The D-measure of net-charge fluctuations quantifies the variance of net charge in strongly interacting matter. It was introduced over 20 years ago as a potential signal of quark-gluon plasma (QGP) in heavy-ion collisions, where it is expected to be suppressed due to the fractional electric charges of quarks. Measurements have been performed at RHIC and LHC, but the conclusion has been elusive in the absence of quantitative calculations for both scenarios. We address this issue by employing a recently developed formalism of density correlations and incorporate resonance decays, local charge conservation, and experimental kinematic cuts. We find that the hadron gas scenario is in fair agreement with the ALICE data for $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$ Pb–Pb collisions only when a very short rapidity range of local charge conservation is enforced, while the QGP scenario is in excellent agreement with experimental data and largely insensitive to the range of local charge conservation. A Bayesian analysis of the data utilizing different priors yields moderate evidence for the freeze-out of charge fluctuations in the QGP phase relative to hadron gas. The upcoming high-fidelity measurements from LHC Run 2 will serve as a precision test of the two scenarios.

The half-lives of 24 isotopes ranging from sulfur to potassium were measured using the ZeroDegree Advanced Decay Station at the Radioactive Isotope Beam Factory, including six of the most neutron-rich—${}^{47}\mathrm{S}$, ${}^{48,49}\mathrm{Cl}$, ${}^{51,52}\mathrm{Ar}$, ${}^{55}\mathrm{K}$—for the first time, while the precision for ${}^{48}\mathrm{Ar}$ and ${}^{53,54}\mathrm{K}$ was significantly improved. Two prominent features are found: First, a half-life drop at ${}^{54}{\mathrm{K}}_{35}$ relative to ${}^{52,53}\mathrm{K}$, supporting the persistence of the $N=34$ subshell closure in potassium with $Z=19$. Second, a high $\beta$-decay rate for ${{}^{48}\mathrm{Cl}}_{31}$ compared to ${}^{47}\mathrm{Cl}$ and ${}^{49}\mathrm{Cl}$, which can be explained by the critical role of the $\nu 1p_{1/2}$ orbital in shell-model calculations. The present calculations indicate that the $N=32$ subshell gap in chlorine with $Z=17$ is slightly smaller than that in calcium ($Z=20$), and the significant excitation across the $N=32$ subshell in ${{}^{48}\mathrm{Cl}}_{31}$ is mainly due to strong configuration mixing.

A long-standing discrepancy between measured and predicted beam-normal single-spin asymmetries $A_n$ in elastic electron scattering off ${}^{208}\mathrm{Pb}$ has challenged our understanding of two-photon exchange (TPE) in heavy nuclei. We report a new measurement at 570 MeV and $Q^2=0.04{\mathrm{GeV}}^2/c^2$, yielding $A_n=[-9.1\pm 2.1(\mathrm{stat})\pm 0.7(\mathrm{syst})]\mathrm{ppm}$. This nonzero value contrasts with previous results at higher energies and suggests a kinematic dependence of TPE effects not captured by current theory, prompting a reevaluation of earlier interpretations.

The solar composition problem has puzzled astrophysicists for more than 20 years. Recent measurements of carbon-nitrogen-oxygen (CNO) neutrinos by the Borexino experiment show a $\sim 2\sigma$ tension with the “low-metallicity” determinations. ${}^{14}\mathrm{N}(p,\gamma {)}^{15}\mathrm{O}$, the slowest reaction in the CNO cycle, plays a crucial role in the standard solar model (SSM) calculations of CNO neutrino fluxes. Here we report a direct measurement of the ${}^{14}\mathrm{N}(p,\gamma {)}^{15}\mathrm{O}$ reaction, in which $S$-factors for all transitions were simultaneously determined in the energy range of $E_{\mathrm{p}}=110–260\mathrm{keV}$ for the first time. Our results resolve previous discrepancies in the ground-state transition, yielding a zero-energy $S$-factor $S_{114}(0)=1.93\pm 0.10\mathrm{keV}\mathrm{b}$, which is 15% higher than the $1.68\pm 0.14\mathrm{keV}\mathrm{b}$ recommended in Solar Fusion III (SF-III). With our $S_{114}$ values, the SSM B23-MB22p, and the latest global analysis of solar neutrino measurements, the C and N photospheric abundance determined by the Borexino experiment is updated to $N_{\mathrm{CN}}=(4.42_{-0.63}^{+0.70})\times {10}^{-4}$. This new $N_{\mathrm{CN}}$ value agrees well with latest “high-metallicity” composition; however, it is also consistent with the “low-metallicity” determination within $\sim 1\sigma$ CL, indicating that the solar metallicity problem remains an open question. In addition, the significant reduction in the uncertainty of $S_{114}$ paves the way for the precise determination of the CN abundance in future large-volume solar neutrino measurements.

We report nuclear charge radii for the isotopes ${}^{104–134}\mathrm{Sn}$, measured using two different collinear laser spectroscopy techniques at ISOLDE-CERN. These measurements clarify the archlike trend in charge radii along the isotopic chain and reveal an odd-even staggering that is more pronounced near the $N=50$ and $N=82$ shell closures. The observed local trends are well described by both nuclear density functional theory and valence space in-medium similarity renormalization group calculations. Both theories predict appreciable contributions from beyond-mean-field correlations to the charge radii of the neutron-deficient tin isotopes. The models, however, fall short of reproducing the magnitude of the known $B(E2)$ transition probabilities, highlighting the remaining challenges in achieving a unified description of both ground-state properties and collective phenomena.

The Sn isotopic chain, exhibiting double shell closures at ${}^{100}\mathrm{Sn}$ and ${}^{132}\mathrm{Sn}$, is a key testing ground for theoretical models of the atomic nucleus. It was originally predicted that the transitional matrix elements between the first $2^{+}$ state and the $0^{+}$ ground state for the even-even isotopes in this chain should show a simple dependence on the neutron number. This prediction was, however, disproven experimentally in some of the first experiments with postaccelerated radioactive beams, a situation that has remained unresolved ever since. Subsequent theoretical work has suggested that the explanation can be found in proton excitations across the $Z=50$ shell gap, with an accompanying experimental signature that the first excited $2^{+}$ state in ${}^{110}\mathrm{Sn}$ should have a distinct oblate shape. In this Letter, we present the first measurements of the spectroscopic quadrupole moment of the $2_1^{+}$ state, $B(E2;4_1^{+}\to 2_1^{+})$ and $B(E2;4_2^{+}\to 2_1^{+})$ values for ${}^{110}\mathrm{Sn}$, as well as the $B(E2;2_1^{+}\to 0_1^{+})$ value with significantly improved precision compared to previous results. From the same experiment, half-lives of the $2_1^{+}$ and $4_1^{+}$ states were measured using the Doppler shift attenuation method. Our combined result, $Q(2_1^{+})=20(8){\mathrm{efm}}^2$ for ${}^{110}\mathrm{Sn}$, is the largest positive value known among the Sn isotopes, indicating an oblate shape of the state by more than $2\sigma$. Comparison of the $E2$ transition strengths and quadrupole moments with recent shell model calculations are presented.

Excited states in the proton drip line nucleus ${}^{61}\mathrm{Ga}$ were populated via the fusion-evaporation reaction ${}^{24}\mathrm{Mg}({}^{40}\mathrm{Ca},p2n){}^{61}\mathrm{Ga}$. The experimental setup at Argonne National Laboratory comprised a novel combination of the Gammasphere array with two CD-shaped double-sided Si-strip detectors inside the Microball CsI(Tl) charged-particle detection array, as well as the Neutron-Shell liquid scintillators and the Fragment Mass Analyzer. Owing to the setup’s unprecedented in-beam proton spectroscopy and tracking capabilities, a coincidence between a 957.6(5)-keV $\gamma$ ray and a 1.876(24)-MeV proton line was observed, which identifies the quasibound proton $\pi g_{9/2}$ single-particle state in ${}^{61}\mathrm{Ga}$ at $E_x=2150(34)\mathrm{keV}$. This probes isospin symmetry at the limit of nuclear binding by providing a unique challenge for the shell-model interpretation of mirror nuclei beyond doubly magic ${}^{56}\mathrm{Ni}$.

We clarify how the weak-interaction-driven bulk viscosity $\zeta$ and the bulk relaxation time ${\tau }_{\mathrm{\Pi }}$ of neutrino-transparent $npe$ matter depend on the nuclear symmetry energy. We show that, at saturation density, the equation-of-state dependence of these transport quantities is fully determined by the experimentally constrained nuclear symmetry energy $S$ and its slope $L$. Variations of $L$ can change the bulk viscosity by orders of magnitude, which can affect both the dissipative and the conservative tidal response of neutron stars. This suggests that both conservative and dissipative effects encoded in the gravitational-wave signatures of binary neutron star inspirals may help constrain nuclear symmetry-energy properties.

We argue that ${}^{23}\mathrm{Na}$ is a potentially significant source of galactic axions. For temperatures $\gtrsim 7\times {10}^8\mathrm{K}$—characteristic of carbon burning in the massive progenitors of supernovae and ONeMg white dwarfs—the 440 keV first excited state of ${}^{23}\mathrm{Na}$ is thermally populated, with its repeated decays pumping stellar energy into escaping axions. Odd-A nuclear abundances are typically very low in high-temperature stellar environments (or absent entirely due to burn-up). ${}^{23}\mathrm{Na}$ is an exception: $\approx 0.1M_{\odot }$ of the isotope is synthesized during carbon burning then maintained at $\approx {10}^9\mathrm{K}$ for times ranging up to $6\times {10}^4\mathrm{y}r$. Using MESA simulations, a galactic model, and sampling over progenitor masses, locations, and evolutionary stages, we find a continuous flux at Earth of $⟨{\varphi }_a⟩\approx 22/{\mathrm{cm}}^2\mathrm{s}$ for $g_{aNN}^{\mathrm{eff}}={10}^{-9}$. Some fraction of these axions converts to photons as they propagate through the galactic magnetic field, producing a distinctive 440 keV line $\gamma$-ray detectable by all-sky detectors like the Compton Spectrometer and Imager (COSI). Assuming a $1\mathrm{\mu }\mathrm{G}$ galactic magnetic field and a sufficiently light axion mass, we find that COSI will be able to probe $|g_{aNN}^{\mathrm{eff}}{g}_{a\gamma \gamma }|\gtrsim 1.8\times {10}^{-22}{\mathrm{GeV}}^{-1}$ at $3\sigma$ after two years of surveying.

We provide the first experimental cross section of the ${}^{73}\mathrm{As}(p,\gamma ){}^{74}\mathrm{Se}$ reaction to constrain one of the main destruction mechanisms of the $p$ nucleus ${}^{74}\mathrm{Se}$ in explosive stellar environments. The measurement was done using a radioactive ${}^{73}\mathrm{As}$ beam at effective center-of-mass energies of 2.9 and $2.3\mathrm{MeV}/\mathrm{nucleon}$. Along with the total cross-section measurement, statistical properties of the ${}^{74}\mathrm{Se}$ compound nucleus were extracted, constraining the reaction cross section in the upper Gamow window of the $\gamma$ process. The impact of the experimentally constrained reaction rate on ${}^{74}\mathrm{Se}$ production in Type II supernovae was investigated through Monte Carlo one-zone network simulations. The results indicate that the overproduction of ${}^{74}\mathrm{Se}$ by Type II supernova models cannot be resolved by nuclear physics alone and point toward the need for a more detailed understanding of the astrophysical conditions of relevance for the $\gamma$ process.

We present the first measurements with a new collinear laser spectroscopy setup at the Argonne Tandem Linac Accelerator System, utilizing its unique capability to deliver neutron-rich refractory metal isotopes produced by the spontaneous fission of ${}^{252}\mathrm{Cf}$. We measured isotope shifts from optical spectra for nine radioactive ruthenium isotopes ${}^{106–114}\mathrm{Ru}$, reaching deep into the mid-shell region. The extracted charge radii are in excellent agreement with predictions from the Brussels-Skyrme-on-a-Grid models that account for the triaxial deformation of nuclear ground states. We show that triaxial deformation impacts charge radii in models that feature shell effects, in contrast to what could be concluded from a liquid drop analysis. This indicates that this exotic type of deformation should not be neglected in regions where it is known to occur, even if its presence cannot be unambiguously inferred through laser spectroscopy.

Fluorine abundance in stars is a sensitive indicator of the physical conditions and processes occurring within their interiors. Recent extrapolated results on the ${}^{19}\mathrm{F}(p,\alpha \gamma ){}^{16}\mathrm{O}$ fluorine destruction cross section suggested an increase of the astrophysical factor by several orders of magnitude at astrophysical energies, with profound implications for our understanding of stellar evolution and nucleosynthesis. We have indirectly measured the ${}^{19}\mathrm{F}(p,\alpha \gamma ){}^{16}\mathrm{O}$ cross section using the Trojan horse method, fully covering astrophysical energies with no need of extrapolations. The strength of the 11 keV resonance was extracted and a significant reduction of the reaction rate was determined, compared to previous studies. The analysis of the astrophysical impact suggests that our measurement challenges existing predictions about fluorine and heavier elements’ abundances, reigniting unresolved questions in the field.

Smashing nuclei at ultrarelativistic speeds and analyzing the momentum distribution of outgoing debris provides a powerful method to probe the many-body properties of the incoming nuclear ground states. Within a perturbative description of initial-state fluctuations in the quark-gluon plasma, we express the measurement of anisotropic flow in ultracentral heavy-ion collisions as the quantum-mechanical average of a specific set of operators measuring the harmonic structure of the two-body azimuthal correlations among nucleons in the colliding states. These observables shed a new light on spatial correlations in atomic nuclei while enabling us to test the complementary pictures of nuclear structure delivered by low- and high-energy experiments on the basis of state-of-the-art theoretical approaches rooted in quantum chromodynamics.

We present the first results of a comprehensive microscopic approach to describe nucleus-nucleus elastic collisions by means of an optical potential derived at first order in multiple-scattering theory and computed by folding the projectile and target nuclear densities with the nucleon-nucleon $t$ matrix, which describes the interaction between each nucleon of the projectile and each nucleon of the target. Chiral interactions are consistently used in the calculation of the $t$ matrix and of the nonlocal nuclear densities, which are computed within the ab initio no-core shell model. Cross sections calculated for $\alpha$ collisions on ${}^{12}\mathrm{C}$ and ${}^{16}\mathrm{O}$ at projectile energies in the range 100–300 MeV are presented and compared with available data. For momentum transfer $q$ up to about $1.0{\mathrm{fm}}^{-1}$ our results are in good agreement with the experimental data, whereas for higher momenta a reduction of the imaginary contributions is needed.

We propose and demonstrate that peripheral neutron-$\alpha$ scattering at low energies can serve as a sensitive and clean probe of the long-range three-nucleon forces. To this aim, we perform ab initio quantum Monte Carlo calculations using two- and three-nucleon interactions derived in chiral effective field theory up to third expansion order. We show that the longest-range three-nucleon force stemming from the two-pion exchange plays a crucial role in the proper description of the neutron-$\alpha$ $D$-wave phase shifts. Our Letter reveals the predictive power of chiral symmetry in the few-body sector and opens a new direction for probing and constraining three-nucleon forces.

The thermalization of quark-gluon plasma created in heavy-ion collisions is crucial for understanding its behavior as a relativistic fluid and the thermodynamic properties of the quantum chromodynamics (QCD). This study investigates the role of fluctuations in the relationship between transverse momentum and particle multiplicity, with a particular focus on their impact on extracting the QCD speed of sound. In a thermalized quark-gluon plasma, these fluctuations mostly originate from quantum fluctuations in the colliding nuclei, and exhibit a Gaussian distribution as a consequence of their independence from thermodynamic response. In contrast, nonthermalized systems display non-Gaussian fluctuations, reflecting the breakdown of thermalization. By leveraging the Gaussianity condition of quantum-initiated fluctuations, the physical value of the speed of sound can be extracted statistically, even in the presence of significant event-by-event fluctuations. This framework provides a robust diagnostic tool for probing thermalization and extracting thermodynamic properties in both large and small collision systems.

The presence of a strong shallow heat source of unknown origin in accreting neutron star crusts has been inferred by analyzing x-ray observations of their cooling in quiescence. We model the cooling of KS 1731–260 using realistic crust compositions and nuclear heating and cooling sources from detailed nuclear reaction network calculations. We find that the required strength of the shallow heat source in KS 1731–260 is reduced by more than a factor of 3 compared to previous analysis, a $5\sigma$ difference that alleviates the need for exotic solutions. Our analysis also suggests the existence of an impure nuclear pasta layer in the inner crust of KS 1731–260, though future observations will provide more stringent constraints. In addition, we obtain constraints on the dominant surface burning modes of KS 1731–260 over its history.

This manuscript reports on the direct observation of a $\beta$-delayed two-neutron emission in a study of ${}^{134}\mathrm{In}$ at the ISOLDE Decay Station using neutron spectroscopy. We also report on the first measurement in ${\beta }^{-}$ decay of the long-sought $13/2^{+}$ excited state in ${}^{133}\mathrm{Sn}$, attributed to be the neutron single-particle $i_{13/2}$ orbital. The observation of sequential neutron emission is used to extract the relative population of the $i_{13/2}$ state, which was found to be much smaller than the predictions of the statistical model. The experiment was possible because of the innovative use of a neutron array with neutron discrimination and interaction tracking capabilities. This is the first study of the details of the two-neutron emission for a nucleus, which belongs to the $r$-process path. Understanding $\beta$-delayed two-neutron emission probabilities is essential to validate models used in astrophysical $r$-process nucleosynthesis calculations. Observing two-neutron emissions in ${\beta }^{-}$ decay paves the way for new experiments to study energy and angular correlations for $\beta$-delayed multineutron emitters.