A multiconfiguration microscopic method has been applied with the Gogny effective interaction to the calculation of low-lying positive-parity states in even-even ${}^{26-32}$Si isotopes. The aim of the study is to compare the results of this approach with those of a standard method of generator coordinate method (GCM) type and to get insight into the predictive power of multiconfiguration methods employed with effective nucleon-nucleon force tailored to mean-field calculations. It is found that the multiconfiguration approach leads to an excellent description of the low-lying spectroscopy of ${}^{26}$Si, ${}^{28}$Si, and ${}^{32}$Si, but gives a systematic energy shift in ${}^{30}$Si. A careful analysis of this phenomenon shows that this discrepancy originates from too large proton-neutron matrix elements supplied by the Gogny interaction at the level of the approximate resolution of the multiparticle-multihole configuration mixing method done in the present study. These proton-neutron matrix elements enter in the definition of both single-particle orbital energies and coupling matrix elements. Finally, a statistical analysis of highly excited configurations in ${}^{28}$Si is performed, revealing exponential convergence in agreement with previous work in the context of the shell model approach. This latter result provides strong arguments toward an implicit treatment of highly excited configurations.

The structure of ${}^{58}$Fe was investigated at Gammasphere using ${}^{48}$Ca(${}^{13,14}$C,$x$$n$) fusion-evaporation reactions at a beam energy of 130 MeV. The level scheme has been revised and extended to $J\sim 17\hslash$ and an excitation energy of 16.6 MeV. Regular band structures consisting of low-energy $\Delta J=1\hslash$ transitions have been observed at moderate spin ($J\sim 8\hslash$–15$\hslash$) and are candidates for magnetic rotational bands. Self-consistent tilted-axis-cranking calculations within a relativistic mean-field theory were applied to investigate these bands and were found to reproduce the experimental results well. In other parts of the level scheme, quasirotational bands composed of stretched-$E2$ transitions have been extended to high spin, and other new bands have been identified. Positive-parity experimental states were compared to predictions of the spherical shell model using the GXPF1A, KB3G, and FPD6 effective interactions in the $fp$ model space. The projected shell model, with a deformed quasiparticle basis including the neutron $\nu g_{9/2}$ orbital, was applied to interpret regular $\Delta J=2\hslash$ band structures that extend beyond the maximum spin available for $\pi$[($f_{7/2}$)${}^{-2}$] $\otimes$ $\nu$[($p_{3/2}{f}_{5/2}{p}_{1/2}$)${}^4$] configurations and exhibit features characteristic of rotational alignment. It is clear that the $\nu g_{9/2}$ intruder orbital plays a crucial role in describing the quasirotational structures in this nucleus, even starting as low as $J\sim 5\hslash$.

Recently it has become apparent that event-by-event fluctuations in the initial state of hydrodynamical modeling of ultrarelativistic heavy-ion collisions are crucial in order to understand the full centrality dependence of the elliptic flow coefficient $v_2$. In particular, in central collisions the density fluctuations play a major role in generating the spatial eccentricity in the initial state. This raises the question to what degree high-$P_T$ physics, in particular leading-parton energy loss, which takes place in the background of an evolving medium, is sensitive to the presence of the event-by-event density fluctuations in the background. In this work, we report results for the effects of fluctuations on the nuclear modification factor $R_{AA}$ in both central and noncentral $\sqrt{s_{NN}}=200$ GeV Au+Au collisions at the Relativistic Heavy Ion Collider. Two different types of energy-loss models, a radiative model and an elastic model, are considered. In particular, we study the dependence of the results on the assumed spatial size of the density fluctuations and discuss the angular modulation of $R_{AA}$ with respect to the event plane.

Recent jet quenching measurements in Pb+Pb collisions at the LHC report a significant energy imbalance of dijets. The imbalance is found to be compensated by a large amount of soft particles produced at large angles with respect to the dijet axis. This observation questions the conventional picture of parton energy loss models, established at RHIC, which typically expect that the radiated gluons are emitted at moderate angles close to the outgoing parton. In this letter, we qualitatively discuss two possible contributions of the underlying heavy-ion background that may have to be taken into account when interpreting the recent data. We show that a large jet $v_3$, potentially caused by a path-length-dependent energy loss in the presence of fluctuating initial conditions, could contribute to the observed excess of soft particles apparently originating from large angle in-medium radiation. In addition, the observed excess could also be induced by multiple jets produced in the vicinity of the leading jet, caused by a potential selection bias imposed on the dijet momentum imbalance.

For the low-energy antineutrino reaction, ${\overline{\nu }}_e+p\to e^{+}+n$, which is of great current interest in connection with on-going high-precision neutrino-oscillation experiments, we calculate the differential cross section in a model-independent effective field theory (EFT), taking into account radiative corrections of order $\alpha$. In EFT, the short-distance radiative corrections are subsumed into well-defined low-energy constants, the values of which can in principle be determined from the available neutron $\beta$-decay data. In our low-energy EFT, the order-$\alpha$ radiative corrections are considered to be of the same order as the nucleon recoil corrections, which include the “weak magnetism” contribution. These recoil corrections have been evaluated as well. We emphasize that EFT allows a systematic evaluation of higher order corrections, providing estimates of theoretical uncertainties in our results.

The CUORICINO experiment was an array of 62 TeO${}_2$ single-crystal bolometers with a total ${}^{130}$Te mass of $11.3$kg. The experiment finished in 2008 after more than 3 yr of active operating time. Searches for both $0\nu$ and $2\nu$ double-$\beta$ decay to the first excited $0^{+}$ state in ${}^{130}$Xe were performed by studying different coincidence scenarios. The analysis was based on data representing a total exposure of $N$(${}^{130}$Te)$·t=9.5\times {10}^{25}$yr. No evidence for a signal was found. The resulting lower limits on the half-lives are $T_{\frac{1}{2}}^{2\nu }{(}^{130}\text{Te}{\to }^{130}{\text{Xe}}^{*})>1.3\times {10}^{23}$yr (90$\%$ C.L.), and $T_{\frac{1}{2}}^{0\nu }{(}^{130}\text{Te}{\to }^{130}{\text{Xe}}^{*})>9.4\times {10}^{23}$yr (90$\%$ CL).

We present results for levels in ${}^{36}$K (the mirror of nucleus ${}^{36}$Ar) that are used in $rp$ reaction rate calculations. The levels are also determined from the isobaric mass multiplet equation and the binding energies of the $T=1$ analog states as a check on the assignment of spins and parity. Where the analog states are not known, the levels are calculated with two-body interactions that use the $sd$-shell interactions USDA and USDB as the charge-independent parts, with a Coulomb, charge-dependent, and charge-asymmetric Hamiltonian added. The $\gamma$-decay lifetimes and ${}^{35}$Al to ${}^{36}$K spectroscopic factors are calculated with the same interactions, and together with experimental information on the levels of excited states, are used to determine the ${}^{35}$Ar($p,\gamma$)${}^{36}$K reaction rates.

We generate a hybrid potential by combining the best features of a microscopic and a phenomenological core-cluster potential and use it to analyze the spectra, $B\left(E2\right)$ transition rates, and the exotic decays of heavy even-even nuclei.

Time delays in fission induced by bombardment of Mo with 170- and 180-MeV ${}^{32}$S, 225- and 240-MeV ${}^{48}$Ti, and 300-MeV ${}^{58}$Ni have been measured by observation of crystal blocking of fission fragments. In contrast to earlier measurements with a W target, the results are consistent with fission of a compound nucleus in competition with mainly neutron emission. Most of the fissions happen on a time scale much shorter than attoseconds but there is a significant component of fission with much longer lifetimes. The measurements are reproduced with a standard statistical model, including a Kramers correction to fission widths from the viscosity of hot nuclear matter. These new results support the interpretation of our earlier measurements with a W target, which indicate that there is a transition in heavy-ion-induced fission at large atomic number and mass, from multichance fission in the standard Bohr-Wheeler picture to fission without formation of a compound nucleus. The process is slowed down by nuclear viscosity, with measured delays of order attoseconds.

A search for double $\beta$ processes in ${}^{106}$Cd was carried out at the Gran Sasso National Laboratories of the INFN (Italy) with the help of a ${}^{106}$CdWO${}_4$ crystal scintillator (215 g) enriched in ${}^{106}$Cd up to 66$\%$. After 6590 h of data taking, new improved half-life limits on the double $\beta$ decay processes in ${}^{106}$Cd were established at the level of ${10}^{19}$–${10}^{21}$ yr; in particular, $T_{1/2}^{2\nu \varepsilon {\beta }^{+}}⩾2.1\times {10}^{20}$ yr, $T_{1/2}^{2\nu 2{\beta }^{+}}⩾4.3\times {10}^{20}$ yr, and $T_{1/2}^{0\nu 2\varepsilon }⩾1.0\times {10}^{21}$ yr. The resonant neutrinoless double-electron captures to the 2718-, 2741-, and 2748-keV excited states of ${}^{106}$Pd are restricted to $T_{1/2}^{0\nu 2K}⩾4.3\times {10}^{20}$ yr, $T_{1/2}^{0\nu K{L}_1}⩾9.5\times {10}^{20}$ yr, and $T_{1/2}^{0\nu K{L}_3}⩾4.3\times {10}^{20}$ yr, respectively (all limits at 90$\%$ confidence level). A possible resonant enhancement of the $0\nu 2\varepsilon$ processes is estimated in the framework of the quasiparticle random phase approximation (QRPA) approach. Radioactive contamination of the ${}^{106}$CdWO${}_4$ crystal scintillator is reported.

As part of an effort to understand how neutron-induced reactions on excited states in deformed nuclei differ from those on ground states, we have carried out coupled-channels calculations of the angle-integrated cross sections on the ground and excited states of several actinide nuclei with differing $K$ values for the ground-state band (${}^{233}$U, $K=\frac{5}{2}$; ${}^{235}$U, $K=\frac{7}{2}$; ${}^{238}$U, $K=0$; and ${}^{239}$Pu, $K=\frac{1}{2}$). Of particular interest is the compound-nucleus formation cross section. We find that the ratio of the excited- to ground-state compound-formation cross sections is very close to unity in all cases (within $\approx$0.1$\%$) over the range studied (1 keV to 20 MeV). This result requires that sufficient levels be coupled to ensure convergence (approximately 14 levels for odd-$A$ nuclei). These results are close to the predictions of the adiabatic model for scattering from statically deformed nuclei. This model yields compound-formation cross sections, as well as total cross sections, that are independent of both the $K$ value of the band and the spin of the target state within the band. Our calculations show that the actual cross sections are surprisingly close to the adiabatic limit, even at very low incident energies. We find similar results for statically deformed rare-earth and $s$-$d$ shell nuclei.

In central Pb-Pb collisions at the Large Hadron Collider the multiplicity of particles produced is so high that it should become feasible to examine the nature of transition from the deconfined quark-gluon state to the confined hadron state by methods that rely on the availability of high-multiplicity events. We consider four classes of the transition process ranging from critical behavior to totally random behavior, depending on whether there is clustering of quarks and whether there is contraction of dense clusters owing to confinement. Fluctuations of bin multiplicities in each event are quantified, and then the event-by-event fluctuations of spatial patterns are analyzed. A sequence of measures is proposed and is shown to be effective in capturing the essence of the differences among the classes of simulated events. It is demonstrated that a specific index has a low value for critical transition but a larger value if the hadronization process is random.

In this article, we extend our previous work to study the $\Sigma$-type heavy baryons ${\Sigma }_c$ and ${\Sigma }_b$ in nuclear matter using QCD sum rules and obtain three coupled QCD sum rules for the masses $M_{{\Sigma }_Q}^{*}$, vector self-energies ${\Sigma }_v$, and pole residues ${\lambda }_{{\Sigma }_Q}^{*}$ in nuclear matter. Then we take into account the effects of the unequal pole residues from different spinor structures, normalize the masses from QCD sum rules in vacuum to the experimental data, and obtain the mass shifts $\delta M_{{\Sigma }_c}=-123\mathrm{MeV}$ and $\delta M_{{\Sigma }_b}=-375\mathrm{MeV}$ in the nuclear matter.

We compute nuclear matrix elements for neutrinoless double electron capture on ${}^{152}$Gd, ${}^{164}$Er, and ${}^{180}$W nuclei. Recent precise mass measurements for these nuclei have shown a large resonance enhancement factor that makes them the most promising candidates for observing this decay mode. We use an advanced energy density functional method which includes beyond mean-field effects such as symmetry restoration and shape mixing. Our calculations reproduce experimental charge radii and $B\left(E2\right)$ values predicting a large deformation for all these nuclei. This fact reduces significantly the values of the NMEs leading to half-lives larger than ${10}^{29}$ years for the three candidates.

The use of highly charged ions increases the precision and resolving power, in particular for short-lived species produced at on-line radio-isotope beam facilities, achievable with Penning trap mass spectrometers. This increase in resolving power provides a new and unique access to resolving low-lying long-lived ($T_{1/2}>50$ ms) nuclear isomers. Recently, the $111.19\left(22\right)$ keV (determined from $\gamma$-ray spectroscopy) isomeric state in ${}^{78}$Rb was resolved from the ground state, in a charge state of $q=8+$ with the TRIUMF Ion Trap for Atomic and Nuclear science at the TRIUMF's Isotope Separator and Accelerator facility. The excitation energy of the isomer was measured to be $108.7\left(6.4\right)$ keV above the ground state. The extracted masses for both the ground and isomeric states, and their difference, agree with the ame2003 and Nuclear Data Sheet values. This proof of principle measurement demonstrates the feasibility of using Penning trap mass spectrometers coupled to charge breeders to study nuclear isomers and opens a new route for isomer searches.

The one-neutron removal cross sections of neutron-rich Al isotopes and longitudinal momentum distributions of the residues have been measured for $A=33$ to 36 at relativistic energies ($\approx$900 MeV/u). The inclusive data have been interpreted within the eikonal approximation. The evolution of the single-particle occupancy in the ground state of ${}^{33,34,35}$Al has been studied and compared with shell model predictions. The inferred $2s_{1/2}$ neutron occupancy in the ${}^{33}$Al ground-state wave function is 20% to 40% lower than the predicted one. The inclusive data do not exclude the presence of intruder states. Some intruder $l=1$ occupancy is found in ${}^{34}$Al, similarly to ${}^{33}$Mg. The single-particle $1f_{7/2}$ occupancy shows a gradual increase at $N=22$. Correspondingly, a decrease of the $1d_{3/2}$ strength has been observed.

I have examined the $B$($E$2)'s in ${}^{12}$Be connecting the first 2${}^{+}$ state to the first two 0${}^{+}$ states. I find that they can be understood in the simple model that has been successful for a variety of other observables in this nucleus, but only if the 2${}^{+}$ state has an excited-core component.

Precise measurements of the proton electromagnetic form factor ratio $R={\mu }_p{G}_E^p/G_M^p$ using the polarization transfer method at Jefferson Lab have revolutionized the understanding of nucleon structure by revealing the strong decrease of $R$ with momentum transfer $Q^2$ for $Q^2\gtrsim 1$ GeV${}^2$, in strong disagreement with previous extractions of $R$ from cross-section measurements. In particular, the polarization transfer results have exposed the limits of applicability of the one-photon-exchange approximation and highlighted the role of quark orbital angular momentum in the nucleon structure. The GEp-II experiment in Jefferson Lab's Hall A measured $R$ at four $Q^2$ values in the range $3.5{\text{GeV}}^2\le Q^2\le 5.6{\text{GeV}}^2$. A possible discrepancy between the originally published GEp-II results and more recent measurements at higher $Q^2$ motivated a new analysis of the GEp-II data. This article presents the final results of the GEp-II experiment, including details of the new analysis, an expanded description of the apparatus, and an overview of theoretical progress since the original publication. The key result of the final analysis is a systematic increase in the results for $R$, improving the consistency of the polarization transfer data in the high-$Q^2$ region. This increase is the result of an improved selection of elastic events which largely removes the systematic effect of the inelastic contamination, underestimated by the original analysis.

The generalized two-center cluster model (GTCM), which can treat covalent and atomic configurations in general two-center systems, is applied to the light neutron-excess system ${}^{12}$Be $=$ $\alpha$ $+$ $\alpha$ $+$ 4$N$. The changes of the orbits of the neutrons are analyzed by calculating adiabatic energy surfaces with a variation of the $\alpha$-$\alpha$ distance. The smooth transition from covalent molecular orbits to atomic He-dimer states is realized in the adiabatic energy surfaces. According to this smooth transition, the adiabatic states are divided into two regions, the internal covalent region and the external He-dimer region, by introducing boundaries of the change in structure. The intrinsic structure of the excited energy levels is investigated. We found that, in an unbound region, the He dimers appear as the molecular resonances of $\alpha$ + ${}^8$He${}_{g.s.}$, ${}^6$He${}_{g.s.}$ + ${}^6$He${}_{g.s.}$, and ${}^5$He${}_{g.s.}$ + ${}^7$He${}_{g.s.}$. An exotic superdeformation, which has a hybrid configuration of both the covalent and He-dimer structures, is also realized in the same energy region. These unbound states can be classified into internal and external states, and the excitation degrees of freedom are assigned for the individual states. The level scheme of these unbound states reveals a strong degenerate feature with a considerable mixture of the different configurations. From the result of the level scheme, the “loose clusters” are introduced to characterize the unbound states in the neutron-excess system ${}^{12}$Be.