The Compton double-polarization observable ${\mathrm{\Sigma }}_{2z}$ has been measured for the first time in the $\mathrm{\Delta }\left(1232\right)$ resonance region using a circularly polarized photon beam incident on a longitudinally polarized proton target at the Mainz Microtron. This paper reports these results, together with the model-dependent extraction of four proton spin polarizabilities from fits to additional asymmetry data using either a dispersion relation calculation or a baryon chiral perturbation theory calculations with the weighted average of these two fits resulting in ${\gamma }_{E1E1}=-2.87\pm 0.52, {\gamma }_{M1M1}=2.70\pm 0.43, {\gamma }_{E1M2}=-0.85\pm 0.72$, and ${\gamma }_{M1E2}=2.04\pm 0.43$, in units of ${10}^{-4}{\mathrm{fm}}^4$.

We report the first evidence of breakup dominance at deep sub-barrier energies for the proton halo nucleus ${}^8\mathrm{B}$ on a heavy target. Angular distribution measurements of the ${}^8\mathrm{B}$ breakup fragment, ${}^7\mathrm{Be}$, on lead were performed at the TwinSol facility of the University of Notre Dame at a beam energy of 30 MeV, 58% of the Coulomb barrier and corresponding to a distance of closest approach of 20.5 fm. The ${}^7\mathrm{Be}$ yield was observed in two double sided silicon strip detector telescopes symmetrical to the radioactive beam and normalized using the ${}^8\mathrm{B}$ Rutherford scattering. The results are in excellent agreement with continuum discretized coupled channel calculations with a total breakup cross section $(326\pm 84)\mathrm{mb}$. This is found to exhaust all of the total reaction cross section for the system ${}^8\mathrm{B}+{}^{208}\mathrm{Pb}$, possibly prohibiting a fusion enhancement. This finding is expected to give more insight to the puzzle of fusion suppression at deep sub-barrier energies with possible major consequences on nuclear astrophysics.

The $\beta$ decay of the semimagic Sn isotopes ${}^{136,137,138}\mathrm{Sn}$ has been studied at the Radioactive Isotope Beam Factory at the RIKEN Nishina Center. The first experimental information on excited states was obtained for ${}^{137}\mathrm{Sb}$ while, in the case of ${}^{136}\mathrm{Sb}$, the established excitation scheme could be extended by ten previously unidentified levels. In the decay of the most-neutron-rich isotope ${}^{138}\mathrm{Sn}$, two $\gamma$ rays were observed for the first time. The new experimental results, in combination with state-of-the-art shell-model calculations, provide the first information with respect to the evolution of the $0g_{7/2}$ and $1d_{5/2}$ proton single-particle states with increasing neutron number beyond $N=84$.

The astrophysical ${}^{29}\mathrm{Si}(p,\gamma$) reaction is expected to play a key role in determining the final ${}^{29}\mathrm{Si}$ yields ejected in nova explosions. Such yields are used to accurately identify the stellar origins of meteoritic stardust and recently, distinctive silicon isotopic ratios have been extracted from a number of presolar grains. Here, the light-ion ${}^{28}\mathrm{Si}({}^3\mathrm{He},p$) fusion-evaporation reaction was used to populate low-spin proton-unbound excited states in the nucleus ${}^{30}\mathrm{P}$ that govern the rate of the astrophysical ${}^{29}\mathrm{Si}(p,\gamma$) reaction. In particular, $\gamma$ decays were observed from resonances up to $E_r=500\mathrm{keV}$, and key resonances at 217 and 315 keV have now been identified as $2^{+}$ and $2^{-}$ levels, respectively. The present paper provides the first estimate of the 217-keV resonance strength and indicates that the strength of the 315-keV resonance, which dominates the rate of the ${}^{29}\mathrm{Si}(p,\gamma$) reaction over the entire peak temperature range of oxygen-neon novae, is higher than previously expected. As such, the abundance of ${}^{29}\mathrm{Si}$ ejected during nova explosions is likely to be less than that predicted by the most recent theoretical models.

Energy production in Type Ia x-ray bursts depends on a number of nuclear reactions that become efficient in a hot environment (up to 2 GK). Model sensitivity studies have been performed in an effort to better identify the reactions that have the largest effect, but these efforts are hampered by the high level of complexity of the astrophysical model and large nuclear physics uncertainties. In a recent study, the ${}^{24}\mathrm{Mg}(\alpha ,p){}^{27}\mathrm{Al}$ reaction was found to significantly affect the energy generation in x-ray bursts. This manuscript reports the first study of the ${}^{24}\mathrm{Mg}(\alpha ,p_{1,2}\gamma ){}^{27}\mathrm{Al}$ reaction at energies relevant for x-ray bursts. The branches to the ${}^{27}\mathrm{Al}$ excited states increase to a small degree the estimates of the total astrophysical ${}^{24}\mathrm{Mg}(\alpha ,p){}^{27}\mathrm{Al}$ reaction rate.

Background: Little data is available for the pygmy dipole resonance (PDR) in axially deformed nuclei. Photon-scattering experiments are complicated by high level densities in the PDR region and the small energy difference of transitions to the ground state and to excited states.

Purpose: We report on an experimental study of the low-energy dipole strength distribution of the well-deformed nucleus ${}^{164}\mathrm{Dy}$ between 4.0–7.7 MeV.

Methods: The low-lying photoresponse of ${}^{164}\mathrm{Dy}$ has been investigated using the method of nuclear resonance fluorescence using a quasimonochromatic linearly polarized $\gamma$-ray beam in the energy range of 4.0–7.7 MeV in steps of 0.2 MeV.

Results: For excitation energies between 4 MeV and 5 MeV, sufficiently low level densities allow for the identification of individual states, including level energies, reduced transition widths and branching ratios. Energy-averaged mean decay branching ratios, mean population ratios and partial absorption cross sections were determined above 5 MeV up to the neutron-separation threshold at 7.7 MeV. A Lorentzian-shaped enhancement of the partial photo absorption cross section followed by decays back to the ground-state band is found at 6.10(5) MeV with a width of 0.77(23) MeV. A comparison with results from complementary measurements is performed using the framework of the statistical model.

Conclusions: The experimental results for the mean population ratios deviate systematically from the statistical model simulation by 30(6)%. However, they are in agreement within one standard deviation of the simulation.

Although the prompt fission neutron spectrum (PFNS) is an essential component of neutron-driven systems that has been measured for decades, there are still multiple glaring unknowns regarding the PFNS of major actinides in the fission neutron incident energy range, specifically with regard to multichance fission and pre-equilibrium neutron emission processes. The only impactful experimental ${}^{239}\mathrm{Pu}$ PFNS measurements included in recent nuclear data evaluations were measured over a limited outgoing neutron energy range at thermal and 1.5-MeV average incident neutron energy, while other potentially impactful measurements have been shown to contain errors that resulted in either large uncertainty increases or in complete exclusion from nuclear data evaluation. We report here a measurement of the ${}^{239}\mathrm{Pu}$ PFNS over a wide range of incident neutron energy (1–20 MeV) and three orders of magnitude in outgoing neutron energy (0.01–10 MeV) resulting from the Chi-Nu experiment at the Los Alamos Neutron Science Center. These results are the combination of separate PFNS measurements in the same experimental area, one using a Li-glass and the other a liquid scintillator detector array. Covariances between all PFNS data points from each detector and within each incident energy range were generated between all other data in both detector arrays and within all other incident neutron energy bins, yielding a single covariance matrix for all 1300 PFNS data points reported here. These covariances are based on a thorough assessment of systematic bias and uncertainties associated with the measurement, PFNS extraction technique, combination of data from each detector type, and other aspects of the analysis. The existence of covariances between PFNS data points in different incident neutron energy ranges yielded covariances between average PFNS energy values at each incident energy to be reported here as well, which allowed for firm statements to be made regarding a shape of a purely experimental mean PFNS energy trend for the first time. Although minor PFNS shape differences exist between the results reported here and recent nuclear data evaluations, the ENDF/B-VIII.0 and JEFF-3.3 PFNS evaluations agree reasonably well with the present results from 1-to 10-MeV incident neutron energy, which spans the well-measured 1.5-MeV incident neutron energy PFNS from Lestone and Shores as well as the onset of second-chance fission. However, while the pre-equilibrium component of the PFNS above 12-MeV incident neutron energy roughly agrees in position and magnitude with ENDF/B-VIII.0 and JEFF-3.3, clear differences relating to the relative magnitude of third-chance fission PFNS features are present in the PFNS shape and in the mean PFNS energy trends.

We study the process $qq\to qqg$ at lowest order in QCD perturbation theory to understand gluon radiation in the fragmentation region of relativistic heavy ion collisions. We arrive at a formula for gluon multiplicity that interpolates between $\sim 1/k_{\perp }^2$ behavior at low $k_{\perp }$, to $\sim 1/k_{\perp }^4$ at large $k_{\perp }$.

We extract the proton magnetic radius from high-precision electron-proton elastic scattering cross section data. Our theoretical framework combines dispersion analysis and chiral effective field theory and implements the dynamics governing the shape of the low-$Q^2$ form factors. It allows us to use data up to $Q^2\approx 0.5{\mathrm{GeV}}^2$ for constraining the radii and overcomes the difficulties of empirical fits and $Q^2\to 0$ extrapolation. We obtain a magnetic radius $r_M^p=0.850\pm 0.001$ ($1\sigma$ fit uncertainty) ${}_{-0.004}^{+0.009}$ (full-range theory uncertainty) fm, significantly different from earlier results obtained from the same data using empirical fits, and close to our extracted electric radius $r_E^p=0.842\pm 0.002$ ($1\sigma$ fit uncertainty) ${}_{-0.002}^{+0.005}$ (full-range theory uncertainty) fm.

In this work, the two-photon-exchange (TPE) effects in $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}$ at small $\sqrt{s}$ are discussed within a hadronic model. In the limit $m_e\to 0$, the TPE contribution to the amplitude can be described by one scalar function ${\overline{c}}_1^{\left(2\gamma \right)}$. The ratio between this function and the corresponding contribution in one-photon exchange $c_1^{\left(1\gamma \right)}$ reflects all the information of the TPE corrections. The numerical results on this ratio are presented and an artificial function is used to fit the numerical results. The latter can be used conveniently in the further experimental data analysis. The numerical results show the asymmetry of the differential cross sections in $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}$ is about $-4\%$ at $\sqrt{s}\approx 0.7$ GeV.

The Magnus expansion is an efficient alternative to solving similarity renormalization group (SRG) flow equations with high-order, memory-intensive ordinary differential equation solvers. The numerical simplifications it offers for operator evolution are particularly valuable for in-medium SRG calculations, though challenges remain for difficult problems involving intruder states. Here we test the Magnus approach in an analogous but more accessible situation, which is the free-space SRG treatment of the spurious bound states arising from a leading-order chiral effective field theory (EFT) potential with very high cutoffs. We show that the Magnus expansion passes these tests and then use the investigations as a springboard to address various aspects of operator evolution that have renewed relevance in the context of the scale and scheme dependence of nuclear processes. These aspects include SRG operator flow with band- versus block-diagonal generators, universality for chiral EFT Hamiltonians and associated operators with different regularization schemes, and the impact of factorization arising from scale separation. Implications for short-range correlations physics and the possibilities for reconciling high- and low-resolution treatments of nuclear structure and reactions are discussed.

A systematic study of the tensor-force impact in neutron-proton drops has been reported using the relativistic Hartree-Fock (RHF) theory with the $\pi \text{−}N$ coupling strength optimized to the relativistic Brueckner-Hartree-Fock (RBHF) results for neutron drops. The evolutions of the neutron spin-orbit splittings as a function of the neutron number for neutron-proton drops with one proton behave similarly to the pure neutron drops, which show the tensor-force effect. By adding one more proton or neutron in the neutron drop with $N=20$, it is found that the tensor-force effect is more prominent between neutrons and protons than between neutrons. This can be attributed to the isospin factor in the tensor term of the $\pi \text{−}N$ interaction in the RHF density functional theory, which reflects the fact that the neutron-proton tensor force is stronger than the neutron-neutron one. Similar behavior for the spin-orbit splitting evolutions has also been found for the neutron-proton drops with 20 protons, where the tensor-force strength $\lambda$ is redetermined according to the RBHF results due to the large central densities of the systems.

We investigate general frameworks for calculating transport coefficients for quasiparticle theories at finite temperature. Hadronic transport coefficients are then computed using the linear $\sigma$ model (LSM). The bulk viscosity over entropy density ($\zeta /s$) is evaluated in the relaxation time approximation (RTA) and the specific shear viscosity ($\eta /s$) and static electrical conductivity (${\sigma }_{\mathrm{el}}/T$) are both obtained in the RTA and using a functional variational approach. Results are shown for different values of the scalar-isoscalar hadron vacuum mass with in-medium masses for the interacting fields. The advantages and limitations of the LSM for studies of strongly interacting matter out of equilibrium are discussed and results are compared with others in the literature.

The recent experimental observation of isospin symmetry breaking (ISB) in the ground states of the $T=3/2$ mirror pair ${}^{73}\mathrm{Sr}\text{−}{}^{73}\mathrm{Br}$ is theoretically studied using large-scale shell-model calculations. The large valence space and the successful PFSDG-U effective interaction used for the nuclear part of the problem capture possible structural changes and provide a robust basis to treat the ISB effects of both electromagnetic and nonelectromagnetic origin. The calculated shifts and mirror-energy differences are consistent with the inversion of the $I^{\pi }=1/2^{-},5/2^{-}$ states between ${}^{73}\mathrm{Sr}$ and ${}^{73}\mathrm{Br}$ and suggest that the role played by the Coulomb interaction is dominant. An isospin breaking contribution of nuclear origin is estimated to be $\approx 25\mathrm{keV}$.

The classic paper by Fleming, Mehen, and Stewart (FMS) [Nucl. Phys. A 677, 313 (2000)] cast doubts on the convergence of spin-triplet nucleon-nucleon partial wave scattering amplitudes when following the proposal of Kaplan, Savage, and Wise to construct nuclear effective field theory (EFT) around the unitary fermion limit with perturbative pion exchange. FMS identified the subclass of iterated one-pion exchange potential graphs as the cause of this poor convergence, which they showed persisted in the chiral limit. Theoretical tools are developed here to compute these Feynman graphs analytically to high order in all angular momentum channels simultaneously, examining the amplitudes computed to seven loops in the $L=J$ channels and three loops in the coupled $L=J\pm 1$ channels. One finds that there is nothing pathological about the perturbative expansion of a $1/r^3$ potential in general and that the expansion converges satisfactorily in all partial waves except those with the lowest angular momentum, particularly the ${}^{3}P_0$ and the coupled ${}^{3}S_1-{}^{3}D_1$ channels. The results corroborate work by Birse [J. Phys. A: Math. Gen. 39, L49 (2005)], which suggests possible avenues to explore for improving the range of validity of the EFT expansion.

The structures of isomeric and collective states in neutron-rich hafnium isotopes have been investigated within the paired cranked Nilsson-Strutinsky-Bogoliubov (CNSB), and the unpaired cranked Nilsson-Strutinsky (CNS) formalisms. We show that by combining these two models, a good understanding of the formation of multiquasiparticle prolate isomers is achieved. The calculations show at angular momenta $I\ge 35$, well-deformed oblate collective rotation strongly competes energetically with the prolate noncollective states. Comparison is made with experimental data, where available, and with other model calculations.

Lifetimes of states in a negative-parity band involving the $\nu h_{11/2}$ orbital in ${}^{100}\mathrm{Pd}$ have been determined through Doppler shift attenuation method (DSAM) measurements performed using Indian National Gamma Array (INGA) spectrometer. The measured quadrupole transition rates, $B\left(E2\right)$, exhibit a decreasing behavior with increasing angular momentum and with large observed ${\Im }^{\left(2\right)}/B\left(E2\right)$ values. The experimental observations and semiclassical particle-rotor model calculations favor the antimagnetic rotation (AMR) phenomenon based on the $\pi {\left(g_{9/2}\right)}^{-4}\otimes \nu \left[h_{11/2}{\left(g_{7/2}\right)}^3\right]$ configuration for the negative-parity band in the ${}^{100}\mathrm{Pd}$ isotope.

Antiproton-nucleon $\left(\overline{p}N\right)$ total cross sections are typically 3–4 times larger than the $NN$ ones at incident energies from a few hundreds to thousands MeV. We investigate antiproton-nucleus scattering as it could work as a probe of the nuclear structure giving the sensitivity differently from a proton probe. High-energy antiproton-nucleus reactions are reasonably described by the Glauber model with a minimal profile function that reproduces the $\overline{p}N$ and $\overline{p}\text{−}{}^{12}\mathrm{C}$ cross section data. In contrast to the proton-nucleus scattering, we find that the complete absorption occurs even beyond the nuclear radius due to the large $\overline{p}N$ elementary cross sections, which shows stronger sensitivity to the nuclear density distribution in the tail region. This sensitivity is quantified in the total reaction cross sections with various density profiles for future measurement including neutron-rich unstable nuclei.