Neutron drops confined in an external field are studied in the framework of relativistic Brueckner-Hartree-Fock theory using the bare nucleon-nucleon interaction. The ground-state energies and radii of neutron drops with even numbers from $N=4$ to $N=50$ are calculated and compared with results obtained from other nonrelativistic ab initio calculations and from relativistic density functional theory. Special attention has been paid to the magic numbers and to the subshell closures. The single-particle energies are investigated and the monopole effect of the tensor force on the evolutions of the spin-orbit and the pseudospin-orbit splittings is discussed. The results provide interesting insights into neutron-rich systems and can form an important guide for future density functionals.

We study the nucleon as a nontopological soliton in a quark medium as well as in a nucleon medium in terms of the Polyakov quark-meson (PQM) model with two flavors at finite temperature and density. The constituent quark masses evolving with the temperature at various baryon chemical potentials are calculated and the equations of motion are solved according to the proper boundary conditions. The PQM model predicts an increasing size of the nucleon and a reduction of the nucleon mass in both hot environment. However, the phase structure is different from each other in quark and nucleon mediums. There is a crossover in the low-density region and a first-order phase transition in the high-density region in quark medium, whereas there exists a crossover characterized by the overlap of the nucleons in nucleon medium.

The production of jets, and high momentum hadrons from jets, produced in deuteron-Au ($d$-Au) collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and proton-Pb ($p$-Pb) collisions at the CERN Large Hadron Collider (LHC) are studied as a function of centrality, a measure of the impact parameter of the collision. A modified version of the event generator pythia, widely used to simulate $p-p$ collisions, is used in conjunction with a nuclear Monte Carlo event generator which simulates the locations of the nucleons within a large nucleus. We demonstrate how events with a hard jet may be simulated, in such a way that the parton distribution function of the projectile is “frozen” during its interaction with the extended nucleus. Using our approach, we demonstrate that the puzzling enhancement seen in peripheral events at RHIC and the LHC, as well as the suppression seen in central events at the LHC, are possibly due to mis-binning of central and semicentral events, containing a jet, as peripheral events. This occurs due to the suppression of soft particle production away from the jet, caused by the depletion of energy available in a nucleon of the deuteron (in $d$-Au at RHIC) or in the proton (in $p$-Pb at LHC), after the production of a hard jet. We conclude that partonic correlations built out of simple energy conservation are responsible for such an effect, though these are sampled at the hard scale of jet production and, as such, represent smaller states.

Higher Fourier harmonics of anisotropic flow ($v_4$ and beyond) get large contributions induced by elliptic and triangular flow through nonlinear response. We present a general framework of nonlinear hydrodynamic response which encompasses the existing one and allows us to take into account the mutual correlation between the nonlinear couplings affecting Fourier harmonics of any order. Using Large Hadron Collider data on Pb+Pb collisions at $\sqrt[]{s}=2.76$ TeV, we perform an application of our formalism to hexagonal flow, $v_6$, a coefficient affected by several nonlinear contributions which are of the same order of magnitude. We obtain the first experimental measure of the coefficient ${\chi }_{624}$, which couples $v_6$ to $v_2$ and $v_4$. This is achieved by putting together the information from several analyses: event-plane correlations, symmetric cumulants, and higher order moments recently analyzed by the ALICE Collaboration. The value of ${\chi }_{624}$ extracted from data is in fair agreement with hydrodynamic calculations, although with large error bars, which would be dramatically reduced by a dedicated analysis. We argue that within our formalism the nonlinear structure of a given higher order harmonic can be determined more accurately than the harmonic itself, and we emphasize potential applications to future measurements of $v_7$ and $v_8$.

The reaction $K^{-}d\to \pi \mathrm{\Sigma }n$ is studied within a Faddeev-type approach, with emphasis on the specific kinematics of the E31 experiment at J-PARC, i.e., $K^{-}$ beam momentum of $p_K=1$ GeV/$c$ and neutron angle of ${\theta }_n=0^{\circ }$. The employed Faddeev approach requires as main input amplitudes for the two-body subsystems $\overline{K}N\to \overline{K}N$ and $\overline{K}N\to \pi \mathrm{\Sigma }$. For the latter, results from recently published chiral unitary models of the $\overline{K}N$ interaction are utilized. The $\overline{K}N\to \overline{K}N$ amplitude itself, however, is taken from a recent partial-wave analysis. Because of the large incoming momentum of the $K^{-}$, the $\overline{K}N$ interaction is probed in a kinematical regime where those chiral potentials are no longer applicable. A comparison of the predicted spectrum for various $\pi \mathrm{\Sigma }$ charge channels with preliminary data is made and reveals a remarkable agreement as far as the magnitude and the line shape in general is concerned. Noticeable differences observed in the $\pi \mathrm{\Sigma }$ spectrum around the $\overline{K}N$ threshold, i.e. in the region of the $\mathrm{\Lambda }$(1405) resonance, indicate a sensitivity to the details of the employed $\overline{K}N\to \pi \mathrm{\Sigma }$ amplitudes and suggest that pertinent high-precision data could indeed provide substantial constraints on the structure of the $\mathrm{\Lambda }$(1405).

We have used superconducting high-resolution radiation detectors to measure the energy level of metastable ${}^{235m}\mathrm{U}$ as 76.737 ± 0.018 eV. The ${}^{235m}\mathrm{U}$ isomer is created from the α decay of ${}^{239}\mathrm{Pu}$ and embedded directly into the detector. When the ${}^{235m}\mathrm{U}$ subsequently decays, the energy is fully contained within the detector and is independent of the decay mode or the chemical state of the uranium. The detector is calibrated using an energy comb from a pulsed UV laser. A comparable measurement of the metastable ${}^{229m}\mathrm{Th}$ nucleus would enable a laser search for the exact transition energy in ${}^{229}\mathrm{Th}-{}^{229m}\mathrm{Th}$ as a step towards developing the first ever nuclear (baryonic) clock.

Excited states in ${}^{127}\mathrm{Xe}$ were populated via ${}^{122}\mathrm{Sn}{(}^9\text{Be},4n\gamma )$ fusion-evaporation reaction at $E_{\text{beam}}=48$ MeV. A rotational band above an isomeric state at 2730.3 keV has been established. $J^{\pi }=23/2^{+}$ has been assigned unambiguously to the bandhead. Structural features, configuration, and reduced hindrance factor per degree of $K$-forbiddenness ($f_{\nu }$) have been discussed in the context of neighboring nuclei. Half-lives of $7/2^{+}$ ($t_{1/2}=37\pm 1$ ns) and $23/2^{+}$ ($t_{1/2}=28\pm 1$ ns) isomeric states have also been estimated and found to be consistent with the earlier reported values. The experimentally observed energy levels of the rotational band have been reproduced successfully by theoretical calculations carried out using the modified particle rotor model (MPRM) with ${\beta }_2\sim 0.22$ and ${15}^{\circ }\lesssim \gamma \lesssim {22}^{\circ }$.

The STAR collaboration has observed an excess production of $e^{+}{e}^{-}$ pairs in relativistic heavy ion collisions, over the expectations from hadronic production models. The excess pairs have transverse momenta $p_T<150\mathrm{MeV}/c$ and are most prominent in peripheral gold-gold and uranium-uranium collisions. The pairs exhibit a peak at the $J/\psi$ mass, but include a wide continuum, with pair invariant masses from $400{\mathrm{MeV}/c}^2$ up to $2.6{\mathrm{GeV}/c}^2$. The ALICE Collaboration observes a similar excess in peripheral lead-lead collisions, but only at the $J/\psi$ mass, without a corresponding continuum. This paper presents a calculation of the cross section and kinematic for two-photon production of $e^{+}{e}^{-}$ pairs, and find general agreement with the STAR data. The calculation is based on the starlight simulation code, which is based on the Weizsäcker-Williams virtual photon approach. The STAR continuum observations are compatible with two-photon production of $e^{+}{e}^{-}$ pairs. The ALICE analysis required individual muon $p_T$ be greater than 1 GeV/c; this eliminated almost all of the pairs from two-photon interactions, while leaving most of the $J/\psi$ decays.

The appearance of new theoretical papers concerning matter radii of neutron-rich oxygen nuclei has prompted a return to this problem. New results provide no better agreement with experimental values than did previous calculations with a simple model. I maintain that there is no reason to adjust the ${}^{22}\mathrm{O}$ core in the ${}^{24}\mathrm{O}$ nucleus, and the case of ${}^{24}\mathrm{O}$ should be reexamined experimentally.

Background: Quasifission (QF) has gained tremendous importance in heavy-ion nuclear physics research because of its strong influence on superheavy-element synthesis. Collisions involving closed-shell nuclei in the entrance channel are found to affect the QF reaction mechanism. Hence, it is important to improve the understanding of their effect on QF. Apart from that, some recent studies show that the difference in $N/Z$ of reaction partners influences the reaction dynamics. Since heavier doubly magic nuclei have different $N/Z$ than lighter doubly magic nuclei, it is important to understand the effect of $N/Z$ mismatch as well as the effect of shell closures.

Purpose: To investigate the effect of entrance-channel shell closures and $N/Z$ asymmetry on QF. The reactions were chosen to decouple these effects from the contributions of other entrance-channel parameters.

Method: Fission fragment mass-angle distributions were measured using the CUBE fission spectrometer, consisting of two large area position-sensitive multi-wire proportional counters (MWPCs), for five reactions, namely, ${}^{50}\mathrm{Cr}+{}^{208}\mathrm{Pb}$, ${}^{52}\mathrm{Cr}+{}^{206,208}\mathrm{Pb}$, ${}^{54}\mathrm{Cr}+{}^{204,208}\mathrm{Pb}$.

Result: Two components were observed in the measured fragment mass angle distribution, a fast mass-asymmetric quasifission and a slow mass-symmetric component having a less significant mass-angle correlation. The ratio of these components was found to depend on spherical closed shells in the entrance channel nuclei and the magnitude of the $N/Z$ mismatch between the two reaction partners, as well as the beam energy.

Conclusions: Entrance-channel spherical closed shells can enhance compound nucleus formation provided the $N/Z$ asymmetry is small. Increase in the $N/Z$ asymmetry is expected to destroy the effect of entrance-channel spherical closed shells, through nucleon transfer reactions.

We formulate a general theory of thermal fluctuations within causal second-order viscous hydrodynamic evolution of matter formed in relativistic heavy-ion collisions. The fluctuation is treated perturbatively on top of a boost-invariant longitudinal expansion. Numerical simulation of thermal noise is performed for a lattice quantum chromodynamics equation of state and for various second-order dissipative evolution equations. Phenomenological effects of thermal fluctuations on the two-particle rapidity correlations are studied.

Using the perturbative chiral quark model (PCQM), we investigate and predict in this work axial charges $g_A^B$ of octet and decuplet $N$, $\mathrm{\Sigma }$, $\mathrm{\Xi }$, $\mathrm{\Delta }$, ${\mathrm{\Sigma }}^{*}$, and ${\mathrm{\Xi }}^{*}$ baryons, considering both the ground and excited states in the quark propagator. The PCQM predictions are in good agreement with the experimental data, lattice-QCD values, and other approaches. In addition, the study reveals that the meson cloud is influential in the PCQM, contributing around 30% to the total values of $g_A^B$, and the meson cloud contribution to $g_A^B$ stems mainly from the diagrams with the ground-state quark propagator while the excited intermediate quark states reduce $g_A^B$ by 10–20%.

An extension of hadron resonance gas (HRG) model is constructed to include interactions using relativistic virial expansion of partition function. The noninteracting part of the expansion contains all the stable baryons and mesons and the interacting part contains all the higher mass resonances which decay into two stable hadrons. The virial coefficients are related to the phase shifts which are calculated using $K$-matrix formalism in the present work. We have calculated various thermodynamics quantities like pressure, energy density, and entropy density of the system. A comparison of thermodynamic quantities with noninteracting HRG model, calculated using the same number of hadrons, shows that the results of the above formalism are larger. A good agreement between equation of state calculated in $K$-matrix formalism and lattice QCD simulations is observed. Specifically, the lattice QCD calculated interaction measure is well described in our formalism. We have also calculated second-order fluctuations and correlations of conserved charges in $K$-matrix formalism. We observe a good agreement of second-order fluctuations and baryon-strangeness correlation with lattice data below the crossover temperature.

We have performed a search for neutrinoless ${\beta }^{{}^{+}}\text{EC}$ decay of ${}^{120}\mathrm{Te}$ using the final CUORE-0 data release. We describe a new analysis method for the simultaneous fit of signatures with different event topology, and of data subsets with different signal efficiency, obtaining a limit on the half-life of the decay of $T_{1/2}>1.6\times {10}^{21}$ yr at $90\%$ credibility interval (CI). Combining this with results from Cuoricino, a predecessor experiment, we obtain the strongest limit to date, corresponding to $T_{1/2}>2.7\times {10}^{21}$ yr at $90\%$ CI.

Background: Self-consistent Green's function theory has recently been extended to the basic formalism needed to account for three-body interactions [Carbone, Cipollone, Barbieri, Rios, and Polls, Phys. Rev. C 88, 054326 (2013)]. The contribution of three-nucleon forces has so far been included in ab initio calculations on nuclear matter and finite nuclei only as averaged two-nucleon forces.

Purpose: We derive the working equations for all possible two- and three-nucleon terms that enter the expansion of the self-energy up to the third order, thus including the interaction-irreducible (i.e., not averaged) diagrams with three-nucleon forces that have been previously neglected.

Methods: We employ the algebraic diagrammatic construction up to the third order as an organization scheme for generating a nonperturbative self-energy, in which ring (particle-hole) and ladder (particle-particle) diagrams are resummed to all orders.

Results: We derive expressions of the static and dynamic self-energy up to the third order, by taking into account the set of diagrams required when either the skeleton or nonskeleton expansions of the single-particle propagator are assumed. A hierarchy of importance among different diagrams is revealed, and a particular emphasis is given to a third-order diagram [see Fig. 2(c)] that is expected to play a significant role among those featuring an interaction-irreducible three-nucleon force.

Conclusion: A consistent formalism to resum at infinite order correlations induced by three-nucleon forces in the self-consistent Green's function theory is now available and ready to be implemented in the many-body solvers.

We study the nucleon electromagnetic form factors (EM FFs) using a recently developed method combining chiral effective field theory ($\chi \mathrm{EFT}$) and dispersion analysis. The spectral functions on the two-pion cut at $t>4M_{\pi }^2$ are constructed using the elastic unitarity relation and an $N/D$ representation. $\chi \mathrm{EFT}$ is used to calculate the real functions $J_{\pm }^1\left(t\right)=f_{\pm }^1\left(t\right)/F_{\pi }\left(t\right)$ (ratios of the complex $\pi \pi \to N\overline{N}$ partial-wave amplitudes and the timelike pion FF), which are free of $\pi \pi$ rescattering. Rescattering effects are included through the empirical timelike pion FF $|F_{\pi }{\left(t\right)|}^2$. The method allows us to compute the isovector EM spectral functions up to $t\sim 1{\mathrm{GeV}}^2$ with controlled accuracy (leading order, next-to-leading order, and partial next-to-next-to-leading order). With the spectral functions we calculate the isovector nucleon EM FFs and their derivatives at $t=0$ (EM radii, moments) using subtracted dispersion relations. We predict the values of higher FF derivatives, which are not affected by higher-order chiral corrections and are obtained almost parameter-free in our approach, and explain their collective behavior. We estimate the individual proton and neutron FFs by adding an empirical parametrization of the isoscalar sector. Excellent agreement with the present low-$Q^2$ FF data is achieved up to $\sim 0.5{\mathrm{GeV}}^2$ for $G_E$, and up to $\sim 0.2{\mathrm{GeV}}^2$ for $G_M$. Our results can be used to guide the analysis of low-$Q^2$ elastic scattering data and the extraction of the proton charge radius.

We address a discrepancy between different computations of $\eta /s$ (shear viscosity over entropy density) of hadronic matter. Substantial deviations of this coefficient are found between transport approaches mainly based on resonance propagation with finite lifetime and other (semianalytical) approaches with energy-dependent cross sections, where interactions do not introduce a timescale. We provide an independent extraction of this coefficient by using the newly developed SMASH (Simulating Many Accelerated Strongly interacting Hadrons) transport code, which is an example of a mainly resonance-based approach. We compare the results from SMASH with numerical solutions of the Boltzmann equation for simple systems using the Chapman-Enskog expansion, as well as previous results in the literature. Our conclusion is that the hadron interaction via resonance formation/decay strongly affects the transport properties of the system, resulting in significant differences in $\eta /s$ with respect to other approaches where binary collisions dominate. We argue that the relaxation time of the system—which characterizes the shear viscosity—is determined by the interplay between the mean free time and the lifetime of resonances. We show how an artificial shortening of the resonance lifetimes, or the addition of a background elastic cross section nicely interpolate between the two discrepant results.

We compare relativistic mean-field models with their low density expansion counterparts used to mimic nonrelativistic models by consistently expanding the baryonic scalar density in powers of the baryonic number density up to $\mathcal{O}(13/3)$, which goes two orders beyond the order considered in previous works. We show that, due to the nontrivial density dependence of the Dirac mass, the convergence of the expansion is very slow, and the validity of the nonrelativistic approximation is questionable even at subsaturation densities. In order to analyze the roles played by strangeness and isospin we consider $n\text{−}\mathrm{\Lambda }$ and $n\text{−}p$ matter separately. Our results indicate that these degrees of freedom play quite different roles in the expansion mechanism and $n\text{−}\mathrm{\Lambda }$ matter can be better described by low density expansions than $n\text{−}p$ matter in general.

In massive stars, the ${}^{41}\mathrm{Ca}(n,\alpha ){}^{38}\mathrm{Ar}$ and ${}^{41}\mathrm{K}(p,\alpha ){}^{38}\mathrm{Ar}$ reactions have been identified as the key reactions governing the abundance of ${}^{41}\mathrm{Ca}$, which is considered as a potential chronometer for solar system formation. So far, due to experimental limitations, the ${}^{41}\mathrm{Ca}(n,\alpha ){}^{38}\mathrm{Ar}$ reaction rate is solely based on statistical model calculations. In the present study, we have measured the time-inverse ${}^{38}\mathrm{Ar}(\alpha ,n){}^{41}\mathrm{Ca}$ and ${}^{38}\mathrm{Ar}(\alpha ,p){}^{41}\mathrm{K}$ reactions using an active target detector. The reactions were studied in inverse kinematics using a 133-MeV ${}^{38}\mathrm{Ar}$ beam and ${}^4\mathrm{He}$ as the active-gas target. Both excitation functions were measured simultaneously in the energy range of $6.8\le E_{\mathrm{c}.\mathrm{m}.}\le 9.3$ MeV. Using detailed balance the ${}^{41}\mathrm{Ca}(n,\alpha ){}^{38}\mathrm{Ar}$ and ${}^{41}\mathrm{K}(p,\alpha ){}^{38}\mathrm{Ar}$ reaction rates were determined, which suggested a 20% increase in the ${}^{41}\mathrm{Ca}$ yield from massive stars.