We report the differential yields at mid-rapidity of the Breit-Wheeler process ($\gamma \gamma \to e^{+}{e}^{-}$) in peripheral $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=54.4$ and 200 GeV with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC), as a function of energy $\sqrt{s_{NN}}, e^{+}{e}^{-}$ transverse momentum $p_{\mathrm{T}}, p_{\mathrm{T}}^2$, invariant mass $M_{ee}$, and azimuthal angle. In the invariant mass range of $0.4<M_{ee}<2.6\mathrm{GeV}/c^2$ at low transverse momentum ($p_{\mathrm{T}}<0.15\mathrm{GeV}/c$), the yields increase while the pair $\sqrt{\langle p_{\mathrm{T}}^2\rangle }$ decreases with increasing $\sqrt{s_{NN}}$, a feature that is correctly predicted by the QED calculation. The energy dependencies of the measured quantities are sensitive to the nuclear form factor, infrared divergence and photon polarization. The data are compiled and used to extract the charge radius of the Au nucleus.

Measurement of higher-order cumulants of conserved quantities, like net-charge, net-baryon, and net-strangeness in heavy-ion collisions, is proposed as a sensitive tool to determine the freeze-out parameters and the nature of phase transitions at the CERN Large Hadron Collider (LHC) energies. Baseline measurements for heavy-ion collisions are essential to understand the experimental observations. Recently, several experimental observations have shown QGP-like scenarios in small systems ($pp$ collisions). The first Monte-Carlo study of the cumulants and their ratios for net-charge, net-hadron, net-kaon, net-baryon, and net-proton distributions in $pp$ collisions at $\sqrt{s}=13$ TeV using perturbative quantum chromodynamics models like pythia8 and herwig have been reported. The effect of different particle production mechanisms and phase space acceptance on the higher-order cumulants has been discussed. This study will serve as a baseline for future measurements at the LHC. Furthermore, it will shed more light on the measurement of cumulants and the connection between small systems and heavy-ion collisions at the LHC.

Proton-$\gamma$ coincidences from $(d,p)$ reactions between a ${}^{66}\mathrm{Ni}$ beam and a deuterated polyethylene target have been analyzed with the inverse-Oslo method to find the nuclear level density (NLD) and $\gamma$-ray strength function ($\gamma \mathrm{SF}$) of ${}^{67}\mathrm{Ni}$. The ${}^{66}\mathrm{Ni}(n,\gamma )$ capture cross section has been calculated using the Hauser-Feshbach model in TALYS using the measured NLD and $\gamma \mathrm{SF}$ as constraints. The results confirm that the ${}^{66}\mathrm{Ni}(n,\gamma )$ reaction acts as a bottleneck when relying on one-zone nucleosynthesis calculations. However, the impact of this reaction is strongly dampened in multizone models of low-metallicity AGB stars experiencing $i$-process nucleosynthesis.

This study investigated the asymmetry among the analogous spin-isospin-flip transition strengths from the $[J^{\pi },T]={[1^{+},0]}_1$ ground state of ${}^{14}\mathrm{N}$ to the ${[2^{+},1]}_1$ and ${[2^{+},1]}_2$ states in the $A=14$ nuclei ${}_6{}^{14}\mathrm{C}_8, {}_7{}^{14}\mathrm{N}_7$, and ${}_8{}^{14}\mathrm{O}_6$. The reduced transition strengths for the excited states in ${}^{14}\mathrm{N}$, denoted by $B({\mathrm{GT}}^0$), were obtained via a ${}^{14}\mathrm{N}(p,p^{\prime }$) experiment at $E_p=200$ MeV performed at iThemba LABS, South Africa. The $B({\mathrm{GT}}^0$) values obtained for the ${[2^{+},1]}_1$ and ${[2^{+},1]}_2$ states in ${}^{14}\mathrm{N}$ were compared with the $B({\mathrm{GT}}^{+}$) and $B({\mathrm{GT}}^{-}$) values for the analogous states in ${}^{14}\mathrm{C}$ and ${}^{14}\mathrm{O}$, which are available from the charge-exchange reaction measurements. Based on the simple two-state model, the off-diagonal matrix elements of the nuclear Hamiltonians $\langle H_C^{+}\rangle$ and $\langle H_C^{-}\rangle$ for ${}^{14}\mathrm{C}$ and ${}^{14}\mathrm{O}$, respectively, were deduced. The obtained $\langle H_C^{\pm }\rangle$ values are roughly proportional to the $T_z$ values of the respective nuclei.

High-spin states in ${}^{217}\mathrm{Ac}$ are reported up to 3.9-MeV excitation energy and $I^{\pi }=41/2^{+}$ where 22 transitions are newly observed. The structure of the yrast and near-yrast states below the $29/2^{+}$ isomer is revisited. The level structure above the $29/2^{+}$ isomer is established with firm spin and parity assignments. Large-basis shell-model calculations with the Kuo-Herling particle effective interaction are performed to compare the experimentally observed level energies with the theoretical predictions. A comparison with the systematics of the $N=128$ isotones suggests that the yrast structures result from a weak coupling of the odd proton to the even-even ${}^{216}\mathrm{Ra}$ core, which is consistent with the shell-model configurations.

The $K^{\pi }=8^{-}$ isomeric states and rotational bands in the even-even $N=150$ isotones with $94⩽Z⩽104$ are investigated by the cranked shell model (CSM) with pairing correlations treated by the particle-number-conserving (PNC) method. The experimental band-head energies and kinematic moments of inertia (MOIs) are reproduced quite well by the PNC-CSM calculation. The two-neutron state with configuration $\nu 9/2^{-}\left[734\right]\otimes \nu 7/2^{+}\left[624\right]$ is the lowest $8^{-}$ state for these isomers. This is a demonstration of the deformed neutron shell at $N=152$. Low-lying two proton ${\pi }^2{8}^{-}(\pi 9/2^{+}\left[624\right]\otimes \pi 7/2^{-}\left[514\right])$ configuration state is predicted only for ${}^{252}\mathrm{No}$ and ${}^{254}\mathrm{Rf}$ due to the deformed proton shell at $Z=100$. A distinct upbending is observed for the ${\nu }^2{8}^{-}$ bands in the lighter isotones while it is absent for bands in the heavier ones. The upbending of the ${\nu }^2{8}^{-}$ band at frequency $\hslash \omega \approx 0.20$ MeV in ${}^{244}\mathrm{Pu}$ attributes to the sudden proton alignment of the interference term $j_x(\pi 5/2^{+}\left[642\right]\otimes \pi 7/2^{+}\left[633\right])$. The irregularity of MOI observed in the $K^{\pi }=8^{-}$ band of ${}^{252}\mathrm{No}$ can be explained by the crossing between the ${\nu }^2{8}^{-}(\nu 9/2^{-}\left[734\right]\otimes \nu 7/2^{+}\left[624\right])$ and ${\pi }^2{8}^{-}(\pi 9/2^{+}\left[624\right]\otimes \pi 7/2^{-}\left[514\right])$ configurations. The $20\%–30\%$ increase of the band head $J^{\left(1\right)}$ for the $8^{-}$ bands comparing to the ground-state band is attributed to the $\sim 5\%$ pairing gap reduction of the two-neutron $\nu 7/2^{+}\left[624\right]\otimes \nu 9/2^{-}\left[734\right]$ configuration state comparing to the ground-state band.

Based on existing experimental data for $A\text{−}A$ collisions starting from the Alternating Gradient Synchrotron energies to those of the CERN Large Hadron Collider, various systematics related to strange hadrons and antihadrons are presented. As in the case of pions, kaons, and protons, the ratio between the average transverse momentum and the square root of the total particle multiplicity per unit rapidity and unit transverse overlap area ($\langle p_T\rangle /\sqrt{\langle dN/dy\rangle /S_{\perp }}$) decreases with collision energy and centrality supporting the predictions of the color glass condensate and percolation approaches. The dependencies on $\sqrt{\langle dN/dy\rangle /S_{\perp }}$ of the slope and offset extracted from the $\langle p_T\rangle$-particle mass correlation and of the average transverse expansion velocity and kinetic freeze-out temperature, parameters obtained from Boltzmann-Gibbs Blast-Wave fits of $p_T$ spectra for strange hadrons, are compared with those for pions, kaons, and protons. The detailed study of the entropy density ($\langle dN/dy\rangle /S_{\perp }$) dependence of the ratio of strange hadron yields per unit rapidity to the total particle multiplicity per unit rapidity ($Y^S/\langle dN/dy\rangle$) at different collision energies and centralities reveals the necessity to study strange hadrons and antihadrons separately. The correlations $Y^S/\langle dN/dy\rangle \text{−}\langle dN/dy\rangle /S_{\perp }$ for single- and multistrange antihadron yields, as a function of the fireball size, are discussed. The $Y^S/\langle dN/dy\rangle \text{−}\langle dN/dy\rangle /S_{\perp }$ correlations for combined and separated strange hadron species, at different centralities, clearly show a maximum in the region where a transition from baryon-dominated matter to meson-dominated matter occurs. Comparison with $pp$ experimental data reveals another similarity between $pp$ and Pb-Pb collisions at CERN Large Hadron Collider energies. To facilitate a possible comparison with theoretical approaches, the different correlations are either fitted with suitable functions or the corresponding experimental data are provided.

First measurements of hadron-$\mathrm{\Lambda }$ ($h\text{−}\mathrm{\Lambda }$) azimuthal angular correlations in $p$-Pb collisions at $\sqrt{s_{NN}} =5.02$ TeV using the ALICE detector at the Large Hadron Collider are presented. These correlations are used to separate the production of associated $\mathrm{\Lambda }$ baryons into three different kinematic regions, namely those produced in the direction of the trigger particle (near side), those produced in the opposite direction (away side), and those whose production is uncorrelated with the jet axis (underlying event). The per-trigger associated $\mathrm{\Lambda }$ yields in these regions are extracted, along with the near- and away-side azimuthal peak widths, and the results are studied as a function of associated particle $p_{\mathrm{T}}$ and event multiplicity. Comparisons with the dpmjet event generator and previous measurements of the $\varphi \left(1020\right)$ meson are also made. The final results indicate that strangeness production in the highest multiplicity $p$-Pb collisions is enhanced relative to low multiplicity collisions in both the jetlike regions and the underlying event. The production of $\mathrm{\Lambda }$ relative to charged hadrons is also enhanced in the underlying event when compared to the jetlike regions. Additionally, the results hint that strange quark production in the away-side of the jet is modified by soft interactions with the underlying event.

A framework for simulating the real-time dynamics of composite particles in a simple model of dense matter that is amenable to quantum computers is developed. As a demonstration, we perform classical simulations of heavy-hadrons propagating through a dense medium in the Schwinger model. Measurements of the time-dependent energy and charge density are used to identify mechanisms responsible for energy loss and hadron production (hadronization). A study of entanglement dynamics highlights the importance of quantum coherence between the particles that make up the dense medium. Throughout this work, care is taken to isolate, and remove, phenomena that arise solely from a finite lattice spacing. It is found that signatures of entanglement are more sensitive to lattice artifacts than other observables. Toward quantum simulations, we present an efficient method and the corresponding quantum circuits for preparing ground states in the presence of heavy mesons. These circuits are used to estimate the resources required to simulate in-medium energy loss and hadronization in the Schwinger model using quantum computers.

Background: Neutron-rich nuclei in the $A\approx 100$ mass region are interesting due to a rapid shape transition, especially pronounced in the Zr isotopes, and more recently observed in Nb isotopes. ${}^{98}\mathrm{Nb}$, with only one proton and one neutron outside the subshell closure nucleus of ${}^{96}\mathrm{Zr}$, is amenable to shell model calculations.

Purpose: To further examine the rapid shape transition, the yrast structure of ${}^{98}\mathrm{Nb}$ was established in this work. This was the only yrast structure missing from all immediate neighbors to ${}^{96}\mathrm{Zr}$.

Method: The yrast structure of ${}^{98}\mathrm{Nb}$ was studied in the fission of the compound systems formed in three heavy-ion induced reactions, ${}^{24}\mathrm{Mg}$ (134.5 MeV) $+{}^{173}\mathrm{Yb}$, ${}^{23}\mathrm{Na}$ (129 MeV) $+{}^{176}\mathrm{Yb}$, and ${}^{18}\mathrm{O}$ (91 MeV) $+{}^{208}\mathrm{Pb}$. Prompt $\gamma$-ray spectroscopy was accomplished using the Gammasphere array.

Results: Excitation energies up to 3 MeV were observed for the first time in ${}^{98}\mathrm{Nb}$. The yrast structure above the previously known ${\left(5\right)}^{+}$ isomer was established. In the process of studying ${}^{98}\mathrm{Nb}$ the yrast structure of positive-parity states in ${}^{99}\mathrm{Mo}$ was extended to 3.7 MeV excitation energy, the previously known ${}^{99}\mathrm{Nb}$ level scheme was enriched, and two new levels were added in the level scheme of ${}^{97}\mathrm{Zr}$.

Conclusions: The coupling of the odd proton occupying the $g_{9/2}$ orbital to the yrast states in the core nucleus of ${}^{97}\mathrm{Zr}$ can account for all observed states in ${}^{98}\mathrm{Nb}$. The yrast structure for the positive-parity states of ${}^{99}\mathrm{Mo}$ is compared to the deformed ground-state bands of the ${}^{101}\mathrm{Ru}$ isotone and of ${}^{98,100}\mathrm{Mo}$.

We measure the average spin of ${}^{144}\mathrm{Ba}$, a common fragment produced in ${}^{252}\mathrm{Cf}$(sf), as a function of the total kinetic energy (TKE). We combine a twin Frisch-gridded ionization chamber with a world-class $\gamma$-ray spectrometer that was designed to measure high-multiplicity $\gamma$-ray events, Gammasphere. The chamber, loaded with a ${}^{252}\mathrm{Cf}$(sf) source, provides a fission trigger, the TKE of the fragments, the approximate fragment masses, and the polar angle of the fission axis. Gammasphere provides the total $\gamma$-ray yield, fragment identification through the tagging of decay $\gamma$ rays, and the feeding of rotational bands in the fragments. We determine the dependence of the average spin of ${}^{144}\mathrm{Ba}$ on the fragments' TKE by correlating the fragment properties with the distribution of discrete levels that are fed. We find that the average spin only changes by about $0.5\hslash$ across the TKE range of 158–203 MeV. The virtual independence of the spin on TKE suggests that spin is not solely generated through the statistical excitation of rotational modes, and more complex mechanisms are required.

We study the system size dependence of heavy quark (HQ) observables at a center-of-mass energy of $\sqrt{s_{NN}}=5.02$ TeV to explore whether it can provide further constraints on the physical processes which are involved: energy loss of HQs in the quark gluon plasma (QGP), hadronization, and hadronic rescattering. We use the EPOS4HQ approach to study $p-p$ and 0–10% central O-O, Ar-Ar, Kr-Kr, and Pb-Pb reactions and investigate in detail the momentum change of heavy quarks from creation until their detection as part of a hadron as well as the enhancement of heavy baryon production at low $p_T$. We investigate furthermore the origin and the system size dependence of the azimuthal correlations between the heavy quark $Q$ and the heavy antiquark $\overline{Q}$ and how one can bypass the problem that correlations are washed out due to the combinatorial background. We conclude that a systematic study of the system size dependence of the momentum loss allows separating the momentum loss due to the passage through the QGP from the momentum change due to hadronization, and that the $Q\overline{Q}$ correlations yield insight into the different pQCD processes in which the heavy quarks are created.

The fully self-consistent and microscopic tilted-axis cranking model based on covariant density functional theory has been applied to investigate the positive-parity $\mathrm{\Delta }I=2$ sequences in ${}^{140}\mathrm{Sm}$ and ${}^{140}\mathrm{Gd}$. The calculated relations between rotational frequency and spin, kinetic ${\mathcal{J}}^{\left(1\right)}$ moments of inertia, and dynamic ${\mathcal{J}}^{\left(2\right)}$ moments of inertia are in good agreement with the available experimental data. The calculated $B\left(E2\right)$ values and ${\mathcal{J}}^{\left(2\right)}$/$B\left(E2\right)$ ratios show the decreasing and increasing tendencies with the increasing rotational frequency, respectively, which are in accordance with the characteristics of the antimagnetic rotation. By further analysis of the orientation of angular momentum and the contributions of antimagnetic rotation to the total angular momentum, another realization of the antimagnetic rotation mechanism is clearly illustrated by the closing of two or four $h_{11/2}$ neutron blades. Moreover, it is found that the contribution of antimagnetic rotation to the total angular momentum increment is nearly proportional to the number of blades in these two nuclei.

State-of-the-art models based on nuclear density functional theory are successful in the description of nuclei throughout the whole nuclear chart. Among them, some differences arise regarding their accuracy. For a given nuclear model, this depends on the procedure adopted to determine the parameters, and, at the same time, new experimental findings constantly challenge theory. In the present work, we present a Bayesian inference study aimed at assessing the performance of the Skyrme energy density functionals. For the sake of simplicity and clarity, we restrict our study to spherical, double-magic nuclei, giving equal emphasis to ground-state and dynamical properties. Our basic constraints are (i) masses and charge radii, which are known to be very sensitive to the saturation energy and density; (ii) spin-orbit splittings, which are associated with the spin-orbit parameter(s); (iii) the electric dipole polarizability and parity-violating asymmetry, which are associated with the density dependence of the symmetry energy; (iv) the excitation energy of the isoscalar giant monopole resonance, to constrain the nuclear matter incompressibility; (v) the energy-weighted sum rule of the isovector giant dipole resonance, to account for the isovector effective mass; and (vi) the excitation energy of the isoscalar quadrupole resonance, which is related to the isoscalar effective mass. We are then able to test the Skyrme ansatz in a statistically meaningful way, by determining the posterior distributions of the parameters. In particular, we have found probability distributions in line with published results, with the only exceptions of the symmetry energy at saturation $J$ and its slope $L$, whose distributions favor lower values than commonly reported. Using our method, we have also been able to discuss the correlations among parameters and observables. Finally, we discuss a few possible future developments.

The dipole strength of the nuclide ${}^{59}\mathrm{Co}$ was studied in photon-scattering experiments using bremsstrahlung produced with electron beams of energies of 8.6 and 12.2 MeV at the bremsstrahlung facility $\gamma \mathrm{ELBE}$. We identified 130 levels up to an excitation energy of 10.5 MeV. The quasicontinuum of unresolved transitions was included in the analysis of the spectra and the intensities of branching transitions were estimated on the basis of simulations of statistical $\gamma$-ray cascades. The photoabsorption cross section up to the neutron-separation energy was determined and is compared with predictions of the statistical reaction model as well as data for even-mass nuclides in this mass region. The experimental dipole strength function is compared with an $M1$ strength function obtained from shell-model calculations.

Background: Saturation of nuclear density is a fundamental property of atomic nuclei but in reality, the nuclear internal density distribution is not uniform, e.g., some nuclei are known to have the so-called bubble structure, in which the central density is depressed.

Purpose: We aim to unveil the emergent mechanism of the nonuniformity of the nucleon density distributions for whole nuclear mass regions, generalizing a typical bubble structure.

Method: We systematically investigate the nucleon density distributions using the Skyrme Hartree-Fock plus Bardeen-Cooper-Schrieffer calculation represented in the three-dimensional Cartesian coordinate space. The ground states of 1389 even-even nuclei are generated. To quantify the nonuniformity of these density distributions, a “generalized bubble parameter” is introduced.

Results: We find that the bubble structure appears around the magic numbers, which correspond to the regions where the $s$ orbit appears near the Fermi surface. The nuclear deformation and pairing correlations strongly affect the occupation number, but the robust bubble structure of a medium-mass nucleus, ${}^{100}\mathrm{Sn}$, is found. We confirm that the Coulomb force enhances the bubble degree in the superheavy region. The nuclear nonuniformity is further generalized by the “multilayered” bubble structure, which exhibits some density depression in the internal regions of the density distributions.

Conclusion: The nonuniformity of the internal density distribution occurs due to the deficiency of the specific single-particle orbits: the nodal $s, p$, and $d$ orbits. This is certainly reflected in the density distribution near the nuclear surface, which can be deduced from proton-elastic scattering.

A systematic study is presented on the effect of the breakup mechanism of the weakly bound projectile ${}^8\mathrm{B}$ on total, complete, and incomplete fusion for reactions with targets ${}^{16}\mathrm{O}$, ${}^{27}\mathrm{Al}$, ${}^{28}\mathrm{Si}$, ${}^{58}\mathrm{Ni}$, ${}^{208}\mathrm{Pb}$, and ${}^{209}\mathrm{B}$. Particular attention is given to the relative effect on the incomplete fusion of the projectile fragments, proton, and ${}^7\mathrm{Be}$. The energy-dependent contributions to the incomplete fusion of these fragments show a very interesting behavior when targets of different mass and charge are considered. The incomplete fusion from proton absorption becomes more important than that of ${}^7\mathrm{Be}$ for light targets for incident energies around and above the barrier. However, the inverse occurs for heavy targets. Also, comparative fusion calculations are presented for the targets ${}^{27}\mathrm{Al}$, ${}^{28}\mathrm{Si}$, and ${}^{208}\mathrm{Pb}$, ${}^{209}\mathrm{Bi}$. In this way, the effect of an additional proton on the nuclear potential of the target is determined. The calculations are performed in two steps. The continuum discretized coupled channel method will determine the relative projectile-target radial wave functions. Subsequently, the angular momentum-dependent model of fusion probabilities will be used to calculate complete, incomplete, and total fusion.