We present a systematic investigation of particle-number fluctuations in the crossover region near the critical end point of a first-order phase transition using molecular dynamics simulations of the classical Lennard-Jones fluid. We extend our prior studies to third- and fourth-order cumulants in both coordinate- and momentum-space acceptances and integrated correlation functions (factorial cumulants). We find that, even near the critical point, non-Gaussian cumulants equilibrate on timescales comparable to those of the second-order cumulants, but show stronger finite-size effects. The presence of interactions and of the critical point leads to strong deviations of the cumulants from the ideal-gas baseline in coordinate space; these deviations are expected to persist in momentum space in the presence of collective expansion. In particular, the kurtosis becomes strongly negative, $\kappa {\sigma }^2\ll -1$, on the crossover side of the critical point. However, this signal is significantly diluted once an efficiency cut used to distinguish protons from baryons is applied, leading to $|\kappa {\sigma }^2|\lesssim 1$ even in the presence of the critical point. We discuss our results in the context of ongoing measurements of proton-number cumulants in heavy-ion collisions in RHIC-BES-II.

This article presents the formulation and numerical implementation of a time-independent wave-packet (TIWP) asymptotic projection scheme for extracting sharp-energy rearrangement and breakup $S$ matrices from wave-packet solutions of the time-dependent Faddeev equations. The TIWP scheme is based on time-to-energy transforms of the numerically propagated interacting and free wave packets and allows the extraction of scattering observables in energy space. The time-dependent Faddeev equations are solved in momentum space for a given initial wave packet using finite-element-type discretizations of the Jacobi momenta in terms of local basis functions and a central-difference scheme for time propagation. Concurrently with the step-by-step numerical time evolution of the wave packet, its time-to-energy-transform is accumulated by trapezoidal rule to be obtained at selected values of the energy. Projection of the time-to-energy transform of the post-collision wave packet on the two-particle bound and continuum states yield sharp-energy rearrangement and breakup $S$ matrices, respectively. Rearrangement and breakup amplitudes over a wide range of collision energies are obtained from a single wave-packet propagation. For benchmark three-body models, rearrangement $S$ matrices are found to be in very good quantitative agreement with reference time-independent calculations. For breakup, the TIWP scheme reproduces the main qualitative features of the breakup amplitudes, although the numerical accuracy is presently limited by discretization and asymptotic-time constraints.

Excited states of ${}^{209}\mathrm{Ac}$ and ${}^{207}\mathrm{Ac}$ were observed, for the first time, by employing a highly selective recoil-decay tagging method and the recoil ion transport unit (RITU) gas-filled recoil separator. The nuclei were produced in the ${}^{180}\mathrm{Hf}({}^{35}\mathrm{Cl}, 6n){}^{209}\mathrm{Ac}$ and ${}^{175}\mathrm{Lu}({}^{36}\mathrm{Ar},4n){}^{207}\mathrm{Ac}$ fusion-evaporation reactions. The ${}^{209}\mathrm{Ac}$ isotope was studied using in-beam spectroscopy. Prompt $\gamma$ rays were observed by the JUROGAM3 Ge-detector array and a level scheme was deduced. The ${}^{207}\mathrm{Ac}$ isotope was probed at the focal plane spectrometer of the separator and a $13/2^{+}$ ($\pi i_{13/2}$) isomeric state was observed for the first time in any $N\le 126$ actinium isotope.

Within the framework of the two-center shell model, the influence of excitation energy and spin-orbit interaction on the potential energy surface and, accordingly, on the axially symmetric and mass-symmetric static fission paths selected on the basis of potential energy surfaces is considered. The relationship between the decay of shell corrections in the ground state and at the saddle point and the conservation of the fission barrier at moderate excitation energies of superheavy nuclei with atomic numbers $Z=108$, 114, 116, and 120 formed in a hot complete fusion reaction is discussed.

I develop a reduced basis emulator for continuum-discretized coupled-channel (CDCC) calculations that achieves speedups of $\approx {10}^2$ while maintaining subpercent accuracy. The emulator is constructed using the proper orthogonal decomposition (POD) method applied to snapshots of CDCC solutions computed at sampled points in the optical potential parameter space. The prediction is performed via Galerkin projection onto the reduced basis. I demonstrate the method using deuteron scattering on ${}^{58}\mathrm{Ni}$ at 21.6 MeV as a test case, emulating 18 optical potential parameters simultaneously. The emulator reproduces elastic-scattering cross sections with errors below 0.1% across a wide parameter range. This development enables efficient uncertainty quantification and Bayesian parameter estimation for nuclear reaction calculations that were previously computationally prohibitive.

This paper presents the first measurement of the angle between different jet axes (denoted as $\mathrm{\Delta }{R}_{\mathrm{axis}}$) in $\text{Pb-Pb}$ collisions. The measurement is carried out in the 0–10 % most-central events at $\sqrt{s_{NN}}=5.02$ TeV. Jets are assembled by clustering charged particles at midrapidity using the $\text{anti-}{k}_{\mathrm{T}}$ algorithm with resolution parameters $R=0.2$ and 0.4 and transverse momenta in the intervals $40<p_{\mathrm{T}}^{\mathrm{ch}\mathrm{jet}}<140\mathrm{GeV}/c$ and $80<p_{\mathrm{T}}^{\mathrm{ch}\mathrm{jet}}<140\mathrm{GeV}/c$, respectively. Measurements at these low transverse momenta enhance the sensitivity to quark-gluon plasma (QGP) effects. A comparison to models implementing various mechanisms of jet energy loss in the QGP suggests that the observed narrowing of the $\text{Pb-Pb}$ distribution relative to $\mathit{pp}$ can be explained if quark-initiated jets are more likely to emerge from the medium than gluon-initiated jets. These new measurements disfavor intrajet $p_{\mathrm{T}}$ broadening as implemented in a simple model calculation with the Baier-Dokshitzer-Mueller-Peigne-Schiff formalism for energy loss in the QGP. The comparison of $\text{Pb-Pb}$ and $\mathit{pp}$ collisions shows sensitivity to the angular scale at which the QGP can resolve two independent splittings, favoring mechanisms that incorporate incoherent energy loss.

Collisions of relativistic light ions, such as oxygen, neon, and magnesium, have been proposed as a way to examine the system-size dependence of dynamics typically associated with the quark-gluon plasma produced in collisions of heavier ions such as xenon, gold, or lead. Recent efforts at both the Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) have produced large datasets of proton-oxygen, oxygen-oxygen, and neon-neon collisions, catalyzing intense interest in experimental backgrounds associated with light-ion collisions. In particular, electromagnetic dissociation of light ions while they are circulating in a collider can result in beam contamination that is difficult to simulate precisely. Here we propose a data-driven method for evaluating the potential impact of beam contaminants on physics analyses. The method exploits the time dependence and smaller size of contaminant ion species to define control regions that can be used to quantify potential contamination effects. A simple model is used to illustrate the method and to study its robustness. This method can inform studies of recent LHC and RHIC data and could also be useful for future light-ion programs at the LHC and beyond.

The $T$ matrix of the heavy quark-antiquark ($Q\overline{Q}$) pair interacting through a screened Cornell potential in the quark-gluon plasma is computed without employing the partial-wave expansion. This is compared with the results obtained using the conventional method of partial-wave expansion. Through a comprehensive survey over a range of screening mass and center-of-mass (c.m.) energy, which, when combined, determine the orbital angular momentum involved in the scattering, it is demonstrated that a substantial number of partial-wave terms are necessary to precisely match the full scattering amplitude directly obtained from the method without partial-wave expansion. For moderate screening masses (corresponding to one to two times the crossover transition temperature) and c.m. energy, the number of partial waves required for satisfactory matching turns out as large as 10–20, substantially larger than what one would expect based on simply measuring the magnitudes of the first few partial-wave amplitudes. This highlights the efficacy and advantage of the new method in directly obtaining the full scattering amplitude needed for further computation of physical observables, which is illustrated by comparing the calculations of heavy quark-antiquark scattering cross section and heavy quark drag coefficient between the two methods. We also employ the new method to calculate the $T$ matrix at c.m. energies below the $Q\overline{Q}$mass threshold, and demonstrate the presence of bound states of different orbital quantum numbers simultaneously in a single energy scan.

Jet suppression in high-energy heavy-ion collisions results from jet energy loss and transverse-momentum broadening during jet propagation through the quark-gluon plasma (QGP). The jet cone size ($R$) dependence of this suppression offers crucial insights into the energy loss mechanisms and QGP transport properties. In our study, we implement a comprehensive approach within the perturbative QCD parton model that incorporates both elastic and inelastic energy loss mechanisms. For elastic processes the contribution from recoiling thermal partons reduces the net in-cone energy loss for a given jet radius. For inelastic processes, we account for the angular distribution of radiated gluons, the thermalization of soft gluons, and transverse-momentum broadening. Using this framework, we calculate the jet nuclear modification factors ($R_{AA}$) and their double ratios $R_{AA}(R=0.2–1.0)/R_{AA}(R=0.2)$, and systematically compare with ALICE, ATLAS, and CMS data in 0–10% and 30–50% $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$. Numerical results show that $R_{AA}$ increases with the cone size $R$ because the in-cone energy loss decreases at larger radii. Specifically, as the radius $R$ grows, the probability for elastically scattered partons to escape the jet cone and the likelihood for radiated gluons to fall outside the cone both decrease, resulting in a net reduction of energy loss. The $R_{AA}$ double ratios are approximately unity for small radii ($R=0.4$ relative to $R=0.2$) and at high $p_{\mathrm{T}}\gtrsim 200\mathrm{GeV}/c$, in agreement with the data within uncertainties.

This paper presents the first measurements of the azimuthal anisotropy coefficients $v_n$, which quantify the $n\mathrm{th}$-order Fourier modulation of charged-particle azimuthal distributions, for $n=2-4$ in $\sqrt{s_{NN}}=5.36\mathrm{TeV}{}^{16}\mathrm{O}+{}^{16}\mathrm{O}$ and ${}^{20}\mathrm{Ne}+{}^{20}\mathrm{Ne}$ collisions recorded with the ATLAS detector at the CERN Large Hadron Collider in 2025. The $v_n$ coefficients are measured as a function of transverse momentum ($p_{\text{T}}$), collision centrality, and event multiplicity. They are extracted using two complementary methods: two-particle correlations with a template-fit subtraction of short-range nonflow contributions, and four-particle subevent cumulants, which intrinsically suppress nonflow effects and provide sensitivity to flow fluctuations. The results show a clear hierarchy $v_2>v_3>v_4$ and a nonmonotonic dependence on $p_{\text{T}}$, reaching a maximum around $2\mathrm{GeV}$, consistent with trends observed in heavy-ion collisions. Detailed comparisons between the two collision systems reveal an enhanced $v_2$ in central ${}^{20}\mathrm{Ne}+{}^{20}\mathrm{Ne}$ collisions, consistent with theory expectations based on the predicted prolate deformation of neon nuclei, in contrast to the slightly tetrahedral structure predicted for oxygen. The four-particle cumulant results highlight strong event-by-event fluctuations and provide the greatest sensitivity to nuclear shape effects. These measurements can place new constraints on the initial geometry and the hydrodynamic response in light-ion collisions, offering valuable input for models of nuclear structure.

The symmetry energy expansion was developed to connect isospin symmetric matter probed in nuclear experiments to asymmetric matter found in neutron stars. Using the isospin asymmetry derived from the Gell-Mann-Nishijima formula, we derive the symmetry energy expansion for quark matter, which has unique properties compared to hadronic matter. To test our methods, we use perturbative Quantum Chromodynamics (pQCD) calculations at next-to-leading order, where realistic quark masses can be included. We find that pQCD at electroweak equilibrium is not isospin symmetric but rather obtains a small skewness term in the symmetry energy expansion. We predict that if equations of state for nuclear matter must match pQCD results, then a nonmonotonic dip in the symmetry energy would appear.

The GlueX experiment at Jefferson Lab has observed $p\overline{p}$ and, for the first time, $\mathrm{\Lambda }\overline{\mathrm{\Lambda }}$ and $p\overline{\mathrm{\Lambda }}$ photoproduction from a proton target at photon energies up to 11.6 GeV. The angular distributions are forward peaked for all produced pairs, consistent with Regge-like $t$-channel exchange. Asymmetric wide-angle antibaryon distributions show the presence of additional processes. In a phenomenological model, we find consistency with a double-$t$-channel exchange process where antibaryons are created only at the middle vertex. The model matches all observed distributions with a small number of free parameters. In the hyperon channels, we observe a clear distinction between photoproduction of the $\mathrm{\Lambda }\overline{\mathrm{\Lambda }}$ and $p\overline{\mathrm{\Lambda }}$ systems but general similarity to the $p\overline{p}$ system. We report both total cross sections and cross sections differential with respect to momentum transfer and the invariant masses of the created particle pairs. No narrow resonant structures were found in these reaction channels. The suppression of $s\overline{s}$ quark pairs relative to $d\overline{d}$ quark pairs is similar to what has been seen in other reactions.

I present a calculation of the ratio $\frac{{\sigma }_r}{F_2}(x,Q^2)$ in a momentum-space approach using the Block-Durand-Ha parametrization of the proton structure function $F_2(x,Q^2)$. The results are compared with the H1 data and extended to high inelasticity. I also examine the ratio $\frac{{\sigma }_r}{F_2}(\frac{Q^2}{s},Q^2)$ obtained at a fixed $\sqrt{s}$ and $Q^2$ to the minimum value of $x$ given by $Q^2/s$, comparing them with both the HERA data and the color dipole model bounds. These results and comparisons with HERA data demonstrate that the suggested method for the ratio $\frac{{\sigma }_r}{F_2}$ can be applied in analyses of the CERN Large Hadron Collider and Future Circular Collider projects. The effect of adding a simple higher twist term of the form $F_2*H_2/Q^2$ to the description of the ratio $\frac{{\sigma }_r}{F_2}(\frac{Q^2}{s},Q^2)$ at low-$x$ and low-$Q^2$ values for comparison with the color dipole bounds and the HERA data is investigated.

Single-particle states in ${}^{199}\mathrm{Hg}$ have been studied with the ${}^{200}\mathrm{Hg}(d,t){}^{199}\mathrm{Hg}$ reaction using 22-MeV deuterons. The reaction products were momentum analyzed using a Q3D magnetic spectrograph, and a position-sensitive cathode-strip detector located at the focal plane recorded the particle spectra. Cross sections for the population of individual states up to approximately 3-MeV excitation energy were determined, and angular distributions have been constructed. In total, 93 levels were observed, including and 52 previously unobserved levels, and spin-parity assignments made for 16 previously established levels. The results were compared with large-scale shell-model calculations that reproduce well the spectroscopic strengths for levels at low excitation energy, and the trends in the cumulative strength to high excitation energy.

While hybrid approaches of relativistic $\mathrm{hydrodynamics}+\mathrm{transport}$ have been well established for the dynamical description of heavy-ion collisions at high beam energies, moving to lower beam energies is challenging. In this work, we propose dynamic initial conditions for the viscous hydrodynamic evolution in heavy-ion collisions at low to intermediate beam energies. They are comprised of core hadrons based on the local energy density during the preequilibrium hadronic evolution. The smash-vhlle hybrid approach is then applied to lower beam energies, achieving good agreement with measured bulk observables between $\sqrt{s_{NN}}=3$ and $9.1\mathrm{GeV}$, thus providing theoretical guidance for the Beam Energy Scan performed by the STAR Collaboration at RHIC and the future Compressed Baryonic Matter experiment at GSI.

We have used the auxiliary-field quantum Monte Carlo (AFQMC) many-body approach on the lattice to study the equation of state for a fermionic impurity interacting with a background sea of spin-polarized fermions. The impurity, or polaron, is an interesting system in both cold atomic and nuclear physics. Our approach is general, and we are able to straightforwardly study the polaron across these regimes. We first study the Fermi polaron at unitarity and for a wide range of scattering lengths, comparing against previous theoretical and experimental studies. We then explore the neutron polaron which has been shown to be a useful constraint for nuclear physics. We have also employed the recently developed parametric matrix model to emulate AFQMC solutions to the two-body problem on the lattice, to accelerate the tuning of our lattice Hamiltonian parameters directly to two-body energies in a periodic box, following Lüscher's formula. Our lattice quantum Monte Carlo results for the polaron in both a cold atomic and nuclear physics context can serve as stringent benchmarks for future theoretical and experimental research.

The lifetimes of the $2_1^{+}$ and $4_1^{+}$ states of ${}^{200}\mathrm{Pt}$ were measured by applying the recoil-distance Doppler-shift method. Excited states were populated in the ${}^{198}\mathrm{Pt}({}^{18}\mathrm{O}$, ${}^{16}\mathrm{O}){}^{200}\mathrm{Pt}$ two-neutron transfer reaction at the 9-MV tandem accelerator at the IFIN-HH in Măgurele, Romania. The resulting $B\left(E2\right)$ values of the $2_1^{+}\to 0_1^{+}$ and $4_1^{+}\to 2_1^{+}$ transitions as well as the $B_{4/2}$ ratio of 2.10(31) indicate an evolution of the nuclear structure toward sphericity when approaching the neutron shell closure at $N=126$. The $B(E2;2_1^{+}\to 0_1^{+})$ values of Pt and Hg are compared to values of Te, Xe, and Ba where similar structural effects are exhibited.

We propose a Quantization-Constrained Parameter Method (QCPM) for determining the Woods-Saxon (WS) potential depth $V_0$ and diffuseness $a$ in studies of $\alpha$ and cluster decay half-lives. In this approach, the parameters are derived analytically by imposing the Bohr-Sommerfeld (BS) quantization condition, thereby eliminating the need for parameter fitting. The calculated diffuseness values exhibit a strong dependence on nuclear shell structure. The reliability of the QCPM-derived WS potential is validated through optical model analyses of elastic $\alpha$ scattering data. The resulting $\alpha$ and cluster decay half-lives show good agreement with experimental values. Our results highlight the significant role of daughter-nucleus deformation in improving the consistency between theoretical predictions and experimental data. In addition, we introduce a modified Woods-Saxon (mWS) potential that effectively approximates the surface behavior of folding potentials incorporating the nuclear medium effect. This modification leads to closer agreement with the measured half-lives. Free of adjustable parameters such as $V_0$ and $a$, the QCPM enhances the predictive power of phenomenological potentials for $\alpha$ and cluster decay studies.

A direct measurement of the ${}^7\mathrm{Li}(p,\alpha ){}^4\mathrm{He}$ reaction at astrophysical energies was performed at the Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering (IFIN-HH) using a scaled-down version of the ELISSA detector array and the 3 MV Tandem accelerator. This reaction plays a crucial role in both primordial and stellar nucleosynthesis. In Big-Bang Nucleosynthesis (BBN), it is directly linked to the long-standing “Cosmological Lithium Problem,” the discrepancy between observed and predicted primordial ${}^7\mathrm{Li}$ abundances. In stellar environments, it constitutes the final step in the hydrogen-to-helium burning chain. The experiment utilized a ${}^7\mathrm{Li}$ beam incident on a ${\mathrm{CH}}_2$ target at ten laboratory energies $\left(E_{\text{lab}}\right)$ corresponding to center-of-mass energies ($E_{\text{c.m.}}$) ranging from 59.5 to 990 keV. The astrophysical $S$ factors were extracted using both the Distorted Wave Born Approximation (DWBA) and polynomial fitting techniques. Updated reaction rates were calculated from the present DWBA results, supplemented by existing experimental data. The impact of the theoretical DWBA calculation on the reaction rate is investigated.

The quantum chromodynamics (QCD) phase diagram at large densities and low temperatures can be probed using both neutron stars and low-energy heavy-ion collisions. Heavy-ion collisions are nearly isospin-symmetric systems, whereas neutron stars are highly isospin asymmetric since they are neutron rich. The symmetry-energy expansion is used to connect these regimes across isospin asymmetry. However, the current symmetry-energy expansion does not account for strange particles. In this work, we include finite strangeness by redefining the isospin-asymmetry parameter and the symmetry-energy expansion in a way that is consistent with QCD SU(3) flavor symmetry. Our new symmetry energy works well beyond typical neutron star central densities and admits a skewness term in the presence of strangeness for the case of weak equilibrium.