Giant resonances (GRs) provide crucial insights into nuclear physics and astrophysics. Exciting GRs using particles like electrons is effective, yet the angular momentum (AM) transfer of electrons, including both intrinsic spin and orbital degrees of freedom in inelastic scattering, has never been studied. Here, we investigate AM transfer in GRs excited by plane-wave and vortex electrons, developing a comprehensive AM-resolved inelastic electron scattering theory. We find that even plane-wave electrons can model-independently extract transition strengths of higher multipolarity by selecting specific AM states of scattered electrons. Additionally, relativistic vortex electrons with an orbital angular momentum of $\pm 1$ can be efficiently generated. Vortex electrons can also be used to extract GR transition strength as in the plane-wave case, regardless of the position of the nucleus relative to the beam axis. Furthermore, relativistic vortex electrons with larger orbital angular momentum can be generated for on-axis nuclei due to AM conservation. Our method offers new perspectives for nuclear structure research and paves the way for generating vortex particles.

We analyze effects of neutron-antineutron transitions in neutron stars, specifically on (i) cooling, (ii) rotation rate, and (iii) for binary pulsars, the increase in the orbital period. We show that these effects are negligibly small.

We report on high-precision atomic mass measurements of ${}^{148–153}\mathrm{La}$ and ${}^{151}\mathrm{Ce}$ performed with the JYFLTRAP double Penning trap using the phase-imaging ion-cyclotron-resonance technique. The masses of ${}^{152,153}\mathrm{La}$ were experimentally determined for the first time. We confirm the sharp kink in the two-neutron separation energies at the neutron number $N=93$ in the cerium ($Z=58$) isotopic chain. Our precision mass measurements of the most exotic neutron-rich lanthanum ($Z=57$) isotopes reveal a unexpected sudden increase in two-neutron separation energies from $N=92$ to $N=93$. Unlike in the cerium isotopic chain, the kink is not sharp but extends to $N=94$ forming a prominent bump. The gain in energy is about 0.4 MeV, making it one of the strongest changes in two-neutron separation energies over the whole chart of nuclides, away from nuclear shell closures. The results, correlated with a predicted onset of quadrupole deformation for $N\ge 92$, call for further studies to elucidate the structure of neutron-rich lanthanum isotopes.

Any experimental evidence of nucleons paired in spin-triplet states will confirm the existence of an exotic phase of nuclear systems. This type of nuclear superfluidity has been hypothesized in heavy nuclei, where the antagonizing spin-orbit effects are damped, and there it oftentimes coexists with traditional spin-singlet pairing, leading to the possibility of mixed-spin pairing. Realistic nuclear deformation, not considered in such studies, could make-or-break these proposals, since its effect on triplet pairing, and the competition (and coexistence) of the two superfluid phases, was expected to be crucial. We report on a thorough study on the effect of deformation on triplet, singlet, and mixed-spin pairing in the relevant region of the nuclear chart. We find that, at low isospin asymmetries, spin-triplet pairing is enhanced by deformation, while below the proton-drip line, the novel superfluid phase survives alongside the usual spin-singlet pairing. These results suggest that spin-triplet superfluidity exists in realistic nuclei and can be probed in the lab.

Measurements of the difference between the squared charge radii of the helion (${}^3\mathrm{He}$ nucleus) and the $\alpha$ particle (${}^4\mathrm{He}$ nucleus) have been characterized by longstanding tensions recently spotlighted in the $3.6\sigma$ discrepancy of the extractions from ordinary atoms versus those from muonic atoms [Karsten Schuhmann et al., arXiv:2305.11679]. Here, we present a novel analysis of uncertainties in nuclear structure corrections that must be supplied by theory to enable the extraction of the difference in radii from spectroscopic experiments. We use modern Bayesian inference techniques to quantify uncertainties stemming from the truncation of the chiral effective field theory expansion of the nuclear force for both muonic and ordinary atoms. With the new nuclear structure input, the helium isotope-shift puzzle cannot be explained, rather, it is reinforced to a $4\sigma$ discrepancy.

This Letter presents the first measurement of event-by-event fluctuations of the net number (difference between the particle and antiparticle multiplicities) of multistrange hadrons ${\mathrm{\Xi }}^{-}$ and ${\overline{\mathrm{\Xi }}}^{+}$ and its correlation with the net-kaon number using the data collected by the ALICE Collaboration in pp, p-Pb, and Pb-Pb collisions at a center-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$. The statistical hadronization model with a correlation over three units of rapidity between hadrons having the same and opposite strangeness content successfully describes the results. On the other hand, string-fragmentation models that mainly correlate strange hadrons with opposite strange quark content over a small rapidity range fail to describe the data.

$\mathit{\gamma }$ decays of the isovector giant dipole resonance (IVGDR) of the deformed nucleus ${}^{154}\mathrm{Sm}$ were measured using $2_1^{+}$-Smekal-Raman and elastic scattering of linearly polarized, quasimonochromatic photon beams. The two scattering processes were disentangled through their distinct angular distributions. Their branching ratio and cross sections were determined at six excitation energies covering the ${}^{154}\mathrm{Sm}$ IVGDR. Both agree with the predictions of the geometrical model for the IVGDR and confirm $\mathit{\gamma }$ decay as an observable sensitive to the structure of the resonance. Consequently, the data place strong constraints on the nuclear shape, including the degree of triaxiality. The derived ${}^{154}\mathrm{Sm}$ shape parameters $\beta =0.2925(25)$ and $\gamma =5.0(15)°$ agree well with other measurements and recent Monte Carlo shell-model calculations.

PHENIX presents a simultaneous measurement of the production of direct $\gamma$ and ${\pi }^0$ in $d+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$ over a $p_T$ range of 7.5 to $18\mathrm{GeV}/c$ for different event samples selected by event activity, i.e., charged-particle multiplicity detected at forward rapidity. Direct-photon yields are used to empirically estimate the contribution of hard-scattering processes in the different event samples. Using this estimate, the average nuclear-modification factor, $R_{d\mathrm{Au},\mathrm{EXP}}^{{\pi }^0}$, is $0.925\pm 0.023(\mathrm{stat})\pm 0.15(\mathrm{scale})$, consistent with unity for minimum-bias (MB) $d+\mathrm{Au}$ collisions. For event classes with low and moderate event activity, $R_{d\mathrm{Au},\mathrm{EXP}}^{{\pi }^0}$ is consistent with the MB value within 5% uncertainty. This result confirms that the previously observed enhancement of high-$p_T$ ${\pi }^0$ production found in small-system collisions with low event activity is a result of a bias in interpreting event activity within the Glauber framework. In contrast, for the top 5% of events with the highest event activity, $R_{d\mathrm{Au},\mathrm{EXP}}^{{\pi }^0}$ is suppressed by 20% relative to the MB value with a significance of $4.5\sigma$, which may be due to final-state effects. This suppression corresponds to a $p_T$ shift of $\delta p_T=0.213\pm 0.055\mathrm{Gev}/c$ at $9\mathrm{Gev}/c$.

Understanding the properties of hypernuclei is crucial for constraining the nature of hyperon-nucleon ($Y\text{−}N$) interactions, which plays a key role in determining the inner structure of compact stars. The lightest hypernuclei and antihypernuclei are the hypertriton (${}_{\mathrm{\Lambda }}{}^3\mathrm{H}$), which consists of a pair of nucleons and a $\mathrm{\Lambda }$ hyperon, and its antinucleus (${}_{\overline{\mathrm{\Lambda }}}{}^3\overline{\mathrm{H}}$). Significant knowledge has recently been acquired regarding the mass, lifetime, and binding energy of ${}_{\mathrm{\Lambda }}{}^3\mathrm{H}$. However, its exact spin, whether $\frac{1}{2}$ or $\frac{3}{2}$, remains undetermined in both experimental and theoretical studies. Here, we present a novel method of using the hypertriton global polarization in heavy-ion collisions to decipher not only its total spin but also its internal spin structure. This method is based on the finding that its three different spin structures exhibit distinct beam energy dependence of its global polarization when it is produced in these collisions from the coalescence of proton, neutron and $\mathrm{\Lambda }$. Future observations of the hypertriton and antihypertriton global polarizations thus provide the opportunity to unveil the spin structures of hypertriton and antihypertriton and their production mechanisms in heavy-ion collisions.

At a fundamental level, the interactions between protons and protons, protons and neutrons, and neutrons and neutrons are not identical. Such isospin nonconserving interactions emerge when comparing the excitation energy of analog states in $T=1$ triplet nuclei. Here, we extend such an analysis to the $A=78$, $T=1$ triplet system—the heaviest system for which such complete data exists—and find strong disagreement with contemporary theory. This was achieved by pioneering the technique of recoil-$\beta \text{−}\beta$ tagging to identify excited states in ${}^{78}\mathrm{Zr}$. We also established a ${}^{78}\mathrm{Zr}$ half-life of ${25}_{-8}^{+17}\mathrm{ms}$ and extended the $T=1$ band in ${}^{78}\mathrm{Y}$ to $J^{\pi }=({10}^{+})$.

Isoscalar dipole transitions are a distinctive fingerprint of cluster structures. A $1^{-}$ resonance at 7.27(10) MeV, located just below the $\alpha$-emission threshold, has been observed in the deuteron inelastic scattering reactions off ${}^{10}\mathrm{Be}$. The deformation lengths of the excited states in ${}^{10}\mathrm{Be}$ below 9 MeV have been inferred from the differential cross sections using coupled channel calculations. This observed $1^{-}$ resonance has isoscalar characteristics and exhausts approximately 5%–15% of the isoscalar dipole energy-weighted sum rule, providing evidence for pronounced $\alpha$ cluster structure in ${}^{10}\mathrm{Be}$. The Gamow coupled channel approach supports this interpretation and suggests the near-threshold effect might be playing an important role in this excitation energy domain. The $\alpha +\alpha +n+n$ four-body calculation reproduces the observed enhanced dipole strength, implying that the four-body cluster structure is essential to describe the $1^{-}$ states in ${}^{10}\mathrm{Be}$.

We report the first ab initio calculation of the nuclear-structure-dependent radiative correction ${\delta }_{\mathrm{NS}}$ to the ${}^{10}\mathrm{C}\to {}^{10}\mathrm{B}$ superallowed transition, computed with the no-core shell model and chiral effective field theory. We obtain ${\delta }_{\mathrm{NS}}=-0.422(29{)}_{\mathrm{nuc}}(12{)}_{n,\mathrm{el}}$ with a 1.6-times reduction in the total uncertainty when compared to the current literature estimate based on the shell model and Fermi gas picture. This Letter paves the way for a precise determination of $V_{ud}$ from superallowed beta decays within a systematically improvable framework.

The spin tensor is fundamental to relativistic spin hydrodynamics, but its definition is ambiguous due to the pseudogauge symmetry. We show that this ambiguity can be solved in interacting field theories. We prove that the mean-field limit of a modified Nambu-Jona-Lasinio model with spin-spin interactions is equivalent to nondissipative spin hydrodynamics with a canonical spin tensor.

Developing high-precision models of the nuclear force and propagating the associated uncertainties in quantum many-body calculations of nuclei and nuclear matter remain key challenges for ab initio nuclear theory. In this Letter, we demonstrate that generative machine learning models can construct novel instances of the nucleon-nucleon interaction when trained on existing potentials from the literature. In particular, we train the generative model on nucleon-nucleon potentials derived at second and third order in chiral effective field theory and at three different choices of the resolution scale. We then show that the model can be used to generate samples of the nucleon-nucleon potential drawn from a continuous distribution in the resolution scale parameter space. The generated potentials are shown to produce high-quality nucleon-nucleon scattering phase shifts. This work provides an important step toward a comprehensive estimation of theoretical uncertainties in nuclear many-body calculations that arise from the arbitrary choice of nuclear interaction and resolution scale.

High-energy nuclear collisions create a quark-gluon plasma, whose initial condition and subsequent expansion vary from event to event, impacting the distribution of the eventwise average transverse momentum [$P([p_{\mathrm{T}}])$]. Disentangling the contributions from fluctuations in the nuclear overlap size (geometrical component) and other sources at a fixed size (intrinsic component) remains a challenge. This problem is addressed by measuring the mean, variance, and skewness of $P([p_{\mathrm{T}}])$ in ${}^{208}\mathrm{Pb}+{}^{208}\mathrm{Pb}$ and ${}^{129}\mathrm{Xe}+{}^{129}\mathrm{Xe}$ collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ and 5.44 TeV, respectively, using the ATLAS detector at the LHC. All observables show distinct features in ultracentral collisions, which are explained by a suppression of the geometrical component as the overlap area reaches its maximum. These results demonstrate a new technique to separate geometrical and intrinsic fluctuations, providing constraints on initial conditions and properties of the quark-gluon plasma, such as the speed of sound.

We give for the first time theoretical estimates of unknown rare electron-capture (EC) decay branchings of ${}^{44}\mathrm{Ti}$, ${}^{57}\mathrm{Co}$, and ${}^{139}\mathrm{Ce}$, relevant for searches of (exotic) dark-matter particles. The nuclear-structure calculations have been done exploiting the nuclear shell model with well-established Hamiltonians and an advanced theory of $\beta$ decay. In the absence of experimental measurements of these rare branches, these estimates are of utmost importance for terrestrial searches of dark-matter particles, such as axionic dark matter in the form of axionlike particles, anapole dark matter, and dark photons in nuclear transitions. Predictions are made for EC-decay rates of second-forbidden unique and second-forbidden nonunique EC transitions that can potentially mimic dark-matter-particle detection in dedicated underground experiments designed to observe the absence of the corresponding nuclear electromagnetic transitions.

Using the $\mathrm{B}\rho$-defined isochronous mass spectrometry technique, we report the first determination of the ${}^{23}\mathrm{Si}$, ${}^{26}\mathrm{P}$, ${}^{27}\mathrm{S}$, and ${}^{31}\mathrm{Ar}$ masses and improve the precision of the ${}^{28}\mathrm{S}$ mass by a factor of 11. Our measurements confirm that these isotopes are bound and fix the location of the proton dripline in P, S, and Ar. We find that the mirror energy differences of the mirror-nuclei pairs ${}^{26}\mathrm{P}\text{−}{}^{26}\mathrm{Na}$, ${}^{27}\mathrm{P}\text{−}{}^{27}\mathrm{Mg}$, ${}^{27}\mathrm{S}\text{−}{}^{27}\mathrm{Na}$, ${}^{28}\mathrm{S}\text{−}{}^{28}\mathrm{Mg}$, and ${}^{31}\mathrm{Ar}\text{−}{}^{31}\mathrm{Al}$ deviate significantly from the values predicted assuming mirror symmetry. In addition, we observe similar anomalies in the excited states, but not in the ground states, of the mirror-nuclei pairs ${}^{22}\mathrm{Al}\text{−}{}^{22}\mathrm{F}$ and ${}^{23}\mathrm{Al}\text{−}{}^{23}\mathrm{Ne}$. Using ab initio VS-IMSRG and mean field calculations, we show that such a mirror-symmetry breaking phenomenon can be explained by the extended charge distributions of weakly bound, proton-rich nuclei. When observed, this phenomenon serves as a unique signature that can be valuable for identifying proton-halo candidates.