The system formed in ultrarelativistic heavy-ion collisions behaves as a nearly perfect fluid. This collective behavior is probed experimentally by two-particle azimuthal correlations, which are typically averaged over the properties of one particle in each pair. In this Rapid Communication, we argue that much additional information is contained in the detailed structure of the correlation. In particular, the correlation matrix exhibits an approximate factorization in transverse momentum, which is taken as strong evidence for the hydrodynamic picture, while deviations from the factorized form are taken as a signal of intrinsic, “nonflow” correlations. We show that hydrodynamics in fact predicts factorization breaking as a natural consequence of initial-state fluctuations and averaging over events. We derive the general inequality relations that hold if flow dominates, and which are saturated if the matrix factorizes. For transverse momenta up to 5 GeV, these inequalities are satisfied in data, but not saturated. We find factorization breaking in event-by-event ideal hydrodynamic calculations that is at least as large as in data and argue that this phenomenon opens a new window on the study of initial fluctuations.

We report new measurements of the neutron-deuteron elastic scattering cross section at energies from 135 to 250 MeV and center-of-mass angles from ${80}^{\circ }$ to ${130}^{\circ }$. Cross sections for neutron-proton elastic scattering were also measured with the same experimental setup for normalization purposes. Our $nd$ cross-section results are compared with predictions based on Faddeev calculations, including three-nucleon forces, and with cross sections measured with charged particle and neutron beams at comparable energies.

The spectroscopy of ${}^{157}$Yb has been studied via ${}^{144}$Sm(${}^{16}$O,$3n$)${}^{157}$Yb fusion-evaporation reaction. The properties of bands associated with the $\nu$$i_{13/2}$ orbital and $\nu$$h_{9/2}$ orbital in ${}^{157}$Yb are analyzed in comparison with the triaxial particle-rotor-model calculations. The characters of signature splitting for both positive-parity $\nu$$i_{13/2}$ and negative-parity $\nu$$h_{9/2}$ bands in ${}^{157}$Yb and heavier odd-A Yb isotopes are discussed. The newly observed bands 1 and 2 in ${}^{157}$Yb are suggested to be the signature partners of the $\nu$$h_{9/2}$ band. A systematic study of the band crossing frequencies associated with the $i_{13/2}$ neutron-pair and $h_{11/2}$ proton-pair alignments for the Yb isotopes, as well as the Er and Hf isotopes, are made.

We introduce a unified approach to nuclear bound and continuum states based on the coupling of the no-core shell model (NCSM), a bound-state technique, with the no-core shell model/resonating group method (NCSM/RGM), a nuclear scattering technique. This new ab initio method, no-core shell model with continuum (NCSMC), leads to convergence properties superior to either NCSM or NCSM/RGM while providing a balanced approach to different classes of states. In the NCSMC, the ansatz for the many-nucleon wave function includes (i) a square-integrable $A$-nucleon component expanded in a complete harmonic oscillator basis and (ii) a binary-cluster component with asymptotic boundary conditions that can properly describe weakly bound states, resonances, and scattering. The Schrödinger equation is transformed into a system of coupled-channel integral-differential equations that we solve using a modified microscopic $R$-matrix formalism within a Lagrange mesh basis. We demonstrate the usefulness of the approach by investigating the unbound ${}^7$He nucleus.

The neutron-proton Fermi-energy difference and the correlation to nucleon separation energies for some magic nuclei are investigated with the Skyrme energy density functionals and nuclear masses, with which the nuclear symmetry energy at subsaturation densities is constrained from 54 Skyrme parameter sets. The extracted nuclear symmetry energy at subsaturation density of 0.11 fm${}^{-3}$ is 26.2 $\pm$ 1.0 MeV with 1.5$\sigma$ uncertainty. By further combining the neutron-skin thickness of ${}^{208}$Pb, ten Skyrme forces with slope parameter of $28\le L\le 65$ are selected for the description of the symmetry energy around saturation densities.

In nucleon-nucleon collisions, a charged particle's multiplicity fluctuates. We have studied the effect of multiplicity fluctuation on flow harmonics in nucleus-nucleus collisions in event-by-event hydrodynamics. Assuming that the charged particle's multiplicity fluctuations are governed by the negative binomial distribution, the Monte Carlo Glauber model of initial condition is generalized to include the fluctuations. Explicit simulations with the generalized Monte Carlo Glauber model initial conditions indicate that the multiplicity fluctuations do not have a large effect on the flow harmonics.

Advances in measurements of jets and collective phenomena in ultrarelativistic heavy ion collisions have led to further understanding of the properties of the medium created in such collisions. Measurements of the correlations between the axes of reconstructed jets and the reaction plane or second-order participant plane of the bulk medium (defined as jet $v_2$), as well as the higher-order participant planes (jet $v_n$), provide information on medium-induced parton energy loss. Additionally, knowledge of jet $v_n$ as well as the ability to reconstruct the event plane in the presence of a jet are necessary in analyses of jet-triggered particle correlations, which are used to study medium-induced jet shape modification. However, the presence of a jet can bias the event plane calculation, leading to an overestimation of jet $v_2$. This paper proposes a method for calculating jet $v_2$ (and by extension, the higher jet $v_n$ harmonics) and the event plane in an unbiased way, using knowledge of the azimuthal angle of the jet axis from full jet reconstruction.

We compute cross sections for incoherent and coherent diffractive $J/\Psi$ production in ultraperipheral nucleus-nucleus and proton-nucleus collisions using two different dipole models fitted to HERA data. We obtain a reasonably good description of the available ALICE data for coherent $J/\Psi$ production and present our prediction for the incoherent cross section. We also find that, while the normalization of the cross section depends quite strongly on the dipole model and vector meson wave function used, the rapidity dependence is very well constrained.

A new measurement of the neutron $\beta$-decay asymmetry $A_0$ has been carried out by the UCNA Collaboration using polarized ultracold neutrons (UCNs) from the solid deuterium UCN source at the Los Alamos Neutron Science Center. Improvements in the experiment have led to reductions in both statistical and systematic uncertainties leading to $A_0=-0.11954{\left(55\right)}_{\mathrm{stat}}{\left(98\right)}_{\mathrm{syst}}$, corresponding to the ratio of axial-vector to vector coupling $\lambda \equiv g_A/g_V=-1.2756\left(30\right)$.

Rotational bands in ${}^{113}$Sb, populated in the reaction ${}^{100}$Mo(${}^{19}$F,$6n$) at a beam energy of 105 MeV, have been studied. Two previously reported strongly coupled high-$K$ bands have been extended and a new sequence of five states, linked to the positive-parity high-$K$ band through interband transitions, is proposed. A comparison of the experimental $B\left(M1\right)/B\left(E2\right)$ ratios for the latter band with the predictions of the geometrical model of D$\ddot{\mathrm{o}}$nau-Frauendorf suggests that the states are axially symmetric with a moderate quadrupole deformation of ${\beta }_2=0.20$. Present directional correlation orientation and $\gamma$-ray polarization studies indicate that the negative-parity states built upon the 3045 keV isomeric level involve a high-$\Omega$ $\pi h_{11/2}$ orbital and have an oblate shape. Mean lifetimes for eight states belonging to the prolate-deformed $\pi h_{11/2}$ band have been measured from Doppler shift attenuation data. The results suggest a large average quadrupole deformation of ${\beta }_2=0.32\pm 0.03$ for states up to 10217 keV. The decrease of the $B$($E$2) rates for the 9063- and 10217 keV states may be interpreted as a signature of band termination at high spin.

Background: Nuclei located in the neutron-deficient Pb region have a complex structure, rapidly evolving as a function of neutron and proton numbers. The most famous example is ${}^{186}$Pb where the three lowest levels are $0^{+}$ states, the two excited $0^{+}$ states being located at low excitation energy around 600 keV. Coexisting structures with different properties are found in the neighboring nuclei. Many experiments have been performed over the last few years in which in-band and out-of-band $\gamma$-ray transition probabilities have been measured.

Purpose: A detailed interpretation of experimental data requires the use of a method going beyond a mean-field approach that permits to determine spectra and transition probabilities. Such methods have already been applied to selected isotopes in this mass region. Our aim is to provide a systematic investigation of this mass region in order to determine how well experimental data can be understood using a state-of-the-art method for nuclear structure.

Method: The starting point of our method is a set of mean-field wave functions generated with a constraint on the axial quadrupole moment and using a Skyrme energy density functional. Correlations beyond the mean field are introduced by projecting mean-field wave functions on angular-momentum and particle number and by mixing the symmetry-restored wave functions as a function of the axial quadrupole moment.

Results: A detailed comparison with the available data is performed for energies, charge radii, spectroscopic quadrupole moments, and $E0$ and $E2$ transition probabilities for the isotopic chains of neutron deficient Hg, Pb, Po, and Rn. The connection between our results and the underlying mean field is also analyzed.

Conclusions: Qualitative agreement with the data is obtained although our results indicate that the actual energy density functionals have to be improved further to achieve a quantitative agreement.

We consider deformed nuclei within an effective theory that exploits the small ratio between rotational and vibrational excitations. For even-even nuclei, the effective theory predicts small changes in the rotational constants of bands built on multi-phonon excitations that are linear in the number of excited phonons. In ${}^{166,168}$Er, this explains the main variations of the rotational constants of the two-phonon $\gamma$ vibrational bands. In ${}^{232}$Th, the effective theory correctly explains the trend that the rotational constants decrease with increasing spin of the bandhead. We also study the effective theory for deformed odd nuclei. Here, time-odd terms enter the Lagrangian and generate effective magnetic forces that yield the high level densities observed in such nuclei.

Parameters of nuclear energy-density-functionals (EDFs) are always derived by an optimization to experimental data. For the minima of appropriately defined penalty functions, a statistical sensitivity analysis provides the uncertainties of the EDF parameters. To quantify theoretical errors of observables given by the model, we studied the propagation of uncertainties within the unedf0 Skyrme-EDF approach. We found that typically the standard errors rapidly increase towards neutron rich nuclei. This can be linked to large uncertainties of the isovector coupling constants of the currently used EDFs.

The radiohalogen chlorine-34$m$ ($T_{1/2}$ $=$ 32.8 min, β${}^{+}$ $=$ 57$\%$, IT $=$ 43$\%$) due to its appropriate γ emission and the incorporation into a variety of chemical compounds is a potent positron emitter for nuclear medicine. This study evaluates the cyclotron production of ${}^{34}$Cl${}^m$ via a variety of nuclear processes and presents the relevant nuclear data. The ${}^{34}$Cl${}^m$ excitation functions of the ${}^{36}$Ar($d$, α), ${}^{\mathrm{nat}}$Cl($p$, $x$),${}^{35}$Cl(α, $x$), ${}^{32}$S(α, $d$), and ${}^{34}$S($p$, $n$) reactions were calculated using talys-1.4 and empire-3.1 nuclear codes, and with the data taken from the TENDL database. In addition, the theoretical calculations were compared with the reported experimental measurements. In addition, the equilibrium and pre-equilibrium affects were considered. The thickness of the targets was obtained by the srim code for the reactions. The ${}^{34}$Cl${}^m$ production yield was evaluated with attention paid to the excitation function and the stopping power.

Centrality dependence of charged particles multiplicity, transverse momentum spectra, and integrated and differential elliptic flow in ${\sqrt{s}}_{NN}$ $=$ 200 GeV Au+Au collisions are analyzed using event-by-event ideal hydrodynamics. The Monte Carlo Glauber model of initial condition, constrained to reproduce experimental charged particle's multiplicity in 0$\%$–10$\%$ Au+Au collisions, reasonably well reproduces all the experimental observables, e.g., centrality dependence of charged particle multiplicity, and integrated and differential elliptic flow. Model predictions for higher flow harmonics, $v_3$, $v_4$, however, overestimate the experimental data, more in the peripheral collisions than in the central collisions. Correlation between initial (spatial) asymmetry measures and flow coefficients are also studied. With the exception of the elliptic flow, for all the higher flow coefficients ($v_n$,$n$ $=$ 3–5), correlation is reduced with collision centrality. In peripheral collisions, higher flow coefficients are only weakly correlated to the asymmetry measures. Elliptic flow, however, remains strongly correlated with initial eccentricity in all the collision centralities.

Quantum Monte Carlo calculations of electromagnetic moments and transitions are reported for $A\le 9$ nuclei. The realistic Argonne $v_{18}$ two-nucleon and Illinois-7 three-nucleon potentials are used to generate the nuclear wave functions. Contributions of two-body meson-exchange current (MEC) operators are included for magnetic moments and $M1$ transitions. The MEC operators have been derived in both a standard nuclear physics approach and a chiral effective field theory formulation with pions and nucleons including up to one-loop corrections. The two-body MEC contributions provide significant corrections and lead to very good agreement with experiment. Their effect is particularly pronounced in the $A=9$, $T=3/2$ systems, in which they provide up to $\sim 20\%$ ($\sim 40\%$) of the total predicted value for the ${}^9$Li (${}^9$C) magnetic moment.

We study the low-energy collective excitations in the inner crust of the neutron star, where a neutron superfluid coexists with a Coulomb lattice of nuclei. The dispersion relation of the modes is calculated systematically from a microscopic theory including neutron band structure effects. These effects are shown to lead to a strong mixing between the Bogoliubov-Anderson bosons of the neutron superfluid and the longitudinal crystal lattice phonons. In addition, the speed of the transverse shear mode is greatly reduced as a large fraction of superfluid neutrons are entrained by nuclei. Not only does the much smaller velocity of the transverse mode increase the specific heat of the inner crust, it also decreases its electron thermal conductivity. These results may impact our interpretation of the thermal relaxation in accreting neutron stars. Due to strong mixing, the mean free path of the superfluid mode is found to be greatly reduced. Our results for the collective mode dispersion relations and their damping may also have implications for neutron star seismology.

While the modification of jets by a medium as created in ultrarelativistic heavy-ion collisions is often thought of as a phenomenon affecting a hard near on-shell parton and hence treated as partonic energy loss, a more realistic view is to think of the medium effect as a relatively small correction to the Quantum Chromodynamics (QCD) vacuum radiation pattern which reduces the initial high virtuality of hard partons and leads to the development of a shower. The uncertainty relation can be used to argue that a significant part of this shower is developed even before a medium can be formed. The initial virtuality of a shower-initiating parton is reflected in the final state in the measured invariant mass of a jet—high mass jets are characterized by more branchings, higher multiplicity, and a wider angular structure. Since most of this structure is determined before the medium affects the jet, selecting a particular jet mass range strongly biases the partonic configuration that enters the medium, and thus the medium is expected to modify high mass jets more strongly than low mass jets. In this work, this scenario is explored using the in-medium shower evolution code yajem and a possible strategy for a measurement is suggested.

Recent $B(E2;0_{\mathrm{g}.\mathrm{s}.}^{+}\to 2_1^{+})$ measurements in light tin isotopes have revealed surprisingly large values relative to standard shell model predictions, generating an unexpected asymmetry in the $B\left(E2\right)$ values with respect to the neutron midshell. This effect has triggered various speculations as to its origin, such as a possible weakening of the $N,Z=50$ shell closure. Here we present new shell model calculations to investigate the origin of the observed asymmetric character of the $B\left(E2\right)$ values in the tin isotopes. By including the effects of the neutron $g_{9/2}$ orbital below the $N=50$ shell gap it is shown that Pauli blocking effects may play an important role near the $N=50$ shell closure. A new set of single-particle energies and monopole interactions, fitted to the experimental data in the region, together with the isospin-dependent effective charge suggested by Bohr and Mottelson is shown to reproduce the experimental transition rate values in the Sn isotopic chain.