The first complete measurement of the $\beta$-decay strength distribution of ${}_{17}{}^{45}{\mathrm{Cl}}_{28}$ was performed at the Facility for Rare Isotope Beams (FRIB) with the FRIB Decay Station Initiator during the second FRIB experiment. The measurement involved the detection of neutrons and $\gamma$ rays in two focal planes of the FRIB Decay Station Initiator in a single experiment for the first time. This enabled an analytical consistency in extracting the $\beta$-decay strength distribution over the large range of excitation energies, including neutron unbound states. We observe a rapid increase in the $\beta$-decay strength distribution above the neutron separation energy in ${}_{18}{}^{45}{\mathrm{Ar}}_{27}$. This was interpreted to be caused by the transitioning of neutrons into protons excited across the $Z=20$ shell gap. The SDPF-MU interaction with reduced shell gap best reproduced the data. The measurement demonstrates a new approach that is sensitive to the proton shell gap in neutron rich nuclei according to SDPF-MU calculations.

${}^{134}\mathrm{Xe}$ is a candidate isotope for neutrinoless double beta decay ($0\nu \beta \beta$) search. In addition, the two-neutrino case ($2\nu \beta \beta$) allowed by the standard model of particle physics has not yet been observed. With the 656-kg natural xenon in the fiducial volume of the PandaX-4T detector, which contains 10.4% of ${}^{134}\mathrm{Xe}$, and its initial 94.9-day exposure, we have established the most stringent constraints on $2\nu \beta \beta$ and $0\nu \beta \beta$ of ${}^{134}\mathrm{Xe}$ half-lives, with limits of $2.8\times {10}^{22}\mathrm{yr}$ and $3.0\times {10}^{23}\mathrm{yr}$ at 90% confidence level, respectively. The $2\nu \beta \beta$ ($0\nu \beta \beta$) limit surpasses the previously reported best result by a factor of 32 (2.7), highlighting the potential of large monolithic natural xenon detectors for double beta decay searches.

We report the first mass measurement of the proton-halo candidate ${}^{22}\mathrm{Al}$ performed with the low energy beam ion trap facility’s 9.4 T Penning trap mass spectrometer at facility for rare isotope beams. This measurement completes the mass information for the lightest remaining proton-dripline nucleus achievable with Penning traps. ${}^{22}\mathrm{Al}$ has been the subject of recent interest regarding a possible halo structure from the observation of an exceptionally large isospin asymmetry [J. Lee et al., Large isospin asymmetry in Si22/O22 Mirror Gamow-Teller transitions reveals the halo structure of ${}^{22}\mathrm{Al}$, Phys. Rev. Lett. 125, 192503 (2020).]. The measured mass excess value of $\mathrm{ME}=18092.5(3)\mathrm{keV}$, corresponding to an exceptionally small proton separation energy of $S_p=100.4(8)\mathrm{keV}$, is compatible with the suggested halo structure. Our result agrees well with predictions from $sd$-shell USD Hamiltonians. While USD Hamiltonians predict deformation in the ${}^{22}\mathrm{Al}$ ground state with minimal $1s_{1/2}$ occupation in the proton shell, a particle-plus-rotor model in the continuum suggests that a proton halo could form at large quadrupole deformation. These results emphasize the need for a charge radius measurement to conclusively determine the halo nature.

We report on a study of the radiative decay of fission fragments populated via neutronless fission of ${}^{252}\mathrm{Cf}(\mathrm{sf})$. Applying the double-energy method a perfect mass identification is achieved for these rare events. In the specific case of the ${}^{120}\mathrm{Cd}/{}^{132}\mathrm{Sn}$ cold fragmentation, we find that ${}^{132}\mathrm{Sn}$ is produced in its ground state. We can therefore directly measure the excitation energy of the complementary fragment, ${}^{120}\mathrm{Cd}$. The reproduction of the $\gamma$-ray spectrum, measured in coincidence with the neutronless fission events, is sensitive to the angular momentum distribution of the studied primary fragment. The latter estimated using a time-dependent collective Hamiltonian model, allows us to constrain for the first time the deformation (${\beta }_2\simeq 0.4$) of the studied fission fragment at scission. The present work demonstrates the high potential of the understudied neutronless fission channel for extracting detailed information on both fission fragments and process.

A precision measurement of the ${\beta }^{+}$ decay of ${}^8\mathrm{B}$ was performed using the Beta-decay Paul Trap to determine the $\beta \text{−}\nu$ angular correlation coefficient $a_{\beta \nu }$. The experimental results were combined with new ab initio symmetry-adapted no-core shell-model calculations to yield the second-most precise measurement from Gamow-Teller decays, $a_{\beta \nu }=-0.3345\pm 0.0019_{\mathrm{stat}}\pm 0.0021_{\mathrm{syst}}$. This value agrees with the standard model value of $-1/3$ and improves uncertainties in ${}^8\mathrm{B}$ by nearly a factor of 2. By combining results from ${}^8\mathrm{B}$ and ${}^8\mathrm{Li}$, a tight limit on tensor current coupling to right-handed neutrinos was obtained. A recent global evaluation of all other precision $\beta$ decay studies suggested a nonzero value for right-handed neutrino coupling in contradiction with the standard model at just above $3\sigma$. The present results are of comparable sensitivity and do not support this finding.

Neutron dark decays have been suggested as a solution to the discrepancy between bottle and beam experiments, providing a dark matter candidate that can be searched for in halo nuclei. The free neutron in the final state following the decay of ${}^6\mathrm{He}$ into ${}^4\mathrm{He}+n+\chi$ provides an exceptionally clean detection signature when combined with a high efficiency neutron detector. Using a high-intensity ${}^6{\mathrm{He}}^{+}$ beam at Grand Accélérateur National d’Ions Lourds, a search for a coincident neutron signal resulted in an upper limit on a dark decay branching ratio of ${\mathrm{Br}}_{\chi }\le 4.0\times {10}^{-10}$ (95% C.L.). Using the dark neutron decay model proposed originally by Fornal and Grinstein, we translate this into an upper bound on a dark neutron branching ratio of $\mathcal{O}({10}^{-5})$, improving over global constraints by one to several orders of magnitude depending on $m_{\chi }$.

We present a model of cold QCD matter that bridges nuclear and quark matter through the duality relation between quarks and baryons. The baryon number and energy densities are expressed as functionals of either the baryon momentum distribution, $f_{\mathrm{B}}$, or the quark distribution, $f_{\mathrm{Q}}$, which are subject to the constraints on fermions, $0\le f_{\mathrm{B},\mathrm{Q}}\le 1$. The theory is ideal in the sense that the confinement of quarks into baryons is reflected in the duality relation between $f_{\mathrm{Q}}$ and $f_{\mathrm{B}}$, while other possible interactions among quarks and baryons are all neglected. The variational problem with the duality constraints is formulated and we explicitly construct analytic solutions, finding two distinct regimes: a nuclear matter regime at low density and a quarkyonic regime at high density. In the quarkyonic regime, baryons underoccupy states at low momenta but form a momentum shell with $f_{\mathrm{B}}=1$ on top of a quark Fermi sea. Such a theory describes a rapid transition from a soft nuclear equation of state to a stiff quarkyonic equation of state. At this transition, there is a rapid increase in the pressure.

The fraction of ${\chi }_{c1}$ and ${\chi }_{c2}$ decays in the prompt $J/\psi$ yield, $F_{{\chi }_c\to J/\psi }={\sigma }_{{\chi }_c\to J/\psi }/{\sigma }_{J/\psi }$, is measured by the LHCb detector in $p\mathrm{Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=8.16\mathrm{TeV}$. The study covers the forward ($1.5<y^{*}<4.0$) and backward ($-5.0<y^{*}<-2.5$) rapidity regions, where $y^{*}$ is the $J/\psi$ rapidity in the nucleon-nucleon center-of-mass system. Forward and backward rapidity samples correspond to integrated luminosities of $13.6\pm 0.3$ and $20.8\pm 0.5{\mathrm{nb}}^{-1}$, respectively. The result is presented as a function of the $J/\psi$ transverse momentum $p_{\mathrm{T},J/\psi }$ in the range $1<p_{\mathrm{T},J/\psi }<20\mathrm{GeV}/c$. The $F_{{\chi }_c\to J/\psi }$ fraction at forward rapidity is compatible with the LHCb measurement performed in $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$, whereas the result at backward rapidity is $2.4\sigma$ larger than in the forward region for $1<p_{\mathrm{T},J/\psi }<3\mathrm{GeV}/c$. The increase of $F_{{\chi }_c\to J/\psi }$ at low $p_{\mathrm{T},J/\psi }$ at backward rapidity is compatible with the suppression of the $\psi (2S)$ contribution to the prompt $J/\psi$ yield. The lack of in-medium dissociation of ${\chi }_c$ states observed in this study sets an upper limit of 180 MeV on the free energy available in these $p\mathrm{Pb}$ collisions to dissociate or inhibit charmonium state formation.

ATLAS measured the centrality dependence of the dijet yield using $165{\mathrm{nb}}^{-1}$ of $p+\mathrm{Pb}$ data collected at $\sqrt{s_{\mathrm{NN}}}=8.16\mathrm{TeV}$ in 2016. The event centrality, which reflects the $p+\mathrm{Pb}$ impact parameter, is characterized by the total transverse energy registered in the Pb-going side of the forward calorimeter. The central-to-peripheral ratio of the scaled dijet yields, $R_{\mathrm{CP}}$, is evaluated, and the results are presented as a function of variables that reflect the kinematics of the initial hard parton scattering process. The $R_{\mathrm{CP}}$ shows a scaling with the Bjorken $x$ of the parton originating from the proton, $x_p$, while no such trend is observed as a function of $x_{\mathrm{Pb}}$. This analysis provides unique input to understanding the role of small proton spatial configurations in $p+\mathrm{Pb}$ collisions by covering parton momentum fractions from the valence region down to $x_p\sim {10}^{-3}$ and $x_{\mathrm{Pb}}\sim 4\times {10}^{-4}$.

On the basis of revisions of some of the systematic errors, we reanalyzed the electron-antineutrino angular correlation ($a$ coefficient) in free neutron decay inferred from the recoil energy spectrum of the protons which are detected in $4\pi$ by the aSPECT spectrometer. With $a=-0.10402(82)$ the new value differs only marginally from the one published in 2020. The experiment also has sensitivity to $b$, the Fierz interference term. From a correlated $(b,a)$ fit to the proton recoil spectrum, we derive a limit of $b=-0.0098(193)$ which translates into a somewhat improved 90% confidence interval region of $-0.041\le b\le 0.022$ on this hypothetical term. Tighter constraints on $b$ can be set from a combined [shown as superscript ($c$)] analysis of the PERKEO III ($\beta$ asymmetry) and aSPECT measurement which suggests a finite value of $b$ with $b^{(c)}=-0.0181\pm 0.0065$ deviating by $2.82\sigma$ from the standard model.

Three $\mathrm{\Delta }I=1$ bands with the $\pi g_{9/2}\otimes \nu g_{9/2}$ configuration have been identified in ${}_{35}{}^{74}{\mathrm{Br}}_{39}$. Angular distribution, linear polarization, and lifetime measurements were performed to determine the multipolarity, type, mixing ratio, and absolute transition probability of the transitions. By comparing these experimental observations with the corresponding fingerprints and the quantum particle rotor model calculations, the second and third lowest bands are, respectively, suggested as the chiral partner and one-phonon wobbling excitation built on the yrast band. The evidence indicates the first chiral wobbler in nuclei.

This work presents the first Bayesian inference study of the $(3+1)\mathrm{D}$ dynamics of relativistic heavy-ion collisions and quark-gluon plasma viscosities using an event-by-event $(3+1)\mathrm{D}$ $\mathrm{hydrodynamics}+\text{hadronic}$ transport theoretical framework and data from the Relativistic Heavy Ion Collider Beam energy scan program. Robust constraints on initial state nuclear stopping and the baryon chemical potential-dependent shear viscosity of the produced quantum chromodynamic (QCD) matter are obtained. The specific bulk viscosity of the QCD matter is found to exhibit a preferred maximum around $\sqrt{s_{\mathrm{NN}}}=19.6\mathrm{GeV}$. This result allows for the alternative interpretation of a reduction (and/or increase) of the speed of sound relative to that of the employed lattice-QCD based equation of state for net baryon chemical potential ${\mu }_B\sim 0.2(0.4)\mathrm{GeV}$.

We present a parameter-free ab initio calculation of the $\alpha$-particle monopole transition form factor in the framework of nuclear lattice effective field theory. We use a minimal nuclear interaction that was previously used to reproduce the ground state properties of light nuclei, medium-mass nuclei, and neutron matter simultaneously with no more than a few percent error in the energies and charge radii. The results for the monopole transition form factor are in good agreement with recent precision data from Mainz.

The cross section of the ${}^{13}\mathrm{C}(\alpha ,n){}^{16}\mathrm{O}$ reaction is needed for nuclear astrophysics and applications to a precision of 10% or better, yet inconsistencies among 50 years of experimental studies currently lead to an uncertainty of $\approx 15\%$. Using a state-of-the-art neutron detection array, we have performed a high resolution differential cross section study covering a broad energy range. These measurements result in a dramatic improvement in the extrapolation of the cross section to stellar energies potentially reducing the uncertainty to $\approx 5\%$ and resolving long standing discrepancies in higher energy data.

The globular cluster NGC 2419 was the first to exhibit a Mg-K anticorrelation, linked to hydrogen burning at temperatures between 80–260 MK. However, the key K-destroying reaction, ${}^{39}\mathrm{K}(p,\gamma ){}^{40}\mathrm{Ca}$, has a large rate uncertainty in this range. We significantly constrain this rate with a high resolution ${}^{39}\mathrm{K}({}^3\mathrm{He},d){}^{40}\mathrm{Ca}$ study. We resolve the ${\mathrm{E}}_{\mathrm{r}}^{\mathrm{c}.\mathrm{m}.}=154\mathrm{keV}$ resonance in ${}^{39}\mathrm{K}+p$ for the first time, increasing the previous rate by up to a factor 13 and reducing its $1\sigma$ width by up to a factor of 42. Reaction network calculations for NGC 2419 suggest that this could lower temperatures needed to reproduce the Mg-K anticorrelation.

We demonstrate that the well-known 2.6 MeV gamma-ray emission line from thallium-208 could serve as a real-time indicator of astrophysical heavy element production, with both rapid ($r$) and intermediate ($i$) neutron capture processes capable of its synthesis. We consider the $r$ process in a Galactic neutron star merger and show Tl-208 to be detectable from $\sim 12$ hours to $\sim \mathrm{ten}$ days, and again $\sim 1–20\mathrm{years}$ postevent. Detection of Tl-208 represents the only identified prospect for a direct signal of lead production (implying gold synthesis), arguing for the importance of future MeV telescope missions which aim to detect Galactic events but may also be able to reach some nearby galaxies in the Local Group.