The nuclear neutron-proton contact is introduced, generalizing Tan’s work, and evaluated from medium energy nuclear photodisintegration experiments. To this end we reformulate the quasideuteron model of nuclear photodisintegration and establish the bridge between the Levinger constant and the contact. Using experimental evaluations of Levinger’s constant, we extract the value of the neutron-proton contact in finite nuclei and in symmetric nuclear matter. Assuming isospin symmetry we propose to evaluate the neutron-neutron contact through the measurement of photonuclear spin correlated neutron-proton pairs.

Recent measurements of the positron energy spectrum obtained from inverse beta decay interactions of reactor electron antineutrinos show an excess in the 4 to 6 MeV region relative to current predictions. First-principles calculations of fission and beta decay processes within a typical pressurized water reactor core identify prominent fission daughter isotopes as a possible origin for this excess. These calculations also predict percent-level substructures in the antineutrino spectrum due to Coulomb effects in beta decay. Precise measurement of these substructures can elucidate the nuclear processes occurring within reactors. These substructures can be a systematic issue for measurements utilizing the detailed spectral shape.

Within the framework of the unrestricted time-dependent density functional theory, we present for the first time an analysis of the relativistic Coulomb excitation of the heavy deformed open shell nucleus ${}^{238}\mathrm{U}$. The approach is based on the superfluid local density approximation formulated on a spatial lattice that can take into account coupling to the continuum, enabling self-consistent studies of superfluid dynamics of any nuclear shape. We compute the energy deposited in the target nucleus as a function of the impact parameter, finding it to be significantly larger than the estimate using the Goldhaber-Teller model. The isovector giant dipole resonance, the dipole pygmy resonance, and giant quadrupole modes are excited during the process. The one-body dissipation of collective dipole modes is shown to lead a damping width ${\mathrm{\Gamma }}_{\downarrow }\approx 0.4\mathrm{MeV}$ and the number of preequilibrium neutrons emitted has been quantified.

The ratio between the prompt $\psi (2S)$ and $J/\psi$ yields, reconstructed via their decays into ${\mu }^{+}{\mu }^{-}$, is measured in Pb-Pb and $p$-$p$ collisions at $\sqrt{s_{NN}}=2.76\mathrm{TeV}$. The analysis is based on Pb-Pb and $p$-$p$ data samples collected by CMS at the Large Hadron Collider, corresponding to integrated luminosities of $150\mu {\mathrm{b}}^{-1}$ and $5.4{\mathrm{pb}}^{-1}$, respectively. The double ratio of measured yields $(N_{\psi (2S)}/N_{J/\psi }{)}_{\mathrm{Pb}\text{−}\mathrm{Pb}}/(N_{\psi (2S)}/N_{J/\psi }{)}_{p\text{−}p}$ is computed in three Pb-Pb collision centrality bins and two kinematic ranges: one at midrapidity, $|y|<1.6$, covering the transverse momentum range $6.5<p_T<30\mathrm{GeV}/c$, and the other at forward rapidity, $1.6<|y|<2.4$, extending to lower $p_T$ values, $3<p_T<30\mathrm{GeV}/c$. The centrality-integrated double ratio changes from $0.45\pm 0.13(\text{stat})\pm 0.07(\text{syst})$ in the first range to $1.67\pm 0.34(\text{stat})\pm 0.27(\text{syst})$ in the second. This difference is most pronounced in the most central collisions.

The electromagnetic polarizabilities of the nucleon are fundamental properties that describe its response to external electric and magnetic fields. They can be extracted from Compton-scattering data—and have been, with good accuracy, in the case of the proton. In contradistinction, information for the neutron requires the use of Compton scattering from nuclear targets. Here, we report a new measurement of elastic photon scattering from deuterium using quasimonoenergetic tagged photons at the MAX IV Laboratory in Lund, Sweden. These first new data in more than a decade effectively double the world data set. Their energy range overlaps with previous experiments and extends it by 20 MeV to higher energies. An analysis using chiral effective field theory with dynamical $\mathrm{\Delta }(1232)$ degrees of freedom shows the data are consistent with and within the world data set. After demonstrating that the fit is consistent with the Baldin sum rule, extracting values for the isoscalar nucleon polarizabilities, and combining them with a recent result for the proton, we obtain the neutron polarizabilities as ${\alpha }_n=[11.55\pm 1.25(\text{stat})\pm 0.2(\mathrm{BSR})\pm 0.8(\mathrm{th})]\times {10}^{-4}{\mathrm{fm}}^3$ and ${\beta }_n=[3.65\mp 1.25(\text{stat})\pm 0.2(\mathrm{BSR})\mp 0.8(\mathrm{th})]\times {10}^{-4}{\mathrm{fm}}^3$, with ${\chi }^2=45.2$ for 44 degrees of freedom.

Deformation, a key concept in our understanding of heavy nuclei, is based on a mean-field description that breaks the rotational invariance of the nuclear many-body Hamiltonian. We present a method to analyze nuclear deformations at finite temperature in a framework that preserves rotational invariance. The auxiliary-field Monte Carlo method is used to generate a statistical ensemble and calculate the probability distribution associated with the quadrupole operator. Applying the technique to nuclei in the rare-earth region, we identify model-independent signatures of deformation and find that deformation effects persist to temperatures higher than the spherical-to-deformed shape phase-transition temperature of mean-field theory.

We optimize chiral interactions at next-to-next-to leading order to observables in two- and three-nucleon systems and compute Gamow-Teller transitions in ${}^{14}\mathrm{C}$ and ${}^{22,24}\mathrm{O}$ using consistent two-body currents. We compute spectra of the daughter nuclei ${}^{14}\mathrm{N}$ and ${}^{22,24}\mathrm{F}$ via an isospin-breaking coupled-cluster technique, with several predictions. The two-body currents reduce the Ikeda sum rule, corresponding to a quenching factor $q^2\approx 0.84–0.92$ of the axial-vector coupling. The half-life of ${}^{14}\mathrm{C}$ depends on the energy of the first excited $1^{+}$ state, the three-nucleon force, and the two-body current.

We report on the first measurement of the fission barrier height in a heavy shell-stabilized nucleus. The fission barrier height of ${}^{254}\mathrm{No}$ is measured to be $B_{\mathrm{f}}=6.0\pm 0.5\mathrm{MeV}$ at spin $15\hslash$ and, by extrapolation, $B_{\mathrm{f}}=6.6\pm 0.9\mathrm{MeV}$ at spin $0\hslash$. This information is deduced from the measured distribution of entry points in the excitation energy versus spin plane. The same measurement is performed for ${}^{220}\mathrm{Th}$ and only a lower limit of the fission barrier height can be determined: $B_{\mathrm{f}}(I)>8\mathrm{MeV}$. Comparisons with theoretical fission barriers test theories that predict properties of superheavy elements.

We decompose the neutrinoless double-$\beta$ decay matrix elements into sums of products over the intermediate nucleus with two less nucleons. We find that the sum is dominated by the $J^{\pi }=0^{+}$ ground state of this intermediate nucleus for both the light and heavy neutrino decay processes. This provides a new theoretical tool for comparing and improving nuclear structure models. It also provides the connection to two-nucleon transfer experiments.

Excited states in the $N=102$ isotones ${}^{166}\mathrm{Gd}$ and ${}^{164}\mathrm{Sm}$ have been observed following isomeric decay for the first time at RIBF, RIKEN. The half-lives of the isomeric states have been measured to be 950(60) and 600(140) ns for ${}^{166}\mathrm{Gd}$ and ${}^{164}\mathrm{Sm}$, respectively. Based on the decay patterns and potential energy surface calculations, including ${\beta }_6$ deformation, a spin and parity of $6^{-}$ has been assigned to the isomeric states in both nuclei. Collective observables are discussed in light of the systematics of the region, giving insight into nuclear shape evolution. The decrease in the ground-band energies of ${}^{166}\mathrm{Gd}$ and ${}^{164}\mathrm{Sm}$ ($N=102$) compared to ${}^{164}\mathrm{Gd}$ and ${}^{162}\mathrm{Sm}$ ($N=100$), respectively, presents evidence for the predicted deformed shell closure at $N=100$.

A strong enhancement at low $\gamma$-ray energies has recently been discovered in the $\gamma$-ray strength function of ${}^{56,57}\mathrm{Fe}$. In this work, we have for the first time obtained theoretical $\gamma$ decay spectra for states up to $\approx 8\mathrm{MeV}$ in excitation for ${}^{56,57}\mathrm{Fe}$. We find large $B(M1)$ values for low $\gamma$-ray energies that provide an explanation for the experimental observations. The role of mixed $E2$ transitions for the low-energy enhancement is addressed theoretically for the first time, and it is found that they contribute a rather small fraction. Our calculations clearly show that the high-$\ell (=f)$ diagonal terms are most important for the strong low-energy $M1$ transitions. As such types of $0\hslash \omega$ transitions are expected for all nuclei, our results indicate that a low-energy $M1$ enhancement should be present throughout the nuclear chart. This could have far-reaching consequences for our understanding of the $M1$ strength function at high excitation energies, with profound implications for astrophysical reaction rates.

We address the question of how to improve the agreement between theoretical nuclear single-particle energies (SPEs) and observations. Empirically, in doubly magic nuclei, the SPEs can be deduced from spectroscopic properties of odd nuclei that have one more or one less neutron or proton. Theoretically, bare SPEs, before being confronted with observations, must be corrected for the effects of the particle vibration coupling (PVC). In the present work, we determine the PVC corrections in a fully self-consistent way. Then, we adjust the SPEs, with PVC corrections included, to empirical data. In this way, the agreement with observations, on average, improves; nevertheless, large discrepancies still remain. We conclude that the main source of disagreement is still in the underlying mean fields, and not in including or neglecting the PVC corrections.

Using a multiphase transport model (AMPT) we calculate the elliptic $v_2$ and triangular $v_3$ Fourier coefficients of the two-particle azimuthal correlation function in proton-nucleus ($p$-Pb) and peripheral nucleus-nucleus (Pb-Pb) collisions. Our results for $v_3$ are in a good agreement with the CMS data collected at the Large Hadron Collider. The $v_2$ coefficient is very well described in $p$-Pb collisions and is underestimated for higher transverse momenta in Pb-Pb interactions. The characteristic mass ordering of $v_2$ in $p$-Pb is reproduced, whereas for $v_3$, this effect is not observed. We further predict the pseudorapidity dependence of $v_2$ and $v_3$ in $p$-Pb and observe that both are increasing when going from a proton side to a Pb-nucleus side. Predictions for the higher-order Fourier coefficients, $v_4$ and $v_5$, in $p$-Pb are also presented.

We study neutron matter and symmetric nuclear matter with the quark-meson model for the two-nucleon interaction. The Bethe-Bruckner-Goldstone many-body theory is used to describe the correlations up to the three hole-line approximation with no extra parameters. At variance with other nonrelativistic realistic interactions, the three hole-line contribution turns out to be non-negligible and to have a substantial saturation effect. The saturation point of nuclear matter, the compressibility, the symmetry energy, and its slope are within the phenomenological constraints. Since the interaction also reproduces fairly well the properties of the three-nucleon system, these results indicate that the explicit introduction of the quark degrees of freedom within the considered constituent quark model is expected to reduce the role of three-body forces.

The Skyrme model has two Skyrmion solutions of baryon number 12, with $D_{3h}$ and $D_{4h}$ symmetries. The first has an equilateral triangular shape and the second an extended linear shape, analogous to the triangle and linear chain structures of three alpha particles. We recalculate the moments of inertia of these Skyrmions, and deduce the energies and spins of their quantized rotational excitations. There is a good match with the ground-state band of carbon-12, and with the recently established rotational band of the Hoyle state. The ratio of the root mean square matter radii also matches the experimental value.

We present the first measurement at the LHC of exclusive $J/\psi$ photoproduction off protons, in ultraperipheral proton-lead collisions at $\sqrt{s_{\text{NN}}}=5.02\mathrm{TeV}$. Events are selected with a dimuon pair produced either in the rapidity interval, in the laboratory frame, $2.5<y<4$ ($p\text{−}\mathrm{Pb}$) or $-3.6<y<-2.6$ ($\mathrm{Pb}\text{−}p$), and no other particles observed in the ALICE acceptance. The measured cross sections $\sigma (\gamma +p\to J/\psi +p)$ are $33.2\pm 2.2(\text{stat})\pm 3.2(\text{syst})\pm 0.7(\text{theor})\mathrm{nb}$ in $p\text{−}\mathrm{Pb}$ and $284\pm 36(\text{stat}{)}_{-32}^{+27}(\text{syst})\pm 26(\text{theor})\mathrm{nb}$ in $\mathrm{Pb}\text{−}p$ collisions. We measure this process up to about 700 GeV in the $\gamma p$ center of mass, which is a factor of two larger than the highest energy studied at HERA. The data are consistent with a power law dependence of the $J/\psi$ photoproduction cross section in $\gamma p$ energies from about 20 to 700 GeV, or equivalently, from Bjorken $x$ scaling variable between $\sim 2\times {10}^{-2}$ and $\sim 2\times {10}^{-5}$, thus indicating no significant change in the gluon density behavior of the proton between HERA and LHC energies.

We present a precise measurement of double-polarization asymmetries in the ${}^3\overrightarrow{\mathrm{He}}(\overrightarrow{\mathrm{e}},e^{\prime }d)$ reaction. This particular process is a uniquely sensitive probe of hadron dynamics in ${}^3\mathrm{He}$ and the structure of the underlying electromagnetic currents. The measurements have been performed in and around quasielastic kinematics at $Q^2=0.25(\mathrm{GeV}/c{)}^2$ for missing momenta up to $270\mathrm{MeV}/c$. The asymmetries are in fair agreement with the state-of-the-art calculations in terms of their functional dependencies on $p_{\mathit{m}}$ and $\omega$, but are systematically offset. Beyond the region of the quasielastic peak, the discrepancies become even more pronounced. Thus, our measurements have been able to reveal deficiencies in the most sophisticated calculations of the three-body nuclear system, and indicate that further refinement in the treatment of their two-and/or three-body dynamics is required.

The $p_T$-differential production cross sections of the prompt charmed mesons $D^0$, $D^{+}$, $D^{*+}$, and $D_s^{+}$ and their charge conjugate in the rapidity interval $-0.96<y_{\text{cms}}<0.04$ were measured in $p\text{−}\mathrm{Pb}$ collisions at a center-of-mass energy $\sqrt{s_{NN}}=5.02\mathrm{TeV}$ with the ALICE detector at the LHC. The nuclear modification factor $R_{p\mathrm{Pb}}$, quantifying the $D$-meson yield in $p\text{−}\mathrm{Pb}$ collisions relative to the yield in $pp$ collisions scaled by the number of binary nucleon-nucleon collisions, is compatible within the 15%–20% uncertainties with unity in the transverse momentum interval $1<p_T<24\mathrm{GeV}/c$. No significant difference among the $R_{p\mathrm{Pb}}$ of the four $D$-meson species is observed. The results are described within uncertainties by theoretical calculations that include initial-state effects. The measurement adds experimental evidence that the modification of the momentum spectrum of $D$ mesons observed in Pb-Pb collisions with respect to $pp$ collisions is due to strong final-state effects induced by hot partonic matter.

The interaction of an $E/A=57.6\text{−}\mathrm{MeV}$ ${}^{17}\mathrm{Ne}$ beam with a Be target is used to populate levels in ${}^{16}\mathrm{Ne}$ following neutron knockout reactions. The decay of ${}^{16}\mathrm{Ne}$ states into the three-body ${}^{14}\mathrm{O}+p+p$ continuum is observed in the High Resolution Array (HiRA). For the first time for a $2p$ emitter, correlations between the momenta of the three decay products are measured with sufficient resolution and statistics to allow for an unambiguous demonstration of their dependence on the long-range nature of the Coulomb interaction. Contrary to previous measurements, our measured limit $\mathrm{\Gamma }<80\mathrm{keV}$ for the intrinsic decay width of the ground state is not in contradiction to the small values (of the order of keV) predicted theoretically.