Effectively charged neutrons involved in one- and two-nucleon tunneling processes in heavy-ion collisions between superfluid nuclei are expected to emit photons. Although the centroid, width, and integrated energy area characterizing the associated $\gamma$-strength functions are rather similar, the corresponding line shapes reflect the thermal equilibrated-like character of the quasiparticle transfer ($1n$ channel, blackbody spectral functional dependence) and the quantal coherent character of the Cooper pair transfer ($2n$ channel, and Gaussian functional dependence), respectively. The predicted angular distributions, polarizations, and analyzing powers provide further insight into the profoundly different physics to be found at the basis of what can be considered transient Joule-like and (ac) Josephson-like nuclear processes.

Population of the 8 eV ${}^{229m}\mathrm{Th}$ isomer via the second nuclear excited state at 29.19 keV by means of coherent x-ray pulses is investigated theoretically. We focus on two nuclear coherent population transfer schemes using partially overlapping x-ray pulses known from quantum optics: stimulated Raman adiabatic passage, and successive $\pi$ pulses. Numerical results are presented for three possible experimental setups. Our results identify the Gamma Factory as the most promising scenario, where two ultraviolet pulses combined with relativistically accelerated ions deliver the required intensities for efficient isomer population. Our simulations require knowledge of the in-band and cross-band nuclear transition probabilities. We give theoretically predicted values for the latter and discuss them in the context of recent experiments.

Within the improved quantum molecular dynamics (ImQMD) model we follow the evolution of nuclear matter for planar Couette flow in a periodic box. We focus on the region of liquid-gas phase transition and extract the shear viscosity coefficient from the local stress tensor, directly following the viscosity definition. By switching on and off the mean field and thus inducing the phase transition, we are able to observe the impact of clumping in the phase transition region on the viscosity.

The Baksan Experiment on Sterile Transitions (BEST) probes the gallium anomaly and its possible connections to oscillations between active and sterile neutrinos. Based on the Gallium-Germanium Neutrino Telescope (GGNT) technology of the SAGE experiment, BEST employs two zones of liquid Ga target to explore neutrino oscillations on the meter scale. Oscillations on this short scale could produce deficits in the ${}^{71}\mathrm{Ge}$ production rates within the two zones, as well as a possible rate difference between the zones. From July 5th to October 13th 2019, the two-zone target was exposed to a primarily monoenergetic, 3.4-MCi ${}^{51}\mathrm{Cr}$ neutrino source 10 times for a total of 20 independent ${}^{71}\mathrm{Ge}$ extractions from the two Ga targets. The ${}^{71}\mathrm{Ge}$ production rates from the neutrino source were measured from July 2019 to March 2020. At the end of these measurements, the counters were filled with ${}^{71}\mathrm{Ge}$ doped gas and calibrated during November 2020. In this paper, results from the BEST sterile neutrino oscillation experiment are presented in details. The ratio of the measured ${}^{71}\mathrm{Ge}$ production rates to the predicted rates for the inner and the outer target volumes are calculated from the known neutrino capture cross section. Comparable deficits in the measured ratios relative to predicted values are found for both zones, with the $4\sigma$ deviations from unity consistent with the previously reported gallium anomaly. If interpreted in the context of neutrino oscillations, the deficits give best-fit oscillation parameters of $\mathrm{\Delta }{m}^2=3.3_{-2.3}^{+\infty }{\mathrm{eV}}^2$ and ${\sin }^{2}2\theta =0.{42}_{-0.17}^{+0.15}$, consistent with ${\nu }_e\to {\nu }_s$ oscillations governed by a surprisingly large mixing angle.

The structure of the unbound ${}^{15}\mathrm{F}$ nucleus is investigated using the inverse kinematics resonant scattering of a radioactive ${}^{14}\mathrm{O}$ beam impinging on a ${\mathrm{CH}}_2$ target. The analysis of ${}^1\mathrm{H}({}^{14}\mathrm{O},\mathrm{p}){}^{14}\mathrm{O}$ and ${}^1\mathrm{H}({}^{14}\mathrm{O},2\mathrm{p}){}^{13}\mathrm{N}$ reactions allowed the confirmation of the previously observed narrow $1/2^{-}$ resonance, near the two-proton decay threshold, and the identification of two new narrow $5/2^{-}$ and $3/2^{-}$ resonances. The newly observed levels decay by 1p emission to the ground of ${}^{14}\mathrm{O}$, and by sequential 2p emission to the ground state of ${}^{13}\mathrm{N}$ via the $1^{-}$ resonance of ${}^{14}\mathrm{O}$. Gamow shell model (GSM) analysis of the experimental data suggests that the wave functions of the $5/2^{-}$ and $3/2^{-}$ resonances may be collectivized by the continuum coupling to nearby 2p- and 1p-decay channels. The observed excitation function ${}^1\mathrm{H}({}^{14}\mathrm{O},\mathrm{p}){}^{14}\mathrm{O}$ and resonance spectrum in ${}^{15}\mathrm{F}$ are well reproduced in the unified framework of the GSM.

The temperature dependence of stellar electron-capture (EC) rates is investigated, with a focus on nuclei near $N=50$, just above $Z=28$, which play an important role during the collapse phase of core-collapse supernovae (CCSN). Two new microscopic calculations of stellar EC rates are obtained from relativistic and nonrelativistic finite-temperature quasiparticle random-phase approximation approaches, for a conventional grid of temperatures and densities. In both approaches, EC rates due to Gamow-Teller transitions are included. In the relativistic calculation, contributions from first-forbidden transitions are also included and add strongly to the EC rates. The new EC rates are compared with large-scale shell-model calculations for the specific case of ${}^{86}\mathrm{Kr}$, providing insight into the finite-temperature effects on the EC rates. At relevant thermodynamic conditions for core collapse, the discrepancies between the different calculations of this paper are within about one order of magnitude. Numerical simulations of CCSN are performed with the spherically symmetric gr1d simulation code to quantify the impact of such differences on the dynamics of the collapse. These simulations also include EC rates based on two parametrized approximations. A comparison of the neutrino luminosities and enclosed mass at core bounce shows that differences between simulations with different sets of EC rates are relatively small ($\approx 5\%$), suggesting that the EC rates used as inputs for these simulations have become well constrained.

The electromagnetic response of hot QCD matter to decaying external magnetic fields is investigated. We examine the validity of Ohm's law and find that the induced electric current increases from zero and relaxes towards the value from Ohm's law. The relaxation time is larger than the lifetime of the external magnetic field for the QCD matter in relativistic heavy-ion collisions. The lower-than-expected electric current significantly suppresses the induced magnetic field and makes the electromagnetic response incomplete. We demonstrate the incomplete electromagnetic response of hot QCD matter by calculations employing the parton transport model combined with the solution of Maxwell's equations. Our results show a strong suppression by two orders of magnitude in the magnetic field relative to calculations assuming the validity of Ohm's law. This may undermine experimental efforts to measure magnetic-field-related effects in heavy-ion collisions.

Collective phenomena in quantum many-body systems are often described in terms of hydrodynamics, an appropriate framework when the involved particle numbers are effectively macroscopic. We propose to use experiments on expanding clouds of few and many interacting cold atoms to investigate the emergence of hydrodynamics as a function of particle number. We consider gases confined in two-dimensional elliptically deformed traps, and we employ the manifestation of elliptic flow as an indicator of collective behavior. We quantify the response of the gas to the deformation of the trapping potential, and show how such information can be used to establish how many atoms are needed for the system to develop a degree of collectivity comparable to that expected in the hydrodynamic limit. This method permits one, in particular, to exploit observations made in expanding atomic gases to shed light on the apparent hydrodynamic behavior of mesoscopic systems of quarks and gluons formed in the scattering of light ions in high-energy collider experiments.

Pairing rotations are the low-energy excitations of finite superfluid systems, connecting systems that differ in their number of Cooper pairs. This paper presents a model-independent derivation of pairing rotations within an effective theory that exploits the emergent breaking of $\text{U}\left(1\right)$ phase symmetries. The symmetries are realized nonlinearly and the Nambu-Goldstone modes depend only on time because the system is finite. Semimagic nuclei exhibit pairing rotational bands while the pairing spectrum becomes an elliptical paraboloid for open-shell nuclei. Model-independent relations between double charge-exchange reactions and $\alpha$ particle capture or knockout in open-shell nuclei are in analogy to the pair transfer reactions in a single superfluid. Odd semimagic nuclei are described by coupling a fermion to the superfluid. The leading-order theories reproduce data for pairing rotational bands within uncertainty estimates.

The STAR collaboration presents jet substructure measurements related to both the momentum fraction and the opening angle within jets in $p+p$ and $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}} =200\mathrm{GeV}$. The substructure observables include SoftDrop groomed momentum fraction ($z_g$), groomed jet radius ($R_g$), and subjet momentum fraction ($z_{\mathrm{SJ}}$) and opening angle (${\theta }_{\mathrm{SJ}}$). The latter observable is introduced for the first time. Fully corrected subjet measurements are presented for $p+p$ collisions and are compared to leading-order Monte Carlo models. The subjet ${\theta }_{\mathrm{SJ}}$ distributions reflect the jets leading opening angle and are utilized as a proxy for the resolution scale of the medium in $\mathrm{Au}+\mathrm{Au}$ collisions. We compare data from $\mathrm{Au}+\mathrm{Au}$ collisions to those from $p+p$ which are embedded in minimum-bias $\mathrm{Au}+\mathrm{Au}$ events in order to include the effects of detector smearing and the heavy-ion collision underlying event. The subjet observables are shown to be more robust to the background than $z_g$ and $R_g$. We observe no significant modifications of the subjet observables within the two highest-energy, back-to-back jets, resulting in a distribution of opening angles and the splittings that are vacuumlike. We also report measurements of the differential dijet momentum imbalance ($A_J$) for jets of varying ${\theta }_{\mathrm{SJ}}$. We find no qualitative differences in energy loss signatures for varying angular scales in the range $0.1< {\theta }_{\mathrm{SJ}}<0.3$, leading to the possible interpretation that energy loss in this population of high-momentum dijet pairs, is due to soft medium-induced gluon radiation from a single color charge as it traverses the medium.

Most atomic nuclei are deformed with a quadrupole shape described by its overall strength ${\beta }_2$ and triaxiality $\gamma$. The deformation can be accessed in high-energy heavy ion collisions by measuring the collective flow response of the produced quark-gluon plasma to the eccentricity ${\varepsilon }_2$ and the density gradient $d_{\perp }$ in the initial state. Using an analytical estimate and a Glauber model, I show that the variances $\langle {\varepsilon }_2^2\rangle$ or $\langle {(\delta d_{\perp }/d_{\perp })}^2\rangle$ and skewnesses $\langle {\varepsilon }_2^2\delta d_{\perp }/d_{\perp }\rangle$ or $\langle {(\delta d_{\perp }/d_{\perp })}^3\rangle$ have a simple analytical form of $a^{\prime }+b^{\prime }{\beta }_2^2$ and $a^{\prime }+[b^{\prime }+c^{\prime }cos\left(3\gamma \right)]{\beta }_2^3$, respectively. From these, I constructed several normalized skewnesses to isolate the $\gamma$ dependence from that of ${\beta }_2$ and show that the correlations between a normalized skewness and a variance can constrain simultaneously ${\beta }_2$ and $\gamma$. Assuming a linear relation with elliptic flow $v_2$ and mean-transverse momentum $\left[p_{\mathrm{T}}\right]$ of final-state particles, $v_2\propto {\varepsilon }_2$ and $\delta \left[p_{\mathrm{T}}\right]/\left[p_{\mathrm{T}}\right]\propto \delta d_{\perp }/d_{\perp }$, similar conclusions are also expected for the variances and skewnesses of $v_2$ and $\left[p_{\mathrm{T}}\right]$, i.e., $a+b{\beta }_2^2$ for $\langle v_2^2\rangle$ and $\langle {(\delta \left[p_{\mathrm{T}}\right]/\left[p_{\mathrm{T}}\right])}^2\rangle$ and $a+[b+ccos\left(3\gamma \right)]{\beta }_2^3$ for $\langle v_2^2\delta \left[p_{\mathrm{T}}\right]/\left[p_{\mathrm{T}}\right]\rangle$ or $\langle {(\delta \left[p_{\mathrm{T}}\right]/\left[p_{\mathrm{T}}\right])}^3\rangle$. My findings motivate a dedicated system scan of high-energy heavy ion collisions at RHIC and LHC to measure triaxiality of atomic nuclei: one first determines the coefficients $b$ and $c$ by collisions of isobaric near prolate nuclei, $cos\left(3\gamma \right)\approx 1$, and near oblate nuclei, $cos\left(3\gamma \right)\approx -1$, with known ${\beta }_2$ values, followed by collisions of other species of interest with similar mass number. The $({\beta }_2,\gamma )$ values for this species can be inferred directly from the measured variance and skewness observables from these collisions. The results demonstrate the unique opportunities offered by high-energy collisions as a tool to perform interdisciplinary nuclear physics studies.

Nuclear properties across the chart of nuclides are key to improving and validating our understanding of the strong interaction in nuclear physics. We present high-precision mass measurements of neutron-rich Fe isotopes performed at the TITAN facility. The multiple-reflection time-of-flight mass spectrometer (MR-ToF-MS), achieving a resolving power greater than $600000$ for the first time, enabled the measurement of ${}^{63–70}\mathrm{Fe}$, including first-time high-precision direct measurements ($\delta m/m\approx {10}^{-7}$) of ${}^{68–70}\mathrm{Fe}$, as well as the discovery of a long-lived isomeric state in ${}^{69}\mathrm{Fe}$. These measurements are accompanied by both mean-field and ab initio calculations using the most recent realizations which enable theoretical assignment of the spin-parities of the ${}^{69}\mathrm{Fe}$ ground and isomeric states. Together with mean-field calculations of quadrupole deformation parameters for the Fe isotope chain, these results benchmark a maximum of deformation in the $N=40$ island of inversion in Fe and shed light on trends in level densities indicated in the newly refined mass surface.

Observables from nuclear and high-energy experiments can be degraded by detector performance and/or methodology in extracting the observables, such as of the final-state characteristics of heavy-ion collisions in relation to a coarsely estimated reaction-plane direction. We propose the use of deblurring methods, such as in optics, to correct for observable degradation. Our main focus is the restoration of triple-differential particle distributions in heavy-ion collisions. We demonstrate that these could be extracted from collision measurements following the Richardson-Lucy deblurring method from optics. We illustrate basic features of the restoration methodology in a schematic model assuming either ideal or more realistic particle detection. The inferred three-dimensional (3D) distributions for collisions may be easier to interpret in terms of collision dynamics and sought properties of bulk matter than the currently employed Fourier coefficients, that combine information from different azimuthal angles relative to the reaction plane.

We conduct a comprehensive survey of the shape parameter space of the nuclear pasta phases in neutron star crusts by conducting three-dimensional $\mathrm{Hartree-Fock}+\mathrm{BCS}$ calculations. Spaghetti, waffles, lasagna, bicontinuous phases and cylindrical holes occupy local minima in the resulting constant-pressure Gibbs energy surfaces, implying multiple geometries coexist at a given depth. Notably, the bicontinuous phase, in which both the neutron gas and nuclear matter extend continuously in all dimensions appears over a large depth range. Our results support the idea that nuclear pasta is a glassy system. At a characteristic temperature, of order ${10}^8\text{–}{10}^9\mathrm{K}$, different phases may become frozen into domains whose sizes we estimate to be 1–50 times the lattice spacing and over which the local density and electron fraction can vary. Above this temperature, very little long-range order exists and matter is an amorphous solid. Electron scattering off domain boundaries may contribute to the disorder resistivity of the pasta phases. Annealing of the domains may occur during cooling; repopulating of local minima during crustal heating might lead to temperature-dependent transport properties in the deep crust layers. We identify four regions distinguished by whether pasta is the true ground state, and whether the pasta structure allows delocalization of protons. The whole pasta region can occupy up to 70% of the crust by mass and 25% by thickness, and the layer in which protons are delocalized could occupy 45% of the crust mass and 15% of its thickness.

We perform first-principle calculations of electron-nucleus scattering on ${}^3\mathrm{He}$ and ${}^3\mathrm{H}$ using the Green's function Monte Carlo method and two approaches based on the factorization of the final hadronic state: the spectral-function formalism and the short-time approximation. These three methods are benchmarked among each other and compared to the experimental data for the longitudinal and transverse electromagnetic response functions of ${}^3\mathrm{He}$, and the inclusive cross sections of both ${}^3\mathrm{He}$ and ${}^3\mathrm{H}$. Since these three approaches are based on the same description of nuclear dynamics of the initial target state, comparing their results enables a precise quantification of the uncertainties inherent to factorization schemes. At sufficiently large values of the momentum transfer, we find an excellent agreement of the Green's function Monte Carlo calculation with experimental data and with both the spectral-function formalism and the short-time approximation. We also analyze the relevance of relativistic effects, whose inclusion becomes crucial to explain data at high momentum and energy transfer.

Background: Abundance anomalies in some globular clusters, such as the enhancement of potassium and the depletion of magnesium, can be explained in terms of an earlier generation of stars polluting the presently observed ones. It was shown that the potential range of temperatures and densities of the polluting sites depends on the strength of a few critical reaction rates. The ${}^{30}\mathrm{Si}(p,\gamma ){}^{31}\mathrm{P}$ reaction has been identified as one of these important reactions.

Purpose: The key ingredient for evaluating the thermonuclear ${}^{30}\mathrm{Si}(p,\gamma ){}^{31}\mathrm{P}$ reaction rate is the strength of the resonances which, at low energy, are proportional to their proton width. Therefore, the goal of this work is to determine the proton widths of unbound ${}^{31}\mathrm{P}$ states.

Method: States in ${}^{31}\mathrm{P}$ were studied at the Maier-Leibnitz-Laboratorium using the one-proton ${}^{30}\mathrm{Si}({}^3\mathrm{He},d){}^{31}\mathrm{P}$ transfer reaction. Deuterons were detected with the high resolution one quadrupole three dipoles (Q3D) magnetic spectrometer. Angular distribution and spectroscopic factors were extracted for 27 states, and proton widths and resonance strengths were calculated for the unbound states.

Results: Several ${}^{31}\mathrm{P}$ unbound states have been observed for the first time in a one-proton transfer reaction. Above 20 MK, the ${}^{30}\mathrm{Si}(p,\gamma ){}^{31}\mathrm{P}$ reaction rate is now entirely estimated from the observed properties of ${}^{31}\mathrm{P}$ states. The reaction rate uncertainty from all resonances other than the $E_r^{\text{c.m.}}=149$ keV resonance has been reduced down to less than a factor of 2 above that temperature. The unknown spin and parity of the $E_r^{\text{c.m.}}=149$ keV resonance dominates the uncertainty in the rate in the relevant temperature range.

Conclusion: The remaining source of uncertainty on the ${}^{30}\mathrm{Si}(p,\gamma ){}^{31}\mathrm{P}$ reaction rate comes from the unknown spin and parity of the $E_r^{\text{c.m.}}=149$ keV resonance which can change the reaction rate by a factor of 10 in the temperature range of interest.

The number of particles detected in a nucleus-nucleus collision strongly depends on the impact parameter of the collision. Therefore, multiplicity fluctuations, as well as rapidity correlations of multiplicities, are dominated by impact parameter fluctuations. We present a method based on Bayesian inference which allows for a robust reconstruction of fluctuations and correlations at fixed impact parameter. We apply the method to ATLAS data on the distribution of charged multiplicity and transverse energy. We argue that multiplicity fluctuations are smaller at large rapidity than around central rapidity. We suggest simple, new analyses to confirm this effect.

In the hydrodynamic model description of heavy ion collisions, the final-state anisotropic flows $v_n$ are linearly related to the strengths of the multipole shape of the distribution of nucleons in the transverse plane, ${\varepsilon }_n$: $v_n\propto {\varepsilon }_n$. The ${\varepsilon }_n$, for $n=1,2,3,4$, are sensitive to the shapes of the colliding ions, characterized by the quadrupole ${\beta }_2$, octupole ${\beta }_3$, and hexadecapole ${\beta }_4$ deformations. This sensitivity is investigated analytically and also in a Monte Carlo Glauber model. One observes a robust linear relation, $\langle {\varepsilon }_n^2\rangle =a_n^{\prime }+b_n^{\prime }{\beta }_n^2$, for events in a fixed centrality. The $\langle {\varepsilon }_1^2\rangle$ has a contribution from ${\beta }_3$ and ${\beta }_4$, and $\langle {\varepsilon }_3^2\rangle$ from ${\beta }_4$. In ultracentral collisions, there are little cross contributions between ${\beta }_2$ and ${\varepsilon }_3$ and between ${\beta }_3$ and ${\varepsilon }_2$, but clear cross contributions are present in noncentral collisions. Additionally, $\langle {\varepsilon }_n^2\rangle$ are insensitive to nonaxial shape parameters such as the triaxiality. This is good news because the measurements of $v_2$, $v_3$, and $v_4$ can be used to constrain simultaneously the ${\beta }_2$, ${\beta }_3$, and ${\beta }_4$ values. This is best done by comparing two colliding ions with similar mass numbers and therefore nearly identical $a_n^{\prime }$, to obtain a simple equation that relates the ${\beta }_n$ of the two species. This opens up the possibility to map the shape of the atomic nuclei at a timescale $(<{10}^{-24}\mathrm{s})$ much shorter than probed by low-energy nuclear structure physics $(<{10}^{-21}\mathrm{s})$, which ultimately may provide information complementary to that obtained in the nuclear structure experiments.

Background: Deep-inelastic scattering (DIS) on the deuteron with spectator nucleon tagging represents a unique method for extracting the free neutron structure functions and exploring the nuclear modifications of bound protons and neutrons. The detection of the spectator (with typical momentum $\lesssim 100$ $\mathrm{MeV/}c$ in the deuteron rest frame) controls the nuclear configuration during the DIS process and enables a differential analysis of nuclear effects. At the future Electron Ion Collider (EIC) such measurements will be performed using far-forward detectors.

Purpose: Simulate deuteron DIS with proton or neutron tagging with the baseline EIC far-forward detector design. Quantify detector acceptance and resolution effects. Study feasibility of free nucleon structure extraction using pole extrapolation in the spectator momentum.

Methods: DIS events with proton and neutron spectators are generated using the BeAGLE Monte Carlo generator. The spectator nucleon momentum is reconstructed including effects of detector acceptance and resolution. Pole extrapolation is performed under realistic conditions. The free nucleon structure extraction is validated by comparing with the input model.

Results: Proton and neutron spectator detection is possible over the full transverse momentum range $0<p_T<100$ $\mathrm{MeV/}c$ needed for pole extrapolation. Resolution effects on the distributions before corrections are $\approx 10\%$ for proton and $\approx 30\%$ for neutron spectators. The overall accuracy of nucleon structure extraction is expected to be at the few-percent level.

Conclusions: Free neutron structure extraction through proton tagging and pole extrapolation is feasible with the baseline EIC far-forward detector design. The corresponding extraction of free proton structure through neutron tagging provides a reference point for future studies of nuclear modifications.

Inclusive electron scattering from nuclear targets has been measured to extract the nuclear dependence of the inelastic cross section (${\sigma }_A$) in Hall C at the Thomas Jefferson National Accelerator facility. Results are presented for ${}^2\mathrm{H}, {}^3\mathrm{He}, {}^4\mathrm{He}, {}^9\mathrm{B}, {}^{12}\mathrm{C}, {}^{63}\mathrm{Cu}$, and ${}^{197}\mathrm{Au}$ at an incident electron beam energy of 5.77 GeV for a range of momentum transfer from $Q^2$ = 2 to 7 (${\mathrm{GeV}/\mathrm{c})}^2$. These data improve the precision of the existing measurements of the EMC effect in the nuclear targets at large $x$ and allow for more detailed examinations of the $A$ dependence of the EMC effect.