Empirical proton-neutron, proton-proton, and neutron-neutron paring and so-called nonpairing interactions are extracted by using experimental data of binding energies. Nonpairing interactions, $\delta V_{pp}^{\left(2\right)}$ and $\delta V_{nn}^{\left(2\right)}$, are very sensitive to the shell and subshell evolution, the phase transition, and the Wigner effect. Odd-even staggerings of one-nucleon separation energies are discussed in terms of empirical pairing interactions.

The shear viscosity $\eta$ has been calculated by using the Green-Kubo relation in the framework of a partonic transport approach solved at cascade level. We compare the numerical results for $\eta$ obtained from the Green-Kubo correlator with the analytical formulas in both the relaxation time approximation (RTA) and the Chapman-Enskog (CE) approximation. We investigate and emphasize the differences between the isotropic and anisotropic cross sections and between the massless and massive particles. We show that in the range of temperature explored in a heavy ion collision and for perturbative-QCD-like cross section, the RTA significantly underestimates the viscosity by about a factor of 2–3, while a good agreement is found between the CE approximation and Gree-Kubo relation already at first-order of approximation. The agreement with the CE approximation supplies an analytical formula that allows us to develop a kinetic transport theory at fixed shear-viscosity to entropy-density ratio, $\eta /s$. This opens the possibility of exploring dissipative nonequilibrium evolution of the distribution functions versus $T$-dependent $\eta /s$ and particle momenta in the dynamics of the quark-gluon plasma created in ultrarelativistic heavy-ion collisions.

Measurements of charged pion and kaon production are presented in centrality selected $\mathrm{Pb}+\mathrm{Pb}$ collisions at 40$A$ GeV and 158$A$ GeV beam energy as well as in semicentral $\mathrm{C}+\mathrm{C}$ and $\mathrm{Si}+\mathrm{Si}$ interactions at 40$A$ GeV. Transverse mass spectra, rapidity spectra, and total yields are determined as a function of centrality. The system-size and centrality dependence of relative strangeness production in nucleus-nucleus collisions at 40$A$ GeV and 158$A$ GeV beam energy are derived from the data presented here and from published data for $\mathrm{C}+\mathrm{C}$ and $\mathrm{Si}+\mathrm{Si}$ collisions at 158$A$ GeV beam energy. At both energies a steep increase with centrality is observed for small systems followed by a weak rise or even saturation for higher centralities. This behavior is compared to calculations using transport models (ultra-relativistic quantum molecular dynamics and hadron-string dynamics), a percolation model, and the core-corona approach.

I investigate the effects of plasma interactions on resonance-enhanced fusion rates in stars. Starting from basic principles we derive an expression for the fusion rate that can serve as a basis for discussion of approximation schemes The present state-of-the-art correction algorithms, based on the classical correlation function for the fusing particles and the classical energy shift for the resonant state, do not follow from this result, even as an approximation. The results of expanding in a perturbation solution for the case of a weakly coupled plasma are somewhat enlightening. But at this point we are at a loss as to how to do meaningful calculations in systems with even moderate plasma coupling strength. Examples where this can matter are the effect of a possible low-energy ${}^{12}$C+${}^{12}$C resonance on x-ray bursts from accreting neutron stars or on supernova 1A simulations, and the calculation of the triple $\alpha$ rate in some of the more strongly coupled regions in which the process enters, such as accretion onto a neutron star.

We show how shape transitions in the neutron-rich exotic Si and S isotopes occur in terms of shell-model calculations with a newly constructed Hamiltonian based on $V_{\mathrm{MU}}$ interaction. We first compare the calculated spectroscopic-strength distributions for the proton $0d_{5/2,3/2}$ and $1s_{1/2}$ orbitals with results extracted from a ${}^{48}\mathrm{Ca}(e,e^{\prime }p)$ experiment to show the importance of the tensor-force component of the Hamiltonian. Detailed calculations for the excitation energies, $B\left(E2\right)$, and two-neutron separation energies for the Si and S isotopes show excellent agreement with experimental data. The potential-energy surface exhibits rapid shape transitions along the isotopic chains towards $N=28$ that are different for Si and S. We explain the results in terms of an intuitive picture by involving a Jahn-Teller-type effect that is sensitive to the tensor-force-driven shell evolution. The closed subshell nucleus ${}^{42}\mathrm{Si}$ is a particularly good example of how the tensor-force-driven Jahn-Teller mechanism leads to a strong oblate rather than a spherical shape.

We study the potential implications of lattice QCD determinations of the $S$-wave nucleon-nucleon scattering lengths with unphysical light quark masses. If the light quark masses are small enough such that nuclear effective field theory (NEFT) can be used to perform quark-mass extrapolations, then the leading quark-mass dependence of not only the effective range and the two-body current, but also all the low-energy deuteron matrix elements up to next-to-leading-order in NEFT can be obtained. As a proof of principle, we compute the quark-mass dependence of the deuteron charge radius, magnetic moment, polarizability, and the deuteron photodisintegration cross section using the lattice calculation of the scattering lengths at 354 MeV pion mass by the ``Nuclear Physics with Lattice QCD'' (NPLQCD) collaboration and the NEFT power counting scheme of Beane, Kaplan, and Vuorinen (BKV), even though it is not yet established that the 354 MeV pion mass is within the radius of convergence of the BKV scheme. Once the lattice result with quark mass within the NEFT radius of convergence is obtained, our observation can be used to constrain the time variation of isoscalar combination of $u$ and $d$ quark mass $m_q$, to help the anthropic principle study to find the $m_q$ range that allows the existence of life, and to provide a weak test of the multiverse conjecture.

Unbound states in ${}^{28}$Ne and ${}^{25}$F were populated in the reaction of a 102 MeV/nucleon ${}^{29}$Na beam on a beryllium target. The measured decay energy of 32(22) keV in the ${}^{27}$Ne+$n$ system corresponds to an unbound excited state in ${}^{28}$Ne at 3.86(11) MeV. This is the first measured unbound state of ${}^{28}$Ne. The decay energy of the ${}^{24}$F+$n$ system was measured as 300(170) keV. This places the second measured unbound state of ${}^{25}$F at 4.66(17) MeV.

We report no-core solutions for properties of light nuclei with three different approaches in order to assess the accuracy and convergence rates of each method. Full configuration interaction (FCI), Monte Carlo shell model (MCSM), and no core full configuration (NCFC) approaches are solved separately for the ground state energy and other properties of seven light nuclei using the realistic JISP16 nucleon-nucleon interaction. The results are consistent among the different approaches. The methods differ significantly in how the required computational resources scale with increasing particle number for a given accuracy.

We discuss the need of including tensor terms in the effective Gogny interaction used in mean-field calculations. We show in one illustrative case that, with the usual tensor term that is employed in the Skyrme interaction (and that allows us to separate the like–nucleon and the neutron-proton tensor contributions), we can describe the evolution of the $N=28$ neutron gap in calcium isotopes. We propose to include a tensor and a tensor-isospin term in finite-range interactions of Gogny type. The parameters of the two tensor terms allow us to treat separately the like-nucleon and the neutron-proton contributions. Two parametrizations of the tensor terms have been chosen to reproduce different neutron single-particle properties in the ${}^{48}$Ca nucleus and the energy of the first $0^{-}$ state in the ${}^{16}$O nucleus. By employing these two parametrizations we analyze the evolution of the $N=14$, 28, and 90 neutron energy gaps in oxygen, calcium, and tin isotopes, respectively. We show that the combination of the parameters governing the like-nucleon contribution is crucial to correctly reproduce the experimental (where available) or shell-model trends for the evolution of the three neutron gaps under study.

Background: One important quantity in nuclear fission is the average number of prompt neutrons emitted from the fission fragments, the prompt neutron multiplicity, $\overline{\nu }$. The total number of prompt fission neutrons, ${\overline{\nu }}_{\text{tot}}$, increases with increasing incident neutron energy. The prompt-neutron multiplicity is also a function of the fragment mass and the total kinetic energy of the fragmentation. Those data are only known in sufficient detail for a few thermal-neutron-induced fission reactions on, for example, ${}^{233,235}$U and ${}^{239}$Pu. The enthralling question has always been asked how the additional excitation energy is shared between the fission fragments. The answer to this question is important in the analysis of fission-fragment data taken with the double-energy technique. Although in the traditional approach the excess neutrons are distributed equally across the mass distribution, a few experiments showed that those neutrons are predominantly emitted by the heavy fragments.

Purpose: We investigated the consequences of the $\nu (A,\mathrm{TKE},E_{\mathrm{n}})$ distribution on the fission fragment observables.

Methods: Experimental data obtained for the ${}^{234}$U($n,f$) reaction with a Twin Frisch Grid Ionization Chamber, were analyzed assuming two different methods for the neutron evaporation correction. The effect of the two different methods on the resulting fragment mass and energy distributions is studied.

Results: We found that the preneutron mass distributions obtained via the double-energy technique become slightly more symmetric, and that the impact is larger for postneutron fission-fragment distributions. In the most severe cases, a relative yield change up to 20–30$\%$ was observed.

Conclusions: We conclude that the choice of the prompt-neutron correction method has strong implications on the understanding and modeling of the fission process and encourages new experiments to measure fission fragments in coincidence with prompt fission neutrons. Even more, the correct determination of postneutron fragment yields has an impact on the reliable assessment of the nuclear waste inventory, as well as on the correct prediction of delayed neutron precursor yields.

Background: Uncertainty in the operating temperatures of Oklo reactor zones impacts the precision of bounds derived for time variation of the fine structure constant $\alpha$. Improved ${}^{176}$Lu/${}^{175}$Lu thermometry has been discussed but its usefulness may be complicated by photoexcitation of the isomeric state ${}^{176m}$Lu by ${}^{176}$Lu($\gamma ,{\gamma }^{\prime }$) fluorescence.

Purpose: We calculate prompt, delayed, and equilibrium $\gamma$-ray fluxes due to fission of ${}^{235}$U in pulsed mode operation of Oklo zone RZ10.

Methods: We use Monte Carlo modeling to calculate the prompt flux. We use improved data libraries to estimate delayed and equilibrium spectra and fluxes.

Results: We find $\gamma$-ray fluxes as a function of energy and derive values for the coefficients ${\lambda }_{\gamma ,{\gamma }^{\prime }}$ that describe burn-up of ${}^{176}$Lu through the isomeric ${}^{176m}$Lu state.

Conclusion: The contribution of the ($\gamma ,{\gamma }^{\prime }$) channel to the ${}^{176}$Lu/${}^{175}$Lu isotopic ratio is negligible in comparison to the neutron burn-up channels. Lutetium thermometry is fully applicable to analyses of Oklo reactor data.

We discuss intermediate-energy single-nucleon removal reactions from deformed projectile nuclei. The removed nucleon is assumed to originate from a given Nilsson model single-particle state and the inclusive cross sections, to all rotational states of the residual nucleus, are calculated. We investigate the sensitivity of both the stripping cross sections and their momentum distributions to the assumed size of the model space in the Nilsson model calculations and to the shape of the projectile and residue. We show that the cross sections for small deformations follow the decomposition of the Nilsson state in a spherical basis. In the case of large and prolate projectile deformations the removal cross sections from prolate-like Nilsson states, having large values for the asymptotic quantum number $n_z$, are reduced. For oblate-like Nilsson states, with small $n_z$, the removal cross sections are increased. Whatever the deformation, the residue momentum distributions are found to remain robustly characteristic of the orbital angular momentum decomposition of the initial state of the nucleon in the projectile.

The structure of ${}^{19,20,22}$C has been investigated using high-energy (around 240 MeV/nucleon) one- and two-neutron removal reactions on a carbon target. Measurements were made of the inclusive cross sections and momentum distributions for the charged residues. Narrow momentum distributions were observed for one-neutron removal from ${}^{19}$C and ${}^{20}$C and two-neutron removal from ${}^{22}$C. Two-neutron removal from ${}^{20}$C resulted in a relatively broad momentum distribution. The results are compared with eikonal-model calculations combined with shell-model structure information. The neutron removal cross sections and associated momentum distributions are calculated for transitions to both the particle-bound and particle-unbound final states. The calculations take into account the population of the mass $A-1$ reaction residues ${}^{A-1}$C and, following one-neutron emission after one-neutron removal, the mass $A-2$ two-neutron removal residues ${}^{A-2}$C. The smaller contributions of direct two-neutron removal, that populate the ${}^{A-2}$C residues in a single step, are also computed. The data and calculations are shown to be in good overall agreement and consistent with the predicted shell-model ground-state configurations and one-neutron overlaps with low-lying states in ${}^{18-21}$C. These suggest significant $\nu s_{1/2}^2$ valence neutron configurations in both ${}^{20}$C and ${}^{22}$C. The results for ${}^{22}$C strongly support the picture of ${}^{22}$C as a two-neutron halo nucleus with a dominant $\nu s_{1/2}^2$ ground-state configuration.

Background: There has been much recent investigation into dijets at the Large Hadron Collider, but predictions for dijets at Relativistic Heavy Ion Collider (RHIC) scales are lacking.

Purpose: We present a systematic study of the dijet suppression at RHIC using the VNI/Bass-Müller-Srivastava parton cascade.

Methods: We examine the modification of the dijet asymmetry $A_j$ and the within-cone transverse energy distribution (jet shape) along with partonic fragmentation distributions $z$ and $j_t$ in terms of $\widehat{q}$, the path length of leading and subleading jets, cuts on the jet energy distributions, the jet cone angle, and the jet-medium interaction mechanism.

Results: We find that $A_j$ is most sensitive to $\widehat{q}$ and relatively insensitive to the nature of the jet-medium interaction mechanism. The jet profile is dominated by $\widehat{q}$ and the nature of the interaction mechanism. The partonic fragmentation distributions clearly show the jet modification and differentiate between elastic and radiative plus elastic modes.

Conclusions: Dijets at RHIC scales are strongly modified by a quark-gluon plasma medium; measurements of their suppression will provide a vital additional data point for understanding the modification of hard probes.

Theoretical studies within the chiral unitary approach, and recent experiments, have provided evidence of the existence of two isoscalar states in the region of the $\Lambda \left(1405\right)$. In this paper we use the same chiral approach to generate energy levels in a finite box. In a second step, assuming that these energies correspond to lattice QCD results, we devise the best strategy of analysis to obtain the two states in the infinite-volume case, with sufficient precision to distinguish them. We find out that by using energy levels obtained with asymmetric boxes and/or with a moving frame, with reasonable errors in the energies, one has a successful scheme to get the two $\Lambda \left(1405\right)$ poles.

Background: The reaction ${}^{17}$O${(p,\gamma )}^{18}$F influences hydrogen-burning nucleosynthesis in several stellar sites, such as red giants, asymptotic giant branch (AGB) stars, massive stars, and classical novae. In the relevant temperature range for these environments ($T_9=0.01$–$0.4$), the main contributions to the rate of this reaction are the direct capture process, two low-lying narrow resonances ($E_r=65.1$ and 183 keV) and the low-energy tails of two broad resonances ($E_r=557$ and 677 keV).

Purpose: Previous measurements and calculations give contradictory results for the direct capture contribution which in turn increases the uncertainty of the reaction rate. In addition, very few published cross section data exist for the high energy region that might affect the interpretation of the direct capture and the contributions of the broad resonances in the lower energy range. This work aims to address these issues.

Method: The reaction cross section was measured in a wide proton energy range ($E_{\mathrm{c}.\mathrm{m}.}=345$–1700 keV) and at several angles (${\theta }_{\mathrm{lab}}=0^{\circ },{45}^{\circ },{90}^{\circ },{135}^{\circ }$). The observed primary $\gamma$ transitions were used as input in an $R$-matrix code in order to obtain the contribution of the direct capture and the two broad resonances to the low-energy region.

Results: The extrapolated $S$ factor from the present data is in good agreement with the existing literature data in the low-energy region. A new reaction rate was calculated from the combined results of this work and literature $S$-factor determinations. Resonance strengths and branchings are reported for several ${}^{18}$F states.

Conclusions: We were able to extrapolate the astrophysical $S$ factor of the reaction ${}^{17}$O${(p,\gamma )}^{18}$F at low energies from cross section data taken at higher energies. No significant changes in the nucleosynthesis are expected from the newly calculated reaction rate.

In stars, ${}^{16}$O represents the endpoint of the helium burning sequence due to the low rate of ${}^{16}$O($\alpha$,$\gamma$)${}^{20}$Ne. We present a new direct measurement of the total cross section of ${}^{16}$O($\alpha$,$\gamma$)${}^{20}$Ne at $E_{\mathrm{c}.\mathrm{m}.}=1.69\mathrm{MeV}$ employing the DRAGON recoil separator. In addition, the branching ratios and strength of the $E_{\mathrm{c}.\mathrm{m}.}=2.426\mathrm{MeV}$ $3^{-}$ resonance were determined.

Search for the neutron-rich hypernucleus ${}_{\Lambda }^9\mathrm{He}$ is reported by the FINUDA experiment at DA$\Phi$NE, INFN-LNF, studying $({\pi }^{+},{\pi }^{-})$ pairs in coincidence from the $K_{\mathrm{stop}}^{-}+{}^9\mathrm{Be}\to {}_{\Lambda }^9\mathrm{He}+{\pi }^{+}$ production reaction followed by ${}_{\Lambda }^9\mathrm{He}\to {}^9\mathrm{Li}+{\pi }^{-}$ weak decay. An upper limit of the production rate of ${}_{\Lambda }^9\mathrm{He}$ undergoing this two-body ${\pi }^{-}$ decay is determined to be $(2.3\pm 1.9)\times {10}^{-6}/K_{\mathrm{stop}}^{-}$ at the 90$\%$ confidence level.

The possibility of detecting neutrinoless double-$\beta$-decay (0$\nu \beta \beta$-decay) in experiments that are currently in operation or under development provides the exciting opportunity to determine the Dirac or Majorana nature of the neutrino and its absolute mass scale. An important datum for interpreting 0$\nu \beta \beta$-decay experimental results is the $Q$ value of the decay. Using Penning trap mass spectrometry we have measured the atomic mass of ${}^{48}$Ca to be $M{[}^{48}$Ca] $=$ 47.952 522 76(21) u which, combined with the mass of ${}^{48}$Ti evaluated by Audi et al. [Nucl. Phys. A 729, 337 (2003)], provides a new determination of the ${}^{48}$Ca $\beta \beta$-decay $Q$ value: $Q_{\beta \beta }$ $=$ 4262.96(84) keV.

The ground state of ${}^{11}$Li is the preeminent example of a two-neutron-halo nucleus and is part of an isobaric sextet. Another member of this sextet, the double isobaric analog of ${}^{11}$Li${}_{\mathrm{g}.\mathrm{s}.}$ in ${}^{11}$B, has been identified in the ${}^{12}$Be($p,2n$)${}^{11}$B reaction. The state was discovered through its two-proton decay branch. From detected $2p+{}^9$Li events, its excitation energy was determined to be 33.57(8) MeV using the invariant mass method. With the known masses of ${}^{11}$Li and its isobaric analog state in ${}^{11}$Be, three members of the same sextet have measured masses for the first time, permitting the masses of the remaining members to be extrapolated using the isobaric multiplet mass equation. All members of this multiplet are expected to have a two-nucleon halo structure and this was found consistent with the evolution of the mass across the sextet. The momentum correlations of the detected protons were found to have both “diproton” and “cigar” components.