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 ${4.0}_{-2.5}^{+3.1}\mathrm{counts}/(\mathrm{FWHM}\mathrm{t}\mathrm{yr})$.

The GERDA experiment searches for the lepton-number-violating neutrinoless double-$\beta$ decay of ${}^{76}\mathrm{Ge}$ (${}^{76}\mathrm{Ge}\to {}^{76}\mathrm{Se}+2e^{-}$) operating bare Ge diodes with an enriched ${}^{76}\mathrm{Ge}$ fraction in liquid argon. The exposure for broad-energy germanium type (BEGe) detectors is increased threefold with respect to our previous data release. The BEGe detectors feature an excellent background suppression from the analysis of the time profile of the detector signals. In the analysis window a background level of $1.0_{-0.4}^{+0.6}\times {10}^{-3}\mathrm{counts}/(\mathrm{keV}\mathrm{kg}\mathrm{yr})$ has been achieved; if normalized to the energy resolution this is the lowest ever achieved in any $0\nu \beta \beta$ experiment. No signal is observed and a new 90% C.L. lower limit for the half-life of $8.0\times {10}^{25}\mathrm{yr}$ is placed when combining with our previous data. The expected median sensitivity assuming no signal is $5.8\times {10}^{25}\mathrm{yr}$.

A new method to tag the barium daughter in the double-beta decay of ${}^{136}\mathrm{Xe}$ is reported. Using the technique of single molecule fluorescent imaging (SMFI), individual barium dication (${\mathrm{Ba}}^{++}$) resolution at a transparent scanning surface is demonstrated. A single-step photobleach confirms the single ion interpretation. Individual ions are localized with superresolution ($\sim 2\mathrm{nm}$), and detected with a statistical significance of $12.9\sigma$ over backgrounds. This lays the foundation for a new and potentially background-free neutrinoless double-beta decay technology, based on SMFI coupled to high pressure xenon gas time projection chambers.

The main decay channels of the anomalous low-energy $3/2^{+}(7.8\pm 0.5\mathrm{eV})$ isomeric level of the ${}^{229}\mathrm{Th}$ nucleus, namely the $\gamma$ emission and internal conversion, inside a dielectric sphere, dielectric thin film, and conducting spherical microcavity are investigated theoretically, taking into account the effect of media interfaces. It is shown that (1) the $\gamma$ decay rate of the nuclear isomer inside a dielectric thin film and dielectric microsphere placed in a vacuum or in a metal cavity can decrease (increase) in dozen of times, (2) the $\gamma$ activity of the distributed source as a function of time can be nonexponential, and (3) the metal cavity, whose size is of the order of the radiation wavelength, does not affect the probability of the internal conversion in ${}^{229}\mathrm{Th}$, because the virtual photon attenuates at much shorter distances and the reflected wave is very weak.

Results from a search for neutrinoless double-beta decay ($0\nu \beta \beta$) of ${}^{136}\mathrm{Xe}$ are presented using the first year of data taken with the upgraded EXO-200 detector. Relative to previous searches by EXO-200, the energy resolution of the detector has been improved to $\sigma /E=1.23\%$, the electric field in the drift region has been raised by 50%, and a system to suppress radon in the volume between the cryostat and lead shielding has been implemented. In addition, analysis techniques that improve topological discrimination between $0\nu \beta \beta$ and background events have been developed. Incorporating these hardware and analysis improvements, the median 90% confidence level $0\nu \beta \beta$ half-life sensitivity after combining with the full data set acquired before the upgrade has increased twofold to $3.7\times {10}^{25}\mathrm{yr}$. No statistically significant evidence for $0\nu \beta \beta$ is observed, leading to a lower limit on the $0\nu \beta \beta$ half-life of $1.8\times {10}^{25}\mathrm{yr}$ at the 90% confidence level.