Background: The deuteron plays a pivotal role in nuclear and hadronic physics, as both the simplest bound multinucleon system and as an effective neutron target. Quasielastic electron scattering on the deuteron is a benchmark reaction to test our understanding of deuteron structure and the properties and interactions of the two nucleons bound in the deuteron.

Purpose: The experimental data presented here can be used to test state-of-the-art models of the deuteron and the two-nucleon interaction in the final state after two-body breakup of the deuteron. Focusing on polarization degrees of freedom, we gain information on spin-momentum correlations in the deuteron ground state (due to the $D$-state admixture) and on the limits of the impulse approximation (IA) picture as it applies to measurements of spin-dependent observables like spin structure functions for bound nucleons. Information on this reaction can also be used to reduce systematic uncertainties on the determination of neutron form factors or deuteron polarization through quasielastic polarized electron scattering.

Method: We measured the beam-target double-spin asymmetry ($A_{\left|\right|}$) for quasielastic electron scattering off the deuteron at several beam energies ($1.6\text{–}1.7$, 2.5, 4.2, and $5.6\text{–}5.8\mathrm{GeV}$), using the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. The deuterons were polarized along (or opposite to) the beam direction. The double-spin asymmetries were measured as a function of photon virtuality $Q^2(0.13\text{–}3.17{(\mathrm{GeV}/c)}^2)$, missing momentum $\left(p_m=0.0\text{–}0.5\mathrm{GeV}/c\right)$, and the angle between the (inferred) spectator neutron and the momentum transfer direction $\left({\theta }_{nq}\right)$.

Results: The results are compared with a recent model that includes final-state interactions (FSI) using a complete parametrization of nucleon-nucleon scattering, as well as a simplified model using the plane wave impulse approximation (PWIA). We find overall good agreement with both the PWIA and FSI expectations at low to medium missing momenta $\left(p_m\le 0.25\mathrm{GeV}/c\right)$, including the change of the asymmetry due to the contribution of the deuteron $D$ state at higher momenta. At the highest missing momenta, our data clearly agree better with the calculations including FSI.

Conclusions: Final-state interactions seem to play a lesser role for polarization observables in deuteron two-body electrodisintegration than for absolute cross sections. Our data, while limited in statistical power, indicate that PWIA models work reasonably well to understand the asymmetries at lower missing momenta. In turn, this information can be used to extract the product of beam and target polarization $\left(P_b{P}_t\right)$ from quasielastic electron-deuteron scattering, which is useful for measurements of spin observables in electron-neutron inelastic scattering. However, at the highest missing (neutron) momenta, FSI effects become important and must be accounted for.

Studies of the $\gamma$-ray strength functions can reveal useful information concerning underlying nuclear structure. Accumulated experimental data on the strength functions show an enhancement in the low $\gamma$ energy region. We have calculated the $M1$ strength functions for the ${}^{49,50}\mathrm{Cr}$ and ${}^{48}\mathrm{V}$ nuclei in the $f_{7/2}$ shell-model basis. We find a low energy enhancement for $\gamma$ decay similar to that obtained for other nuclei in previous studies, but for the first time we are also able to study the complete distribution related to $M1$ emission and absorption. We find that $M1$ strength distribution peaks at zero transition energy and falls off exponentially. The height of the peak and the slope of the exponential are approximately independent of the nuclei studied in this model space and the range of initial angular momenta. We show that the slope of the exponential fall off is proportional to the energy of the $T=1$ pairing gap.

We perform a detailed analysis of the fundamental mode of nonradial pulsations of color flavor locked strange stars. Solving the general relativistic equations for nonradial pulsations for an equation of state derived within the MIT bag model, we calculate the frequency and the gravitational damping time of the fundamental mode for all the parametrizations of the equation of state that lead to self-bound matter. Our results show that color flavor locked strange stars can emit gravitational radiation in the optimal range for present gravitational wave detectors and that it is possible to constrain the equation of state's parameters if the fundamental oscillation mode is observed and the stellar mass is determined. We also show that the $f$-mode frequency can be fitted as a function of the square root of the average stellar density $\sqrt{M/R^3}$ by a single linear relation that fits quite accurately the results for all parametrizations of the equation of state. All results for the damping time can also be fitted as a function of the compactness $M/R$ by a single empirical relation. Therefore, if a given compact object is identified as a color flavor locked strange star these two relations could be used to determine the mass and the radius from the knowledge of the frequency and the damping time of gravitational waves from the $f$ mode.

We investigate the influences of the nuclear composition on the weak interaction rates of heavy nuclei during the core collapse of massive stars. The nuclear abundances in nuclear statistical equilibrium (NSE) are calculated by some equation of state (EOS) models including in-medium effects on nuclear masses. We systematically examine the sensitivities of electron capture and neutrino-nucleus scattering on heavy nuclei to the nuclear shell effects and the single-nucleus approximation. We find that the washout of the shell effect at high temperatures brings significant change to weak rates by smoothing the nuclear abundance distribution: the electron capture rate decreases by $\sim 20\%$ in the early phase and increases by $\sim 40\%$ in the late phase at most, while the cross section for neutrino-nucleus scattering is reduced by $\sim 15\%$. This is because the open-shell nuclei become abundant instead of those with closed neutron shells as the shell effects disappear. We also find that the single-nucleus description based on the average values leads to underestimations of weak rates. Electron captures and neutrino coherent scattering on heavy nuclei are reduced by $\sim 80\%$ in the early phase and by $\sim 5\%$ in the late phase, respectively. These results indicate that NSE like EOS accounting for shell washout is indispensable for the reliable estimation of weak interaction rates in simulations of core-collapse supernovae.

It is argued that final state enhancements in production reactions at large momentum transfers, such as $pp\to K^{+}\mathrm{\Lambda }p$, are primarily sensitive to the position of a virtual bound state pole in the $\mathrm{\Lambda }p$ system rather than the $\mathrm{\Lambda }p$ scattering length and effective range. These arguments are supported by a study of the dispersion relation derived to describe such processes as a function of the cut-off energy. This shows that the position of the virtual bound state is independent of the cut-off energy.

We construct a simple model of heavy-ion collisions, local in the impact parameter plane, and appropriate for energies available at the CERN Super Proton Synchrotron (SPS). This model can be regarded as a new realization of the “fire-streak” approach, originally applied to studies of lower-energy nucleus-nucleus reactions. Starting from local energy and momentum conservation, we nicely describe the broadening of the pion rapidity distribution when going from central to peripheral $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=17.3$ GeV. The results of our calculations are compared with SPS experimental data. We discuss the resulting implications on the role of energy and momentum conservation for the dynamics of particle production in heavy-ion collisions. A specific space-time picture emerges, where the longitudinal evolution of the system strongly depends on the position in the impact parameter ($b_x,b_y$) plane. This picture is consistent with our earlier findings on the longitudinal evolution of the system as deduced from electromagnetic effects on charged-pion directed flow and can provide an explanation for specific low-$p_T$ phenomena seen in the fragmentation region of $\mathrm{Pb}+\mathrm{Pb}$ collisions.

Modern experimental facilities have provided a tremendous volume of reaction data, often with wide energy and angular coverage, and with increasing precision. For reactions with two hadrons in the final state, these data are often presented as multiple sets of panels, with angular distributions at numerous specific energies. Such presentations have limited visual appeal, and their physical content is typically extracted through some model-dependent treatment. Instead, we explore the use of a Legendre series expansion with a relatively small number of essential coefficients. This approach has been applied in several recent experimental investigations. We present some general properties of the Legendre coefficients in the helicity framework and consider what physical information can be extracted without any model-dependent assumptions.

Excited levels of ${}^{88}\mathrm{Br}$ populated in the $\beta$ decay of ${}^{88}\mathrm{Se}$ have been studied by means of $\beta \gamma$ and $\gamma \gamma$ spectroscopy methods. Neutron-rich parent ${}^{88}\mathrm{Se}$ nuclei were produced with proton-induced fission of ${}^{238}\mathrm{U}$ using the Ion Guide Isotope Separator On-Line (IGISOL) method and separated from contaminants using a dipole magnet and the coupled JYFLTRAP Penning trap at the Accelerator Laboratory of the University of Jyväskylä. The level scheme of ${}^{88}\mathrm{Br}$ has been constructed and $logft$ values of levels were determined. The ground-state spin of ${}^{88}\mathrm{Br}$ is now firmly determined to be $1^{-}$. Low-energy levels in ${}^{88}\mathrm{Br}$ were interpreted as members of the $\pi p_{3/2}{\left(\nu d_{5/2}\right)}^3, \pi p_{3/2}^{-1}{\left(\nu d_{5/2}\right)}^3, \pi f_{5/2}^{-1}{\left(\nu d_{5/2}\right)}^3$, and $\pi g_{9/2}\nu g_{7/2}$ multiplets. The shell-model calculations performed in this work reproduce well the experimental results.

The multinucleon transfer reaction has been investigated within the dinuclear system model. The nucleon transfer is coupled to the dissipation of relative motion energy and angular momentum by solving a set of microscopically derived master equations. A barrier distribution approach is implemented in the model in order to include the contributions of different orientations and dynamical effects. The available data of fragment production via multinucleon transfer reactions could be understood with the model for the reactions of ${}^{136}\mathrm{Xe}+{}^{198}\mathrm{Pt}/{}^{208}\mathrm{Pb}$ near Coulomb barrier energies. It is found that the production of heavy neutron-rich nuclei weakly depends on the incident energy. However, the yields of proton-rich nuclei increase with the incident energy.

By using the $R$-matrix approach we calculate the radiative width for a resonance decaying to a bound state through electric-dipole $E1$ transitions. The total radiative width is determined by the interference of the nuclear internal and external radiative width amplitudes. For a given channel radius the external radiative width amplitude is model independent and is determined by the asymptotic normalization coefficient (ANC) of the bound state to which the resonance decays. It also depends on the partial resonance width. To calculate the internal radiative width amplitude we show that a single-particle-potential model is appropriate. We compare our results with a few experimental data.

The lifetime of the recently discovered $2p$ emitter ${}^{67}\mathrm{Kr}$ was found to be considerably below the lower limit predicted theoretically. This communication addresses this issue. Different separation energy systematics are analyzed and different mechanisms for $2p$ emission are evaluated. We find that the most plausible reason for this disagreement is the decay mechanism of ${}^{67}\mathrm{Kr}$, which is not “true $2p$” emission but rather “transitional dynamics” on the borderline between true $2p$ and sequential $2p$ decay mechanisms. If this is correct, this imposes stringent limits of $E_r=1.35$–1.42 MeV on the ground-state energy of ${}^{66}\mathrm{Br}$ relative to the ${}^{65}\mathrm{Se}-p$ threshold.

We investigate the decay of ${}^{87,88}\mathrm{Br}$ and ${}^{94}\mathrm{Rb}$ using total absorption $\gamma$-ray spectroscopy. These important fission products are $\beta$-delayed neutron emitters. Our data show considerable $\beta \gamma$ intensity, so far unobserved in high-resolution $\gamma$-ray spectroscopy, from states at high excitation energy. We also find significant differences with the $\beta$ intensity that can be deduced from existing measurements of the $\beta$ spectrum. We evaluate the impact of the present data on reactor decay heat using summation calculations. Although the effect is relatively small it helps to reduce the discrepancy between calculations and integral measurements of the photon component for ${}^{235}\mathrm{U}$ fission at cooling times in the range $1\text{–}100$ s. We also use summation calculations to evaluate the impact of present data on reactor antineutrino spectra. We find a significant effect at antineutrino energies in the range of 5 to 9 MeV. In addition, we observe an unexpected strong probability for $\gamma$ emission from neutron unbound states populated in the daughter nucleus. The $\gamma$ branching is compared to Hauser-Feshbach calculations, which allow one to explain the large value for bromine isotopes as due to nuclear structure. However the branching for ${}^{94}\mathrm{Rb}$, although much smaller, hints of the need to increase the radiative width ${\mathrm{\Gamma }}_{\gamma }$ by one order of magnitude. This increase in ${\mathrm{\Gamma }}_{\gamma }$ would lead to a similar increase in the calculated $(\mathrm{n},\gamma )$ cross section for this very neutron-rich nucleus with a potential impact on $r$ process abundance calculations.

Background: Although uncertainty quantification has been making its way into nuclear theory, these methods have yet to be explored in the context of reaction theory. For example, it is well known that different parameterizations of the optical potential can result in different cross sections, but these differences have not been systematically studied and quantified.

Purpose: The purpose of this work is to investigate the uncertainties in nuclear reactions that result from fitting a given model to elastic-scattering data, as well as to study how these uncertainties propagate to the inelastic and transfer channels.

Method: We use statistical methods to determine a best fit and create corresponding 95% confidence bands. A simple model of the process is fit to elastic-scattering data and used to predict either inelastic or transfer cross sections. In this initial work, we assume that our model is correct, and the only uncertainties come from the variation of the fit parameters.

Results: We study a number of reactions involving neutron and deuteron projectiles with energies in the range of 5–25 MeV/u, on targets with mass $A=12–208$. We investigate the correlations between the parameters in the fit. The case of deuterons on ${}^{12}\mathrm{C}$ is discussed in detail: the elastic-scattering fit and the prediction of ${}^{12}\mathrm{C}$($d,p$)${}^{13}\mathrm{C}$ transfer angular distributions, using both uncorrelated and correlated ${\chi }^2$ minimization functions. The general features for all cases are compiled in a systematic manner to identify trends.

Conclusions: Our work shows that, in many cases, the correlated ${\chi }^2$ functions (in comparison to the uncorrelated ${\chi }^2$ functions) provide a more natural parameterization of the process. These correlated functions do, however, produce broader confidence bands. Further optimization may require improvement in the models themselves and/or more information included in the fit.

Background: The isobaric ratio difference scaling phenomenon, which has been found for the fragments produced in projectile fragmentation reactions, is related to the nuclear density change in reaction systems.

Purpose: To verify whether the isobaric ratio difference scaling exists in the fragments produced in the spallation and fission reactions.

Methods: The isobaric ratio difference scaling, denoted by $S_{\mathrm{\Delta }ln{R}_{21}}$, is in theory deduced within the framework of the canonical ensemble theory at the grand-canonical limitation. The fragments measured in a series of projectile fragmentation, spallation, and fission reactions have been analyzed.

Results: A good $S_{\mathrm{\Delta }ln{R}_{21}}$ scaling phenomenon is shown for the fragments produced both in the projectile fragmentation reactions and in the spallation reactions, whereas the $S_{\mathrm{\Delta }ln{R}_{21}}$ scaling phenomenon for the fragments in the fission reaction is less obvious.

Conclusions: The $S_{\mathrm{\Delta }ln{R}_{21}}$ scaling is used to probe the properties of the equilibrium system at the time of fragment formation. The good scaling of $S_{\mathrm{\Delta }ln{R}_{21}}$ suggests that the equilibrium state can be achieved in the projectile fragmentation and spallation reactions. Whereas in the fission reaction, the result of $S_{\mathrm{\Delta }ln{R}_{21}}$ indicates that the equilibrium of the system is hard to achieve.

The internal excitation of nuclei after multinucleon transfer is estimated by using the time-dependent mean-field theory. Transfer probabilities for each channel as well as the energy loss after reseparation are calculated. By combining these two pieces of information, we show that the excitation energy distribution of the transfer fragments can be obtained separately for the different transfer channels. The method is applied to the reaction involving a ${}^{238}\mathrm{U}$ beam on a ${}^{12}\mathrm{C}$ target, which has recently been measured at GANIL. It is shown that the excitation energy calculated with the microscopic theory compares well with the experimental observation, provided that the competition with fusion is properly taken into account. The reliability of the excitation energy is further confirmed by the comparison with the phenomenological heavy-ion phase-space model at higher center-of-mass energies.

Nuclear modification factors $R_{\mathrm{cp}}$ of protons and pions are investigated by simulating Au+Au collisions from $0.8A$ to $1.8A$ GeV in a framework of an isospin-dependent quantum molecular dynamics (IQMD) model. The $R_{\mathrm{cp}}$ of protons rise with an increase in the transverse particle momentum $p_T$ at different beam energies owing to radial flow and the multiple-collision effect. The rate of increase of $R_{\mathrm{cp}}$ is suppressed at higher beam energies. While the $R_{\mathrm{cp}}$ of pions display weaker $p_T$ dependence. By changing the in-medium nucleon-nucleon cross section, the $R_{\mathrm{cp}}$ of protons change a lot, while the $R_{\mathrm{cp}}$ of pions do not. In addition, by deactivating the $N\mathrm{\Delta }\to NN$ and $\pi N\to \mathrm{\Delta }$ channels, the $R_{\mathrm{cp}}$ of protons change slightly in their increasing rates compared with the “original” case (with these two channels). However, the $R_{\mathrm{cp}}$ of pions is shifted down for the “no $N\mathrm{\Delta }\to NN$” case and has an inverse trend for the “no $\pi N\to \mathrm{\Delta }$” case. Based on these observations, we argue that the observable $R_{\mathrm{cp}}$ is a suitable tool to better distinguish in-medium effects of protons and pions.

We present a dynamical scheme for hadronization with first-order confinement phase transition. The thermodynamical conditions of phase equilibrium, the fluid velocity profile, and the dissipative effect determine the macroscopic changes of the parton volume and the corresponding hadron volume during the phase transition. The macroscopic volume changes are the basis for building up a dynamical scheme by considering microscopic transition processes from partons to hadrons and backwards. The established scheme is proved by comparing the numerical results with the analytical solutions in the case of a one-dimensional expansion of a dissipative fluid with Bjorken boost invariance. The comparisons show almost perfect agreements, which demonstrate the applicability of the introduced scheme.