A nuclear spectroscopy experiment was conducted to study $\alpha$-decay chains stemming from isotopes of flerovium (element $Z=114$). An upgraded TASISpec decay station was placed behind the gas-filled separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. The fusion-evaporation reactions ${}^{48}\mathrm{Ca}+{}^{242}\mathrm{Pu}$ and ${}^{48}\mathrm{Ca}+{}^{244}\mathrm{Pu}$ provided a total of 32 flerovium-candidate decay chains, of which two and eleven were firmly assigned to ${}^{286}\mathrm{Fl}$ and ${}^{288}\mathrm{Fl}$, respectively. A prompt coincidence between a 9.60(1)-MeV $\alpha$ particle event and a 0.36(1)-MeV conversion electron marked the first observation of an excited state in an even-even isotope of the heaviest man-made elements, namely ${}^{282}\mathrm{Cn}$. Spectroscopy of ${}^{288}\mathrm{Fl}$ decay chains fixed $Q_{\alpha }=10.06(1)\mathrm{MeV}$. In one case, a $Q_{\alpha }=9.46(1)$-MeV decay from ${}^{284}\mathrm{Cn}$ into ${}^{280}\mathrm{Ds}$ was observed, with ${}^{280}\mathrm{Ds}$ fissioning after only $518\mu \mathrm{s}$. The impact of these findings, aggregated with existing data on decay chains of ${}^{286,288}\mathrm{Fl}$, on the size of an anticipated shell gap at proton number $Z=114$ is discussed in light of predictions from two beyond-mean-field calculations, which take into account triaxial deformation.

We predict the limits of existence of atomic nuclei, the proton and neutron drip lines, from the light through medium-mass regions. Starting from a chiral two- and three-nucleon interaction with good saturation properties, we use the valence-space in-medium similarity renormalization group to calculate ground-state and separation energies from helium to iron, nearly 700 isotopes in total. We use the available experimental data to quantify the theoretical uncertainties for our ab initio calculations towards the drip lines. Where the drip lines are known experimentally, our predictions are consistent within the estimated uncertainty. For the neutron-rich sodium to chromium isotopes, we provide predictions to be tested at rare-isotope beam facilities.

The GERmanium Detector Array (GERDA) experiment searched for the lepton-number-violating neutrinoless double-$\beta$ ($0\nu \beta \beta$) decay of ${}^{76}\mathrm{Ge}$, whose discovery would have far-reaching implications in cosmology and particle physics. By operating bare germanium diodes, enriched in ${}^{76}\mathrm{Ge}$, in an active liquid argon shield, GERDA achieved an unprecedently low background index of $5.2\times {10}^{-4}\mathrm{counts}/(\mathrm{keV}\mathrm{kg}\mathrm{yr})$ in the signal region and met the design goal to collect an exposure of 100 kg yr in a background-free regime. When combined with the result of Phase I, no signal is observed after 127.2 kg yr of total exposure. A limit on the half-life of $0\nu \beta \beta$ decay in ${}^{76}\mathrm{Ge}$ is set at $T_{1/2}>1.8\times {10}^{26}\mathrm{yr}$ at 90% C.L., which coincides with the sensitivity assuming no signal.

We present a measurement of the low-energy (0–60 keV) $\gamma$-ray spectrum produced in the $\alpha$ decay of ${}^{233}\mathrm{U}$ using a dedicated cryogenic magnetic microcalorimeter. The energy resolution of $\sim 10\mathrm{eV}$, together with exceptional gain linearity, allows us to determine the energy of the low-lying isomeric state in ${}^{229}\mathrm{Th}$ using four complementary evaluation schemes. The most precise scheme determines the ${}^{229}\mathrm{Th}$ isomer energy to be 8.10(17) eV, corresponding to 153.1(32) nm, superseding in precision previous values based on $\gamma$ spectroscopy, and agreeing with a recent measurement based on internal conversion electrons. We also measure branching ratios of the relevant excited states to be $b_{29}=9.3(6)\%$ and $b_{42}<0.7\%$.

The first evidence of spin alignment of vector mesons ($K^{*0}$ and $\varphi$) in heavy-ion collisions at the Large Hadron Collider (LHC) is reported. The spin density matrix element ${\rho }_{00}$ is measured at midrapidity ($|y|<0.5$) in Pb-Pb collisions at a center-of-mass energy ($\sqrt{s_{\mathrm{NN}}}$) of 2.76 TeV with the ALICE detector. ${\rho }_{00}$ values are found to be less than $1/3$ ($1/3$ implies no spin alignment) at low transverse momentum ($p_T<2\mathrm{GeV}/c$) for $K^{*0}$ and $\varphi$ at a level of $3\sigma$ and $2\sigma$, respectively. No significant spin alignment is observed for the $K_S^0$ meson ($\text{spin}=0$) in Pb-Pb collisions and for the vector mesons in $pp$ collisions. The measured spin alignment is unexpectedly large but qualitatively consistent with the expectation from models which attribute it to a polarization of quarks in the presence of angular momentum in heavy-ion collisions and a subsequent hadronization by the process of recombination.

In an experiment performed at Lawrence Berkeley National Laboratory’s 88-inch cyclotron, the isotope ${}^{244}\mathrm{Md}$ was produced in the ${}^{209}\mathrm{Bi}({}^{40}\mathrm{Ar},5n)$ reaction. Decay properties of ${}^{244}\mathrm{Md}$ were measured at the focal plane of the Berkeley Gas-filled Separator, and the mass number assignment of $A=244$ was confirmed with the apparatus for the identification of nuclide $A$. The isotope ${}^{244}\mathrm{Md}$ is reported to have one, possibly two, $\alpha$-decaying states with $\alpha$ energies of 8.66(2) and 8.31(2) MeV and half-lives of ${0.4}_{-0.1}^{+0.4}$ and $\sim 6\mathrm{s}$, respectively. Additionally, first evidence of the $\alpha$ decay of ${}^{236}\mathrm{Bk}$ was observed and is reported.

The heaviest bound isotope of boron ${}^{19}\mathrm{B}$ has been investigated using exclusive measurements of its Coulomb dissociation, into ${}^{17}\mathrm{B}$ and two neutrons, in collisions with Pb at $220\mathrm{MeV}/\mathrm{nucleon}$. Enhanced electric dipole ($E1$) strength is observed just above the two-neutron decay threshold with an integrated $E1$ strength of $B(E1)=1.64\pm 0.06(\mathrm{stat})\pm 0.12(\mathrm{sys})e^2{\mathrm{fm}}^2$ for relative energies below 6 MeV. This feature, known as a soft $E1$ excitation, provides the first firm evidence that ${}^{19}\mathrm{B}$ has a prominent two-neutron halo. Three-body calculations that reproduce the energy spectrum indicate that the valence neutrons have a significant $s$-wave configuration and exhibit a dineutronlike correlation.

We report the first measurement of the $(e,e^{\prime }p)$ three-body breakup reaction cross sections in helium-3 (${}^3\mathrm{He}$) and tritium (${}^3\mathrm{H}$) at large momentum transfer [$⟨Q^2⟩\approx 1.9(\mathrm{GeV}/c{)}^2$] and $x_B>1$ kinematics, where the cross section should be sensitive to quasielastic (QE) scattering from single nucleons. The data cover missing momenta $40\le p_{\text{miss}}\le 500\mathrm{MeV}/c$ that, in the QE limit with no rescattering, equals the initial momentum of the probed nucleon. The measured cross sections are compared with state-of-the-art ab initio calculations. Overall good agreement, within $\pm 20\%$, is observed between data and calculations for the full $p_{\text{miss}}$ range for ${}^3\mathrm{H}$ and for $100\le p_{\text{miss}}\le 350\mathrm{MeV}/c$ for ${}^3\mathrm{He}$. Including the effects of rescattering of the outgoing nucleon improves agreement with the data at $p_{\text{miss}}>250\mathrm{MeV}/c$ and suggests contributions from charge-exchange (SCX) rescattering. The isoscalar sum of ${}^3\mathrm{He}$ plus ${}^3\mathrm{H}$, which is largely insensitive to SCX, is described by calculations to within the accuracy of the data over the entire $p_{\text{miss}}$ range. This validates current models of the ground state of the three-nucleon system up to very high initial nucleon momenta of $500\mathrm{MeV}/c$.

We demonstrate that a committee of deep neural networks is capable of predicting the ground-state and excited energies of more than 1800 atomic nuclei with an accuracy akin to the one achieved by state-of-the-art nuclear energy density functionals (EDFs) and with significantly less computational cost. An active learning strategy is proposed to train this algorithm with a minimal set of 210 nuclei. This approach enables future fast studies of the influence of EDF parametrizations on structure properties over the whole nuclear chart and suggests that for the first time a machine learning framework successfully encoded several correlated aspects of nuclear deformation.

We report new results from the search for neutrinoless double-beta decay in ${}^{130}\hspace{0.17em}\mathrm{Te}$ with the CUORE detector. This search benefits from a fourfold increase in exposure, lower trigger thresholds, and analysis improvements relative to our previous results. We observe a background of $(1.38\pm 0.07)\times {10}^{-2}\mathrm{counts}/(\mathrm{keV}\mathrm{kg}\mathrm{yr})$) in the $0\nu \beta \beta$ decay region of interest and, with a total exposure of 372.5 kg yr, we attain a median exclusion sensitivity of $1.7\times {10}^{25}\mathrm{yr}$. We find no evidence for $0\nu \beta \beta$ decay and set a 90% credibility interval Bayesian lower limit of $3.2\times {10}^{25}\mathrm{yr}$ on the ${}^{130}\hspace{0.17em}\mathrm{Te}$ half-life for this process. In the hypothesis that $0\nu \beta \beta$ decay is mediated by light Majorana neutrinos, this results in an upper limit on the effective Majorana mass of 75–350 meV, depending on the nuclear matrix elements used.

The rare phenomenon of nuclear wobbling motion has been investigated in the nucleus ${}^{187}\mathrm{Au}$. A longitudinal wobbling-bands pair has been identified and clearly distinguished from the associated signature-partner band on the basis of angular distribution measurements. Theoretical calculations in the framework of the particle rotor model are found to agree well with the experimental observations. This is the first experimental evidence for longitudinal wobbling bands where the expected signature partner band has also been identified, and establishes this exotic collective mode as a general phenomenon over the nuclear chart.

Level structures in the neutron-rich ${}^{144}\mathrm{Ba}$ nucleus have been reinvestigated by measuring prompt $\gamma$ rays in the spontaneous fission of ${}^{252}\mathrm{Cf}$. The previous $s=+1$ octupole band structure with reflection asymmetric shape has been expanded, and a side quadrupole band structure based on a $3^{+}$ state with reflection symmetric shape is identified. Thus, the results show the coexistence of reflection asymmetric and symmetric shapes in ${}^{144}\mathrm{Ba}$. This is a first identification of such a shape coexistence structure in a nuclear structure. The other structural characteristics are discussed.

A significant fraction of stars between 7 and 11 solar masses are thought to become supernovae, but the explosion mechanism is unclear. The answer depends critically on the rate of electron capture on ${}^{20}\mathrm{Ne}$ in the degenerate oxygen-neon stellar core. However, because of the unknown strength of the transition between the ground states of ${}^{20}\mathrm{Ne}$ and ${}^{20}\mathrm{F}$, it has not previously been possible to fully constrain the rate. By measuring the transition, we establish that its strength is exceptionally large and that it enhances the capture rate by several orders of magnitude. This has a decisive impact on the evolution of the core, increasing the likelihood that the star is (partially) disrupted by a thermonuclear explosion rather than collapsing to form a neutron star. Importantly, our measurement resolves the last remaining nuclear physics uncertainty in the final evolution of degenerate oxygen-neon stellar cores, allowing future studies to address the critical role of convection, which at present is poorly understood.

The low-lying isomeric state of ${}^{229}\mathrm{Th}$ provides unique opportunities for high-resolution laser spectroscopy of the atomic nucleus. We determine the energy of this isomeric state by taking the absolute energy difference between the excitation energy required to populate the 29.2-keV state from the ground state and the energy emitted in its decay to the isomeric excited state. A transition-edge sensor microcalorimeter was used to measure the absolute energy of the 29.2-keV $\gamma$ ray. Together with the cross-band transition energy ($29.2\mathrm{keV}\to \mathrm{ground}$) and the branching ratio of the 29.2-keV state measured in a recent study, the isomer energy was determined to be $8.30\pm 0.92\mathrm{eV}$. Our result is in agreement with the latest measurements based on different experimental techniques, which further confirms that the isomeric state of ${}^{229}\mathrm{Th}$ is in the laser-accessible vacuum ultraviolet range.

The underlying structure of low-lying collective bands of atomic nuclei is discussed from a novel perspective on the interplay between single-particle and collective degrees of freedom, by utilizing state-of-the-art configuration interaction calculations on heavy nuclei. Besides the multipole components of the nucleon-nucleon interaction that drive collective modes forming those bands, the monopole component is shown to control the resistance against such modes. The calculated structure of ${}^{154}\mathrm{Sm}$ corresponds to the coexistence between prolate and triaxial shapes, while that of ${}^{166}\mathrm{Er}$ exhibits a deformed shape with a strong triaxial instability. Both findings differ from traditional views based on $\beta /\gamma$ vibrations. The formation of collective bands is shown to be facilitated from a self-organization mechanism.

A search for the heaviest isotopes of fluorine, neon, and sodium was conducted by fragmentation of an intense ${}^{48}\mathrm{Ca}$ beam at $345\mathrm{MeV}/\mathrm{nucleon}$ with a 20-mm-thick beryllium target and identification of isotopes in the large-acceptance separator BigRIPS at the RIKEN Radioactive Isotope Beam Factory. No events were observed for ${}^{32,33}\mathrm{F}$, ${}^{35,36}\mathrm{Ne}$, and ${}^{38}\mathrm{Na}$ and only one event for ${}^{39}\mathrm{Na}$ after extensive running. Comparison with predicted yields excludes the existence of bound states of these unobserved isotopes with high confidence levels. The present work indicates that ${}^{31}\mathrm{F}$ and ${}^{34}\mathrm{Ne}$ are the heaviest bound isotopes of fluorine and neon, respectively. The neutron dripline has thus been experimentally confirmed up to neon for the first time since ${}^{24}\mathrm{O}$ was confirmed to be the dripline nucleus nearly 20 years ago. These data provide new keys to understanding the nuclear stability at extremely neutron-rich conditions.

From detailed spectroscopy of ${}^{110}\mathrm{Cd}$ and ${}^{112}\mathrm{Cd}$ following the ${\beta }^{+}$/electron-capture decay of ${}^{110,112}\mathrm{In}$ and the ${\beta }^{-}$ decay of ${}^{112}\mathrm{Ag}$, very weak decay branches from nonyrast states are observed. The transition rates determined from the measured branching ratios and level lifetimes obtained with the Doppler-shift attenuation method following inelastic neutron scattering reveal collective enhancements that are suggestive of a series of rotational bands. In ${}^{110}\mathrm{Cd}$, a $\gamma$ band built on the shape-coexisting intruder configuration is suggested. For ${}^{112}\mathrm{Cd}$, the $2^{+}$ and $3^{+}$ intruder $\gamma$-band members are suggested, the $0_3^{+}$ band is extended to spin $4^{+}$, and the $0_4^{+}$ band is identified. The results are interpreted using beyond-mean-field calculations employing the symmetry conserving configuration mixing method with the Gogny D1S energy density functional and with the suggestion that the Cd isotopes exhibit multiple shape coexistence.

The elusive ${\beta }^{-}{p}^{+}$ decay was observed in ${}^{11}\mathrm{Be}$ by directly measuring the emitted protons and their energy distribution for the first time with the prototype Active Target Time Projection Chamber in an experiment performed at ISAC-TRIUMF. The measured ${\beta }^{-}{p}^{+}$ branching ratio is orders of magnitude larger than any previous theoretical model predicted. This can be explained by the presence of a narrow resonance in ${}^{11}\mathrm{B}$ above the proton separation energy.

Earth is constantly bombarded with extraterrestrial dust containing invaluable information about extraterrestrial processes, such as structure formation by stellar explosions or nucleosynthesis, which could be traced back by long-lived radionuclides. Here, we report the very first detection of a recent ${}^{60}\mathrm{Fe}$ influx onto Earth by analyzing 500 kg of snow from Antarctica by accelerator mass spectrometry. By the measurement of the cosmogenically produced radionuclide ${}^{53}\mathrm{Mn}$, an atomic ratio of ${}^{60}\mathrm{Fe}/{}^{53}\mathrm{Mn}=0.017$ was found, significantly above cosmogenic production. After elimination of possible terrestrial sources, such as global fallout, the excess of ${}^{60}\mathrm{Fe}$ could only be attributed to interstellar ${}^{60}\mathrm{Fe}$ which might originate from the solar neighborhood.

We present a precision measurement of the axial-vector coupling constant $g_A$ in the decay of polarized free neutrons. For the first time, a pulsed cold neutron beam was used for this purpose. By this method, leading sources of systematic uncertainty are suppressed. From the electron spectra we obtain $\lambda =g_A/g_V=-1.27641(45{)}_{\mathrm{stat}}(33{)}_{\mathrm{sys}}$, which confirms recent measurements with improved precision. This corresponds to a value of the parity violating beta asymmetry parameter of $A_0=-0.11985(17{)}_{\mathrm{stat}}(12{)}_{\mathrm{sys}}$. We discuss implications on the Cabibbo-Kobayashi-Maskawa matrix element $V_{ud}$ and derive a limit on left-handed tensor interaction.