The production of ${}^{26}\mathrm{Al}$ in massive stars is sensitive to the ${}^{23}\mathrm{Na}(\alpha ,p){}^{26}\mathrm{Mg}$ cross section. Recent experimental data suggest the currently recommended cross sections are underestimated by a factor of $\sim 40$. We present here differential cross sections for the ${}^{23}\mathrm{Na}(\alpha ,p){}^{26}\mathrm{Mg}$ reaction measured in the energy range $E_{\mathrm{c}.\mathrm{m}.}=1.7–2.5\mathrm{MeV}$. Concurrent measurements of Rutherford scattering provide absolute normalizations that are independent of variations in target properties. Angular distributions are measured for both $p_0$ and $p_1$ permitting the determination of total cross sections. The results show no significant deviation from the statistical model calculations upon which the recommended rates are based. We therefore retain the previous recommendation without the increase in cross section and resulting stellar reaction rates by a factor of 40, impacting the ${}^{26}\mathrm{Al}$ yield from massive stars by more than a factor of 3.

${}^{26}\mathrm{Al}$ is an important radioisotope in astrophysics that provides evidence of ongoing nucleosynthesis in the Galaxy. The ${}^{23}\mathrm{Na}(\alpha ,p){}^{26}\mathrm{Mg}$ reaction has been identified by a sensitivity study as being one of the most important reactions for the production of ${}^{26}\mathrm{Al}$ in the convective C/Ne burning shell of massive stars. Owing to large uncertainties in previous experimental data, model calculations are used for the reaction rate of ${}^{23}\mathrm{Na}(\alpha ,p){}^{26}\mathrm{Mg}$ in this sensitivity study. Current experimental data suggest a reaction rate a factor of $\sim 40$ higher than model calculations. However, a new measurement of this reaction cross section has been made in inverse kinematics in the energy range $E_{\mathrm{c}.\mathrm{m}.}=1.28–3.15\mathrm{MeV}$ at TRIUMF, and found to be in reasonable agreement with the model calculation. A new reaction rate is calculated and tight constraints on the uncertainty in the production of ${}^{26}\mathrm{Al}$, due to this reaction, are determined.

We have measured the hyperfine splitting of the $7P_{1/2}$ state at the 100 ppm level in Fr isotopes (${}^{206g,206m,207,209,213,221}\mathrm{Fr}$) near the closed neutron shell ($N=126$ in ${}^{213}\mathrm{Fr}$). The measurements in five isotopes and a nuclear isomeric state of francium, combined with previous determinations of the $7S_{1/2}$ splittings, reveal the spatial distribution of the nuclear magnetization, i.e., the Bohr-Weisskopf effect. We compare our results with a simple shell model consisting of unpaired single valence nucleons orbiting a spherical nucleus, and find good agreement over a range of neutron-deficient isotopes (${}^{207–213}\mathrm{Fr}$). Also, we find near-constant proton anomalies for several even-$N$ isotopes. This identifies a set of Fr isotopes whose nuclear structure can be understood well enough for the extraction of weak interaction parameters from parity nonconservation studies.

The anomalous rod shape in carbon isotopes has been investigated in the framework of the cranking covariant density functional theory, and two mechanisms to stabilize such a novel shape with respect to the bending motion, extreme spin, and isospin are simultaneously discussed for the first time in a self-consistent and microscopic way. By adding valence neutrons and rotating the system, we have found the mechanism stabilizing the rod shape; i.e., the $\sigma$ orbitals (parallel to the symmetry axis) of the valence neutrons, important for the rod shape, are lowered by the rotation due to the Coriolis term. The spin and isospin effects enhance the stability of the rod-shaped configuration. This provides a strong hint that a rod shape could be realized in nuclei towards extreme spin and isospin.

The low-lying structure of the neutron-rich nucleus ${}^{50}\mathrm{Ar}$ has been investigated at the Radioactive Isotope Beam Factory using in-beam $\gamma$-ray spectroscopy with ${}^9\mathrm{Be}({}^{54}\mathrm{Ca},{}^{50}\mathrm{Ar}+\gamma )X$, ${}^9\mathrm{Be}({}^{55}\mathrm{Sc},{}^{50}\mathrm{Ar}+\gamma )X$, and ${}^9\mathrm{Be}({}^{56}\mathrm{Ti},{}^{50}\mathrm{Ar}+\gamma )X$ multinucleon removal reactions at $\sim 220\mathrm{MeV}/\mathrm{u}$. A $\gamma$-ray peak at 1178(18) keV is reported and assigned as the transition from the first $2^{+}$ state to the $0^{+}$ ground state. A weaker, tentative line at 1582(38) keV is suggested as the $4_1^{+}\to 2_1^{+}$ transition. The experimental results are compared to large-scale shell-model calculations performed in the $sdpf$ model space using the SDPF-MU effective interaction with modifications based on recent experimental data for exotic calcium and potassium isotopes. The modified Hamiltonian provides a satisfactory description of the new experimental results for ${}^{50}\mathrm{Ar}$ and, more generally, reproduces the energy systematics of low-lying states in neutron-rich Ar isotopes rather well. The shell-model calculations indicate that the $N=32$ subshell gap in ${}^{50}\mathrm{Ar}$ is similar in magnitude to those in ${}^{52}\mathrm{Ca}$ and ${}^{54}\mathrm{Ti}$ and, notably, predict an $N=34$ subshell closure in ${}^{52}\mathrm{Ar}$ that is larger than the one recently reported in ${}^{54}\mathrm{Ca}$.

The dynamics of topological domains which break parity ($\mathcal{P}$) and charge-parity ($\mathcal{C}\mathcal{P}$) symmetry of QCD are studied. We derive in a general setting that those local domains will generate an axial current and quantify the strength of the induced axial current. Our findings are verified in a top-down holographic model. The relation between the real time dynamics of those local domains and the chiral magnetic field is also elucidated. We finally argue that such an induced axial current would be phenomenologically important in a heavy-ion collisions experiment.

An intriguing and elusive feature of the timelike hadron form factor is the possible presence of an imaginary part associated to rescattering processes. We find evidence of that in the recent and precise data on the proton timelike form factor measured by the BABAR Collaboration. By plotting these data as a function of the 3-momentum of the relative motion of the final proton and antiproton, a systematic sinusoidal modulation is highlighted in the near-threshold region. Our analysis attributes this pattern to rescattering processes at a relative distance of 0.7–1.5 fm between the centers of the forming hadrons. This distance implies a large fraction of inelastic processes in $\overline{p}p$ interactions, and a large imaginary part in the related $e^{+}{e}^{-}\to \overline{p}p$ reaction because of unitarity.

We report the first direct measurement of the ${}^{14}\mathrm{O}$ superallowed Fermi $\beta$-decay $Q_{EC}$ value, the last of the so-called “traditional nine” superallowed Fermi $\beta$ decays to be measured with Penning trap mass spectrometry. ${}^{14}\mathrm{O}$, along with the other low-$Z$ superallowed $\beta$ emitter, ${}^{10}\mathrm{C}$, is crucial for setting limits on the existence of possible scalar currents. The new ground state $Q_{EC}$ value, 5144.364(25) keV, when combined with the energy of the $0^{+}$ daughter state, $E_x(0^{+})=2312.798(11)\mathrm{keV}$ [, Nucl. Phys. A523, 1 (1991)], provides a new determination of the superallowed $\beta$-decay $Q_{EC}$ value, $Q_{EC}(\mathrm{sa})=2831.566(28)\mathrm{keV}$, with an order of magnitude improvement in precision, and a similar improvement to the calculated statistical rate function $f$. This is used to calculate an improved $\mathcal{F}t$ value of 3073.8(2.8) s.

At the Mainz Microtron MAMI, the first high-resolution pion spectroscopy from decays of strange systems was performed by electron scattering off a ${}^9\mathrm{Be}$ target in order to study the $\mathrm{\Lambda }$ binding energy of light hypernuclei. Positively charged kaons were detected by a short-orbit spectrometer with a broad momentum acceptance at 0° forward angles with respect to the beam, efficiently tagging the production of strangeness in the target nucleus. Coincidentally, negatively charged decay pions were detected by two independent high-resolution spectrometers. About ${10}^3$ pionic weak decays of hyperfragments and hyperons were observed. The pion momentum distribution shows a monochromatic peak at $p_{\pi }\approx 133\mathrm{MeV}/c$, corresponding to the unique signature for the two-body decay of hyperhydrogen ${}_{\mathrm{\Lambda }}{}^4\mathrm{H}\to {}^4\mathrm{He}+{\pi }^{-}$, stopped inside the target. Its $\mathrm{\Lambda }$ binding energy was determined to be $B_{\mathrm{\Lambda }}=2.12\pm 0.01(\text{stat})\pm 0.09(\text{syst})\mathrm{MeV}$ with respect to the ${}^3\mathrm{H}+\mathrm{\Lambda }$ mass.

We provide a unified ab initio description of the ${}^6\mathrm{Li}$ ground state and elastic scattering of deuterium ($d$) on ${}^4\mathrm{He}$ ($\alpha$) using two- and three-nucleon forces from chiral effective field theory. We analyze the influence of the three-nucleon force and reveal the role of continuum degrees of freedom in shaping the low-lying spectrum of ${}^6\mathrm{Li}$. The calculation reproduces the empirical binding energy of ${}^6\mathrm{Li}$, yielding an asymptotic $D$- to $S$-state ratio of the ${}^6\mathrm{Li}$ wave function in the $d+\alpha$ configuration of $-0.027$, in agreement with a determination from ${}^6\mathrm{Li}\text{−}{}^4\mathrm{He}$ elastic scattering, but overestimates the excitation energy of the $3^{+}$ state by 350 keV. The bulk of the computed differential cross section is in good agreement with data. These results endorse the application of the present approach to the evaluation of the ${}^2\mathrm{H}(\alpha ,\gamma ){}^6\mathrm{Li}$ radiative capture, responsible for the big-bang nucleosynthesis of ${}^6\mathrm{Li}$.

The Galactic 1.809-MeV $\gamma$-ray signature from the $\beta$ decay of ${}^{26g}\mathrm{Al}$ is a dominant target of $\gamma$-ray astronomy, of which a significant component is understood to originate from massive stars. The ${}^{26g}\mathrm{Al}(p,\gamma ){}^{27}\mathrm{Si}$ reaction is a major destruction pathway for ${}^{26g}\mathrm{Al}$ at stellar temperatures, but the reaction rate is poorly constrained due to uncertainties in the strengths of low-lying resonances in ${}^{27}\mathrm{Si}$. The ${}^{26g}\mathrm{Al}(d,p){}^{27}\mathrm{Al}$ reaction has been employed in inverse kinematics to determine the spectroscopic factors, and hence resonance strengths, of proton resonances in ${}^{27}\mathrm{Si}$ via mirror symmetry. The strength of the 127-keV resonance is found to be a factor of 4 higher than the previously adopted upper limit, and the upper limit for the 68-keV resonance has been reduced by an order of magnitude, considerably constraining the ${}^{26g}\mathrm{Al}$ destruction rate at stellar temperatures.

Results on the production of the double strange cascade hyperon ${\mathrm{\Xi }}^{-}$ are reported for collisions of $p(3.5\mathrm{GeV})+\mathrm{Nb}$, studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18 at GSI Helmholtzzentrum for Heavy-Ion Research, Darmstadt. For the first time, subthreshold ${\mathrm{\Xi }}^{-}$ production is observed in proton-nucleus interactions. Assuming a ${\mathrm{\Xi }}^{-}$ phase-space distribution similar to that of $\mathrm{\Lambda }$ hyperons, the production probability amounts to $P_{{\mathrm{\Xi }}^{-}}=[2.0\pm 0.4(\text{stat})\pm 0.3(\text{norm})\pm 0.6(\text{syst})]\times 10^{-4}$ resulting in a ${\mathrm{\Xi }}^{-}/(\mathrm{\Lambda }+{\mathrm{\Sigma }}^0)$ ratio of $P_{{\mathrm{\Xi }}^{-}}/P_{\mathrm{\Lambda }+{\mathrm{\Sigma }}^0}=[1.2\pm 0.3(\text{stat})\pm 0.4(\text{syst})]\times 10^{-2}$. Available model predictions are significantly lower than the measured ${\mathrm{\Xi }}^{-}$ yield.

The recently confirmed neutron-shell closure at $N=32$ has been investigated for the first time below the magic proton number $Z=20$ with mass measurements of the exotic isotopes ${}^{52,53}\mathrm{K}$, the latter being the shortest-lived nuclide investigated at the online mass spectrometer ISOLTRAP. The resulting two-neutron separation energies reveal a 3 MeV shell gap at $N=32$, slightly lower than for ${}^{52}\mathrm{Ca}$, highlighting the doubly magic nature of this nuclide. Skyrme-Hartree-Fock-Bogoliubov and ab initio Gorkov-Green function calculations are challenged by the new measurements but reproduce qualitatively the observed shell effect.

The equation of state of QCD matter for temperatures near and above the quark-hadron transition ($\sim 165\mathrm{MeV}$) is inferred within a Bayesian framework through the comparison of data from the Relativistic Heavy Ion Collider and from the Large Hadron Collider to theoretical models. State-of-the-art statistical techniques are applied to simultaneously analyze multiple classes of observables while varying 14 independent model parameters. The resulting posterior distribution over possible equations of state is consistent with results from lattice gauge theory.

New results are reported from a measurement of ${\pi }^0$ electroproduction near threshold using the $p(e,e^{\prime }p){\pi }^0$ reaction. The experiment was designed to determine precisely the energy dependence of $s$- and $p$-wave electromagnetic multipoles as a stringent test of the predictions of chiral perturbation theory (ChPT). The data were taken with an electron beam energy of 1192 MeV using a two-spectrometer setup in Hall A at Jefferson Lab. For the first time, complete coverage of the ${\varphi }_{\pi }^{*}$ and ${\theta }_{\pi }^{*}$ angles in the $p{\pi }^0$ center of mass was obtained for invariant energies above threshold from 0.5 up to 15 MeV. The 4-momentum transfer $Q^2$ coverage ranges from 0.05 to $0.155(\mathrm{GeV}/c{)}^2$ in fine steps. A simple phenomenological analysis of our data shows strong disagreement with $p$-wave predictions from ChPT for $Q^2>0.07(\mathrm{GeV}/c{)}^2$, while the $s$-wave predictions are in reasonable agreement.

The first conclusive evidence of a dipole resonance in ${}^{11}\mathrm{Li}$ having isoscalar character observed from inelastic scattering with a novel solid deuteron target is reported. The experiment was performed at the newly commissioned IRIS facility at TRIUMF. The results show a resonance peak at an excitation energy of $1.03\pm 0.03\mathrm{MeV}$ with a width of $0.51\pm 0.11\mathrm{MeV}$ (FWHM). The angular distribution is consistent with a dipole excitation in the distorted-wave Born approximation framework. The observed resonance energy together with shell model calculations show the first signature that the monopole tensor interaction is important in ${}^{11}\mathrm{Li}$. The first ab initio calculations in the coupled cluster framework are also presented.

The experimental $E1$ strength distribution below 4 MeV in rare-earth nuclei suggests a local breaking of isospin symmetry. In addition to the octupole states, additional $J^{\pi }=1^{-}$ states with enhanced $E1$ strength have been observed in rare-earth nuclei by means of ($\gamma$,$\gamma$′) experiments. By reproducing the experimental results, the $spdf$ interacting boson model calculations provide further evidence for the formation of an $\alpha$ cluster in medium-mass nuclei and might provide a new understanding of the origin of low-lying $E1$ strength.