Exclusive cross sections and momentum distributions have been measured for quasifree one-neutron knockout reactions from a ${}^{54}\mathrm{Ca}$ beam striking on a liquid hydrogen target at $\sim 200\mathrm{MeV}/u$. A significantly larger cross section to the $p_{3/2}$ state compared to the $f_{5/2}$ state observed in the excitation of ${}^{53}\mathrm{Ca}$ provides direct evidence for the nature of the $N=34$ shell closure. This finding corroborates the arising of a new shell closure in neutron-rich calcium isotopes. The distorted-wave impulse approximation reaction formalism with shell model calculations using the effective GXPF1Bs interaction and ab initio calculations concur our experimental findings. Obtained transverse and parallel momentum distributions demonstrate the sensitivity of quasifree one-neutron knockout in inverse kinematics on a thick liquid hydrogen target with the reaction vertex reconstructed to final state spin-parity assignments.

The $\mathrm{\Lambda }$ ($\overline{\mathrm{\Lambda }}$) hyperon polarization along the beam direction has been measured in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$, for the first time in heavy-ion collisions. The polarization dependence on the hyperons’ emission angle relative to the elliptic flow plane exhibits a second harmonic sine modulation, indicating a quadrupole pattern of the vorticity component along the beam direction, expected due to elliptic flow. The polarization is found to increase in more peripheral collisions, and shows no strong transverse momentum ($p_T$) dependence at $p_T$ greater than $1\mathrm{GeV}/c$. The magnitude of the signal is about 5 times smaller than those predicted by hydrodynamic and multiphase transport models; the observed phase of the emission angle dependence is also opposite to these model predictions. In contrast, the kinematic vorticity calculations in the blast-wave model tuned to reproduce particle spectra, elliptic flow, and the azimuthal dependence of the Gaussian source radii measured with the Hanbury Brown–Twiss intensity interferometry technique reproduce well the modulation phase measured in the data and capture the centrality and transverse momentum dependence of the polarization signal.

We report on the first measurements of $J/\psi$ production at very low transverse momentum ($p_T<0.2\mathrm{GeV}/c$) in hadronic $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$ and $\mathrm{U}+\mathrm{U}$ collisions at $\sqrt{s_{NN}}=193\mathrm{GeV}$. Remarkably, the inferred nuclear modification factor of $J/\psi$ at midrapidity in $\mathrm{Au}+\mathrm{Au}$ ($\mathrm{U}+\mathrm{U}$) collisions reaches about 24 (52) for $p_T<0.05\mathrm{GeV}/c$ in the 60%–80% collision centrality class. This noteworthy enhancement cannot be explained by hadronic production accompanied by cold and hot medium effects. In addition, the $dN/dt$ distribution of $J/\psi$ for the very low $p_T$ range is presented for the first time. The distribution is consistent with that expected from the Au nucleus and shows a hint of interference. Comparison of the measurements to theoretical calculations of coherent production shows that the excess yield can be described reasonably well and reveals a partial disruption of coherent production in semicentral collisions, perhaps due to the violent hadronic interactions. Incorporating theoretical calculations, the results strongly suggest that the dramatic enhancement of $J/\psi$ yield observed at extremely low $p_T$ originates from coherent photon-nucleus interactions. In particular, coherently produced $J/\psi$’s in violent hadronic collisions may provide a novel probe of the quark-gluon plasma.

Fission product yields are key infrastructure data for nuclear applications in many aspects. It is a challenge both experimentally and theoretically to obtain accurate and complete energy-dependent fission yields. We apply the Bayesian neural network (BNN) approach to learn existing fission yields and predict unknowns with uncertainty quantification. We demonstrated that the BNN is particularly useful for evaluations of fission yields when incomplete experimental data are available. The BNN evaluation results are quite satisfactory on distribution positions and energy dependencies of fission yields.

One of the few exact results for the description of the time evolution of an inhomogeneous, interacting many-particle system is given by the harmonic potential theorem (HPT). The relevance of this theorem is that it sets a tight constraint on time-dependent many-body approximations. In this contribution, we show that the original formulation of the HPT is valid also for the case of spin-, velocity-, and density-dependent interactions. This result is completely general and relevant, among the rest, for nuclear structure theory both in the case of ab initio and of more phenomenological approaches. As an example, we report on a numerical implementation by testing the small-amplitude limit of the time-dependent Hartree-Fock—also known as the random phase approximation—for the translational frequencies of a neutron system trapped in a harmonic potential.

An extensive, model-independent analysis of the nature of triaxial deformation in ${}^{76}\mathrm{Ge}$, a candidate for neutrinoless double-beta ($0\nu \beta \beta$) decay, was carried out following multistep Coulomb excitation. Shape parameters deduced on the basis of a rotational-invariant sum-rule analysis provided considerable insight into the underlying collectivity of the ground-state and $\gamma$ bands. Both sequences were determined to be characterized by the same $\beta$ and $\gamma$ deformation parameter values. In addition, compelling evidence for low-spin, rigid triaxial deformation in ${}^{76}\mathrm{Ge}$ was obtained for the first time from the analysis of the statistical fluctuations of the quadrupole asymmetry deduced from the measured $E2$ matrix elements. These newly determined shape parameters are important input and constraints for calculations aimed at providing, with suitable accuracy, the nuclear matrix elements relevant to $0\nu \beta \beta$.

A direct and complete measurement of isotopic fission-fragment yields of ${}^{239}\mathrm{U}$ has been performed for the first time. The ${}^{239}\mathrm{U}$ fissioning system was produced with an average excitation energy of 8.3 MeV in one-neutron transfer reactions between a ${}^{238}\mathrm{U}$ beam and a ${}^9\mathrm{Be}$ target at Coulomb barrier energies. The fission fragments were detected and isotopically identified using the VAMOS++ spectrometer at the GANIL facility. The measurement allows us to directly evaluate the fission models at excitation energies of fast neutrons, which are relevant for next-generation nuclear reactors. The present data, in agreement with model calculations, do not support the recently reported anomaly in the fission-fragment yields of ${}^{239}\mathrm{U}$, and they confirm the persistence of spherical shell effects in the Sn region at excitation energies exceeding the fission barrier by a few mega-electron volts.

The most remote isotope from the proton dripline (by 4 atomic mass units) has been observed: ${}^{31}\mathrm{K}$. It is unbound with respect to three-proton ($3p$) emission, and its decays have been detected in flight by measuring the trajectories of all decay products using microstrip detectors. The $3p$ emission processes have been studied by the means of angular correlations of ${}^{28}\mathrm{S}+3p$ and the respective decay vertices. The energies of the previously unknown ground and excited states of ${}^{31}\mathrm{K}$ have been determined. This provides its $3p$ separation energy value $S_{3p}$ of $-4.6(2)\mathrm{MeV}$. Upper half-life limits of 10 ps of the observed ${}^{31}\mathrm{K}$ states have been derived from distributions of the measured decay vertices.

We derive ab initio optical potentials from self-consistent Green’s function theory and compute the elastic scattering of neutrons off oxygen and calcium isotopes. The comparison with scattering data is satisfactory at low scattering energies. The method is benchmarked against the no-core shell model with continuum calculations, showing that virtual excitations of the target are crucial to predict proper fragmentation and absorption at higher energies. This is a significant step toward deriving optical potentials for medium mass nuclei and complex many-body systems in general.

Differences between ${\nu }_e$ and ${\nu }_{\mu }$ quasielastic cross sections are essential in neutrino oscillation analyses and $CP$ violation searches for experiments such as DUNE and T2HK. The ratio of these is however poorly known experimentally and for certain kinematic regions theoretical models give contradictory answers. We use two independent mean-field based models to investigate this ratio using ${}^{40}\mathrm{Ar}$ and ${}^{12}\mathrm{C}$ targets. We demonstrate that a proper treatment of the final nucleon’s wave function confirms the dominance of ${\nu }_{\mu }$ over ${\nu }_e$ induced cross sections at forward lepton scattering.

We report the first measurement of the neutron cross section on argon in the energy range of 100–800 MeV. The measurement was obtained with a 4.3-h exposure of the Mini-CAPTAIN detector to the WNR/LANSCE beam at LANL. The total cross section is measured from the attenuation coefficient of the neutron flux as it traverses the liquid argon volume. A set of 2631 candidate interactions is divided in bins of the neutron kinetic energy calculated from time-of-flight measurements. These interactions are reconstructed with custom-made algorithms specifically designed for the data in a time projection chamber the size of the Mini-CAPTAIN detector. The energy averaged cross section is $0.91\pm 0.10(\text{stat})\pm 0.09(\text{syst})\mathrm{b}$. A comparison of the measured cross section is made to the GEANT4 and FLUKA event generator packages, where the energy averaged cross sections in this range are 0.60 and 0.68 b, respectively.

I consider the $\gamma W$-box correction to superallowed nuclear $\beta$ decays in the framework of dispersion relations. I address a novel effect of a distortion of the emitted electron energy spectrum by nuclear polarizabilities and show that this effect, while neglected in the literature, is sizable. The respective correction to the ${\beta }^{+}$ spectrum is estimated to be ${\mathrm{\Delta }}_R(E)=(1.6\pm 1.6)\times {10}^{-4}E/\mathrm{MeV}$ assuming a conservative 100% uncertainty. The effect is positive definite and can be observed if a high-precision measurement of the positron spectrum is viable. If only the full rate is observed, it should be included in the calculated $\mathcal{F}t$ values of nuclear decays. I argue that this novel effect should be included in the analyses of nuclear beta decay experiments to ensure the correct extraction of $V_{ud}$ from decay rates, and of the Fierz interference term from precision measurements of decay spectra.

The observed correlation between the EMC effect and the contribution of short-range correlations (SRCs) in nuclei suggests that the modification of the quark distributions of bound protons and neutrons might occur within SRCs. This raises the possibility that the EMC effect may have an isospin dependence arising from the $np$ dominance of SRCs. We discuss previous attempts to test this possibility and perform a new analysis of existing data. We find no experimental support for the observation of an isospin dependence of the EMC effect.

In the past two decades, deeply virtual Compton scattering of electrons has been successfully used to advance our knowledge of the partonic structure of the free proton and investigate correlations between the transverse position and the longitudinal momentum of quarks inside the nucleon. Meanwhile, the structure of bound nucleons in nuclei has been studied in inclusive deep-inelastic lepton scattering experiments off nuclear targets, showing a significant difference in longitudinal momentum distribution of quarks inside the bound nucleon, known as the EMC effect. In this Letter, we report the first beam spin asymmetry (BSA) measurement of exclusive deeply virtual Compton scattering off a proton bound in ${}^4\mathrm{He}$. The data used here were accumulated using a 6 GeV longitudinally polarized electron beam incident on a pressurized ${}^4\mathrm{He}$ gaseous target placed within the CLAS spectrometer in Hall-B at the Thomas Jefferson National Accelerator Facility. The azimuthal angle ($\varphi$) dependence of the BSA was studied in a wide range of virtual photon and scattered proton kinematics. The $Q^2$, $x_B$, and t dependencies of the BSA on the bound proton are compared with those on the free proton. In the whole kinematical region of our measurements, the BSA on the bound proton is smaller by 20% to 40%, indicating possible medium modification of its partonic structure.

CUPID-0 is the first pilot experiment of CUPID, a next-generation project for the measurement of neutrinoless double beta decay ($0\nu \mathrm{DBD}$) with scintillating bolometers. The detector, consisting of 24 enriched and 2 natural ZnSe crystals, has been taking data at Laboratori Nazionali del Gran Sasso from June 2017 to December 2018, collecting a ${}^{82}\mathrm{Se}$ exposure of $5.29\mathrm{kg}\times \mathrm{yr}$. In this Letter we present the phase-I results in the search for $0\nu \mathrm{DBD}$. We demonstrate that the technology implemented by CUPID-0 allows us to reach the lowest background for calorimetric experiments: $({3.5}_{-0.9}^{+1.0})\times {10}^{-3}\mathrm{counts}/(\mathrm{keV}\mathrm{kg}\mathrm{yr})$. Monitoring $3.88\times {10}^{25}$ ${}^{82}\mathrm{Se}$ $\mathrm{nuclei}\times \mathrm{yr}$ we reach a 90% credible interval median sensitivity of $T_{1/2}^{0\nu }>5.0\times {10}^{24}\mathrm{yr}$ and set the most stringent limit on the half-life of ${}^{82}\mathrm{Se}$ $0\nu \mathrm{DBD}$: $T_{1/2}^{0\nu }>3.5\times {10}^{24}\mathrm{yr}$ (90% credible interval), corresponding to ${\mathrm{m}}_{\beta \beta }<(311–638)\mathrm{meV}$ depending on the nuclear matrix element calculations.

The PHENIX collaboration presents first measurements of low-momentum ($0.4<p_T<3\mathrm{GeV}/c$) direct-photon yields from $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=39$ and 62.4 GeV. For both beam energies the direct-photon yields are substantially enhanced with respect to expectations from prompt processes, similar to the yields observed in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200$. Analyzing the photon yield as a function of the experimental observable $d{N}_{\mathrm{ch}}/d\eta$ reveals that the low-momentum ($>1\mathrm{GeV}/c$) direct-photon yield $d{N}_{\gamma }^{\mathrm{dir}}/d\eta$ is a smooth function of $d{N}_{\mathrm{ch}}/d\eta$ and can be well described as proportional to $(d{N}_{\mathrm{ch}}/d\eta {)}^{\alpha }$ with $\alpha \approx 1.25$. This scaling behavior holds for a wide range of beam energies at the Relativistic Heavy Ion Collider and the Large Hadron Collider, for centrality selected samples, as well as for different $A+A$ collision systems. At a given beam energy, the scaling also holds for high $p_T$ ($>5\mathrm{GeV}/c$), but when results from different collision energies are compared, an additional $\sqrt{s_{NN}}$-dependent multiplicative factor is needed to describe the integrated-direct-photon yield.

We present extractions of the nucleon nonsinglet moments utilizing new precision data on the deuteron $F_2$ structure function at large Bjorken-$x$ determined via the Rosenbluth separation technique at Jefferson Lab Experimental Hall C. These new data are combined with a complementary set of data on the proton previously measured in Hall C at similar kinematics and world datasets on the proton and deuteron at lower $x$ measured at SLAC and CERN. The new Jefferson Lab data provide coverage of the upper third of the $x$ range, crucial for precision determination of the higher moments. In contrast to previous extractions, these moments have been corrected for nuclear effects in the deuteron using a new global fit to the deuteron and proton data. The obtained experimental moments represent an order of magnitude improvement in precision over previous extractions using high $x$ data. Moreover, recent exciting developments in lattice QCD calculations provide a first ever comparison of these new experimental results with calculations of moments carried out at the physical pion mass, as well as a new approach that first calculates the quark distributions directly before determining moments.

A new summation method model of the reactor antineutrino energy spectrum is presented. It is updated with the most recent evaluated decay databases and with our total absorption gamma-ray spectroscopy measurements performed during the last decade. For the first time, the spectral measurements from the Daya Bay experiment are compared with the antineutrino energy spectrum computed with the updated summation method without any renormalization. The results exhibit a better agreement than is obtained with the Huber-Mueller model in the 2–5 MeV range, the region that dominates the detected flux. A systematic trend is found in which the antineutrino flux computed with the summation model decreases with the inclusion of more pandemonium-free data. The calculated flux obtained now lies only 1.9% above that detected in the Daya Bay experiment, a value that may be reduced with forthcoming new pandemonium-free data, leaving less room for a reactor anomaly. Eventually, the new predictions of individual antineutrino spectra for the ${}^{235}\mathrm{U}$, ${}^{239}\mathrm{Pu}$, ${}^{241}\mathrm{Pu}$, and ${}^{238}\mathrm{U}$ are used to compute the dependence of the reactor antineutrino spectral shape on the fission fractions.