We demonstrate the damping of quantum octupole vibrations near the touching point when two colliding nuclei approach each other in the mass-asymmetric ${}^{16}\mathrm{O}$ + ${}^{208}\mathrm{Pb}$ system, for which the strong fusion hindrance was clearly observed. We, for the first time, apply the random-phase approximation method to the heavy-mass asymmetric dinuclear system to calculate the transition strength $B$($E3)$ as a function of the center-of-mass distance. The obtained $B(E3)$ strengths are substantially damped near the touching point, because the single-particle wave functions of the two nuclei strongly mix with each other and a neck is formed. The energy-weighted sums of $B(E3)$ are also strongly correlated with the damping factor, which is phenomenologically introduced in the standard coupled-channel calculations to reproduce the fusion hindrance. This strongly indicates that the damping of the quantum vibrations universally occurs in the deep sub-barrier fusion reactions.

Isoscalar giant resonances have been measured in the unstable ${}^{68}\mathrm{Ni}$ nucleus using inelastic alpha and deuteron scattering at $50A$ MeV in inverse kinematics with the active target MAYA at GANIL. Using alpha scattering, the extracted isoscalar giant monopole resonance (ISGMR) centroid was determined to be $21.1\pm 1.9$ MeV and the isoscalar giant quadrupole resonance (ISGQR) to be $15.9\pm 1.3$ MeV. Indications for soft isoscalar monopole and dipole modes are provided. Results obtained with both $\left(\alpha ,{\alpha }^{\prime }\right)$ and $\left(d,d^{\prime }\right)$ probes are compatible. The evolution of isoscalar giant resonances along the Ni isotopic chain from ${}^{56}\mathrm{Ni}$ to ${}^{68}\mathrm{Ni}$ is discussed.

Fully converged calculations of deuteron-deuteron elastic scattering observables are performed at energies above three- and four-body breakup threshold. Differential cross sections and analyzing powers are obtained using realistic nucleon-nucleon force models together with the Coulomb repulsion between protons. For all observables we find a very reasonable agreement with the available experimental data limited to deuteron beam energies up to 25.3 MeV.

Background: The ground state neutron density of a medium mass nucleus contains fundamental nuclear structure information and is at present relatively poorly known.

Purpose: We explore if parity violating elastic electron scattering can provide a feasible and model independent way to determine not just the neutron radius but the full radial shape of the neutron density ${\rho }_n\left(r\right)$ and the weak charge density ${\rho }_W\left(r\right)$ of a nucleus.

Methods: We expand the weak charge density of ${}^{48}\mathrm{Ca}$ in a model independent Fourier Bessel series and calculate the statistical errors in the individual coefficients that might be obtainable in a model parity violating electron scattering experiment.

Results: We find that it is feasible to determine roughly six Fourier Bessel coefficients of the weak charge density of ${}^{48}\mathrm{Ca}$ within a reasonable amount of beam time. However, it would likely be much harder to determine the full weak density of a significantly heavier nucleus such as ${}^{208}\mathrm{Pb}$.

Conclusions: Parity violating elastic electron scattering can determine the full weak charge density of a medium mass nucleus in a model independent way. This weak density contains fundamental information on the size, surface thickness, shell oscillations, and saturation density of the neutron distribution in a nucleus. The measured ${\rho }_W\left(r\right)$, combined with the previously known charge density ${\rho }_{ch}\left(r\right)$, will literally provide a detailed textbook picture of where the neutrons and protons are located in an atomic nucleus.

Background: Dynamic core-excitation effects have been found to be of importance in breakup reactions and may be of relevance when obtaining spectroscopic information from transfer reactions.

Purpose: In this paper we extend the distorted-wave Born approximation (DWBA) formalism in order to allow for noncentral components in the core-core term appearing in the transition operator, which allows for dynamic core-excitation effects. Then we study these effects by applying the formalism to different $(d,p)$ reactions.

Methods: The expression of the nonlocal kernels required for the evaluation of the DWBA amplitudes has been extended so as to include noncentral parts in the core-core interaction. The DWBA scattering amplitude is then obtained by solving the corresponding inhomogeneous equation, with the new computed kernels, and the usual outgoing boundary conditions. A new DWBA code has been developed for this purpose.

Results: For ${}^{10}\mathrm{Be}(d,p){}^{11}\mathrm{Be}$, core-excitation effects are found to be almost negligible $(<3\%)$. The importance of this effect has been found to depend to a large extent on the excitation energy of the core. This has been confirmed in the ${}^{30}\mathrm{Ne}(d,p){}^{31}\mathrm{Ne}$ case, for which the excitation energy of the first $2^{+}$ state is 0.8 MeV, and the effect of core excitation increases to $\approx 10\%$.

Conclusions: We find dynamic core-excitation effects in transfer reactions to have small contributions to cross sections, in general. However, they should not be neglected, since they may modify the spectroscopic information obtained from these reactions and may become of importance in reactions with nuclei with a core with high deformation and low excitation energy.

The PHENIX experiment at RHIC has measured the centrality dependence of the direct photon yield from $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{{}_{\mathit{N}N}}}=200 \mathrm{GeV}$ down to $p_T=0.4 \mathrm{GeV}/c$. Photons are detected via photon conversions to $e^{+}{e}^{-}$ pairs and an improved technique is applied that minimizes the systematic uncertainties that usually limit direct photon measurements, in particular at low $p_T$. We find an excess of direct photons above the $N_{\mathrm{coll}}$-scaled yield measured in $p+p$ collisions. This excess yield is well described by an exponential distribution with an inverse slope of about $240\mathrm{MeV}/c$ in the $p_T$ range $0.6–2.0 \mathrm{GeV}/c$. While the shape of the $p_T$ distribution is independent of centrality within the experimental uncertainties, the yield increases rapidly with increasing centrality, scaling approximately with $N_{\mathrm{part}}^{\alpha }$, where $\alpha =1.38\pm 0.03\left(\mathrm{stat}\right)\pm 0.07\left(\mathrm{syst}\right)$.

Background: A major goal of nuclear theory is to understand the strong interaction in nuclei as it manifests itself in terms of two- and many-body forces among the nuclear constituents, the protons and neutrons, and the interactions of these constituents with external electroweak probes via one- and many-body currents.

Purpose: The objective of the present work is to calculate the quasielastic electroweak response functions in light nuclei within the realistic dynamical framework outlined above. These response functions determine the inclusive cross section as function of the lepton momentum and energy transfers.

Methods: Their ab initio calculation is a very challenging quantum many-body problem, since it requires summation over the entire excitation spectrum of the nucleus and inclusion in the electroweak currents of one- and many-body terms. Green's functions Monte Carlo methods allow one to circumvent both difficulties by computing the response in imaginary time (the so-called Euclidean response) and hence summing implicitly over the bound and continuum states of the nucleus, and by implementing specific algorithms designed to deal with the complicated spin-isospin structure of nuclear many-body operators.

Results: Theoretical predictions for ${}^4\mathrm{He}$ and ${}^{12}\mathrm{C}$, confirmed by experiment in the electromagnetic case, show that two-body currents generate excess transverse strength from threshold to the quasielastic to the dip region and beyond.

Conclusions: These results challenge the conventional picture of quasielastic inclusive scattering as being largely dominated by single-nucleon knockout processes.

We discuss the contributions to the equation of state for the $\text{N}\ell \text{LO}$ Skyrme pseudopotential $(\ell =2,3)$. We show that by adding fourth- and sixth-order gradient terms, it is possible to fairly reproduce the spin/isospin decomposition of an equation of state obtained from ab initio methods. Moreover, by inspecting the partial-wave decomposition of the equation of state, we show for the first time a possible way to add explicit constraints on the sign of the tensor terms of the Skyrme interaction.

Background: Polarized ${}^3\mathrm{He}$ targets have been used as effective polarized neutron targets for electron scattering experiments for over twenty years. Over the last ten years, the effective luminosity of polarized ${}^3\mathrm{He}$ targets based on spin-exchange optical pumping has increased by over an order of magnitude. This has come about because of improvements in commercially-available lasers and an improved understanding of the physics behind the polarization process.

Purpose: We present the development of high-performance polarized ${}^3\mathrm{He}$ targets for use in electron scattering experiments. Improvements in the performance of polarized ${}^3\mathrm{He}$ targets, target properties, and operating parameters are documented.

Methods: We utilize the technique of alkali-hybrid spin-exchange optical pumping to polarize the ${}^3\mathrm{He}$ targets. Spectrally narrowed diode lasers used for the optical pumping greatly improved the performance. A simulation of the alkali-hybrid spin-exchange optical pumping process was developed to provide guidance in the design of the targets. Data was collected during the characterization of 24 separate glass target cells, each of which was constructed while preparing for one of four experiments at Jefferson Laboratory in Newport News, Virginia.

Results: From the data obtained we made determinations of the so-called $X$-factors that quantify a temperature-dependent and as-yet poorly understood spin-relaxation mechanism that limits the maximum achievable ${}^3\mathrm{He}$ polarization to well under 100%. The presence of the $X$-factor spin-relaxation mechanism was clearly evident in our data. Good agreement between the simulation and the actual target performance was obtained by including details such as off-resonant optical pumping. Included in our results is a measurement of the $\mathrm{K}\text{−}{}^3\mathrm{He}$ spin-exchange rate coefficient $k_{\mathrm{se}}^{\mathrm{K}}=(7.46\pm 0.62)\times {10}^{-20}{\mathrm{cm}}^3/\mathrm{s}$ over the temperature range 503 K to 563 K.

Conclusions: In order to achieve high performance under the operating conditions described in this paper, the K to Rb alkali vapor density ratio should be about $5\pm 2$ and the line width of the optical pumping lasers should be no more than $0.3$ nm. Our measurements of the $X$-factors under these conditions seem to indicate the ${}^3\mathrm{He}$ polarization is limited to $\approx 90$%. The simulation results, now benchmarked against experimental data, are useful for the design of future targets. Further work is required to better understand the temperature dependence of the $X$-factor spin-relaxation mechanism and the limitations of our optical pumping simulation.

Recent work has shown that a temperature dependence of the shear-viscosity-to-entropy ratio $\eta /s$ influences the collective flow pattern in heavy-ion collisions in characteristic ways that can be measured by studying hadron transverse momentum spectra and their anisotropies. Here we point out that it also affects the pair momentum dependence of the Hanbury-Brown–Twiss (HBT) radii (the source size parameters extracted from two-particle intensity interferometry) and the variance of their event-by-event fluctuations. This observation establishes interferometric signatures as useful observables to complement the constraining power of single-particle spectra on the temperature dependence of $\eta /s$.

I give an estimate for the skewness and the kurtosis of the baryon number distribution in two representative models; i.e., models of a hadron resonance gas and relativistic mean-field nuclear matter. I emphasize formal similarity between these two descriptions. The hadron resonance gas leads to a deviation from the Skellam distribution if quantum statistical correlation is taken into account at high baryon density, but this effect is not strong enough to explain fluctuation data seen in the beam-energy scan at RHIC/STAR. In the calculation of mean-field nuclear matter, the density correlation with the vector $\omega$ field rather than the effective mass with the scalar $\sigma$ field renders the kurtosis suppressed at higher baryon density so as to account for the experimentally observed behavior of the kurtosis. Finally, I discuss the difference between the baryon number and the proton number fluctuations from correlation effects in isospin space. The numerical results suggest that such effects are only minor even in the case of complete randomization of isospin.

An excited metastable nuclear state of ${}^{192}\mathrm{Os}$ in a hydrogen-like charge state has been studied for the first time. It was populated in projectile fragmentation of a ${}^{197}\mathrm{Au}$ beam on a ${}^9\mathrm{Be}$ target with the UNILAC-SIS accelerators at GSI. Fragmentation products in the region of interest were passed through the fragment separator and injected into the experimental storage ring (ESR). Cooling of the injected beam particles enabled Schottky mass spectrometry to be performed. Analysis shows the lifetime of the state to be considerably longer than that of the neutral ion $[{\tau }_{\mathrm{neut}}=8.5\left(14\right)\mathrm{s}]$; this change is attributed to hindrance of internal conversion in hydrogen-like ${}^{192}\mathrm{Os}$. Calculations have been performed to estimate the lifetime, and the result has been compared with that measured experimentally. There is good agreement between the expected $[{\tau }_{\mathrm{H}-\mathrm{like}}=13.0\left(24\right)\mathrm{s}]$ and measured lifetimes (${\tau }_{\mathrm{rest}}=15.1_{-1.3}^{+1.5}$ s) from the internal decay of ${}^{192m}\mathrm{Os}$. This provides a test for the reliability of the values obtained from internal conversion coefficient calculations in highly ionized systems and is the first measurement of its kind to be performed using the ESR setup.

The $\beta$ decay of molecular tritium currently provides the highest sensitivity in laboratory-based neutrino mass measurements. The upcoming Karlsruhe Tritium Neutrino (KATRIN) experiment will improve the sensitivity to 0.2 eV, making a percent-level quantitative understanding of molecular effects essential. The modern theoretical calculations available for neutrino mass experiments agree with spectroscopic data. Moreover, when neutrino mass experiments performed in the 1980s with gaseous tritium are reevaluated using these modern calculations, the extracted neutrino mass squared values are consistent with zero instead of being significantly negative. However, the calculated molecular final-state branching ratios are in conflict with dissociation experiments performed in the 1950s. We reexamine the theory of the final-state spectrum of molecular-tritium decay and its effect on the determination of the neutrino mass, with an emphasis on the role of the vibrational- and rotational-state distribution in the ground electronic state. General features can be reproduced quantitatively from considerations of kinematics and zero-point motion. We summarize the status of validation efforts and suggest means for resolving the apparent discrepancy in dissociation rates.

Proton-${}^3\mathrm{H}$ elastic scattering and charge-exchange reaction ${}^3\mathrm{H}(p,n){}^3\mathrm{He}$ in the energy regime above the four-nucleon breakup threshold are described in the momentum-space transition operator framework. Fully converged results are obtained by using realistic two-nucleon potentials and a two-proton Coulomb force as dynamic input. Differential cross section, proton analyzing power, outgoing neutron polarization, and proton-to-neutron polarization transfer coefficients are calculated between 6 and 30 MeV proton beam energy. Good agreement with the experimental data is found for the differential cross section both in elastic and charge-exchange reactions; the latter shows a complicated energy and angular dependence. The most sizable discrepancies between predictions and data are found for the proton analyzing power and outgoing neutron polarization in the charge-exchange reaction, while the respective proton-to-neutron polarization transfer coefficients are well described by the calculations.

A precision measurement of the ${}^{71}\mathrm{Ga}({}^3\mathrm{He},t){}^{71}\mathrm{Ge}$ charge-exchange reaction was performed. By using a rather complete set of theoretical form factors to describe the cross-section angular distributions over a large angular range, the Gamow-Teller strength distribution up to the effective neutron-separation energy in ${}^{71}\mathrm{Ge}$ was extracted. The data and the analysis constrain the ${}^{71}\mathrm{Ga}({\nu }_e,e^{-})$ solar neutrino rate in a neutrino nonoscillation scenario. For nonoscillating neutrinos we report a solar neutrino capture rate of $122.4\pm 3.4\left(\mathrm{stat}\right)\pm 1.1\left(\mathrm{sys}\right)$ SNU, which is lower than the presently accepted value of $132\pm 18$ SNU, though not in disagreement given the quoted errors.

We investigate the two-particle intensity correlation function of $\Lambda$ in relativistic heavy-ion collisions. We find that the behavior of the $\Lambda \Lambda$ correlation function at small relative momenta is fairly sensitive to the interaction potential and collective flows. By comparing the results of different source functions and potentials, we explore the effect of intrinsic collective motions on the correlation function. We find that the recent STAR data give a strong constraint on the scattering length and effective range of $\Lambda \Lambda$ interaction, as $-1.8{\mathrm{fm}}^{-1}<1/a_0<-0.8{\mathrm{fm}}^{-1}$ and $3.5\mathrm{fm}<r_{\mathrm{eff}}<7\mathrm{fm}$, respectively, if $\Lambda$ samples do not include the feed-down contribution from long-lived particles. We find that the feed-down correction for ${\Sigma }^0$ decay reduces the sensitivity of the correlation function to the detail of the $\Lambda \Lambda$ interaction. As a result, we obtain a weaker constraint, $1/a_0<-0.8 {\mathrm{fm}}^{-1}$. Implication for the signal of existence of $H$-dibaryon is discussed. Comparison with the scattering parameters obtained from the double $\Lambda$ hypernucleus may reveal in-medium effects in the $\Lambda \Lambda$ interaction.

We present state-of-the-art calculations of viscous photon emission from nuclear collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC). Fluctuating initial density profiles are evolved with event-by-event viscous hydrodynamics. Momentum spectra of thermal photons radiated by these explosively expanding fireballs and their $p_T$-differential anisotropic flow coefficients $v_n\left(p_T\right)$ are computed, both with and without accounting for viscous corrections to the standard thermal emission rates. Viscous corrections to the rates are found to have a larger effect on the $v_n$ coefficients than the viscous suppression of hydrodynamic flow anisotropies. The benefits of taking the ratio of elliptic to triangular flow, $v_2/v_3$, are discussed, and the space-time regions that contribute dominantly to the photon flow harmonics are identified. The directed flow $v_1$ of thermal photons is predicted for the energies currently available at the RHIC and the LHC.

In most heavy ion collision simulations involving relativistic hydrodynamics, the Cooper-Frye formula is applied to transform the hydrodynamical fields to particles. In this article the so-called negative contributions in the Cooper-Frye formula are studied using a coarse-grained transport approach. The magnitude of negative contributions is investigated as a function of hadron mass, collision energy in the range of $E_{\mathrm{lab}}=5\text{–}160A$ GeV, collision centrality, and the energy density transition criterion defining the hypersurface. The microscopic results are compared to negative contributions expected from hydrodynamical treatment assuming local thermal equilibrium. The main conclusion is that the number of actual microscopic particles flying inward is smaller than the negative contribution one would expect in an equilibrated scenario. The largest impact of negative contributions is found to be on the pion rapidity distribution at midrapidity in central collisions. For this case negative contributions in equilibrium constitute 8–13% of positive contributions, depending on collision energy, but only 0.5–4% in cascade calculation. The dependence on the collision energy itself is found to be nonmonotonous with a maximum at $10–20A$ GeV.

A new critical survey is presented of all half-life, decay-energy, and branching-ratio measurements related to 20 superallowed $0^{+}\to 0^{+}\beta$ decays. Included are 222 individual measurements of comparable precision obtained from 177 published references. Compared with our last review in 2008, we have added results from 24 new publications and eliminated 9 references, the results from which having been superseded by much more precise modern data. We obtain world-average $ft$ values for each of the 18 transitions that have a complete set of data, then apply radiative and isospin-symmetry-breaking corrections to extract “corrected” $\mathcal{F}t$ values. Fourteen of these $\mathcal{F}t$ values now have a precision of order 0.1% or better. In the process of obtaining these results we carefully evaluate the available calculations of the isospin-symmetry-breaking corrections by testing the extent to which they lead to $\mathcal{F}t$ values consistent with conservation of the vector current. Only one set of calculations satisfactorily meets this condition. The resultant average $\mathcal{F}t$ value, when combined with the muon lifetime, yields the up-down quark-mixing element of the Cabibbo-Kobayashi-Maskawa matrix, $V_{ud}=0.97417\pm 0.00021.$ The unitarity test on the top row of the matrix becomes $|V_{ud}{|}^2+|V_{us}{|}^2+{\left|V_{ub}\right|}^2=0.99978\pm 0.00055$ if the Particle Data Group (PDG) recommended value for $V_{us}$ is used. However, recent lattice QCD calculations, not included yet in the PDG evaluation, have introduced some inconsistency into kaon-decay measurements of $V_{us}$ and $V_{us}/V_{ud}.$ We examine the impact of these new results on the unitarity test and conclude that there is no evidence of any statistically significant violation of unitarity. Finally, from the $\mathcal{F}t$-value data we also set limits on the possible existence of scalar interactions.

We investigate ${}^9\mathrm{Be}+{}^{208}\mathrm{Pb}$ elastic scattering, breakup, and fusion at energies around the Coulomb barrier. The three processes are described simultaneously, with identical conditions of calculations. The ${}^9\mathrm{Be}$ nucleus is defined in an $\alpha +\alpha +n$ three-body model, using the hyperspherical coordinate method. We first analyze spectroscopic properties of ${}^9\mathrm{Be}$ and show that the model provides a fairly good description of the low-lying states. The scattering with ${}^{208}\mathrm{Pb}$ is then studied with the continuum discretized coupled channel method, where the $\alpha +\alpha +n$ continuum is approximated by a discrete number of pseudostates. The use of a three-body model for ${}^9\mathrm{Be}$ improves previous theoretical works, where ${}^9\mathrm{Be}$ is assumed to have a two-body structure (${}^8\mathrm{Be}+n$ or ${}^5\mathrm{He}+\alpha$), although neither ${}^8\mathrm{Be}$ nor ${}^5\mathrm{He}$ are bound. Optical potentials for the $\alpha +{}^{208}\mathrm{Pb}$ and  $n+{}^{208}\mathrm{Pb}$ systems are taken from the literature. We present cross sections at different energies, and we investigate the convergence with respect to the truncation of the $\alpha +\alpha +n$ continuum. In general, good agreement with experiment is obtained, despite no parameter fitting being made. We show that continuum effects increase at low energies, and we confirm that breakup channels enhance the fusion cross sections below the Coulomb barrier.