This paper considers the possibility that two charged particles with an attractive short-ranged potential between them which is not strong enough to form bound states in free space, may bind in uniform magnetic fields. It is shown that in the formal limit where Coulomb repulsion is negligible ($q\to 0\text{and}{B}_0\to \infty \text{with}q{B}_0\text{fixed}$, where $q$ is the charge and $B_0$ the field strength) there always exists a bound state for a system of two identical charged particles in a constant magnetic field, provided that there is a short-range uniformly attractive potential between them. Moreover, it is shown that in this limit any potential with an attractive s-wave scattering length will possess bound states provided that the range of the potential is much smaller than the characteristic magnetic length, $r_0\equiv (\frac{q{B}_0}{4}){}^{-1/2}$. For this case, the binding is computed numerically. We estimate the size of the magnetic field needed to approximately reach a regime where the formal limit considered becomes a good approximation to the dynamics. These numerical estimates indicate that two protons in an extremely strong magnetic field such as might be found in a magnetar will bind to form a diproton.

The quasistable odd-odd-mass nucleus ${}^{176}\mathrm{Lu}$ is of special interest in nuclear structure physics and, above all, in nuclear astrophysics. Systematic photon scattering experiments have been performed at the bremsstrahlung facility of the 4.3-MV Stuttgart Dynamitron accelerator with bremsstrahlung end-point energies of 2.3 and 3.1 MeV to determine the low-energy dipole strength distribution in the s-only isotope ${}^{176}\mathrm{Lu}$. The main goal was to pin down possible intermediate states (IS) for the photoactivation of the short-lived 123-keV isomer, which is the key process determining the effective lifetime of ${}^{176}\mathrm{Lu}$ in a stellar photon bath and hence for the use of this isotope as a stellar chronometer. Using an enriched sample, 29 transitions ascribed to ${}^{176}\mathrm{Lu}$ were detected below 2.9-MeV excitation energy. The corresponding excitation strengths were determined. For the previously proposed lowest IS at 839 keV, an upper limit for the excitation strength corresponding to a lifetime of $\tau ⩾$ 1.5 ps can be given. Astrophysical consequences, also in view of new Stuttgart photoactivation experiments, are discussed. The fragmentation of the dipole strength is compared to those in neighboring even-even and odd-even nuclei.

The anisotropy of the fission fragment angular distribution defined at the saddle point and the neutron multiplicities emitted prior to scission for fissioning nuclei ${}^{224}\mathrm{Th}$, ${}^{229}\mathrm{Np}$, ${}^{248}\mathrm{Cf}$, and ${}^{254}\mathrm{Fm}$ are calculated simultaneously by using a set of realistic coupled two-dimensional Langevin equations, where the $\{c,h,\alpha =0\}$ nuclear parametrization is employed. In comparison with the one-dimensional stochastic model without neck variation, our two-dimensional model produces results that are in better agreement with the experimental data, and the one-dimensional model is available only for low excitation energies. Indeed, to determine the temperature of the nucleus at the saddle point, we investigate the neutron emission during nucleus oscillation around the saddle point for different friction mechanisms. It is shown that the neutrons emitted during the saddle oscillation cause the temperature of a fissioning nuclear system at the saddle point to decrease and influence the fission fragment angular distribution.

In two recent papers a negative $g$ factor was reported for the $4_1^{+}$ state in ${}^{68}\mathrm{Zn}$. The negative sign is unexpected. It is not consistent with the systematics of $g$ factors in the neighboring Zn and Ge isotopes and could not be explained by shell-model calculations even when significant contributions of the 0$g_{9/2}$ neutrons were included. Therefore, an independent $g$ factor measurement was performed, using ${}^{68}\mathrm{Zn}$ projectiles which were accelerated to a higher energy in order to obtain a higher yield for the $4_1^{+}$ state. The new measurement yielded a positive $g$ factor, $g(4_1^{+})=+0.6(3)$, which agrees with the results of full $\mathit{fp}$ spherical shell model calculations, as well as with $Z/A$, the collective model prediction.

Positivity constraints have proved to be important for spin observables of exclusive reactions involving polarized initial and final particles. Attention is focused on the photoproduction of pseudoscalar mesons from spin $1/2$ baryons, more specifically $\gamma N\to K\Lambda ,\gamma N\to K\Sigma$, for which new experimental data are becoming available.

With a resolution of 3 keV, the two lowest $0^{-}$ states in ${}^{208}\mathrm{Pb}$ are identified by measurements of the reaction ${}^{207}\mathrm{Pb}$$(d,p)$ with the München Q3D magnetic spectrograph in the region $E_x=5.2\text{−}5.7$ MeV where the average level spacing is 6 keV. Precise relative spectroscopic factors are determined. Matrix elements of the residual interaction among one-particle one-hole configurations in a two-level scheme are derived for the two lowest $0^{-}$ states in ${}^{208}\mathrm{Pb}$. The off-diagonal mixing strength is determined as $110\pm 10\text{(experimental)}\pm 15\text{(systematic)}$ keV. Measurements of the reaction ${}^{208}\mathrm{Pb}$$(p,p^{\text{'}})$ via isobaric analog resonances in ${}^{209}\mathrm{Bi}$ support the structure information obtained.

The differential cross section angular distribution and the analyzing powers ${}^T{T}_{10},{}^T{T}_{20}$, for ${}^7\mathrm{Li}$+${}^{16}\mathrm{O}$ elastic scattering were measured at $E_{\mathrm{lab}}({}^7\overrightarrow{\mathrm{Li}}$) = 42 MeV. These and previously published ${}^7\mathrm{Li}$+${}^{16}\mathrm{O}$ scattering data measured at $E_{c.m.}$ = 6.26−34.78 MeV were analyzed with the optical model and coupled-reaction channels (CRC) methods to determine the energy dependence of the parameters of the scattering potential. It was found that the optical model potentials are energy independent for ${}^7\mathrm{Li}$ laboratory bombarding energies above 28 MeV, except for a slight decrease in the real potential strength as the bombarding energy increases. The calculations presented show that the tensor analyzing power ${}^T{T}_{20}$ arises from a coherent combination of contributions from the ground-state reorientation and central scattering potential. The energy-dependent CRC potentials were shown to describe the data for the ${}^{16}\mathrm{O}$(${}^7\mathrm{Li}$,$t$)${}^{20}\mathrm{Ne}$ reaction.

In the framework of the macroscopic-microscopic model, this study investigates fission barriers in the region of actinide nuclei. A very effective four-dimensional shape parametrization for fissioning nuclei is proposed. Taking, in particular, the left-right mass asymmetric and nonaxial shapes into account is demonstrated to have a substantial effect on fission barrier heights. The influence of proton versus neutron deformation differences on the potential energy landscape of fissioning nuclei is also discussed.

The already detailed study of ${}^{107}\mathrm{Tc}$ nucleus was complemented by a search for microsecond isomers at very low energy. For this purpose, this neutron-rich nucleus was produced by thermal-neutron-induced fission of ${}^{241}\mathrm{Pu}$. We have found a new 30.1 keV microsecond isomeric state which deexcites to the ground state by a strongly-hindered $E1$ transition. This isomer was identified as the $3/2^{+}$ level of the $1/2^{+}$[431] intruder band in ${}^{107}\mathrm{Tc}$ and is also the lowest-lying member of the band. The very low energy of the band head suggests a large quadrupole deformation. From a comparison with ${}^{105}\mathrm{Tc}$, where more information is known about the intruder band, it is deduced that the $1/2^{+}$[431] band has a quadrupole deformation, ${\epsilon }_2⩾0.35$ and a possible triaxial shape, $\gamma \approx {20}^{°}$.

Global transverse-momentum conservation induces correlations between any number of particles, which contribute in particular to the two- and three-particle correlations measured in heavy-ion collisions. These correlations are examined in detail, and their importance for studies of jets and their interaction with the medium is discussed.

In the last few years, the low-momentum nucleon-nucleon ($\mathit{NN}$) interaction $V_{\mathrm{low}\text{−}k}$ derived from free-space $\mathit{NN}$ potentials has been successfully used in shell-model calculations. $V_{\mathrm{low}\text{−}k}$ is a smooth potential which preserves the deuteron binding energy as well as the half-on-shell $T$ matrix of the original $\mathit{NN}$ potential up to a momentum cutoff Λ. In this paper, we test a new low-momentum $\mathit{NN}$ potential derived from chiral perturbation theory at next-to-next-to-next-to-leading order with a sharp low-momentum cutoff at 2.1 fm${}^{-1}$. Shell-model calculations for the oxygen isotopes using effective Hamiltonians derived from both types of low-momentum potential are performed. We find that the two potentials show the same perturbative behavior and yield very similar results.

Inclusive transverse momentum spectra of η mesons in the range $p_T\approx 2$–12 GeV/$c$ have been measured at midrapidity ($\left|\eta \right|<0.35$) by the PHENIX experiment at RHIC in $p+p,d$+Au, and Au+Au collisions at $\sqrt{s_{\mathit{NN}}}=200$ GeV. The η mesons are reconstructed through their $\eta \to \gamma \hspace{1em}\gamma$ channel for the three colliding systems as well as through the $\eta \to {\pi }^0{\pi }^{+}{\pi }^{-}$ decay mode in $p+p$ and $d$+Au collisions. The nuclear modification factor in $d$+Au collisions, $R_{d\mathrm{Au}}(p_T)\approx 1.0$–1.1, suggests at most only modest $p_T$ broadening (“Cronin enhancement”). In central Au+Au reactions, the η yields are significantly suppressed, with $R_{\mathrm{AuAu}}(p_T)\approx 0.2$. The ratio of η to ${\pi }^0$ yields is approximately constant as a function of $p_T$ for the three colliding systems in agreement with the high-$p_T$ world average of $R_{\eta /{\pi }^0}\approx 0.5$ in hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions for a wide range of center-of-mass energies ($\sqrt{s_{\mathit{NN}}}\approx 3$–1800 GeV) as well as, for high scaled momentum $x_p$, in $e^{+}{e}^{-}$ annihilations at $\sqrt{s}=91.2$ GeV. These results are consistent with a scenario where high-$p_T$ η production in nuclear collisions at the Relativistic Heavy Ion Collider is largely unaffected by initial-state effects but where light-quark mesons (${\pi }^0,\eta$) are equally suppressed due to final-state interactions of the parent partons in the dense medium produced in Au+Au reactions.

Transverse momentum spectra of pions, kaons, protons, and antiprotons from Au+Au collisions at $\sqrt{s_{\mathit{NN}}}$ = 62.4 GeV have been measured by the PHOBOS experiment at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The identification of particles relies on three different methods: low momentum particles stopping in the first detector layers; the specific energy loss ($\mathit{dE}/\mathit{dx}$) in the silicon spectrometer, and time-of-flight measurement. These methods cover the transverse momentum ranges 0.03–0.2, 0.2–1.0, and 0.5–3.0 GeV/$c$, respectively. Baryons are found to have substantially harder transverse momentum spectra than mesons. The $p_T$ region in which the proton to pion ratio reaches unity in central Au+Au collisions at $\sqrt{s_{\mathit{NN}}}$ = 62.4 GeV fits into a smooth trend as a function of collision energy. At low transverse mass, the spectra of various species exhibit a significant deviation from transverse mass scaling. The observed particle yields at very low $p_T$ are comparable to extrapolations from higher $p_T$ for kaons, protons and antiprotons. By comparing our results to Au+Au collisions at $\sqrt{s_{\mathit{NN}}}$ = 200 GeV, we conclude that the net proton yield at midrapidity is proportional to the number of participant nucleons in the collision.

The $N\overline{\Omega }$ systems with spin $S=1$ and $S=2$ are dynamically investigated in the chiral SU(3) quark model and the extended chiral SU(3) quark model by solving the equation in the framework of the resonating group method (RGM). The model parameters are taken from our previous work, which gave a good description of the energies of the baryon ground states, the binding energy of deuteron, and the experimental data of the nucleon-nucleon $(\mathit{NN})$ and nucleon-hyperon $(\mathit{NY})$ scattering processes. The results show that $N\overline{\Omega }$ states with spin $S=1$ and $S=2$ can be bound in both the chiral SU(3) and the extended chiral SU(3) quark models, and the binding energies are about 28–59 MeV. When the $s$-channel interaction is considered, the binding energies increase to about 37– 130 MeV, which indicates that the effect of $s$-channel interaction plays a relatively important role in forming a $N\overline{\Omega }$ bound state. At the same time, the $N\overline{\Omega }$ elastic scattering processes are also studied, and the $S,P,D$ partial wave phase shifts and the total cross sections of $S=1$ and $S=2$ channels are obtained.

Dilepton emission rates from a hadronic gas at finite temperature and baryon density are completely constrained by broken chiral symmetry in a density expansion. The rates can be expressed in terms of vacuum correlations which are measured in $e^{+}{e}^{-}$ annihilation, τ decays, and photoreactions on nucleons and nuclei [1–3]. In this paper, the theoretical results are summarized and the total dimuon yield is calculated by integrating the dimuon rates over the space-time history of a fireball based on hydrodynamic calculations with CERN Super Proton Synchrotron (SPS) conditions. We compare the resulting dimuon yield with the recent measurements reported by NA60 [4].

In previous works we considered the number of pairs of particles with angular momentum $J_{12}$ for systems with total angular momentum zero. Here we extend the the work to states of any total angular momentum. We find simplified relations satisfied for a system of four nucleons with isospins zero and two.

We have measured the ratio of $K$-shell internal conversion coefficients, ${\alpha }_K$, for the 127.5-keV $E3$ transition in ${}^{134}\mathrm{Cs}$ and the 661.7-keV $M4$ transition in ${}^{137}\mathrm{Ba}$. Previous measurements of these ${\alpha }_K$ values led to a ratio that differed from calculated internal conversion coefficients. Our measured result, 30.01(15), disagrees with, but is a factor of three more precise than, the previous average of all experimental results. Our new result is consistent with calculations.

The positive-parity doublet bands based on the $\pi h_{11/2}\otimes \nu h_{11/2}$ configuration in ${}^{126}\mathrm{Cs}$ were investigated in the two quasiparticles coupled with a triaxial rotor model. The energy spectra $E(I)$, energy staggering parameter $S(I)=[E(I)-E(I-1)]/2I,B(M1)$ and $B(E2)$ values, intraband $B(M1)/B(E2)$ ratios, $B(M1){}_{\mathrm{in}}/B(M1){}_{\mathrm{out}}$ ratios, and orientation of the angular momentum for the rotor as well as the valence proton and neutron are calculated. After including the pairing correlation, good agreement has been obtained between the calculated results and the data available, which supports the interpretation of this positive-parity doublet bands as chiral bands.

The atomic nucleus ${}^{106}\mathrm{Cd}$ was studied via the β-decay of ${}^{106}\mathrm{In}$ and using nuclear resonance fluorescence. The decay pattern of five $J=1$ states and precise lifetimes of three spin 1 states have been deduced. By combining both data sets a candidate for the quadrupole-octupole coupled $1^{-}$ state was identified at 2825 keV. Only this state shows the decay pattern comparable with the known quadrupole-octupole coupled $1^{-}$ states in the other even-even stable cadmium isotopes ${}^{108-116}\mathrm{Cd}$. For the description of this collective state a good agreement with predictions of the $Q$-phonon approach using a fermionic configurational space and microscopic calculations on the basis of the random phase approximation was found.