We study the impact of a magnetic field, generated in collisions of relativistic heavy ions, on the decay probability of a quarkonium produced in the central rapidity region. The quark and antiquark components are subject to mutually orthogonal electric and magnetic fields in the quarkonium comoving frame. In the presence of an electric field, the quarkonium has a finite dissociation probability. We use the WKB approximation to derive the dissociation probability. We find that the quarkonium dissociation energy, i.e., the binding energy at which the dissociation probability is of order unity, increases with the magnetic field strength. It also increases with quarkonium momentum in the laboratory frame owing to the Lorentz boost of the electric field in the comoving frame. We argue that $J/\psi$'s produced in heavy-ion collisions at the Large Hadron Collider with $P_{\perp }>9$ GeV would dissociate even in vacuum. In plasma, the $J/\psi$ dissociation in a magnetic field is much stronger because of the decrease of its binding energy with temperature. We discuss phenomenological implications of our results.

A chiral quark-model approach is adopted to study the $\eta$ photoproduction off the quasifree neutron and proton from a deuteron target. Good descriptions of the differential cross sections, total cross sections, and beam asymmetries for these two processes are obtained in the low-energy region. For $\gamma p\to \eta p$, the dominant resonances are $S_{11}\left(1535\right)$, $S_{11}\left(1650\right)$, $D_{13}\left(1520\right)$, $D_{13}\left(1700\right)$, and $P_{13}\left(1720\right)$. For the $\gamma n\to \eta n$ process, the dominant resonances are $S_{11}\left(1535\right)$, $S_{11}\left(1650\right)$, $D_{13}\left(1520\right)$, $D_{15}\left(1675\right)$, and $P_{13}\left(1720\right)$. Furthermore, the $u$-channel backgrounds contribute significantly to the $\eta$ photoproduction processes. The configuration mixings in $S_{11}(1535,1650)$ and $D_{13}(1520,1700)$ can be extracted (i.e., ${\theta }_S\simeq {26}^{\circ }$ and ${\theta }_D\simeq {21}^{\circ }$). It shows that the narrow bump-like structure around $W=1.68$ GeV observed in $\gamma n\to \eta n$ can be naturally explained by the constructive interferences between $S_{11}\left(1535\right)$ and $S_{11}\left(1650\right)$. In contrast, the destructive interference between $S_{11}\left(1535\right)$ and $S_{11}\left(1650\right)$ produces the shallow dip around $W=1.67$ GeV in $\gamma p\to \eta p$. The $S$-wave interfering behavior in the proton and neutron reactions is correlated with each other in the quark-model framework, and no new exotic nucleon resonances are needed in these two reactions. The helicity amplitudes of $S_{11}\left(1535\right)$, $S_{11}\left(1650\right)$, $D_{13}\left(1520\right)$, $D_{13}\left(1700\right)$, and $D_{15}\left(1675\right)$ are extracted from the reactions as well.

We use Lee-Suzuki mappings and related techniques to construct effective two-body $p$-shell interactions and neutrinoless double-$\beta$ operators that exactly reproduce the results of large no-core-shell-model calculations of (fictitious) double-$\beta$ decay in nuclei with mass number $A=6$. We then apply the effective operators to the (also fictitious) decay of nuclei with $A=7$, 8, and 10, again comparing with no-core calculations in much larger spaces. The results with the effective two-body operators are generally good. In some cases, however, they differ non-negligibly from the full no-core results, suggesting that three-body corrections to the decay operator in heavier nuclei may be important. An application of our procedure and related ideas to $fp$-shell nuclei such as ${}^{76}$Ge should be feasible within coupled-cluster theory.

Two-neutron transfer associated with the pair correlation in superfluid neutron-rich nuclei is studied with focus on low-lying $0^{+}$ states in Sn isotopes beyond the $N=82$ magic number. We describe microscopically the two-neutron addition and removal transitions by means of the Skyrme-Hartree-Fock-Bogoliubov mean-field model and the continuum quasiparticle random phase approximation formulated in the coordinate space representation. It is found that the pair transfer strength for the transitions between the ground states becomes significantly large for the isotopes with $A⩾140$, reflecting very small neutron separation energy and long tails of the weakly bound $3p$ orbits. In ${}^{132–140}$Sn, a peculiar feature of the pair transfer is seen in transitions to low-lying excited $0^{+}$ states. They can be regarded as a kind of pair vibrational mode which is characterized by an anomalously long tail of the transition density extending to far outside of the nuclear surface, and a large strength comparable to that of the ground-state transitions. The presence of the weakly bound neutron orbits plays a central role for these anomalous behaviors.

The fusion and evaporation residue cross sections for the ${}^{50}$Ti${+}^{249}$Cf and ${}^{54}$Cr${+}^{248}$Cm reactions calculated by the combined dinuclear system and advanced statistical models are compared. These reactions are considered to be used to synthesize the heaviest superheavy element. The ${}^{50}$Ti${+}^{249}$Cf reaction is more mass asymmetric than ${}^{54}$Cr${+}^{248}$Cm, and the fusion excitation function for the former reaction is higher than the one for the latter reaction. The evaporation residue excitation functions for the mass asymmetric reaction is higher in comparison with the one for the ${}^{54}$Cr${+}^{248}$Cm reaction. The use of the mass values of superheavy nuclei calculated in the framework of the macroscopic-microscopic model by the Warsaw Group [Muntian, Z. Patyk, and A. Sobiczewski, Phys. At. Nuclei 66, 1015 (2003)] leads to a smaller evaporation residue cross section for both the reactions in comparison with the case of using the masses calculated by Möller and Nix [J. Phys. G: Nucl. Part. Phys. 20, 1681 (1994)]. The ${}^{50}$Ti${+}^{249}$Cf reaction is more favorable in comparison with the ${}^{54}$Cr${+}^{248}$Cm reaction: the maximum values of the excitation function of the 3$n$ channel of the evaporation residue formation for the ${}^{50}$Ti${+}^{249}$Cf and ${}^{54}$Cr${+}^{248}$Cm reactions are about 0.1 and 0.07 pb, respectively, but the yield of the 4$n$ channel for the former reaction is lower (0.004 pb) in comparison with the one (0.01 pb) for the latter reaction.

Various versions of proximity potentials, with different isospin dependence, are used within the Wong model for fitting the fusion-evaporation cross sections from ${}^{58}$Ni + ${}^{58}$Ni, ${}^{64}$Ni + ${}^{64}$Ni, and ${}^{64}$Ni + ${}^{100}$Mo reactions in an intermediate mass region and capture cross sections from ${}^{48}$Ca + ${}^{238}$U, ${}^{244}$Pu, and ${}^{248}$Cm reactions in a superheavy mass region, known for fusion hindrance phenomena in coupled-channel calculations. It is found that proximity 1988 gives results close to experimental data in a comparison of proximity 1977 and proximity 2000 within the Wong formula, so this Proximity 1988 (Prox 1988) is then used within the extended Wong model. This combination can fit the cross sections for the ${}^{58}$Ni + ${}^{58}$Ni and ${}^{64}$Ni + ${}^{64}$Ni reactions but deviates a little from the experimental data for the ${}^{64}$Ni + ${}^{100}$Mo reaction at a center-of-mass energy below the Coulomb barrier. But the variation of ${\ell }_{\text{max}}$ with $E_{\text{c.m.}}$ at sub-barrier energies is absurd for these three reactions. So, a different type of strong nuclear interaction is required that accounts for isospin effect and asymmetry of the colliding nuclei, which is obtained here by a slight adjustment of the coefficient ${\gamma }_0$ of the nuclear surface energy constant of the Prox 1988 potential, in order to fit the experimental data for this reaction and named it mod-Prox 1988. The surface energy constant $\gamma$ depends on the neutron/proton excess, and change in one of its constants, ${\gamma }_0$, used in Prox 1988, introduces the required barrier modification for fitting the experimental data. Thus, change in $\gamma$ leads to change in barrier characteristics, i.e., barrier height ($V_B^{\ell }$), position ($R_B^{\ell }$), and oscillator frequency ($\hslash {\omega }_{\ell }$). Using this modified proximity potential within the extended Wong model, experimental data for all three Ni-induced reactions is fitted with a smooth variation of deduced ${\ell }_{\text{max}}\left(E_{\text{c.m.}}\right)$ at above- as well as below-barrier energies. The effect of isospin is more prominent at below-barrier energies. As an application, mod-Prox 1988 is then employed for the capture cross-section data from ${}^{48}$Ca + ${}^{238}$U, ${}^{244}$Pu, and ${}^{248}$Cm reactions in superheavy mass regions and it successfully fits the data point to point with a smooth variation of ${\ell }_{\text{max}}$ with $E_{\text{c.m.}}$. Thus, mod-Prox 1988 within the extended Wong model leads to a simultaneous explanation of several reactions displaying a hindrance to fusion. Thus, below the Coulomb barrier a stronger nuclear interaction is required as the $N/Z$ ratio increases and colliding nuclei become more and more asymmetric. The effects of multipole deformations are included here up to hexadecapole in the calculations, and orientation degrees of freedom are integrated for the coplanar configuration.

The production of large $P_T$ dileptons and photons originating from photoproduction processes in $pp$, $dA$, and $AA$ collisions is calculated. We find that the contribution of dileptons and photons produced by photoproduction processes is not prominent at Relativistic Heavy Ion Collider (RHIC) energies. However, the numerical results indicate that the modification of photoproduction processes becomes evident in the large $P_T$ region for $pp$, $dA$ and $AA$ collisions at Large Hadron Collider (LHC) energies.

Using a multiphase transport model that includes both initial partonic and final hadronic scatterings, we have studied higher-order anisotropic flows as well as dihadron correlations as functions of pseudorapidity and azimuthal angular differences between trigger and associated particles in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV. With parameters in the model determined previously from fitting the measured multiplicity density of mid-pseudorapidity charged particles in central collisions and their elliptic flow in midcentral collisions, the calculated higher-order anisotropic flows from the two-particle cumulant method reproduce approximately those measured by the ALICE Collaboration, except at small centralities where they are slightly overestimated. Similar to experimental results, the two-dimensional dihadron correlations at most central collisions show a ridge structure at the near side and a broad structure at the away side. The short- and long-range dihadron azimuthal correlations, corresponding to small and large pseudorapidity differences, respectively, are studied for triggering particles with different transverse momenta and are found to be qualitatively consistent with experimental results from the CMS Collaboration. The relation between the short-range and long-range dihadron correlations with that induced by back-to-back jet pairs produced from initial hard collisions is also discussed.

Covariant density functional theory is used to study the effect of strong magnetic fields, up to the limit predicted for neutron stars (for magnetars $B\approx {10}^{18}$ G), on nuclear structure. All new terms in the equation of motion resulting from time-reversal symmetry breaking by the magnetic field and the induced currents, as well as axial deformation, are taken into account in a self-consistent fashion. For nuclei in the iron region of the nuclear chart it is found that fields on the order of magnitude of ${10}^{17}$ G significantly affect bulk properties such as masses and radii.

The reaction paths of two proposed nucleosynthetic processes on the proton-rich side of stability, the $rp$ and $\nu p$ processes, pass through a region of isotopes between Mo and Pd where masses had long gone unmeasured. Precise knowledge of the paths and final abundances of these two processes has been limited by the corresponding lack of precision in the proton-separation energies $S_p$ when derived from extrapolated masses. The masses of 18 neutron-deficient isotopes of Nb, Mo, Tc, Ru, and Rh have been measured using the Canadian Penning trap mass spectrometer. Three of the masses presented, ${}^{90}$Mo, ${}^{91}$Mo, and ${}^{93}$Tc, provide the first direct measurement of the masses of these nuclides, and the others provide confirmation of recent measurements using other Penning traps. Included in this work is a measurement of the mass of ${}^{87}$Mo, which differs by $3.7\sigma$ from the mass presented in the 2003 Atomic Mass Evaluation. This leads to a change in the $S_p$ value of ${}^{88}$Tc which reduces the suppression of flow of the $\nu p$-process path through ${}^{87}$Mo($p,\gamma$)${}^{88}$Tc reported following the mass measurement of ${}^{88}$Tc [C. Weber et al., Phys. Rev. C 78, 054310 (2008)]. This in turn affects the resulting $\nu p$-process abundances.

The reaction ${}^{141}$Pr($\alpha ,n$)${}^{144}$Pm was investigated between $E_{\alpha }=$ 11 MeV and 15 MeV with the activation method using the $\gamma \gamma$ coincidence method with a segmented clover-type high-purity Germanium (HPGe) detector. Measurements with four other HPGe detectors were additionally made. The comparison proves that the $\gamma \gamma$ coincidence method is an excellent tool to investigate cross sections down to the microbarn range. The ($\alpha ,n$) reaction at low energy is especially suited to test $\alpha +\text{nucleus}$ optical-model potentials for application in the astrophysical $p$ process. The experimentally determined cross sections were compared to Hauser-Feshbach statistical model calculations using different optical potentials and generally an unsatisfactory reproduction of the data was found. A local potential was constructed to improve the description of the data. The consequences of applying the same potential to calculate astrophysical ($\gamma ,\alpha$) rates for ${}^{145}$Pm and ${}^{148}$Gd were explored. In summary, the data and further results underline the problems in global predictions of $\alpha +\text{nucleus}$ optical potentials at astrophysically relevant energies.

Total-Routhian-surface calculations by means of the pairing-deformation-frequency self-consistent cranked shell model have been carried out for even-even germanium and selenium isotopes to search for possible stable triaxial deformations of nuclear states. The maximum triaxiality of $\left|\gamma \right|\approx {30}^{\circ }$ is found in the ground and excited rotational states of the nuclei ${}^{64,74}$Ge. The calculations are compared with available experimental data, giving a general agreement with observed triaxiality in the isotopes.

A self-consistent scheme for constructing $K^{-}$ nuclear optical potentials from subthreshold in-medium $\overline{K}N$ $s$-wave scattering amplitudes is presented and applied to analysis of kaonic atoms data and to calculations of $K^{-}$ quasibound nuclear states. The amplitudes are taken from a chirally motivated meson-baryon coupled-channel model, both at the Tomozawa-Weinberg leading order and at the next to leading order. Typical kaonic atoms potentials are characterized by a real part $-\mathrm{Re}{V}_{K^{-}}^{\mathrm{chiral}}=85\pm 5$ MeV at nuclear matter density, in contrast to half this depth obtained in some derivations based on in-medium $\overline{K}N$ threshold amplitudes. The moderate agreement with data is much improved by adding complex $\rho$- and ${\rho }^2$-dependent phenomenological terms, found to be dominated by ${\rho }^2$ contributions that could represent $\overline{K}NN\to YN$ absorption and dispersion, outside the scope of meson-baryon chiral models. Depths of the real potentials are then near 180 MeV. The effects of $p$-wave interactions are studied and found secondary to those of the dominant $s$-wave contributions. The in-medium dynamics of the coupled-channel model is discussed and systematic studies of $K^{-}$ quasibound nuclear states are presented.

Big Bang nucleosynthesis calculations, constrained by the Wilkinson Microwave Anisotropy Probe results, produce ${}^7$Li abundances almost a factor of four larger than those extrapolated from observations. Since primordial ${}^7$Li is believed to be mostly produced by the beta decay of ${}^7$Be, one proposed solution to this discrepancy is a resonant enhancement of the ${}^7$Be($d,p$)2$\alpha$ reaction rate through the 5/2${}^{+}$ 16.7-MeV state in ${}^9$B. The ${}^2$H(${}^7$Be,$d$)${}^7$Be reaction was used to search for such a resonance; none was observed. An upper limit on the width of the proposed resonance was deduced.

A method of using a gravitational ultracold neutron (UCN) spectrometer for the search for long-range forces between neutrons and atoms is proposed. The constraints on the strength of long-range forces within the range of 10${}^{-10}$--10${}^{-4}$ cm can be obtained from experiments on measurements of the total cross section of the interaction of UCN with atoms of noble gases (He, Ne, Ar, Kr) and data on the coherent neutron-scattering length of the nucleus. The first result of such an analysis is presented. Further prospects for the UCN method are discussed.

The evolution of the structure of the first ${2_1}^{+}$ state along the chain of Sn isotopes is investigated within the quasiparticle-phonon model through the analysis of the energies and the $B(E2;{0_1}^{+}\to {2_1}^{+})$ strengths. The calculation reproduces the trend of the energies and, partly, the observed deviations of the $E2$ strengths from the parabolic behavior obtained in some large-scale shell-model calculations. Such an asymmetric trend is shown to be the outcome of several factors: single-particle energies, polarization of the $N=Z=50$ core, interplay between pairing plus quadrupole, and quadrupole pairing interactions.

Particle detectors that use liquid xenon (LXe) as detection medium are among the leading technologies in the search for dark matter weakly interacting massive particles (WIMPs). A key enabling element has been the low-energy detection threshold for recoiling nuclei produced by the interaction of WIMPs in LXe targets. In these detectors, the nuclear recoil energy scale is based on the LXe scintillation signal and thus requires knowledge of the relative scintillation efficiency of nuclear recoils, ${\mathcal{L}}_{\mathrm{eff}}$. The uncertainty in ${\mathcal{L}}_{\mathrm{eff}}$ at low energies is the largest systematic uncertainty in the reported results from LXe WIMP searches at low masses. In the context of the XENON Dark Matter project, a new LXe scintillation detector has been designed and built specifically for the measurement of ${\mathcal{L}}_{\mathrm{eff}}$ at low energies, with an emphasis on maximizing the scintillation light detection efficiency to obtain the lowest possible energy threshold. We report new measurements of ${\mathcal{L}}_{\mathrm{eff}}$ at low energies performed with this detector. Our results suggest a ${\mathcal{L}}_{\mathrm{eff}}$ which slowly decreases with decreasing energy, from $0.144\pm 0.009$ at 15 keV down to ${0.088}_{-0.015}^{+0.014}$ at 3 keV.

High-spin states have been studied in ${}_{59}^{135}$Pr, populated through the ${}^{116}$Cd(${}^{23}$Na,$4n$) reaction at 115 MeV, using the Gammasphere $\gamma$-ray spectrometer. The negative-parity yrast band has been significantly extended to spin $\sim$45$\hslash$ and excitation energy 21.5 MeV, showing evidence for several rotational alignments. The positive-parity yrast band of ${}_{58}^{134}$Ce, populated through the $p4n$ channel of this reaction, was also populated to spin $\sim$38$\hslash$ and excitation energy 18 MeV. Cranking calculations indicate that these nuclei are soft with respect to the triaxiality parameter $\gamma$ and that several competing nuclear shapes occur at high spin.

We present a systematic analysis of $\alpha$ transitions from the ground state of the parent nucleus to members of the favored band in the daughter nucleus. By using measured $\alpha$-decay energies and partial half-lives, the well-known Geiger-Nuttall law is examined for these transitions in both even-even and odd-$A$ nuclei. Accurate expressions are proposed for the evaluation of partial half-lives of these transitions based on microscopic quantum tunneling theory. The calculated partial $\alpha$-decay half-lives are in good agreement with the experimental data. The root-mean-square deviations of our expressions are $\sigma \equiv {\{{\sum }_{i=1}^n{\left[({\log }_{10}{T}_{\mathrm{cal}}^i-{\log }_{10}{T}_{\exp }^i)\right]}^2/n\}}^{1/2}=0.41$ for the even-even nuclei and $\sigma =0.35$ for the odd-$A$ nuclei. A set of parameters for the Viola-Seaborg (V-S) formula is also given by fitting the available experimental data. The proposed expressions and the V-S formula with our parameters will help experimentalists quickly evaluate the expected $\alpha$-decay half-lives during the design of experiments and check the measured decay energies and half-lives after experiments.

Heavy neutron-rich nuclei were populated via the fragmentation of a $E/A=1$ GeV ${}^{208}{}_{82}$Pb beam. Secondary fragments were separated and identified and subsequently implanted in a passive stopper. By the detection of delayed $\gamma$ rays, isomeric decays associated with these nuclei have been identified. A total of 49 isomers were detected, with the majority of them observed for the first time. The newly discovered isomers are in ${}^{204,205}{}_{80}$Hg, ${}^{201,202,204,205}{}_{79}$Au, ${}^{197,203,204}{}_{78}$Pt, ${}^{195,199-203}{}_{77}$Ir, ${}^{193,197-199}{}_{76}$Os, ${}^{196}{}_{75}$Re, ${}^{190,191}{}_{74}$W, and ${}^{189}{}_{73}$Ta. Possible level schemes are constructed and the structure of the nuclei discussed. To aid the interpretation, shell-model as well as BCS calculations were performed.