In anticipation of results from current and future double-$\beta$ decay studies, we report a measurement resulting in a ${}^{82}\mathrm{Se}$ double-$\beta$ decay $Q$ value of 2997.9(3) keV, an order of magnitude more precise than the currently accepted value. We also present preliminary results of a calculation of the ${}^{82}\mathrm{Se}$ neutrinoless double-$\beta$ decay nuclear matrix element that corrects in part for the small size of the shell model single-particle space. The results of this work are important for designing next generation double-$\beta$ decay experiments and for the theoretical interpretations of their observations.

An experiment with a newly developed high-resolution kaon spectrometer and a scattered electron spectrometer with a novel configuration was performed in Hall C at Jefferson Lab. The ground state of a neutron-rich hypernucleus, ${}_{\Lambda }{}^7\mathrm{He}$, was observed for the first time with the ($e$, $e^{\prime }{K}^{+}$) reaction with an energy resolution of $\sim 0.6\mathrm{MeV}$. This resolution is the best reported to date for hypernuclear reaction spectroscopy. The ${}_{\Lambda }{}^7\mathrm{He}$ binding energy supplies the last missing information of the $A=7$, $T=1$ hypernuclear isotriplet, providing a new input for the charge symmetry breaking effect of the $\Lambda N$ potential.

The impact of coherent light propagation on the excitation and fluorescence of thorium nuclei in a crystal lattice environment is investigated theoretically. We find that in the forward direction, the fluorescence signal exhibits characteristic intensity modulations dominated by a sped-up initial decay signal that is orders of magnitude faster. This feature can be exploited for the optical determination of the isomeric transition energy. In order to obtain a unmistakable signature of the isomeric nuclear fluorescence, we put forward a novel scheme for the direct measurement of the transition energy via electromagnetically modified nuclear forward scattering involving two fields that couple to three nuclear states.

We present a new dispersive formulation of the $\gamma Z$ box radiative corrections to weak charges of bound protons and neutrons in atomic parity violation measurements on heavy nuclei such as ${}^{133}\mathrm{Cs}$ and ${}^{213}\mathrm{Ra}$. We evaluate for the first time a small but important additional correction arising from Pauli blocking of nucleons in a heavy nucleus. Overall, we find a significant shift in the $\gamma Z$ correction to the weak charge of ${}^{133}\mathrm{Cs}$, approximately 4 times larger than the current uncertainty on the value of ${sin}^2{\widehat{\theta }}_W$, but with a reduced error compared to earlier estimates.

The density dependence of nuclear symmetry energy remains poorly constrained. Starting from precise empirical values of the nuclear volume and surface symmetry energy coefficients and the nuclear saturation density, we show how in the ambit of microscopic calculations with different energy density functionals, the value of the symmetry energy slope parameter $L$ along with that for neutron skin can be put in tighter bounds. The value of $L$ is found to be $L=64\pm 5\mathrm{MeV}$. For ${}^{208}\mathrm{Pb}$, the neutron skin thickness comes out to be $0.188\pm 0.014\mathrm{fm}$. Knowing $L$, the method can be applied to predict neutron skin thicknesses of other nuclei.

The first measurement of the elastic scattering of the halo nucleus ${}^{11}\mathrm{Li}$ and its core ${}^9\mathrm{Li}$ on ${}^{208}\mathrm{Pb}$ at energies near the Coulomb barrier is presented. The ${}^{11}\mathrm{Li}+{}^{208}\mathrm{Pb}$ elastic scattering shows a strong reduction with respect to the Rutherford cross section, even at energies well below the barrier and down to very small scattering angles. This drastic change of the elastic differential cross section observed in ${}^{11}\mathrm{Li}+{}^{208}\mathrm{Pb}$ is the consequence of the halo structure of ${}^{11}\mathrm{Li}$, as it is not observed in the elastic scattering of its core ${}^9\mathrm{Li}$ at the same energies. Four-body continuum-discretized coupled-channels calculations, based on a three-body model of the ${}^{11}\mathrm{Li}$ projectile, are found to explain the measured angular distributions and confirm that the observed reduction is mainly due to the strong Coulomb coupling to the dipole states in the low-lying continuum of ${}^{11}\mathrm{Li}$. These calculations suggest the presence of a low-lying dipole resonance in ${}^{11}\mathrm{Li}$ close to the breakup threshold.

The first measurement of neutron emission in electromagnetic dissociation of ${}^{208}\mathrm{Pb}$ nuclei at the LHC is presented. The measurement is performed using the neutron zero degree calorimeters of the ALICE experiment, which detect neutral particles close to beam rapidity. The measured cross sections of single and mutual electromagnetic dissociation of Pb nuclei at $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$ with neutron emission are ${\sigma }_{\mathrm{singleEMD}}=187.4\pm 0.2(\mathrm{stat}{)}_{-11.2}^{+13.2}(\mathrm{syst})\mathrm{b}$ and ${\sigma }_{\mathrm{mutualEMD}}=5.7\pm 0.1(\mathrm{stat})\pm 0.4(\mathrm{syst})\mathrm{b}$, respectively. The experimental results are compared to the predictions from a relativistic electromagnetic dissociation model.

In this Letter we report the first results on ${\pi }^{\pm }$, $K^{\pm }$, $p$, and $\overline{p}$ production at midrapidity ($|y|<0.5$) in central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$, measured by the ALICE experiment at the LHC. The $p_{\mathrm{T}}$ distributions and yields are compared to previous results at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ and expectations from hydrodynamic and thermal models. The spectral shapes indicate a strong increase of the radial flow velocity with $\sqrt{s_{\mathrm{NN}}}$, which in hydrodynamic models is expected as a consequence of the increasing particle density. While the $K/\pi$ ratio is in line with predictions from the thermal model, the $p/\pi$ ratio is found to be lower by a factor of about 1.5. This deviation from thermal model expectations is still to be understood.

The excited state of the ${}^{12}\mathrm{C}$ nucleus known as the “Hoyle state” constitutes one of the most interesting, difficult, and timely challenges in nuclear physics, as it plays a key role in the production of carbon via fusion of three alpha particles in red giant stars. In this Letter, we present ab initio lattice calculations which unravel the structure of the Hoyle state, along with evidence for a low-lying spin-2 rotational excitation. For the ${}^{12}\mathrm{C}$ ground state and the first excited spin-2 state, we find a compact triangular configuration of alpha clusters. For the Hoyle state and the second excited spin-2 state, we find a “bent-arm” or obtuse triangular configuration of alpha clusters. We also calculate the electromagnetic transition rates between the low-lying states of ${}^{12}\mathrm{C}$.

The PHENIX experiment has measured electrons and positrons at midrapidity from the decays of hadrons containing charm and bottom quarks produced in $d+\mathrm{Au}$ and $p+p$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$ in the transverse-momentum range $0.85\le p_T^e\le 8.5\mathrm{GeV}/c$. In central $d+\mathrm{Au}$ collisions, the nuclear modification factor $R_{dA}$ at $1.5<p_T<5\mathrm{GeV}/c$ displays evidence of enhancement of these electrons, relative to those produced in $p+p$ collisions, and shows that the mass-dependent Cronin enhancement observed at the Relativistic Heavy Ion Collider extends to the heavy $D$ meson family. A comparison with the neutral-pion data suggests that the difference in cold-nuclear-matter effects on light- and heavy-flavor mesons could contribute to the observed differences between the ${\pi }^0$ and heavy-flavor-electron nuclear modification factors $R_{\mathrm{AA}}$.

The phenomenon of core excitation in the breakup of a two-body halo nucleus is investigated. We show that this effect plays a significant role in the reaction dynamics and, furthermore, its interference with the valence excitation mechanism has sizable and measurable effects on the breakup angular distributions. These effects have been studied in the resonant breakup of ${}^{11}\mathrm{Be}$ on a carbon target, populating the resonances at 1.78 MeV ($5/2^{+}$) and 3.41 MeV ($3/2^{+}$). The calculations have been performed using a recent extension of the distorted-wave Born approximation method, which takes into account the effect of core excitation in both the structure of the halo nucleus and in the reaction mechanism. The calculated angular distributions have been compared with the available data [Fukuda et al., Phys. Rev. C 70, 054606 (2004).]. Although each of these resonances is dominated by one of the two considered mechanisms, the angular patterns of these resonances depend in a very delicate way on the interference between them. This is the first clear evidence of this effect but the phenomenon is likely to occur in other similar reactions.

We investigate the possibility of the existence of the exotic torus configuration in the high-spin excited states of ${}^{40}\mathrm{Ca}$. We here consider the spin alignments about the symmetry axis. To this end, we use a three-dimensional cranked Skyrme Hartree-Fock method and search for stable single-particle configurations. We find one stable state with the torus configuration at the total angular momentum $J=60\hslash$ and an excitation energy of about 170 MeV in all calculations using various Skyrme interactions. The total angular momentum $J=60\hslash$ consists of aligned 12 nucleons with the orbital angular momenta $\Lambda =+4$, $+5$, and $+6$ for spin-up or -down neutrons and protons. The obtained results strongly suggest that a macroscopic amount of circulating current breaking the time-reversal symmetry emerges in the high-spin excited state of ${}^{40}\mathrm{Ca}$.

A power expansion scheme is set up to determine the Wigner function that satisfies the quantum kinetic equation for spin-$1/2$ charged fermions in a background electromagnetic field. Vector and axial-vector current induced by magnetic field and vorticity are obtained simultaneously from the Wigner function. The chiral magnetic and vortical effect and chiral anomaly are shown as natural consequences of the quantum kinetic equation. The axial-vector current induced by vorticity is argued to lead to a local polarization effect along the vorticity direction in heavy-ion collisions.

The ground state of ${}^{10}\mathrm{He}$ was populated using a $2p2n$-removal reaction from a $59\mathrm{MeV}/\mathrm{u}$ ${}^{14}\mathrm{Be}$ beam. The decay energy of the three-body system, ${}^8\mathrm{He}+n+n$, was measured and a resonance was observed at $E=1.60(25)\mathrm{MeV}$ with a 1.8(4) MeV width. This result is in agreement with previous invariant mass spectroscopy measurements, using the ${}^{11}\mathrm{Li}(-p)$ reaction, but is inconsistent with recent transfer reaction results. The proposed explanation that the difference, about 500 keV, is due to the effect of the extended halo nature of ${}^{11}\mathrm{Li}$ in the one-proton knockout reaction is no longer valid as the present work demonstrates that the discrepancy between the transfer reaction results persists despite using a very different reaction mechanism, ${}^{14}\mathrm{Be}(-2p2n)$.

The ${}^{13}\mathrm{C}(\alpha ,n){}^{16}\mathrm{O}$ reaction is the neutron source for the main component of the $s$-process, responsible for the production of most nuclei in the mass range $90\lesssim A\lesssim 204$. It is active inside the helium-burning shell in asymptotic giant branch stars, at temperatures $\lesssim {10}^8\mathrm{K}$, corresponding to an energy interval where the ${}^{13}\mathrm{C}(\alpha ,n){}^{16}\mathrm{O}$ is effective from 140 to 230 keV. In this region, the astrophysical $S(E)$-factor is dominated by the $-3\mathrm{keV}$ subthreshold resonance due to the 6.356 MeV level in ${}^{17}\mathrm{O}$, giving rise to a steep increase of the $S(E)$-factor. Notwithstanding that it plays a crucial role in astrophysics, no direct measurements exist inside the $s$-process energy window. The magnitude of its contribution is still controversial as extrapolations, e.g., through the $R$ matrix and indirect techniques, such as the asymptotic normalization coefficient (ANC), yield inconsistent results. The discrepancy amounts to a factor of 3 or more right at astrophysical energies. Therefore, we have applied the Trojan horse method to the ${}^{13}\mathrm{C}({}^6\mathrm{Li},n{}^{16}\mathrm{O})d$ quasifree reaction to achieve an experimental estimate of such contribution. For the first time, the ANC for the 6.356 MeV level has been deduced through the Trojan horse method as well as the $n$-partial width, allowing to attain an unprecedented accuracy in the ${}^{13}\mathrm{C}(\alpha ,n){}^{16}\mathrm{O}$ study. Though a larger ANC for the 6.356 MeV level is measured, our experimental $S(E)$-factor agrees with the most recent extrapolation in the literature in the 140–230 keV energy interval, the accuracy being greatly enhanced thanks to this innovative approach.

The suppression of the individual ${\rm Y}(nS)$ states in PbPb collisions with respect to their yields in $pp$ data has been measured. The PbPb and $pp$ data sets used in the analysis correspond to integrated luminosities of $150\mu {\mathrm{b}}^{-1}$ and $230{\mathrm{nb}}^{-1}$, respectively, collected in 2011 by the CMS experiment at the LHC, at a center-of-mass energy per nucleon pair of 2.76 TeV. The ${\rm Y}(nS)$ yields are measured from the dimuon invariant mass spectra. The suppression of the ${\rm Y}(nS)$ yields in PbPb relative to the yields in $pp$, scaled by the number of nucleon-nucleon collisions, $R_{AA}$, is measured as a function of the collision centrality. Integrated over centrality, the $R_{AA}$ values are $0.56\pm 0.08(\mathrm{stat})\pm 0.07(\mathrm{syst})$, $0.12\pm 0.04(\mathrm{stat})\pm 0.02(\mathrm{syst})$, and lower than 0.10 (at 95% confidence level), for the ${\rm Y}(1S)$, ${\rm Y}(2S)$, and ${\rm Y}(3S)$ states, respectively. The results demonstrate the sequential suppression of the ${\rm Y}(nS)$ states in PbPb collisions at LHC energies.

Extending a previously developed two-phase equation of state, we simulate head-on relativistic lead-lead collisions with fluid dynamics, augmented with a finite-range term, and study the effects of the phase structure on the evolution of the baryon density. For collision energies that bring the bulk of the system into the mechanically unstable spinodal region of the phase diagram, the density irregularities are being amplified significantly. The resulting density clumping may be exploited as a signal of the phase transition, possibly through an enhanced production of composite particles.

We report final-state-exclusive measurements of the light charged fragments in coincidence with ${}^{26}\mathrm{Ne}$ residual nuclei following the direct two-proton removal from a neutron-rich ${}^{28}\mathrm{Mg}$ secondary beam. A Dalitz-plot analysis and comparisons with simulations show that a majority of the triple-coincidence events with two protons display phase-space correlations consistent with the (two-body) kinematics of a spatially correlated pair-removal mechanism. The fraction of such correlated events, 56(12)%, is consistent with the fraction of the calculated cross section, 64%, arising from spin $S=0$ two-proton configurations in the entrance-channel (shell-model) ${}^{28}\mathrm{Mg}$ ground state wave function. This result promises access to an additional and more specific probe of the spin and spatial correlations of valence nucleon pairs in exotic nuclei produced as fast secondary beams.

The neutron capture cross section of ${}^{235}\mathrm{U}$ was measured for the neutron incident energy region between 4 eV and 1 MeV at the DANCE facility at the Los Alamos Neutron Science Center with an unprecedented accuracy of 2–3% at 1 keV. The new methodology combined three independent measurements. In the main experiment, a thick actinide sample was used to determine neutron capture and neutron-induced fission rates simultaneously. In the second measurement, a fission tagging detector was used with a thin actinide sample and detailed characteristics of the prompt-fission gamma rays were obtained. In the third measurement, the neutron scattering background was characterized using a sample of ${}^{208}\mathrm{Pb}$. The relative capture cross section was obtained from the experiment with the thick ${}^{235}\mathrm{U}$ sample using a ratio method after the subtraction of the fission and neutron scattering backgrounds. Our result indicates errors that are as large as 30% in the 0.5–2.5 keV region, in the current knowledge of neutron capture as embodied in major nuclear data evaluations. Future modifications of these databases using the improved precision data given herein will have significant impacts in neutronics calculations for a variety of nuclear technologies.

We introduce a novel photon production mechanism stemming from the conformal anomaly of $\mathrm{QCD}\times \mathrm{QED}$ and the existence of strong (electro)magnetic fields in heavy ion collisions. Using the hydrodynamical description of the bulk modes of QCD plasma, we show that this mechanism leads to the photon production yield that is comparable to the yield from conventional sources. This mechanism also provides a significant positive contribution to the azimuthal anisotropy of photons, $v_2$, as well as to the radial “flow.” We compare our results to the data from the PHENIX Collaboration.