The change in mean-square nuclear charge radii $\delta ⟨r^2⟩$ along the even-$A$ tin isotopic chain ${}^{108-134}\mathrm{Sn}$ has been investigated by means of collinear laser spectroscopy at ISOLDE/CERN using the atomic transitions $5p^2{{}^{1}S}_0\to 5p6s{{}^{1}P}_1$ and $5p^2{{}^{3}P}_0\to 5p6s{{}^{3}P}_1$. With the determination of the charge radius of ${}^{134}\mathrm{Sn}$ and corrected values for some of the neutron-rich isotopes, the evolution of the charge radii across the $N=82$ shell closure is established. A clear kink at the doubly magic ${}^{132}\mathrm{Sn}$ is revealed, similar to what has been observed at $N=82$ in other isotopic chains with larger proton numbers, and at the $N=126$ shell closure in doubly magic ${}^{208}\mathrm{Pb}$. While most standard nuclear density functional calculations struggle with a consistent explanation of these discontinuities, we demonstrate that a recently developed Fayans energy density functional provides a coherent description of the kinks at both doubly magic nuclei, ${}^{132}\mathrm{Sn}$ and ${}^{208}\mathrm{Pb}$, without sacrificing the overall performance. A multiple correlation analysis leads to the conclusion that both kinks are related to pairing and surface effects.

A new short-lived neutron-deficient isotope ${}^{220}\mathrm{Np}$ was synthesized in the fusion-evaporation reaction ${}^{185}\mathrm{Re}({}^{40}\mathrm{Ar},5n){}^{220}\mathrm{Np}$ at the gas-filled recoil separator SHANS. Based on the measurement of the correlated $\alpha$-decay chains, the decay properties of ${}^{220}\mathrm{Np}$ with $E_{\alpha }=10040(18)\mathrm{keV}$ and $T_{1/2}=25_{-7}^{+14}\mu \mathrm{s}$ were determined, which are in good agreement with theoretical predictions. From the new experimental results coupled with the recently reported $\alpha$-decay data of ${}^{219,223}\mathrm{Np}$, the $\alpha$-decay systematics for Np isotopes around $N=126$ was established, which allows us for the first time to test the robustness of the $N=126$ shell closure in $Z=93$ Np isotopes. The results also indicate that, in the region of nuclei with $Z\ge 83$, the proton drip line has been reached for all odd-$Z$ isotopes up to Np.

We calculate the lifetime of the deuteron with dimension-nine quark operators that violate baryon number by two units. We construct an effective field theory for $|\mathrm{\Delta }B|=2$ interactions that give rise to neutron-antineutron ($n\text{−}\overline{n}$) oscillations and dinucleon decay within a consistent power counting. We calculate the ratio of the deuteron lifetime to the square of the $n\text{−}\overline{n}$ oscillation time up to next-to-leading order. Our result, which is analytical and has a quantified uncertainty, is smaller by a factor $\simeq 2.5$ than earlier estimates based on nuclear models, which impacts the indirect bound on the $n\text{−}\overline{n}$ oscillation time and future experiments. We discuss how combined measurements of $n\text{−}\overline{n}$ oscillations and deuteron decay can help to identify the sources of baryon-number violation.

High-energy nuclear collisions produce a nonequilibrium plasma of quarks and gluons which thermalizes and exhibits hydrodynamic flow. There are currently no practical frameworks to connect the early particle production in classical field simulations to the subsequent hydrodynamic evolution. We build such a framework using nonequilibrium Green’s functions, calculated in QCD kinetic theory, to propagate the initial energy-momentum tensor to the hydrodynamic phase. We demonstrate that this approach can be easily incorporated into existing hydrodynamic simulations, leading to stronger constraints on the energy density at early times and the transport properties of the QCD medium. Based on (conformal) scaling properties of the Green’s functions, we further obtain pragmatic bounds for the applicability of hydrodynamics in nuclear collisions.

One of the most exotic light neutron-rich nuclei currently accessible for experimental study is ${}^{40}\mathrm{Mg}$, which lies at the intersection of the nucleon magic number $N=28$ and the neutron drip line. Low-lying excited states of ${}^{40}\mathrm{Mg}$ have been studied for the first time following a one-proton removal reaction from ${}^{41}\mathrm{Al}$, performed at the Radioactive Isotope Beam Factory of RIKEN Nishina Center with the DALI2 $\gamma$-ray array and the ZeroDegree spectrometer. Two $\gamma$-ray transitions were observed, suggesting an excitation spectrum that shows unexpected properties as compared to both the systematics along the $Z=12$, $N\ge 20\mathrm{Mg}$ isotopes and available state-of-the-art theoretical model predictions. A possible explanation for the observed structure involves weak-binding effects in the low-lying excitation spectrum.

An experiment was performed at Lawrence Berkeley National Laboratory’s 88-in. Cyclotron to determine the mass number of a superheavy element. The measurement resulted in the observation of two $\alpha$-decay chains, produced via the ${}^{243}\mathrm{Am}{({}^{48}\mathrm{Ca},xn)}^{291-x}\mathrm{Mc}$ reaction, that were separated by mass-to-charge ratio ($A/q$) and identified by the combined $\mathrm{BGS}+\mathrm{FIONA}$ apparatus. One event occurred at $A/q=284$ and was assigned to ${}^{284}\mathrm{Nh}$ ($Z=113$), the $\alpha$-decay daughter of ${}^{288}\mathrm{Mc}$ ($Z=115$), while the second occurred at $A/q=288$ and was assigned to ${}^{288}\mathrm{Mc}$. This experiment represents the first direct measurements of the mass numbers of superheavy elements, confirming previous (indirect) mass-number assignments.

We report the first observation of the ${}^{108}\mathrm{Xe}\to {}^{104}\mathrm{Te}\to {}^{100}\mathrm{Sn}$ $\alpha$-decay chain. The $\alpha$ emitters, ${}^{108}\mathrm{Xe}$ [$E_{\alpha }=4.4(2)\mathrm{MeV}$, $T_{1/2}=58_{-23}^{+106}\mu \mathrm{s}$] and ${}^{104}\mathrm{Te}$ [$E_{\alpha }=4.9(2)\mathrm{MeV}$, $T_{1/2}<18\mathrm{ns}$], decaying into doubly magic ${}^{100}\mathrm{Sn}$ were produced using a fusion-evaporation reaction ${}^{54}\mathrm{Fe}({}^{58}\mathrm{Ni},4n){}^{108}\mathrm{Xe}$, and identified with a recoil mass separator and an implantation-decay correlation technique. This is the first time $\alpha$ radioactivity has been observed to a heavy self-conjugate nucleus. A previous benchmark for study of this fundamental decay mode has been the decay of ${}^{212}\mathrm{Po}$ into doubly magic ${}^{208}\mathrm{Pb}$. Enhanced proton-neutron interactions in the $N=Z$ parent nuclei may result in superallowed $\alpha$ decays with reduced $\alpha$-decay widths significantly greater than that for ${}^{212}\mathrm{Po}$. From the decay chain, we deduce that the $\alpha$-reduced width for ${}^{108}\mathrm{Xe}$ or ${}^{104}\mathrm{Te}$ is more than a factor of 5 larger than that for ${}^{212}\mathrm{Po}$.

A common challenge faced in quantum physics is finding the extremal eigenvalues and eigenvectors of a Hamiltonian matrix in a vector space so large that linear algebra operations on general vectors are not possible. There are numerous efficient methods developed for this task, but they generally fail when some control parameter in the Hamiltonian matrix exceeds some threshold value. In this Letter we present a new technique called eigenvector continuation that can extend the reach of these methods. The key insight is that while an eigenvector resides in a linear space with enormous dimensions, the eigenvector trajectory generated by smooth changes of the Hamiltonian matrix is well approximated by a very low-dimensional manifold. We prove this statement using analytic function theory and propose an algorithm to solve for the extremal eigenvectors. We benchmark the method using several examples from quantum many-body theory.

The discovery of the important neutron-rich nucleus ${}_{20}{}^{60}{\mathrm{Ca}}_{40}$ and seven others near the limits of nuclear stability is reported from the fragmentation of a $345\mathrm{MeV}/u$ ${}^{70}\mathrm{Zn}$ projectile beam on ${}^9\mathrm{Be}$ targets at the radioactive ion-beam factory of the RIKEN Nishina Center. The produced fragments were analyzed and unambiguously identified using the BigRIPS two-stage in-flight separator. The eight new neutron-rich nuclei discovered, ${}^{47}\mathrm{P}$, ${}^{49}\mathrm{S}$, ${}^{52}\mathrm{Cl}$, ${}^{54}\mathrm{Ar}$, ${}^{57}\mathrm{K}$, ${}^{59,60}\mathrm{Ca}$, and ${}^{62}\mathrm{Sc}$, are the most neutron-rich isotopes of the respective elements. In addition, one event consistent with ${}^{59}\mathrm{K}$ was registered. The results are compared with the drip lines predicted by a variety of mass models and it is found that the models in best agreement with the observed limits of existence in the explored region tend to predict the even-mass Ca isotopes to be bound out to at least ${}^{70}\mathrm{Ca}$.

Until recently, ground-state nuclear moments of the heaviest nuclei could only be inferred from nuclear spectroscopy, where model assumptions are required. Laser spectroscopy in combination with modern atomic structure calculations is now able to probe these moments directly, in a comprehensive and nuclear-model-independent way. Here we report on unique access to the differential mean-square charge radii of ${}^{252,253,254}\mathrm{No}$, and therefore to changes in nuclear size and shape. State-of-the-art nuclear density functional calculations describe well the changes in nuclear charge radii in the region of the heavy actinides, indicating an appreciable central depression in the deformed proton density distribution in ${}^{252,254}\mathrm{No}$ isotopes. Finally, the hyperfine splitting of ${}^{253}\mathrm{No}$ was evaluated, enabling a complementary measure of its (quadrupole) deformation, as well as an insight into the neutron single-particle wave function via the nuclear spin and magnetic moment.

We report the result of the search for neutrinoless double beta decay of ${}^{82}\mathrm{Se}$ obtained with CUPID-0, the first large array of scintillating $\mathrm{Zn}{}^{82}\mathrm{Se}$ cryogenic calorimeters implementing particle identification. We observe no signal in a 1.83 kg yr ${}^{82}\mathrm{Se}$ exposure, and we set the most stringent lower limit on the $0\nu \beta \beta$ ${}^{82}\mathrm{Se}$ half-life $T_{1/2}^{0\nu }>2.4\times {10}^{24}\mathrm{yr}$ (90% credible interval), which corresponds to an effective Majorana neutrino mass $m_{\beta \beta }<(376–770)\mathrm{meV}$ depending on the nuclear matrix element calculations. The heat-light readout provides a powerful tool for the rejection of $\alpha$ particles and allows us to suppress the background in the region of interest down to $({3.6}_{-1.4}^{+1.9})\times {10}^{-3}\mathrm{counts}/(\mathrm{keV}\mathrm{kg}\mathrm{yr})$, an unprecedented level for this technique.

We show that the neutron star in the transient system MXB 1659-29 has a core neutrino luminosity that substantially exceeds that of the modified Urca reactions (i.e., $n+n\to n+p+e^{-}+{\overline{\nu }}_e$ and inverse) and is consistent with the direct Urca ($n\to p+e^{-}+{\overline{\nu }}_e$ and inverse) reaction occurring in a small fraction of the core. Observations of the thermal relaxation of the neutron star crust following 2.5 yr of accretion allow us to measure the energy deposited into the core during accretion, which is then reradiated as neutrinos, and infer the core temperature. For a nucleonic core, this requires that the nucleons are unpaired and that the proton fraction exceeds a critical value to allow the direct Urca reaction to proceed. The neutron star in MXB 1659-29 is the first with a firmly detected thermal component in its x-ray spectrum that needs a fast neutrino-cooling process. Measurements of the temperature variation of the neutron star core during quiescence would place an upper limit on the core specific heat and serve as a check on the fraction of the neutron star core in which nucleons are unpaired.

The historical first detection of a binary neutron star merger by the LIGO-Virgo Collaboration [B. P. Abbott et al., Phys. Rev. Lett. 119, 161101 (2017)] is providing fundamental new insights into the astrophysical site for the $r$ process and on the nature of dense matter. A set of realistic models of the equation of state (EOS) that yield an accurate description of the properties of finite nuclei, support neutron stars of two solar masses, and provide a Lorentz covariant extrapolation to dense matter are used to confront its predictions against tidal polarizabilities extracted from the gravitational-wave data. Given the sensitivity of the gravitational-wave signal to the underlying EOS, limits on the tidal polarizability inferred from the observation translate into constraints on the neutron-star radius. Based on these constraints, models that predict a stiff symmetry energy, and thus large stellar radii, can be ruled out. Indeed, we deduce an upper limit on the radius of a $1.4M_{\odot }$ neutron star of $R_{\star }^{1.4}<13.76\mathrm{km}$. Given the sensitivity of the neutron-skin thickness of ${}^{208}\mathrm{Pb}$ to the symmetry energy, albeit at a lower density, we infer a corresponding upper limit of about $R_{\mathrm{skin}}^{208}\lesssim 0.25\mathrm{fm}$. However, if the upcoming PREX-II experiment measures a significantly thicker skin, this may be evidence of a softening of the symmetry energy at high densities—likely indicative of a phase transition in the interior of neutron stars.

The detection of gravitational waves originating from a neutron-star merger, GW170817, by the LIGO and Virgo Collaborations has recently provided new stringent limits on the tidal deformabilities of the stars involved in the collision. Combining this measurement with the existence of two-solar-mass stars, we generate a generic family of neutron-star-matter equations of state (EOSs) that interpolate between state-of-the-art theoretical results at low and high baryon density. Comparing the results to ones obtained without the tidal-deformability constraint, we witness a dramatic reduction in the family of allowed EOSs. Based on our analysis, we conclude that the maximal radius of a 1.4-solar-mass neutron star is 13.6 km, and that the smallest allowed tidal deformability of a similar-mass star is $\mathrm{\Lambda }(1.4M_{\odot })=120$.

We link the structure of nuclei around ${}^{100}\mathrm{Sn}$, the heaviest doubly magic nucleus with equal neutron and proton numbers ($N=Z=50$), to nucleon-nucleon ($NN$) and three-nucleon ($NNN$) forces constrained by data of few-nucleon systems. Our results indicate that ${}^{100}\mathrm{Sn}$ is doubly magic, and we predict its quadrupole collectivity. We present precise computations of ${}^{101}\mathrm{Sn}$ based on three-particle–two-hole excitations of ${}^{100}\mathrm{Sn}$, and we find that one interaction accurately reproduces the small splitting between the lowest $J^{\pi }=7/2^{+}$ and $5/2^{+}$ states.

The emission of neutron pairs from the neutron-rich $N=12$ isotones ${}^{18}\mathrm{C}$ and ${}^{20}\mathrm{O}$ has been studied by high-energy nucleon knockout from ${}^{19}\mathrm{N}$ and ${}^{21}\mathrm{O}$ secondary beams, populating unbound states of the two isotones up to 15 MeV above their two-neutron emission thresholds. The analysis of triple fragment-$n\text{−}n$ correlations shows that the decay ${}^{19}\mathrm{N}(-1p){{}^{18}\mathrm{C}}^{*}\to {}^{16}\mathrm{C}+n+n$ is clearly dominated by direct pair emission. The two-neutron correlation strength, the largest ever observed, suggests the predominance of a ${}^{14}\mathrm{C}$ core surrounded by four valence neutrons arranged in strongly correlated pairs. On the other hand, a significant competition of a sequential branch is found in the decay ${}^{21}\mathrm{O}(-1n){{}^{20}\mathrm{O}}^{*}\to {}^{18}\mathrm{O}+n+n$, attributed to its formation through the knockout of a deeply bound neutron that breaks the ${}^{16}\mathrm{O}$ core and reduces the number of pairs.

Data from heavy ion collisions suggest that the evolution of a parton shower is modified by interactions with the color charges in the dense partonic medium created in these collisions, but it is not known where in the shower evolution the modifications occur. The momentum ratio of the two leading partons, resolved as subjets, provides information about the parton shower evolution. This substructure observable, known as the splitting function, reflects the process of a parton splitting into two other partons and has been measured for jets with transverse momentum between 140 and 500 GeV, in $pp$ and PbPb collisions at a center-of-mass energy of 5.02 TeV per nucleon pair. In central PbPb collisions, the splitting function indicates a more unbalanced momentum ratio, compared to peripheral PbPb and $pp$ collisions.. The measurements are compared to various predictions from event generators and analytical calculations.

Nuclear-spin-dependent parity violation (NSD-PV) effects in atoms and molecules arise from $Z^0$ boson exchange between electrons and the nucleus, and from the magnetic interaction between electrons and the parity-violating nuclear anapole moment. We demonstrate measurements of NSD-PV that use an enhancement of the effect in diatomic molecules, here using the test system ${}^{138}\mathrm{Ba}{}^{19}\mathrm{F}$. Our sensitivity surpasses that of any previous atomic parity violation measurement. We show that systematic errors can be suppressed to at least the level of the present statistical sensitivity. We measure the matrix element $W$ of the NSD-PV interaction with total uncertainty $\delta W/(2\pi )<0.7\mathrm{Hz}$, for each of two configurations where $W$ must have different signs. This sensitivity would be sufficient to measure NSD-PV effects of the size anticipated across a wide range of nuclei including ${}^{137}\mathrm{Ba}$ in ${}^{137}\mathrm{BaF}$, where $|W|/(2\pi )\approx 5\mathrm{Hz}$ is expected.

The CUORE experiment, a ton-scale cryogenic bolometer array, recently began operation at the Laboratori Nazionali del Gran Sasso in Italy. The array represents a significant advancement in this technology, and in this work we apply it for the first time to a high-sensitivity search for a lepton-number-violating process: ${}^{130}\mathrm{Te}$ neutrinoless double-beta decay. Examining a total ${\mathrm{TeO}}_2$ exposure of 86.3 kg yr, characterized by an effective energy resolution of $(7.7\pm 0.5)\mathrm{keV}$ FWHM and a background in the region of interest of $(0.014\pm 0.002)\mathrm{counts}/(\mathrm{keV}\mathrm{kg}\mathrm{yr})$, we find no evidence for neutrinoless double-beta decay. Including systematic uncertainties, we place a lower limit on the decay half-life of $T_{1/2}^{0\nu }({}^{130}\mathrm{Te})>1.3\times {10}^{25}\mathrm{yr}$ (90% C.L.); the median statistical sensitivity of this search is $7.0\times {10}^{24}\mathrm{yr}$. Combining this result with those of two earlier experiments, Cuoricino and CUORE-0, we find $T_{1/2}^{0\nu }({}^{130}\mathrm{Te})>1.5\times {10}^{25}\mathrm{yr}$ (90% C.L.), which is the most stringent limit to date on this decay. Interpreting this result as a limit on the effective Majorana neutrino mass, we find $m_{\beta \beta }<(110-520)\mathrm{meV}$, where the range reflects the nuclear matrix element estimates employed.

The Majorana Collaboration is operating an array of high purity Ge detectors to search for neutrinoless double-$\beta$ decay in ${}^{76}\mathrm{Ge}$. The Majorana Demonstrator comprises 44.1 kg of Ge detectors (29.7 kg enriched in ${}^{76}\mathrm{Ge}$) split between two modules contained in a low background shield at the Sanford Underground Research Facility in Lead, South Dakota. Here we present results from data taken during construction, commissioning, and the start of full operations. We achieve unprecedented energy resolution of 2.5 keV FWHM at $Q_{\beta \beta }$ and a very low background with no observed candidate events in 9.95 kg yr of enriched Ge exposure, resulting in a lower limit on the half-life of $1.9\times {10}^{25}\mathrm{yr}$ (90% C.L.). This result constrains the effective Majorana neutrino mass to below 240–520 meV, depending on the matrix elements used. In our experimental configuration with the lowest background, the background is ${4.0}_{-2.5}^{+3.1}\mathrm{counts}/(\mathrm{FWHM}\mathrm{t}\mathrm{yr})$.