strength of the $\mathrm{\Delta }{T}_z=+1$ channel disappears rather quickly by increasing the asymmetry, the $\mathrm{\Delta }{T}_z=-1$ channel develops a stronger and stronger collective mode that in the regime typical of neutron star matter at $\beta$ equilibrium almost completely exhausts the excitation spectrum of the system. The neutrino mean free paths obtained from the TDLIDA responses are strongly dependent on $\xi$ and on the presence of collective modes, leading to a sizable difference with respect to the prediction of the Fermi gas model.

It is pointed out that the ground state of $n$ neutrons and $n$ protons in a single-$j$ shell, interacting through an isoscalar ($T=0$) pairing force, is not paired, $J=0$, but rather spin aligned, $J=n$. This observation is explained in the context of a model of isoscalar $P$ ($J=1$) pairs, which is mapped onto a system of $p$ bosons, leading to an approximate analytic solution of the isoscalar-pairing limit in $jj$ coupling.

The neutron-rich ${}^{39}\mathrm{S}$ nucleus has been studied using binary grazing reactions produced by the interaction of a 215-MeV beam of ${}^{36}\mathrm{S}$ ions with a thin ${}^{208}\mathrm{Pb}$ target. The magnetic spectrometer, PRISMA, and the $\gamma$-ray array, CLARA, were used in the measurements. Gamma-ray transitions of the following energies were observed: 339, 398, 466, 705, 1517, 1656, and 1724 keV. Five of the observed transitions have been tentatively assigned to the decay of excited states with spins up to ($11/2^{-}$). The results of a state-of-the-art shell-model calculation of the level scheme of ${}^{39}\mathrm{S}$ using the SDPF-U effective interaction are also presented. The systematic behavior of the excitation energy of the first $11/2^{-}$ states in the odd-$A$ isotopes of sulfur and argon is discussed in relation to the excitation energy of the first excited $2^{+}$ states of the adjacent even-$A$ isotopes. The states of ${}^{39}\mathrm{S}$ that have the components in their wave functions corresponding to three neutrons in the $1f_{7/2}$ orbital outside the $N=20$ core have also been discussed within the context of the 0 $\hslash \omega$ shell-model calculations presented here.

The ${}^9\mathrm{Be}(\gamma ,n){}^8\mathrm{Be}$ reaction is enhanced by a near-threshold $1/2^{+}$ state. Contradictions between existing measurements of this reaction cross section affect calculations of astrophysical $r$-process yields, dark matter detector calibrations, and the theory of the nuclear structure of ${}^9\mathrm{Be}$. Select well-documented radioisotope ${}^9\mathrm{Be}(\gamma ,n)$ source yield measurements have been reanalyzed, providing a set of high-accuracy independently measured cross sections without the large systematic errors from recent beamline experiments [Arnold, Clegg, Iliadis, Karwowski, Rich, Tompkins, and Howell, Phys. Rev. C 85, 044605 (2012); Utsunomiya, Katayama, Gheorghe, Imai, Yamaguchi, Kahl, Sakaguchi, Shima, Takahisa, and Miyamoto, Phys. Rev. C 92, 064323 (2015)]. A single-level Breit-Wigner fit of these corrected measurement yields are $E_R=1736.8\left(18\right)$ keV, ${\mathrm{\Gamma }}_{\gamma }=0.742\left(25\right)$ eV, and ${\mathrm{\Gamma }}_n=252\left(17\right)$ keV for the $1/2^{+}$ state, excluding a virtual state solution.

The effects of event-by-event fluctuations in the initial geometry of colliding nuclei are important in the analysis of final flow observables in relativistic heavy-ion collisions. We use hydrodynamic simulations to study the amplitude correlations between different orders of event-by-event fluctuating anisotropic flow harmonics. While the general trends seen in the experimental data are qualitatively reproduced by the model, deviations in detail, in particular for peripheral collisions, point to the need for more elaborate future calculations with a hybrid approach that describes the late hadronic stage of the evolution microscopically. It is demonstrated explicitly that the observed anticorrelation between $v_2$ and $v_3$ is the consequence of approximately linear hydrodynamic response to a similar anticorrelation of the corresponding initial eccentricities ${\epsilon }_2$ and ${\epsilon }_3$. For $n>3$, the hydrodynamic correlations between $v_{2,3}$ and $v_n$ deviate from the rescaled correlations among the corresponding initial eccentricities, demonstrating a nonlinear mode coupling effect in higher-order flows.

Deviations from thermal distribution functions of produced particles in relativistic heavy-ion collisions are discussed as indicators for nonequilibrium processes. The focus is on rapidity distributions of produced charged hadrons as functions of collision energy and centrality, which are used to infer the fraction of particles produced from a central fireball as compared with that from the fragmentation sources that are out of equilibrium with the rest of the system. Overall thermal equilibrium would only be reached for large times $t\to \infty$.

The interference of ${\rho }^0$ and $\omega$ mesons has been studied in the hadronic and leptonic decay channels, i.e., dipion and dilepton decay channels respectively, but this interference has not been studied yet in the semihadronic or semileptonic decay channel, e.g., $V\to {\pi }^0\gamma$. $V$ denotes either a ${\rho }^0$ or $\omega$ meson. To look for this interference in the ${\pi }^0\gamma$ decay channel as well as the contribution of the $\rho$ meson to the cross section, the correlated ${\pi }^0\gamma$ invariant mass distribution spectra are calculated in the photonuclear reaction in the multi-GeV region. It is assumed that these bosons arise in the final state due to the decay of ${\rho }^0$ and $\omega$ mesons which are photoproduced coherently in the isoscalar nucleus. The elementary reaction in the nucleus is considered to proceed as $\gamma N\to VN$, $V\to {\pi }^0\gamma$. The forward propagation of the $\rho$ and $\omega$ mesons and the near forward emission of pions are considered, so that they can be described by the eikonal form. The meson-nucleus interactions are evaluated using the $t\varrho$ approximation. Replacing the decay vertex $V\to {\pi }^0\gamma$ by $V\to {\pi }^{+}{\pi }^{-}$ in the above formalism, it is also used to study the $\rho -\omega$ interference in the ${\pi }^{+}{\pi }^{-}$ decay channel.