We demonstrate a new technique for obtaining fission data for nuclei away from $\beta$ stability. These types of data are pertinent to the astrophysical $r$ process, crucial to a complete understanding of the origin of the heavy elements, and for developing a predictive model of fission. These data are also important considerations for terrestrial applications related to power generation and safeguarding. Experimentally, such data are scarce due to the difficulties in producing the actinide targets of interest. The solenoidal-spectrometer technique, commonly used to study nucleon-transfer reactions in inverse kinematics, has been applied to the case of transfer-induced fission as a means to deduce the fission-barrier height, among other variables. The fission-barrier height of ${}^{239}\mathrm{U}$ has been determined via the ${}^{238}\mathrm{U}(d,pf)$ reaction in inverse kinematics, the results of which are consistent with existing neutron-induced fission data indicating the validity of the technique.

We report the triton ($t$) production in midrapidity ($|y|<0.5$) $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=7.7–200\mathrm{GeV}$ measured by the STAR experiment from the first phase of the beam energy scan at the Relativistic Heavy Ion Collider. The nuclear compound yield ratio ($N_t\times N_p/N_d^2$), which is predicted to be sensitive to the fluctuation of local neutron density, is observed to decrease monotonically with increasing charged-particle multiplicity ($d{N}_{ch}/d\eta$) and follows a scaling behavior. The $d{N}_{ch}/d\eta$ dependence of the yield ratio is compared to calculations from coalescence and thermal models. Enhancements in the yield ratios relative to the coalescence baseline are observed in the 0%-10% most central collisions at 19.6 and 27 GeV, with a significance of $2.3\sigma$ and $3.4\sigma$, respectively, giving a combined significance of $4.1\sigma$. The enhancements are not observed in peripheral collisions or model calculations without critical fluctuation, and decreases with a smaller $p_T$ acceptance. The physics implications of these results on the QCD phase structure and the production mechanism of light nuclei in heavy-ion collisions are discussed.

We present the first measurement of the $\alpha \text{−}\beta \text{−}\nu$ angular correlation in the Gamow-Teller ${\beta }^{+}$ decay of ${}^8\mathrm{B}$. This was accomplished using the Beta-decay Paul Trap, expanding on our previous work on the ${\beta }^{-}$ decay of ${}^8\mathrm{Li}$. The ${}^8\mathrm{B}$ result is consistent with the $V\text{−}A$ electroweak interaction of the standard model and, on its own, provides a limit on the exotic right-handed tensor current relative to the axial-vector current of $|C_T/C_A{|}^2<0.013$ at the 95.5% confidence level. This represents the first high-precision angular correlation measurements in mirror decays and was made possible through the use of an ion trap. By combining this ${}^8\mathrm{B}$ result with our previous ${}^8\mathrm{Li}$ results, we demonstrate a new pathway for increased precision in searches for exotic currents.

Using a novel method of isochronous mass spectrometry, the masses of ${}^{62}\mathrm{Ge}$, ${}^{64}\mathrm{As}$, ${}^{66}\mathrm{Se}$, and ${}^{70}\mathrm{Kr}$ are measured for the first time, and the masses of ${}^{58}\mathrm{Zn}$, ${}^{61}\mathrm{Ga}$, ${}^{63}\mathrm{Ge}$, ${}^{65}\mathrm{As}$, ${}^{67}\mathrm{Se}$, ${}^{71}\mathrm{Kr}$, and ${}^{75}\mathrm{Sr}$ are redetermined with improved accuracy. The new masses allow us to derive residual proton-neutron interactions ($\delta V_{pn}$) in the $N=Z$ nuclei, which are found to decrease (increase) with increasing mass $A$ for even-even (odd-odd) nuclei beyond $Z=28$. This bifurcation of $\delta V_{pn}$ cannot be reproduced by the available mass models, nor is it consistent with expectations of a pseudo-SU(4) symmetry restoration in the $fp$ shell. We performed ab initio calculations with a chiral three-nucleon force (3NF) included, which indicate the enhancement of the $T=1$ $pn$ pairing over the $T=0$ $pn$ pairing in this mass region, leading to the opposite evolving trends of $\delta V_{pn}$ in even-even and odd-odd nuclei.

We predict heavy quark production cross sections in deep inelastic scattering at high energy by applying the color glass condensate effective theory. We demonstrate that, when the calculation is performed consistently at next-to-leading order accuracy with massive quarks, it becomes possible, for the first time in the dipole picture with perturbatively calculated center-of-mass energy evolution, to simultaneously describe both the light and heavy quark production data at small $x_{\mathrm{Bj}}$. Furthermore, we show how the heavy quark cross section data provides additional strong constraints on the extracted nonperturbative initial condition for the small-$x_{\mathrm{Bj}}$ evolution equations.

We report on the first proton-induced single proton- and neutron-removal reactions from the neutron-deficient ${}^{14}\mathrm{O}$ nucleus with large Fermi-surface asymmetry $S_n-S_p=18.6\mathrm{MeV}$ at $\sim 100\mathrm{MeV}/\text{nucleon}$, a widely used energy regime for rare-isotope studies. The measured inclusive cross sections and parallel momentum distributions of the ${}^{13}\mathrm{N}$ and ${}^{13}\mathrm{O}$ residues are compared to the state-of-the-art reaction models, with nuclear structure inputs from many-body shell-model calculations. Our results provide the first quantitative contributions of multiple reaction mechanisms including the quasifree knockout, inelastic scattering, and nucleon transfer processes. It is shown that the inelastic scattering and nucleon transfer, usually neglected at such energy regime, contribute about 50% and 30% to the loosely bound proton and deeply bound neutron removal, respectively. These multiple reaction mechanisms should be considered in analyses of inclusive one-nucleon removal cross sections measured at intermediate energies for quantitative investigation of single-particle strengths and correlations in atomic nuclei.

We propose a general approach to freezing out fluctuations in heavy-ion collisions using the principle of maximum entropy. We find the results naturally expressed as a direct relationship between the irreducible relative correlators quantifying the deviations of hydrodynamic as well as hadron gas fluctuations from the ideal hadron gas baseline. The method also allows us to determine heretofore unknown parameters crucial for the freeze-out of fluctuations near the QCD critical point in terms of the QCD equation of state.

We simulate the space-time dynamics of high-energy collisions based on a microscopic kinetic description in the conformal relaxation time approximation, in order to determine the range of applicability of an effective description in relativistic viscous hydrodynamics. We find that hydrodynamics provides a quantitatively accurate description of collective flow when the average inverse Reynolds number ${\mathrm{Re}}^{-1}$ is sufficiently small and the early preequilibrium stage is properly accounted for. We further discuss the implications of our findings for the (in)applicability of hydrodynamics in proton-proton, proton-nucleus, and light nucleus collisions.

We analyze the recoil corrections in superallowed beta decays of $T=1$, $J^P=0^{+}$ nuclei by fixing the mean square charged weak radius model independently using the data of multiple charge radii across the nuclear isotriplet. By comparing to model estimations, we argue that the existing theory uncertainty in the statistical rate function $f$ might have been substantially underestimated. We discuss the implications of our proposed strategy for precision tests of the standard model, including a potential alleviation of the first-row CKM unitarity deficit, and motivate new experiments for charge radii measurements.

We report results of $\mathrm{\Lambda }$ hyperon production in semi-inclusive deep-inelastic scattering off deuterium, carbon, iron, and lead targets obtained with the CLAS detector and the Continuous Electron Beam Accelerator Facility 5.014 GeV electron beam. These results represent the first measurements of the $\mathrm{\Lambda }$ multiplicity ratio and transverse momentum broadening as a function of the energy fraction ($z$) in the current and target fragmentation regions. The multiplicity ratio exhibits a strong suppression at high $z$ and an enhancement at low $z$. The measured transverse momentum broadening is an order of magnitude greater than that seen for light mesons. This indicates that the propagating entity interacts very strongly with the nuclear medium, which suggests that propagation of diquark configurations in the nuclear medium takes place at least part of the time, even at high $z$. The trends of these results are qualitatively described by the Giessen Boltzmann-Uehling-Uhlenbeck transport model, particularly for the multiplicity ratios. These observations will potentially open a new era of studies of the structure of the nucleon as well as of strange baryons.

Experimental studies of nuclear fission induced by fusion, transfer, spallation, fragmentation, and electromagnetic reactions in combination with state-of-the-art calculations are successful to investigate the nuclear dissipation mechanism in normal nuclear matter, containing only nucleons. The dissipation mechanism has been widely studied by the use of many different fission observables and nowadays the dissipation coefficients involved in transport theories are well constrained. However, the existence of hypernuclei and the possible presence of hyperons in neutron stars make it necessary to extend the investigation of the nuclear dissipation coefficient to the strangeness sector. In this Letter, we use fission reactions of hypernuclei to constrain for the first time the dissipation coefficient in hypernuclear matter, observing that this coefficient increases a factor of 6 in the presence of a single $\mathrm{\Lambda }$ hyperon with respect to normal nuclear matter.

The excited states of $N=44$ ${}^{74}\mathrm{Zn}$ were investigated via $\gamma$-ray spectroscopy following ${}^{74}\mathrm{Cu}$ $\beta$ decay. By exploiting $\gamma \text{−}\gamma$ angular correlation analysis, the $2_2^{+}$, $3_1^{+}$, $0_2^{+}$, and $2_3^{+}$ states in ${}^{74}\mathrm{Zn}$ were firmly established. The $\gamma$-ray branching and $E2/M1$ mixing ratios for transitions deexciting the $2_2^{+}$, $3_1^{+}$, and $2_3^{+}$ states were measured, allowing for the extraction of relative $B(E2)$ values. In particular, the $2_3^{+}\to 0_2^{+}$ and $2_3^{+}\to 4_1^{+}$ transitions were observed for the first time. The results show excellent agreement with new microscopic large-scale shell-model calculations, and are discussed in terms of underlying shapes, as well as the role of neutron excitations across the $N=40$ gap. Enhanced axial shape asymmetry (triaxiality) is suggested to characterize ${}^{74}\mathrm{Zn}$ in its ground state. Furthermore, an excited $K=0$ band with a significantly larger softness in its shape is identified. A shore of the $N=40$ “island of inversion” appears to manifest above $Z=26$, previously thought as its northern limit in the chart of the nuclides.

We present a theoretical study of the processes $d(d,p){}^3\mathrm{H}$ and $d(d,n){}^3\mathrm{He}$ at energies of interest for energy production and for big-bang nucleosynthesis. We accurately solve the four body scattering problem using the ab initio hyperspherical harmonics method, starting from nuclear Hamiltonians which include modern two- and three-nucleon interactions, derived in chiral effective field theory. We report results for the astrophysical $S$ factor, the quintet suppression factor, and various single and double polarized observables. A first estimate of the theoretical uncertainty for all these quantities is provided by varying the cutoff parameter used to regularize the chiral interactions at high momentum.

We consider theoretically isomeric excitation of ${}^{229}\mathrm{Th}$ in a laser-heated cluster. A ${}^{229}\mathrm{Th}$ cluster is first radiated by an intense femtosecond laser pulse, causing ionization of the constituting atoms. The cluster will then survive for a time on the order of 1 ps, during which the electrons collide with the nuclei repeatedly and excite them to the isomeric state. Two mechanisms are responsible for the isomeric excitation: nuclear excitation by electron capture (NEEC) and nuclear excitation by inelastic electron scattering (NEIES). By changing the laser intensity, one can tune between NEEC and NEIES continuously. This laser-heated-cluster scheme not only provides a highly efficient means for isomeric excitation, but also provides an approach for the confirmation of the NEEC process, which has been predicted for over forty years without conclusive experimental verifications.

We demonstrate that a paradigm shift from considering the deuteron as a system of a bound proton and neutron to that of a pseudovector system in which we observe a proton and neutron results in the possibility of probing a new “incomplete” $P$-statelike structure on the light front (LF). This occurs at extremely large internal momenta, which can be achieved in a high energy transfer electrodisintegration of the deuteron. Investigating the deuteron on the light front, where the vacuum fluctuations are suppressed, we found that this new structure, together with the conventional $S$ and $D$ states, is leading order in transferred energy of the reaction and thus not suppressed on the light front. The incompleteness of the observed $P$ state results in a violation of the angular condition that can happen only if the deuteron contains non-nucleonic structures, such as $\mathrm{\Delta }$ $\mathrm{\Delta }$, $N^{*}N$ or hidden color components. We demonstrate that experimentally verifiable signatures of incomplete $P$ states are angular anisotropy of the light front momentum distribution of the nucleon in the deuteron, as well as an enhancement of the tensor polarization strength beyond the $S$- and $D$-wave predictions at large internal momenta in the deuteron.

Much effort is devoted to measuring the nuclear symmetry energy through neutron star (NS) and nuclear observables. Since matter in the NS core may be nonhadronic, observables like radii and tidal deformability may not provide reliable constraints on properties of nucleonic matter. By performing the first consistent inference using ensembles of core and crust equations of state from astrophysical and nuclear data, we demonstrate that coincident timing of a resonant shattering flare (RSF) and gravitational wave signal during binary NS inspiral probes the crust-core transition region and provides constraints on the symmetry energy comparable to terrestrial nuclear experiments. We show that nuclear masses, RSFs, and measurements of NS radii and tidal deformabilities constrain different density ranges of the equation of state, providing complementary probes.

We report on measurements of sequential $\mathrm{\Upsilon }$ suppression in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$ with the STAR detector at the Relativistic Heavy Ion Collider (RHIC) through both the dielectron and dimuon decay channels. In the 0%–60% centrality class, the nuclear modification factors ($R_{AA}$), which quantify the level of yield suppression in heavy-ion collisions compared to $p+p$ collisions, for $\mathrm{\Upsilon }(1S)$ and $\mathrm{\Upsilon }(2S)$ are $0.40\pm 0.03(\mathrm{stat})\pm 0.03(\mathrm{sys})\pm 0.09(\mathrm{norm})$ and $0.26\pm 0.08(\mathrm{stat})\pm 0.02(\mathrm{sys})\pm 0.06(\mathrm{norm})$, respectively, while the upper limit of the $\mathrm{\Upsilon }(3S)$ $R_{AA}$ is 0.17 at a 95% confidence level. This provides experimental evidence that the $\mathrm{\Upsilon }(3S)$ is significantly more suppressed than the $\mathrm{\Upsilon }(1S)$ at RHIC. The level of suppression for $\mathrm{\Upsilon }(1S)$ is comparable to that observed at the much higher collision energy at the Large Hadron Collider. These results point to the creation of a medium at RHIC whose temperature is sufficiently high to strongly suppress excited $\mathrm{\Upsilon }$ states.