Absolute cross sections for isotopically identified products formed in multinucleon transfer in the ${}^{136}\mathrm{Xe}+{}^{198}\mathrm{Pt}$ system at $\sim 8\mathrm{MeV}/\mathrm{nucleon}$ are reported. The isotopic distributions obtained using a large acceptance spectrometer demonstrated the production of the “hard-to-reach” neutron-rich isotopes for $Z<78$ around the $N=126$ shell closure far from stability. The main contribution to the formation of these exotic nuclei is shown to arise in collisions with a small kinetic energy dissipation. The present experimental finding corroborates for the first time recent predictions that multinucleon transfer reactions would be the optimum method to populate and characterize neutron-rich isotopes around $N=126$ which are crucial for understanding both astrophysically relevant processes and the evolution of “magic” numbers far from stability.

We report the first measurement of the target single-spin asymmetry, $A_y$, in quasielastic scattering from the inclusive reaction ${{}^3\mathrm{He}}^{\uparrow }(e,e^{\prime })$ on a ${}^3\mathrm{He}$ gas target polarized normal to the lepton scattering plane. Assuming time-reversal invariance, this asymmetry is strictly zero for one-photon exchange. A nonzero $A_y$ can arise from the interference between the one- and two-photon exchange processes which is sensitive to the details of the substructure of the nucleon. An experiment recently completed at Jefferson Lab yielded asymmetries with high statistical precision at $Q^2=0.13$, 0.46, and $0.97{\mathrm{GeV}}^2$. These measurements demonstrate, for the first time, that the ${}^3\mathrm{He}$ asymmetry is clearly nonzero and negative at the $4\sigma –9\sigma$ level. Using measured proton-to-${}^3\mathrm{He}$ cross-section ratios and the effective polarization approximation, neutron asymmetries of $-(1–3)\%$ were obtained. The neutron asymmetry at high $Q^2$ is related to moments of the generalized parton distributions (GPDs). Our measured neutron asymmetry at $Q^2=0.97{\mathrm{GeV}}^2$ agrees well with a prediction based on two-photon exchange using a GPD model and thus provides a new, independent constraint on these distributions.

Excited states of the neutron-rich nuclei ${}^{97,99}\mathrm{Rb}$ were populated for the first time using the multistep Coulomb excitation of radioactive beams. Comparisons of the results with particle-rotor model calculations provide clear identification for the ground-state rotational band of ${}^{97}\mathrm{Rb}$ as being built on the $\pi g_{9/2}$ $[431]3/2^{+}$ Nilsson-model configuration. The ground-state excitation spectra of the Rb isotopes show a marked distinction between single-particle-like structures below $N=60$ and rotational bands above. The present study defines the limits of the deformed region around $A\sim 100$ and indicates that the deformation of ${}^{97}\mathrm{Rb}$ is essentially the same as that observed well inside the deformed region. It further highlights the power of the Coulomb-excitation technique for obtaining spectroscopic information far from stability. The ${}^{99}\mathrm{Rb}$ case demonstrates the challenges of studies with very short-lived postaccelerated radioactive beams.

We present the mass excesses of ${}^{52–57}\mathrm{Sc}$, obtained from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. The masses of ${}^{56}\mathrm{Sc}$ and ${}^{57}\mathrm{Sc}$ were determined for the first time with atomic mass excesses of $-24.85(59){(}_{-54}^{+0})\mathrm{MeV}$ and $-21.0(1.3)\mathrm{MeV}$, respectively, where the asymmetric uncertainty for ${}^{56}\mathrm{Sc}$ was included due to possible contamination from a long-lived isomer. The ${}^{56}\mathrm{Sc}$ mass indicates a small odd-even mass staggering in the $A=56$ mass chain towards the neutron drip line, significantly deviating from trends predicted by the global FRDM mass model and favoring trends predicted by the UNEDF0 and UNEDF1 density functional calculations. Together with new shell-model calculations of the electron-capture strength function of ${}^{56}\mathrm{Sc}$, our results strongly reduce uncertainties in model calculations of the heating and cooling at the ${}^{56}\mathrm{Ti}$ electron-capture layer in the outer crust of accreting neutron stars. We find that, in contrast to previous studies, neither strong neutrino cooling nor strong heating occurs in this layer. We conclude that Urca cooling in the outer crusts of accreting neutron stars that exhibit superbursts or high temperature steady-state burning, which are predicted to be rich in $A\approx 56$ nuclei, is considerably weaker than predicted. Urca cooling must instead be dominated by electron capture on the small amounts of adjacent odd-$A$ nuclei contained in the superburst and high temperature steady-state burning ashes. This may explain the absence of strong crust Urca cooling inferred from the observed cooling light curve of the transiently accreting x-ray source MAXI J0556-332.

New technical developments have led to a 2 orders of magnitude improvement of the resolution of the collinear resonance ionization spectroscopy (CRIS) experiment at ISOLDE, CERN, without sacrificing the high efficiency of the CRIS technique. Experimental linewidths of 20(1) MHz were obtained on radioactive beams of francium, allowing us for the first time to determine the electric quadrupole moment of the short lived [$t_{1/2}=22.0(5)\mathrm{ms}$] ${}^{219}\mathrm{Fr}$ $Q_s=-1.21(2)\mathrm{eb}$, which would not have been possible without the advantages offered by the new method. This method relies on a continuous-wave laser and an external Pockels cell to produce narrow-band light pulses, required to reach the high resolution in two-step resonance ionization. Exotic nuclei produced at rates of a few hundred ions/s can now be studied with high resolution, allowing detailed studies of the anchor points for nuclear theories.

Two isomers decaying by electromagnetic transitions with half-lives of 4.7(1.1) and $247(73)\mu \mathrm{s}$ have been discovered in the heavy ${}^{254}\mathrm{Rf}$ nucleus. The observation of the shorter-lived isomer was made possible by a novel application of a digital data acquisition system. The isomers were interpreted as the $K^{\pi }=8^{-}$, ${\nu }^2(7/2^{+}[624],9/2^{-}[734])$ two-quasineutron and the $K^{\pi }=16^{+}$, $8^{-}{\nu }^2(7/2^{+}[624],9/2^{-}[734])\otimes 8^{-}{\pi }^2(7/2^{-}[514],9/2^{+}[624])$ four-quasiparticle configurations, respectively. Surprisingly, the lifetime of the two-quasiparticle isomer is more than 4 orders of magnitude shorter than what has been observed for analogous isomers in the lighter $N=150$ isotones. The four-quasiparticle isomer is longer lived than the ${}^{254}\mathrm{Rf}$ ground state that decays exclusively by spontaneous fission with a half-life of $23.2(1.1)\mu \mathrm{s}$. The absence of sizable fission branches from either of the isomers implies unprecedented fission hindrance relative to the ground state.

We investigate the consequences of a nonzero bulk viscosity coefficient on the transverse momentum spectra, azimuthal momentum anisotropy, and multiplicity of charged hadrons produced in heavy ion collisions at LHC energies. The agreement between a realistic 3D hybrid simulation and the experimentally measured data considerably improves with the addition of a bulk viscosity coefficient for strongly interacting matter. This paves the way for an eventual quantitative determination of several QCD transport coefficients from the experimental heavy ion and hadron-nucleus collision programs.

We present a nucleon-nucleon potential at fifth order in chiral effective field theory. We find a substantial improvement in the description of nucleon-nucleon phase shifts as compared to the fourth-order results utilizing a coordinate-space regularization. This provides clear evidence of the corresponding two-pion exchange contributions with all low-energy constants being determined from pion-nucleon scattering. The fifth-order corrections to nucleon-nucleon observables appear to be of a natural size, which confirms the good convergence of the chiral expansion for nuclear forces. Furthermore, the obtained results provide strong support for the novel way of quantifying the theoretical uncertainty due to the truncation of the chiral expansion proposed by the authors. Our work opens up new perspectives for precision ab initio calculations in few- and many-nucleon systems and is especially relevant for ongoing efforts towards a quantitative understanding of the structure of the three-nucleon force in the framework of chiral effective field theory.

Low-energy spectra of $4n$ nuclei are described with high accuracy in terms of four-body correlated structures (“quartets”). The states of all $N\ge Z$ nuclei belonging to the $A=24$ isobaric chain are represented as a superposition of two-quartet states, with quartets being characterized by isospin $T$ and angular momentum $J$. These quartets are assumed to be those describing the lowest states in ${}^{20}\mathrm{Ne}$ ($T_z=0$), ${}^{20}\mathrm{F}$ ($T_z=1$), and ${}^{20}\mathrm{O}$ ($T_z=2$). We find that the spectrum of the self-conjugate nucleus ${}^{24}\mathrm{Mg}$ can be well reproduced in terms of $T=0$ quartets only and that, among these, the $J=0$ quartet plays by far the leading role in the structure of the ground state. The same conclusion is drawn in the case of the three-quartet $N=Z$ nucleus ${}^{28}\mathrm{Si}$. As an application of the quartet formalism to nuclei not confined to the $sd$ shell, we provide a description of the low-lying spectrum of the proton-rich ${}^{92}\mathrm{Pd}$. The results achieved indicate that, in $4n$ nuclei, four-body degrees of freedom are more important and more general than usually expected.

The antineutrino spectra measured in recent experiments at reactors are inconsistent with calculations based on the conversion of integral beta spectra recorded at the ILL reactor. ${}^{92}\mathrm{Rb}$ makes the dominant contribution to the reactor antineutrino spectrum in the 5–8 MeV range but its decay properties are in question. We have studied ${}^{92}\mathrm{Rb}$ decay with total absorption spectroscopy. Previously unobserved beta feeding was seen in the 4.5–5.5 region and the GS to GS feeding was found to be 87.5(25)%. The impact on the reactor antineutrino spectra calculated with the summation method is shown and discussed.

We report the results of a search for neutrinoless double-beta decay in a 9.8 kg yr exposure of ${}^{130}\mathrm{Te}$ using a bolometric detector array, CUORE-0. The characteristic detector energy resolution and background level in the region of interest are $5.1\pm 0.3\mathrm{keV}$ FWHM and $0.058\pm 0.004(\text{stat})\pm 0.002(\text{syst})\mathrm{counts}/(\mathrm{keV}\mathrm{kg}\mathrm{yr})$, respectively. The median 90% C.L. lower-limit half-life sensitivity of the experiment is $2.9\times {10}^{24}\mathrm{yr}$ and surpasses the sensitivity of previous searches. We find no evidence for neutrinoless double-beta decay of ${}^{130}\mathrm{Te}$ and place a Bayesian lower bound on the decay half-life, $T_{1/2}^{0\nu }>2.7\times {10}^{24}\mathrm{yr}$ at 90% C.L. Combining CUORE-0 data with the 19.75 kg yr exposure of ${}^{130}\mathrm{Te}$ from the Cuoricino experiment we obtain $T_{1/2}^{0\nu }>4.0\times {10}^{24}\mathrm{yr}$ at 90% C.L. (Bayesian), the most stringent limit to date on this half-life. Using a range of nuclear matrix element estimates we interpret this as a limit on the effective Majorana neutrino mass, $m_{\beta \beta }<270–760\mathrm{meV}$.

Differential cross sections of isoscalar and isovector spin-$M1$ ($0^{+}\to 1^{+}$) transitions are measured using high-energy-resolution proton inelastic scattering at $E_p=295\mathrm{MeV}$ on ${}^{24}\mathrm{Mg}$, ${}^{28}\mathrm{Si}$, ${}^{32}\mathrm{S}$, and ${}^{36}\mathrm{Ar}$ at 0°–14°. The squared spin-$M1$ nuclear transition matrix elements are deduced from the measured differential cross sections by applying empirically determined unit cross sections based on the assumption of isospin symmetry. The ratios of the squared nuclear matrix elements accumulated up to $E_x=16\mathrm{MeV}$ compared to a shell-model prediction are 1.01(9) for isoscalar and 0.61(6) for isovector spin-$M1$ transitions, respectively. Thus, no quenching is observed for isoscalar spin-$M1$ transitions, while the matrix elements for isovector spin-$M1$ transitions are quenched by an amount comparable with the analogous Gamow-Teller transitions on those target nuclei.

We present a determination of the pion-nucleon ($\pi N$) $\sigma$ term ${\sigma }_{\pi N}$ based on the Cheng-Dashen low-energy theorem (LET), taking advantage of the recent high-precision data from pionic atoms to pin down the $\pi N$ scattering lengths as well as of constraints from analyticity, unitarity, and crossing symmetry in the form of Roy-Steiner equations to perform the extrapolation to the Cheng-Dashen point in a reliable manner. With isospin-violating corrections included both in the scattering lengths and the LET, we obtain ${\sigma }_{\pi N}=(59.1\pm 1.9\pm 3.0)\mathrm{MeV}=(59.1\pm 3.5)\mathrm{MeV}$, where the first error refers to uncertainties in the $\pi N$ amplitude and the second to the LET. Consequences for the scalar nucleon couplings relevant for the direct detection of dark matter are discussed.

Total absorption spectroscopy is used to investigate the $\beta$-decay intensity to states above the neutron separation energy followed by $\gamma$-ray emission in ${}^{87,88}\mathrm{Br}$ and ${}^{94}\mathrm{Rb}$. Accurate results are obtained thanks to a careful control of systematic errors. An unexpectedly large $\gamma$ intensity is observed in all three cases extending well beyond the excitation energy region where neutron penetration is hindered by low neutron energy. The $\gamma$ branching as a function of excitation energy is compared to Hauser-Feshbach model calculations. For ${}^{87}\mathrm{Br}$ and ${}^{88}\mathrm{Br}$ the $\gamma$ branching reaches 57% and 20%, respectively, and could be explained as a nuclear structure effect. Some of the states populated in the daughter can only decay through the emission of a large orbital angular momentum neutron with a strongly reduced barrier penetrability. In the case of neutron-rich ${}^{94}\mathrm{Rb}$ the observed 4.5% branching is much larger than the calculations performed with standard nuclear statistical model parameters, even after proper correction for fluctuation effects on individual transition widths. The difference can be reconciled by introducing an enhancement of 1 order of magnitude in the photon strength to neutron strength ratio. An increase in the photon strength function of such magnitude for very neutron-rich nuclei, if it proves to be correct, leads to a similar increase in the ($\mathit{n},\gamma$) cross section that would have an impact on $r$ process abundance calculations.

The atomic mass difference of ${}^{163}\mathrm{Ho}$ and ${}^{163}\mathrm{Dy}$ has been directly measured with the Penning-trap mass spectrometer SHIPTRAP applying the novel phase-imaging ion-cyclotron-resonance technique. Our measurement has solved the long-standing problem of large discrepancies in the $Q$ value of the electron capture in ${}^{163}\mathrm{Ho}$ determined by different techniques. Our measured mass difference shifts the current $Q$ value of 2555(16) eV evaluated in the Atomic Mass Evaluation 2012 [G. Audi et al., Chin. Phys. C 36, 1157 (2012)] by more than $7\sigma$ to $2833({30}_{\text{stat}})({15}_{\mathrm{sys}})\mathrm{eV}/c^2$. With the new mass difference it will be possible, e.g., to reach in the first phase of the ECHo experiment a statistical sensitivity to the neutrino mass below 10 eV, which will reduce its present upper limit by more than an order of magnitude.

In Wolf-Rayet and asymptotic giant branch (AGB) stars, the ${}^{26g}\mathrm{Al}(p,\gamma ){}^{27}\mathrm{Si}$ reaction is expected to govern the destruction of the cosmic $\gamma$-ray emitting nucleus ${}^{26}\mathrm{Al}$. The rate of this reaction, however, is highly uncertain due to the unknown properties of key resonances in the temperature regime of hydrogen burning. We present a high-resolution inverse kinematic study of the ${}^{26g}\mathrm{Al}(d,p){}^{27}\mathrm{Al}$ reaction as a method for constraining the strengths of key astrophysical resonances in the ${}^{26g}\mathrm{Al}(p,\gamma ){}^{27}\mathrm{Si}$ reaction. In particular, the results indicate that the resonance at $E_r=127\mathrm{keV}$ in ${}^{27}\mathrm{Si}$ determines the entire ${}^{26g}\mathrm{Al}(p,\gamma ){}^{27}\mathrm{Si}$ reaction rate over almost the complete temperature range of Wolf-Rayet stars and AGB stars.

Experimental evidence has recently put the validity of the Porter-Thomas distribution (PTD) for partial neutron widths into question. We identify two terms in the effective Hamiltonian that violate orthogonal invariance (the basis for the PTD). Both are due to the coupling to the decay channels. We show that realistic estimates for the coupling to the neutron channel and for nonstatistical $\gamma$ decays yield significant modifications of the PTD, similar to the observed ones.