Nuclear reactions induced by a strong zeptosecond laser pulse are studied theoretically in the quasiadiabatic regime where the photon absorption rate is comparable to the nuclear equilibration rate. We find that multiple photon absorption leads to the formation of a compound nucleus in the so-far unexplored regime of excitation energies several hundred MeV above the yrast line. At these energies, further photon absorption is limited by neutron decay and/or induced nucleon emission. With a laser pulse of $\approx 50\mathrm{zs}$ duration, proton-rich nuclei far off the line of stability are produced.

An ab initio calculation of the sum rules of the neutral weak response functions in ${}^{12}\mathrm{C}$ is reported, based on a realistic Hamiltonian, including two- and three-nucleon potentials, and on realistic currents, consisting of one- and two-body terms. We find that the sum rules of the response functions associated with the longitudinal and transverse components of the (spacelike) neutral current are largest and that a significant portion ($\simeq 30\%$) of the calculated strength is due to two-body terms. This fact may have implications for the MiniBooNE and other neutrino quasielastic scattering data on nuclei.

The study of exclusive ${\pi }^{\pm }$ electroproduction on the nucleon, including separation of the various structure functions, is of interest for a number of reasons. The ratio $R_L={\sigma }_L^{{\pi }^{-}}/{\sigma }_L^{{\pi }^{+}}$ is sensitive to isoscalar contamination to the dominant isovector pion exchange amplitude, which is the basis for the determination of the charged pion form factor from electroproduction data. A change in the value of $R_T={\sigma }_T^{{\pi }^{-}}/{\sigma }_T^{{\pi }^{+}}$ from unity at small $-t$, to $1/4$ at large $-t$, would suggest a transition from coupling to a (virtual) pion to coupling to individual quarks. Furthermore, the mentioned ratios may show an earlier approach to perturbative QCD than the individual cross sections. We have performed the first complete separation of the four unpolarized electromagnetic structure functions above the dominant resonances in forward, exclusive ${\pi }^{\pm }$ electroproduction on the deuteron at central $Q^2$ values of 0.6, 1.0, $1.6{\mathrm{GeV}}^2$ at $W=1.95\mathrm{GeV}$, and $Q^2=2.45{\mathrm{GeV}}^2$ at $W=2.22\mathrm{GeV}$. Here, we present the $L$ and $T$ cross sections, with emphasis on $R_L$ and $R_T$, and compare them with theoretical calculations. Results for the separated ratio $R_L$ indicate dominance of the pion-pole diagram at low $-t$, while results for $R_T$ are consistent with a transition between pion knockout and quark knockout mechanisms.

Single-neutron states in ${}^{133}\mathrm{Sn}$ and ${}^{209}\mathrm{Pb}$, which are analogous to single-electron states outside of closed atomic shells in alkali metals, were populated by the (${}^9\mathrm{Be}$, ${}^8\mathrm{Be}$) one-neutron transfer reaction in inverse kinematics using particle-$\gamma$ coincidence spectroscopy. In addition, the $s_{1/2}$ single-neutron hole-state candidate in ${}^{131}\mathrm{Sn}$ was populated by (${}^9\mathrm{Be}$, ${}^{10}\mathrm{Be}$). Doubly closed-shell ${}^{132}\mathrm{Sn}$ (radioactive) and ${}^{208}\mathrm{Pb}$ (stable) beams were used at sub-Coulomb barrier energies of 3 MeV per nucleon. Level energies, $\gamma$-ray transitions, absolute cross sections, spectroscopic factors, asymptotic normalization coefficients, and excited-state lifetimes are reported and compared with shell-model expectations. The results include a new transition and precise level energy for the $3p_{1/2}$ candidate in ${}^{133}\mathrm{Sn}$, new absolute cross sections for the $1h_{9/2}$ candidate in ${}^{133}\mathrm{Sn}$ and $3s_{1/2}$ candidate in ${}^{131}\mathrm{Sn}$, and new lifetimes for excited states in ${}^{133}\mathrm{Sn}$ and ${}^{209}\mathrm{Pb}$. This is the first report on excited-state lifetimes of ${}^{133}\mathrm{Sn}$, which allow for a unique test of the nuclear shell model and ${}^{132}\mathrm{Sn}$ double-shell closure.

A comprehensive description of all single-particle properties associated with the nucleus ${}^{40}\mathrm{Ca}$ is generated by employing a nonlocal dispersive optical potential capable of simultaneously reproducing all relevant data above and below the Fermi energy. The introduction of nonlocality in the absorptive potentials yields equivalent elastic differential cross sections as compared to local versions but changes the absorption profile as a function of angular momentum suggesting important consequences for the analysis of nuclear reactions. Below the Fermi energy, nonlocality is essential to allow for an accurate representation of particle number and the nuclear charge density. Spectral properties implied by ($e$, $e^{\prime }p$) and ($p$, $2p$) reactions are correctly incorporated, including the energy distribution of about 10% high-momentum nucleons, as experimentally determined by data from Jefferson Lab. These high-momentum nucleons provide a substantial contribution to the energy of the ground state, indicating a residual attractive contribution from higher-body interactions for ${}^{40}\mathrm{Ca}$ of about $0.64\mathrm{MeV}/\mathrm{A}$.

Rapidity-odd directed flow ($v_1$) measurements for charged pions, protons, and antiprotons near midrapidity ($y=0$) are reported in $\sqrt{s_{NN}}=7.7$, 11.5, 19.6, 27, 39, 62.4, and 200 GeV Au+Au collisions as recorded by the STAR detector at the Relativistic Heavy Ion Collider. At intermediate impact parameters, the proton and net-proton slope parameter $d{v}_1/dy{|}_{y=0}$ shows a minimum between 11.5 and 19.6 GeV. In addition, the net-proton $d{v}_1/dy{|}_{y=0}$ changes sign twice between 7.7 and 39 GeV. The proton and net-proton results qualitatively resemble predictions of a hydrodynamic model with a first-order phase transition from hadronic matter to deconfined matter, and differ from hadronic transport calculations.

Coulomb-excitation experiments to study electromagnetic properties of radioactive even-even Hg isotopes were performed with $2.85\mathrm{MeV}/\mathrm{nucleon}\mathrm{mercury}$ beams from REX-ISOLDE. Magnitudes and relative signs of the reduced $E2$ matrix elements that couple the ground state and low-lying excited states in ${}^{182-188}\mathrm{Hg}$ were extracted. Information on the deformation of the ground and the first excited $0^{+}$ states was deduced using the quadrupole sum rules approach. Results show that the ground state is slightly deformed and of oblate nature, while a larger deformation for the excited $0^{+}$ state was noted in ${}^{182,184}\mathrm{Hg}$. The results are compared to beyond mean field and interacting-boson based models and interpreted within a two-state mixing model. Partial agreement with the model calculations was obtained. The presence of two different structures in the light even-mass mercury isotopes that coexist at low excitation energy is firmly established.

In a recent breakup-reaction experiment using a ${}^{12}\mathrm{Be}$ beam at $29\mathrm{MeV}/\text{nucleon}$, the $0^{+}$ band head of the expected ${}^4\mathrm{He}+{}^8\mathrm{He}$ molecular rotation was clearly identified at about 10.3 MeV, from which a large monopole matrix element of $7.0\pm 1.0{\mathrm{fm}}^2$ and a large cluster-decay width were determined for the first time. These findings support the picture of strong clustering in ${}^{12}\mathrm{Be}$, which has been a subject of intense investigations over the past decade. The results were obtained thanks to a specially arranged detection system around zero degrees, which is essential in determining the newly emphasized monopole strengths to signal the cluster formation in a nucleus.

The 1809-keV $\gamma$ ray from the decay of ${}^{26}{\mathrm{Al}}^g$ is an important target for $\gamma$-ray astronomy. In the convective C/Ne burning shell of massive presupernova stars, the ${}^{23}\mathrm{Na}(\alpha ,p){}^{26}\mathrm{Mg}$ reaction directly influences the production of ${}^{26}\mathrm{Al}$. We have performed a direct measurement of the ${}^{23}\mathrm{Na}(\alpha ,p){}^{26}\mathrm{Mg}$ reaction cross section at the appropriate astrophysically important energies. The stellar rate calculated in the present work is larger than the recommended rate by nearly a factor of 40 and could strongly affect the production of ${}^{26}\mathrm{Al}$ in massive stars.

We have studied the fission-neutron emission competition in highly excited ${}^{274}\mathrm{Hs}$ ($Z=108$) (where the fission barrier is due to shell effects) formed by a hot fusion reaction. Matching cross bombardments (${}^{26}\mathrm{Mg}+{}^{248}\mathrm{Cm}$ and ${}^{25}\mathrm{Mg}+{}^{248}\mathrm{Cm}$) were used to identify the properties of first chance fission of ${}^{274}\mathrm{Hs}$. A Harding-Farley analysis of the fission neutrons emitted in the ${}^{25,26}\mathrm{Mg}+{}^{248}\mathrm{Cm}$ was performed to identify the prescission and postscission components of the neutron multiplicities in each system. (${\mathrm{\Gamma }}_n/{\mathrm{\Gamma }}_t$) for the first chance fission of ${}^{274}\mathrm{Hs}$ ($E^{*}=63\mathrm{MeV}$) is $0.89\pm 0.13$; i.e., $\sim 90\%$ of the highly excited nuclei survive. The high value of that survival probability is due to dissipative effects during deexcitation. A proper description of the survival probabilities of excited superheavy nuclei formed in hot fusion reactions requires consideration of both dynamic and static (shell-related) effects.

We derive the rotation-vibration spectrum of a $4\alpha$ configuration with tetrahedral symmetry ${\mathcal{T}}_d$ and show evidence for the occurrence of this symmetry in the low-lying spectrum of ${}^{16}\mathrm{O}$. All vibrational states with $A$, $E$, and $F$ symmetry appear to have been observed as well as the rotational bands with $L^P=0^{+}$, $3^{-}$, $4^{+}$, $6^{+}$ on the $A$ states and part of the rotational bands built on the $E$, $F$ states. We derive analytic expressions for the form factors and $B(EL)$ values of the ground-state rotational band and show that the measured values support the tetrahedral symmetry of this band.

We discuss a novel effect in neutrinoless double-$\beta$ ($0\nu \beta \beta$) decay related with the fact that its underlying mechanisms take place in the nuclear matter environment. We study the neutrino exchange mechanism and demonstrate the possible impact of nuclear medium via lepton-number-violating (LNV) four-fermion interactions of neutrinos with quarks from a decaying nucleus. The net effect of these interactions is the generation of an effective in-medium Majorana neutrino mass matrix. The enhanced rate of the $0\nu \beta \beta$ decay can lead to the apparent incompatibility of observations of the $0\nu \beta \beta$ decay with the value of the neutrino mass determined or restricted by the $\beta$-decay and cosmological data. The effective neutrino masses and mixing are calculated for the complete set of the relevant four-fermion neutrino-quark operators. Using experimental data on the $0\nu \beta \beta$ decay in combination with the $\beta$-decay and cosmological data, we evaluate the characteristic scales of these operators: ${\mathrm{\Lambda }}_{\mathrm{LNV}}\ge 2.4\mathrm{TeV}$.

The transition rates from the yrast $2^{+}$ and $4^{+}$ states in the self-conjugate ${}^{72}\mathrm{Kr}$ nucleus were studied via lifetime measurements employing the GRETINA array with a novel application of the recoil-distance method. The large collectivity observed for the $4^{+}\to 2^{+}$ transition suggests a prolate character of the excited states. The reduced collectivity previously reported for the $2^{+}\to 0^{+}$ transition was confirmed. The irregular behavior of collectivity points to the occurrence of a rapid oblate-prolate shape transition in ${}^{72}\mathrm{Kr}$, providing stringent tests for advanced theories to describe the shape coexistence and its evolution.

The halo structure of ${}^{31}\mathrm{Ne}$ is studied using $1n$-removal reactions on C and Pb targets at $230\mathrm{MeV}/\text{nucleon}$. A combined analysis of the cross sections of these nuclear and Coulomb dominated reactions that feed directly the ${}^{30}\mathrm{Ne}$ ground-state reveals ${}^{31}\mathrm{Ne}$ to have a small neutron separation energy, $0.15_{-0.10}^{+0.16}\mathrm{MeV}$, and spin-parity $3/2^{-}$. Consistency of the data with reaction and large-scale shell-model calculations identifies ${}^{31}\mathrm{Ne}$ as deformed and having a significant $p$-wave halo component, suggesting that halos are more frequent occurrences at the neutron drip line.

We report on the first observation of the unbound proton-rich nucleus ${}^{15}\mathrm{Ne}$. Its ground state and first excited state were populated in two-neutron knockout reactions from a beam of 500 MeV/u ${}^{17}\mathrm{Ne}$. The ${}^{15}\mathrm{Ne}$ ground state is found to be unbound by 2.522(66) MeV. The decay proceeds directly to ${}^{13}\mathrm{O}$ with simultaneous two-proton emission. No evidence for sequential decay via the energetically allowed $2^{-}$ and $1^{-}$ states in ${}^{14}\mathrm{F}$ is observed. The ${}^{15}\mathrm{Ne}$ ground state is shown to have a strong configuration with two protons in the ($sd$) shell around ${}^{13}\mathrm{O}$ with a 63(5)% $(1s_{1/2}{)}^2$ component.

The charge form factor of ${}^4\mathrm{He}$ has been extracted in the range $29{\mathrm{fm}}^{-2}\le Q^2\le 77{\mathrm{fm}}^{-2}$ from elastic electron scattering, detecting ${}^4\mathrm{He}$ recoil nuclei and electrons in coincidence with the high resolution spectrometers of the Hall A Facility of Jefferson Lab. The measurements have uncovered a second diffraction minimum for the form factor, which was predicted in the $Q^2$ range of this experiment. The data are in qualitative agreement with theoretical calculations based on realistic interactions and accurate methods to solve the few-body problem.