The (${}^{10}\mathrm{Be},{}^{10}{\mathrm{B}}^{*}[1.74\mathrm{MeV}]$) charge-exchange reaction at $100A\mathrm{MeV}$ is presented as a new probe for isolating the isovector ($\mathrm{\Delta }T=1$) nonspin-transfer ($\mathrm{\Delta }S=0$) response of nuclei, with ${}^{28}\mathrm{Si}$ being the first nucleus studied. By using a secondary ${}^{10}\mathrm{Be}$ beam produced by fast fragmentation of ${}^{18}\mathrm{O}$ nuclei at the NSCL Coupled Cyclotron Facility, applying the dispersion-matching technique with the S800 magnetic spectrometer to determine the excitation energy in ${}^{28}\mathrm{Al}$, and performing high-resolution $\gamma$-ray tracking with the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) to identify the 1022-keV $\gamma$ ray associated with the decay from the 1.74-MeV $T=1$ isobaric analog state in ${}^{10}\mathrm{B}$, a $\mathrm{\Delta }S=0$ excitation-energy spectrum in ${}^{28}\mathrm{Al}$ was extracted. Monopole and dipole contributions were determined through a multipole-decomposition analysis, and the isovector giant dipole resonance and isovector giant monopole resonance (IVGMR) were identified. The results show that this probe is a powerful tool for studying the elusive IVGMR, which is of interest for performing stringent tests of modern density functional theories at high excitation energies and for constraining the bulk properties of nuclei and nuclear matter. The extracted distributions were compared with theoretical calculations based on the normal-modes formalism and the proton-neutron relativistic time-blocking approximation. Calculated cross sections based on these strengths underestimate the data by about a factor of 2, which likely indicates deficiencies in the reaction calculations based on the distorted wave Born approximation.

We present the first measurement of the two-particle transverse momentum differential correlation function, $P_2\equiv ⟨\mathrm{\Delta }{p}_T\mathrm{\Delta }{p}_T⟩/⟨p_T{⟩}^2$, in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76\mathrm{TeV}$. Results for $P_2$ are reported as a function of the relative pseudorapidity ($\mathrm{\Delta }\eta$) and azimuthal angle ($\mathrm{\Delta }\phi$) between two particles for different collision centralities. The $\mathrm{\Delta }\varphi$ dependence is found to be largely independent of $\mathrm{\Delta }\eta$ for $|\mathrm{\Delta }\eta |\ge 0.9$. In the 5% most central Pb-Pb collisions, the two-particle transverse momentum correlation function exhibits a clear double-hump structure around $\mathrm{\Delta }\phi =\pi$ (i.e., on the away side), which is not observed in number correlations in the same centrality range, and thus provides an indication of the dominance of triangular flow in this collision centrality. Fourier decompositions of $P_2$, studied as a function of the collision centrality, show that correlations at $|\mathrm{\Delta }\eta |\ge 0.9$ can be well reproduced by a flow ansatz based on the notion that measured transverse momentum correlations are strictly determined by the collective motion of the system.

The relative modification of the prompt $\psi (2S)$ and $J/\psi$ yields from $pp$ to PbPb collisions, at the center-of-mass energy of 5.02 TeV per nucleon pair, is presented. The analysis is based on $pp$ and PbPb data samples collected by the CMS experiment at the LHC in 2015, corresponding to integrated luminosities of $28.0{\mathrm{pb}}^{-1}$ and $464\mu {\mathrm{b}}^{-1}$, respectively. The double ratio of measured yields of prompt charmonia reconstructed through their decays into muon pairs, $(N_{\psi (2S)}/N_{J/\psi }{)}_{\mathrm{PbPb}}/(N_{\psi (2S)}/N_{J/\psi }{)}_{pp}$, is determined as a function of PbPb collision centrality and charmonium transverse momentum $p_T$, in two kinematic intervals: $|y|<1.6$ covering $6.5<p_T<30\mathrm{GeV}/c$ and $1.6<|y|<2.4$ covering $3<p_T<30\mathrm{GeV}/c$. The centrality-integrated double ratios are $0.36\pm 0.08(\mathrm{stat})\pm 0.05(\mathrm{syst})$ in the first interval and $0.24\pm 0.22(\mathrm{stat})\pm 0.09(\mathrm{syst})$ in the second. The double ratio is lower than unity in all the measured bins, suggesting that the $\psi (2S)$ yield is more suppressed than the $J/\psi$ yield in the explored phase space.

Prompt $\gamma$-ray spectroscopy of the neutron-rich ${}^{96}\mathrm{Kr}$, produced in transfer- and fusion-induced fission reactions, has been performed using the combination of the Advanced Gamma Tracking Array and the $\mathrm{VAMOS}++$ spectrometer. A second excited state, assigned to $J^{\pi }=4^{+}$, is observed for the first time, and a previously reported level energy of the first $2^{+}$ excited state is confirmed. The measured energy ratio $R_{4/2}=E(4^{+})/E(2^{+})=2.12(1)$ indicates that this nucleus does not show a well-developed collectivity contrary to that seen in heavier $N=60$ isotones. This new measurement highlights an abrupt transition of the degree of collectivity as a function of the proton number at $Z=36$, of similar amplitude to that observed at $N=60$ at higher $Z$ values. A possible reason for this abrupt transition could be related to the insufficient proton excitations in the $g_{9/2}$, $d_{5/2}$, and $s_{1/2}$ orbitals to generate strong quadrupole correlations or to the coexistence of competing different shapes. An unexpected continuous decrease of $R_{4/2}$ as a function of the neutron number up to $N=60$ is also evidenced. This measurement establishes the Kr isotopic chain as the low-$Z$ boundary of the island of deformation for $N=60$ isotones. A comparison with available theoretical predictions using different beyond mean-field approaches shows that these models fail to reproduce the abrupt transitions at $N=60$ and $Z=36$.

We show that the total kinetic energy (TKE) of nuclei after the spontaneous fission of ${}^{258}\mathrm{Fm}$ can be well reproduced using simple assumptions on the quantum collective phase space explored by the nucleus after passing the fission barrier. Assuming energy conservation and phase-space exploration according to the stochastic mean-field approach, a set of initial densities is generated. Each density is then evolved in time using the nuclear time-dependent density-functional theory with pairing. This approach goes beyond the mean-field theory by allowing spontaneous symmetry breaking as well as a wider dynamical phase-space exploration leading to larger fluctuations in collective space. The total kinetic energy and mass distributions are calculated. New information on the fission process: fluctuations in scission time, strong correlation between TKE and collective deformation, as well as prescission particle emission, are obtained. We conclude that fluctuations of the TKE and mass are triggered by quantum fluctuations.

Angular distributions of the elastic, inelastic, and breakup cross sections of the halo nucleus ${}^{11}\mathrm{Be}$ on ${}^{197}\mathrm{Au}$ were measured at energies below ($E_{\text{lab}}=31.9\mathrm{MeV}$) and around (39.6 MeV) the Coulomb barrier. These three channels were unambiguously separated for the first time for reactions of ${}^{11}\mathrm{Be}$ on a high-$Z$ target at low energies. The experiment was performed at TRIUMF (Vancouver, Canada). The differential cross sections were compared with three different calculations: semiclassical, inert-core continuum-coupled-channels and continuum-coupled-channels ones with including core deformation. These results show conclusively that the elastic and inelastic differential cross sections can only be accounted for if core-excited admixtures are taken into account. The cross sections for these channels strongly depend on the $\mathcal{B}(E1)$ distribution in ${}^{11}\mathrm{Be}$, and the reaction mechanism is sensitive to the entanglement of core and halo degrees of freedom in ${}^{11}\mathrm{Be}$.

We merge two successful ab initio nuclear-structure methods, the no-core shell model (NCSM) and the multireference in-medium similarity renormalization group (IM-SRG) to define a new many-body approach for the comprehensive description of ground and excited states of closed and open-shell nuclei. Building on the key advantages of the two methods—the decoupling of excitations at the many-body level in the IM-SRG and the access to arbitrary nuclei, eigenstates, and observables in the NCSM—their combination enables fully converged no-core calculations for an unprecedented range of nuclei and observables at moderate computational cost. We present applications in the carbon and oxygen isotopic chains, where conventional NCSM calculations are still feasible and provide an important benchmark. The efficiency and rapid convergence of the new approach make it ideally suited for ab initio studies of the complete spectroscopy of nuclei up into the medium-mass regime.

Despite the more than 1 order of magnitude difference between the measured dipole moments in ${}^{144}\mathrm{Ba}$ and ${}^{146}\mathrm{Ba}$, the octupole correlations in ${}^{146}\mathrm{Ba}$ are found to be as strong as those in ${}^{144}\mathrm{Ba}$ with a similarly large value of $B(E3;3^{-}\to 0^{+})$ determined as $48(\begin{array}{c}+21\\ -29\end{array})\mathrm{W}.\mathrm{u}.$ The new results not only establish unambiguously the presence of a region of octupole deformation centered on these neutron-rich Ba isotopes, but also manifest the dependence of the electric dipole moments on the occupancy of different neutron orbitals in nuclei with enhanced octupole strength, as revealed by fully microscopic calculations.

We report the results of a study of neutrino-carbon interactions at beam energies ranging between a few hundred MeV’s and a few tens of GeVs carried out within the framework of the impulse approximation using a realistic spectral function. The contributions of quasielastic scattering, resonance production, and deep inelastic scattering—consistently obtained, for the first time, from a model based on a realistic description of the nuclear ground state—are compared and analyzed.

Anisotropy in the speed of light that has been constrained by Michelson-Morley-type experiments also generates anisotropy in the Coulomb interactions. This anisotropy can manifest itself as an energy anisotropy in nuclear and atomic experiments. Here the experimental limits on Lorentz violation in ${}_{10}{}^{21}\mathrm{Ne}$ are used to improve the limits on Lorentz symmetry violations in the photon sector, namely, the anisotropy of the speed of light and the Coulomb interactions, by 7 orders of magnitude in comparison with previous experiments: the speed of light is isotropic to a part in ${10}^{28}$.

The OLYMPUS Collaboration reports on a precision measurement of the positron-proton to electron-proton elastic cross section ratio, $R_{2\gamma }$, a direct measure of the contribution of hard two-photon exchange to the elastic cross section. In the OLYMPUS measurement, 2.01 GeV electron and positron beams were directed through a hydrogen gas target internal to the DORIS storage ring at DESY. A toroidal magnetic spectrometer instrumented with drift chambers and time-of-flight scintillators detected elastically scattered leptons in coincidence with recoiling protons over a scattering angle range of $\approx 20°$ to 80°. The relative luminosity between the two beam species was monitored using tracking telescopes of interleaved gas electron multiplier and multiwire proportional chamber detectors at 12°, as well as symmetric Møller or Bhabha calorimeters at 1.29°. A total integrated luminosity of $4.5{\mathrm{fb}}^{-1}$ was collected. In the extraction of $R_{2\gamma }$, radiative effects were taken into account using a Monte Carlo generator to simulate the convolutions of internal bremsstrahlung with experiment-specific conditions such as detector acceptance and reconstruction efficiency. The resulting values of $R_{2\gamma }$, presented here for a wide range of virtual photon polarization $0.456<\epsilon <0.978$, are smaller than some hadronic two-photon exchange calculations predict, but are in reasonable agreement with a subtracted dispersion model and a phenomenological fit to the form factor data.

Low-energy $M1$ strength functions of ${}^{60,64,68}\mathrm{Fe}$ are determined on the basis of large-scale shell-model calculations with the goal to study their development from the bottom to the middle of the neutron shell. We find that the zero-energy spike, which characterizes nuclei near closed shells, develops toward the middle of the shell into a bimodal structure composed of a weaker zero-energy spike and a scissorslike resonance around 3 MeV, where the summed strengths of the two structures change within only 8% around a value of $9.8{\mu }_N^2$. The summed strength of the scissors region exceeds the total $\gamma$ absorption strength from the ground state by a factor of about three, which explains the discrepancy between total strengths of the scissors resonance derived from ($\gamma$, ${\gamma }^{\prime }$) experiments and from experiments using light-ion induced reactions.

Radioactive ${}^{136}\mathrm{Te}$ has two valence protons and two valence neutrons outside of the ${}^{132}\mathrm{Sn}$ double shell closure, providing a simple laboratory for exploring the emergence of collectivity and nucleon-nucleon interactions. Coulomb excitation of ${}^{136}\mathrm{Te}$ on a titanium target was utilized to determine an extensive set of electromagnetic moments for the three lowest-lying states, including $B(E2;0_1^{+}\to 2_1^{+})$, $Q(2_1^{+})$, and $g(2_1^{+})$. The results indicate that the first-excited state, $2_1^{+}$, composed of the simple $2p\oplus 2n$ system, is prolate deformed, and its wave function is dominated by excited valence neutron configurations, but not to the extent previously suggested. It is demonstrated that extreme sensitivity of $g(2_1^{+})$ to the proton and neutron contributions to the wave function provides unique insight into the nature of emerging collectivity, and $g(2_1^{+})$ was used to differentiate among several state-of-the-art theoretical calculations. Our results are best described by the most recent shell model calculations.

The $\beta$-decay half-lives of 94 neutron-rich nuclei ${}^{144-151}\mathrm{Cs}$, ${}^{146-154}\mathrm{Ba}$, ${}^{148-156}\mathrm{La}$, ${}^{150-158}\mathrm{Ce}$, ${}^{153-160}\mathrm{Pr}$, ${}^{156-162}\mathrm{Nd}$, ${}^{159-163}\mathrm{Pm}$, ${}^{160-166}\mathrm{Sm}$, ${}^{161-168}\mathrm{Eu}$, ${}^{165-170}\mathrm{Gd}$, ${}^{166-172}\mathrm{Tb}$, ${}^{169-173}\mathrm{Dy}$, ${}^{172-175}\mathrm{Ho}$, and two isomeric states ${}^{174m}\mathrm{Er}$, ${}^{172m}\mathrm{Dy}$ were measured at the Radioactive Isotope Beam Factory, providing a new experimental basis to test theoretical models. Strikingly large drops of $\beta$-decay half-lives are observed at neutron-number $N=97$ for ${}_{58}\mathrm{Ce}$, ${}_{59}\mathrm{Pr}$, ${}_{60}\mathrm{Nd}$, and ${}_{62}\mathrm{Sm}$, and $N=105$ for ${}_{63}\mathrm{Eu}$, ${}_{64}\mathrm{Gd}$, ${}_{65}\mathrm{Tb}$, and ${}_{66}\mathrm{Dy}$. Features in the data mirror the interplay between pairing effects and microscopic structure. $r$-process network calculations performed for a range of mass models and astrophysical conditions show that the 57 half-lives measured for the first time play an important role in shaping the abundance pattern of rare-earth elements in the solar system.

The cross sections of the ${}^7\mathrm{Be}(n,\alpha ){}^4\mathrm{He}$ reaction for $p$-wave neutrons were experimentally determined at $E_{\mathrm{c}.\mathrm{m}.}=0.20–0.81\mathrm{MeV}$ slightly above the big bang nucleosynthesis (BBN) energy window for the first time on the basis of the detailed balance principle by measuring the time-reverse reaction. The obtained cross sections are much larger than the cross sections for $s$-wave neutrons inferred from the recent measurement at the n_TOF facility in CERN, but significantly smaller than the theoretical estimation widely used in the BBN calculations. The present results suggest the ${}^7\mathrm{Be}(n,\alpha ){}^4\mathrm{He}$ reaction rate is not large enough to solve the cosmological lithium problem, and this conclusion agrees with the recent result from the direct measurement of the $s$-wave cross sections using a low-energy neutron beam and the evaluated nuclear data library ENDF/B-VII.1.

Previous experiments observed a $4^{+}$ state in the $N=28$ nucleus ${}^{44}\mathrm{S}$ and suggested that this state may exhibit a hindered $E2$-decay rate, inconsistent with being a member of the collective ground state band. We populate this state via two-proton knockout from a beam of exotic ${}^{46}\mathrm{Ar}$ projectiles and measure its lifetime using the recoil distance method with the GRETINA $\gamma$-ray spectrometer. The result, $76(14{)}_{\mathrm{stat}}(20{)}_{\mathrm{syst}}\mathrm{ps}$, implies a hindered transition of $B(E2;4^{+}\to 2_1^{+})=0.61(19)$ single-particle or Weisskopf units strength and supports the interpretation of the $4^{+}$ state as a $K=4$ isomer, the first example of a high-$K$ isomer in a nucleus of such low mass.

We perform a combined analysis of recent NEOS and Daya Bay data on the reactor antineutrino spectrum. This analysis includes approximately 1.5 million antineutrino events, which is the largest neutrino event sample analyzed to date. We use a double ratio which cancels flux model dependence and related uncertainties as well as the effects of the detector response model. We find at 3–4 standard deviation significance level, that plutonium-239 and plutonium-241 are disfavored as the single source for the so-called 5 MeV bump. This analysis method has general applicability and, in particular, with higher statistics data sets, will be able to shed significant light on the issue of the bump. With some caveats, this should also allow us to improve the sensitivity for sterile neutrino searches in NEOS.