We present the results of a multimethodological study aimed at investigating the interaction between graphene and tritium during its $\beta$-decay to helium, under different levels of loading and geometrical configurations. We combine density-functional theory (DFT) to evaluate the interaction potentials, with calculations of the decay rate, in order to study the consequences that the presence of the substrate has on the $\beta$-decay spectrum of tritium. We determine the shape of the event rate, accounting for the effects of (part of) the corresponding condensed-matter degrees of freedom. In the context of future neutrino experiments, our results provide important information aimed at the optimization of hosting material. Furthermore, our work outlines a novel theoretical and computational scheme to account for the different timescales involved in the process and to address a question at the boundary between high- and low-energy physics. This requires nonconventional declinations of DFT combined with full quantum treatments of the nuclear configuration involved in the decay process. Our results pave the way for future studies aimed at determining the physics reach of upcoming neutrino mass experiments.

The dinuclear system model incorporates several essential input physical quantities, including nuclear mass, fission barrier, shell correction energy, level density parameter, shell damping factor, etc., which are derived from diverse nuclear structure models. To achieve theoretical consistency, we try to generate these essential input physical quantities from the finite-temperature covariant density functional theory using the PC-PK1 energy density functional, with pairing correlations treated via the BCS approach. With microscopically determined input parameters, the dinuclear system model can successfully reproduce experimental results for (i) cold fusion reaction systems (${}^{48}\mathrm{Ca}+{}^{204,206–208}\mathrm{Pb}\to {}^{252,254–256}\mathrm{No}^{*}$) and (ii) hot fusion reaction systems (${}^{48}\mathrm{Ca} + {}^{239,240,242,244}\mathrm{Pu} \to {}^{287,288,290,292}\mathrm{Fl}^{*}$). Furthermore, we perform calculations for the fusion reactions ${}^{50}\mathrm{Ti}+{}^{249}\mathrm{Cf}, {}^{51}\mathrm{V}+{}^{249}\mathrm{Bk}, {}^{54}\mathrm{Cr}+{}^{248}\mathrm{Cm}$, and ${}^{55}\mathrm{Mn}+{}^{243}\mathrm{Am}$, targeting the synthesis of element 120. It is found that the maximum synthesis cross sections for these four reactions are 48.20, 12.33, 5.25, and 0.47 fb corresponding to ${}^{50}\mathrm{Ti}({}^{249}\mathrm{Cf},4n$)${}^{295}120$ at $E_{\mathrm{CN}}^{*}$ = 41 MeV, ${}^{51}\mathrm{V}({}^{249}\mathrm{Bk},3n$)${}^{297}120$ at $E_{\mathrm{CN}}^{*}$ = 34 MeV, ${}^{54}\mathrm{Cr}({}^{248}\mathrm{Cm},3n$)${}^{299}120$ at $E_{\mathrm{CN}}^{*}$ = 32 MeV, and ${}^{55}\mathrm{Mn}({}^{243}\mathrm{Am},5n$)${}^{293}120$ at $E_{\mathrm{CN}}^{*}$ = 53 MeV, respectively.

High-order perturbative ab initio calculations are challenging due to the rapidly growing configuration space and the difficulty of assessing convergence. In this letter, we introduce perturbation theory quantum Monte Carlo (PTQMC), a stochastic approach designed to compute high-order many-body perturbative corrections. By representing the perturbative wave function with random walkers in configuration space, PTQMC avoids the exponential scaling inherent to conventional constructions of high-rank excitation operators. Benchmark calculations for the Richardson pairing model demonstrate that PTQMC accurately reproduces exact many-body perturbation theory (MBPT) coefficients up to 16th order, even in strongly divergent regimes. We further show that combining PTQMC with series resummation techniques yields stable and precise energy estimates in cases where the straightforward perturbative series fails. Finally, we propose the effective number of configurations, $e^S$, as a global measure of perturbative wave-function complexity that can be directly extracted within PTQMC. We demonstrate that the saturation behavior of $e^S$ provides a more reliable indicator of the validity of perturbative expansions than energy convergence alone.

The cryogenic approach to the search for the neutron electric dipole moment—performing the experiment in superfluid liquid helium—holds promise for a substantial increase in sensitivity, potentially enabling a sensitivity level of ${10}^{-28}$ $e\mathrm{cm}$. A crucial component in realizing such an experiment is the high-voltage and electrode system capable of providing an electric field of 75 kV/cm. This, in turn, requires an electric potential of 635 kV to be applied to the high-voltage electrode, while simultaneously satisfying other experimental constraints, such as those on heat load and magnetic noise requirements. This paper describes the outcome of a comprehensive development program addressing these challenges. It outlines the system requirements, discusses new insights into relevant physical phenomena, and details selected technical solutions with their corresponding experimental demonstrations and expected performance. The results collectively demonstrate the successful development of the necessary technology for the high-voltage and electrode system for this approach.

Radiative strength functions (RSFs) model the bulk electromagnetic response of highly excited nuclei and are critical inputs for statistical reaction codes. In this paper, we present a definition of the RSF that is consistent with Hauser-Feshbach reaction codes and that can be efficiently computed with the shell model using the Lanczos strength-function (LSF) method. We introduce a variant of the shell-model LSF method that exploits the energy-localized Brink-Axel hypothesis, which makes it possible to compute both electric and magnetic RSFs across all energies relevant to capture reactions. We verify agreement with the conventional definition of RSFs with benchmark calculations of ${}^{24}\mathrm{Mg}$ and then present novel results for ${}^{56}\mathrm{Fe}$. For ${}^{56}\mathrm{Fe}$ we find that (i) the $M1$ RSF shape evolves smoothly with excitation energy, consistent with the energy-localized Brink-Axel hypothesis; (ii) both $M1$ and $E1$ transitions contribute significantly to the radiative strength below the photoabsorption threshold; and (iii) within the sdpf model space, the strength below 3 MeV observed in Oslo-type experiments cannot be fully reproduced. These results pave the way for a coherent microscopic description of RSFs and further motivate the use of energy-dependent RSFs in modern reaction codes.

We present a microscopic triaxial quadrupole-octupole collective Hamiltonian (TQOCH) that unifies collective rotations, quadrupole-octupole vibrations, and their couplings to model low-lying nuclear states of both parities. The TQOCH's dynamics are governed by collective parameters derived from multidimensionally constrained covariant density functional theory. The model's validity is demonstrated through calculations of ${}^{152}\mathrm{Sm}$, including its deformation energy surfaces, excitation spectra, and transition probabilities. As a predictive tool, the TQOCH probes complex nuclear phenomena like shape coexistence and phase transitions, directly connecting their microscopic origins to spectroscopic observables.

We report on high-precision mass measurements of the ground and first isomeric state of ${}^{75}\mathrm{Zn}$, performed using the time-of-flight ion-cyclotron-resonance technique at the ISOLTRAP Penning-trap mass spectrometer at ISOLDE/CERN. The isomeric state was produced using in-trap decay of ${}^{75}\mathrm{Cu}$. This marks the first direct investigation of the isomeric state of ${}^{75}\mathrm{Zn}$ via mass spectrometry. The isomer was observed at an excitation energy of $123.7\left(20\right)\mathrm{keV}$, in $2\sigma$ agreement with the value previously determined through decay spectroscopy. In addition, our measurements correct a misassignment of the ground-state mass excess based on a previous measurement by Baruah et al., revising the value to $-62681.0\left(21\right)\mathrm{keV}$. To further investigate the earlier discrepancy, we explored the spin-parity assignments of the ground and isomeric states in ${}^{75}\mathrm{Zn}$ using Skyrme Hartree-Fock plus Bardeen-Cooper-Schrieffer theoretical calculations, given the absence of definitive experimental data. In light of the laser spectroscopy results from Wraith et al., our results add strong evidence for a spin-1/2 ground state, which would agree with large-scale shell-model predictions as well as explaining disagreements with the Monte Carlo shell model.

Motivated by recent findings on the separability of optical potentials that are derived from folding off-shell densities with off-shell nucleon-nucleon amplitudes, we study the off-shell character of one-body density matrices created within the no-core shell model. Concentrating on nuclei with a $0^{+}$ ground state from ${}^4\mathrm{He}$ through ${}^{48}\mathrm{Ca}$, we investigate the off-shell character of their one-body density matrices in momentum space when using the momentum transfer and the average momentum as variables. A singular value decomposition of the one-body density matrices reveals that they can be characterized by only very few terms, depending on the mass number of the nucleus. These findings are independent of the nucleon-nucleon interactions employed, as well as of computational specifics, such as grid spacing and size of the model space.

Background: Physics-based emulators offer a fast and reliable replacement for an exact solution of the scattering problem in nuclear physics. Previous work developed a reduced-basis single channel emulator for nonaffine projectile-target interactions, such as optical potentials, to describe elastic scattering.

Purpose: Since many reactions of interest can be cast as a coupled-channel problem, the purpose of this work is to extend the reduced basis methods (RBM) to a coupled-channel framework.

Method: We generalize the reduced basis method to coupled-channel equations (CC-RBM) to describe inelastic scattering. Although our framework is general, in this work we apply it to reactions where the Hamiltonian coupling term comes from assuming a rotational structure model for the target. From a set of training coupled-channel wave functions, we perform a singular value decomposition to obtain a reduced set of basis wave functions, and then solve the extended (Petrov-)Galerkin equations in that basis. In addition, the empirical interpolation method is used to expand the nonaffine coupling potentials.

Results: We apply the CC-RBM method to elastic and inelastic scattering of neutrons on ${}^{48}\mathrm{Ca}$ including a quadrupole coupling to populate the first $2^{+}$ state, and neutrons on ${}^{208}\mathrm{Pb}$, including an octupole coupling to populate its first $3^{-}$ state. We demonstrate that the CC-RBM calculated elastic and inelastic cross sections match those obtained using traditional finite-difference (high-fidelity) methods. We show that the CC-RBM results can reliably reproduce the nuclear scattering cross sections at different energy regimes.

Conclusions: The computational accuracy versus time plots demonstrate that the CC-RBM method efficiently increases precision with increasing basis size. Most importantly, for the precisions required in reaction calculations (a percent on the cross section), we find the CC-RBM method offers roughly 1.5 orders of magnitude gain in computational speed compared to the traditional coupled-channels solver. However, we also discuss how this scaling becomes less favorable, the larger the number of channels included in the original coupled-channel set.

Exploring the reaction mechanisms responsible for the production of neutron-rich nuclides, we undertook a systematic study of the momentum distributions of projectile-like fragments from peripheral collisions of ${}^{86}\mathrm{Kr}$ at 15 MeV/nucleon with ${}^{64}\mathrm{Ni}$ and ${}^{124}\mathrm{Sn}$. For this purpose, our previous data collected with the momentum achromat recoil separator (MARS) at the Cyclotron Institute of Texas A&M were adopted. The momentum per nucleon ($p/A$) distributions of the ejectiles are characterized by a quasi-elastic peak just below the projectile velocity and a region at lower velocities corresponding to dissipative events. Two-body kinematics was employed to extract the total excitation energies of these regions. It was found that very neutron-rich isotopes can be probed in these reactions, especially with the heavier target via processes involving proton removal, neutron pickup, or a combination of these, up to a triple charge exchange process observed in the data. The experimental data were systematically compared with calculations employing the deep-inelastic transfer (DIT) model and the constrained molecular dynamics (CoMD) model followed by the GEMINI deexcitation code. The DIT model, phenomenologically treating the sequential exchange of nucleons, offered an overall qualitative description of the experimental momentum distributions, however underestimating the data in the quasielastic part of most of the channels. The CoMD model, based on a fully microscopic $N$-body approach, offered an overall better description of the majority of the data, whereas, in some cases, it led to overestimation of the quasielastic part of the momentum distributions. The detailed comparison of the model calculations with the experimental data provided valuable insight into the reaction mechanisms in this energy regime, suggesting, apart from independent nucleon exchange, the contribution of target inelastic excitation and direct reaction processes involving neutron and proton pair transfer, cluster transfer, and meson-mediated charge exchange. This work paves the way to a systematic investigation of the mechanisms of multinucleon transfer reactions involving medium-mass heavy ions below the Fermi energy and provides guidance for the production of exotic neutron-rich nuclei.

We solve the nuclear two-body and three-body bound states via quantum simulations of pionless effective field theory on a lattice in position space. While the employed lattice remains small, the usage of local Hamiltonians including two- and three-body forces ensures that the number of Pauli terms scales linearly with increasing numbers of lattice sites. We use an adaptive ansatz grown from unitary coupled cluster theory to parametrize the ground states of the deuteron and ${}^3\mathrm{He}$, compute their corresponding energies, and analyze the scaling of the required computational resources. Our quantum simulations reproduce exact benchmarks for ${}^2\mathrm{H}$ and ${}^3\mathrm{He}$ within 100 keV, requiring at most 30 layers in the ansatz and thus resulting in modest circuit depths. Additionally, we find the number of shots required to reach a given precision scales linearly in the lattice size and more mildly in the system size. Based on the agreement with exact benchmarks and mild scaling, we conclude that this can be an efficient, scalable approach for quantum computations of nuclear ground states, particularly to prepare initial states for quantum phase estimation or other filtering algorithms.

Using $(1.0087\pm 0.0044)\times {10}^{10} J/\psi$ events collected with the BESIII detector at the BEPCII storage ring, the reactions ${\mathrm{\Sigma }}^{+}n\to \mathrm{\Lambda }p$ and ${\mathrm{\Sigma }}^{+}n\to {\mathrm{\Sigma }}^{0}p$ are studied, where the ${\mathrm{\Sigma }}^{+}$ baryon is produced in the process $J/\psi \to {\mathrm{\Sigma }}^{+}{\overline{\mathrm{\Sigma }}}^{-}$ and the neutron is a component of the ${}^9\mathrm{Be}, {}^{12}\mathrm{C}$, and ${}^{197}\mathrm{Au}$ nuclei in the beam pipe. Clear signals of these two reactions are observed for the first time. Their cross sections are measured to be $\sigma ({\mathrm{\Sigma }}^{+}+{}^9\mathrm{Be}\to \mathrm{\Lambda }+p+X)=(45.2\pm 12.1_{\mathrm{stat}}\pm 7.2_{\mathrm{sys}})$ mb and $\sigma ({\mathrm{\Sigma }}^{+}+{}^9\mathrm{Be}\to {\mathrm{\Sigma }}^0+p+X)=(29.8\pm 9.7_{\mathrm{stat}}\pm 6.9_{\mathrm{sys}})$ mb for a ${\mathrm{\Sigma }}^{+}$ average momentum of $0.992\mathrm{GeV}/c$, within a range of $\pm 0.015\mathrm{GeV}/c$, where $X$ represents the residual nucleus. This is the first study of ${\mathrm{\Sigma }}^{+}$-nucleon scattering at an electron-positron collider. The measured results serve as a significant element in enhancing the comprehensive understanding of hyperon-nucleon interactions, and also constitute an important factor in resolving the “hyperon puzzle” of neutron stars.

We perform a high-statistics lattice QCD calculation of the low-energy two-nucleon scattering amplitudes. To address discrepancies in the literature, the calculation is performed at a heavy pion mass in the limit that the light quark masses are equal to the physical strange quark mass, $m_{\pi }=m_K\simeq 714\mathrm{MeV}$. Using a state-of-the-art momentum space method, we rule out the presence of a bound di-nucleon in both the isospin 0 (deuteron) and 1 (di-neutron) channels, in contrast with many previous results that made use of compact hexaquark creation operators. To diagnose the discrepancy, we add such hexaquark interpolating operators to our basis and find that they do not affect the determination of the two-nucleon finite-volume spectrum, and thus they do not couple to deeply bound di-nucleons that are missed by the momentum-space operators. Furthermore, we perform a high-statistics calculation of the HAL QCD potential on the same gauge ensembles and find qualitative agreement with our main results. We conclude that di-nucleons do not form bound states at heavy pion masses and that previous identification of deeply bound di-nucleons must have arisen from a misidentification of the spectrum from off-diagonal elements of a correlation function.

We formulate a renormalizable pionless effective field theory ($\cancel{\pi }\mathrm{EFT}$) with a nonperturbative treatment of the Coulomb interaction up to next-to-leading order (NLO) for few-nucleon systems. We extract scattering observables for charged clusters by employing two-, three-, and four-body contact interactions and using the stochastic variational method with a Coulomb-corrected harmonic oscillator trap. Our NLO results yield a $pd$ spin-quartet scattering length and effective range of $a_{pd}^{3/2}=12.76\left(29\right)\mathrm{fm}$ and $r_{pd}^{3/2}=1.17\left(7\right)\mathrm{fm}$; for $dd$ scattering in the spin-quintet channel we find $a_{dd}^2=6.26\left(3\right)\mathrm{fm}$ and $r_{dd}^2=1.41\left(7\right)\mathrm{fm}$; and for $p^3\mathrm{He}$ scattering the spin-singlet and spin-triplet channels are characterized by $a_{p^3\mathrm{He}}^0=11.26\left(4\right)\mathrm{fm}, r_{p^3\mathrm{He}}^0=1.65\left(26\right)\mathrm{fm}$ and $a_{p^3\mathrm{He}}^1=9.06\left(4\right)\mathrm{fm}, r_{p^3\mathrm{He}}^1=1.36\left(25\right)\mathrm{fm}$, respectively. Our predictions exhibit mild cutoff dependence and agree well with existing experimental phase shift analyses and potential model calculations. This demonstrates the predictive power of $\cancel{\pi }\mathrm{EFT}$ for charged few-nucleon systems.

Benchmarking simulation codes for electron transport and scattering in matter is a crucial step for estimating uncertainties in many applications. However, experimental data for electron energies of a few MeV are too scarce to make such comparisons. We report here the measurement and the quantitative analysis of backscattering probabilities of electrons in the energy range 0.1 to 3.4 MeV impinging on a Ce-doped ${\mathrm{YAlO}}^3$ (YAP:Ce) scintillator. The setup consists of a $2\times 2\pi$ calorimeter which enables, in particular, the inclusion of large incidence angles. The results are used to benchmark various scattering models incorporated in Geant4, showing relative deviations smaller than 5% between experiment and simulations. They demonstrate the current rather high reliability of the simulations when employing appropriate electromagnetic physics lists.

The ${}^{12}\mathrm{C}(\alpha ,\gamma ){}^{16}\mathrm{O}$ reaction governs the carbon-to-oxygen ratio set during helium burning, shaping white-dwarf structure and Type Ia supernova yields. At the astrophysical energy $E\approx 300\mathrm{keV}$, the cross section is controlled by the subthreshold $1^{-}$ (7.12 MeV) and $2^{+}$ (6.92 MeV) states, whose contributions depend on their asymptotic normalization coefficients (ANCs) $C_1$ and $C_2$, respectively. I perform a Bayesian analysis of the $S_{E1}$ and $S_{E2}$ factors using calibrated $R$-matrix mappings and contemporary ANC constraints for the $1^{-}, 2^{+}$, and $0^{+}$ ground state. For $S_{E1}$, a flat prior on the $1^{-}$ ANC yields a broad posterior (MAP $\approx 95.5\mathrm{keV}\mathrm{b}$), while Gaussian priors centered at the low and high anchors produce narrower posteriors with MAPs $\approx 75.4$ and $\approx 93.2\mathrm{keV}\mathrm{b}$, respectively. For $S_{E2}$, I employ a calibrated quadratic map in $(C_2,C_0)$ that captures the interference between the subthreshold $2^{+}$ capture and the external direct capture; the resulting posteriors reflect how the joint $(C_2,C_0)$ posterior loads the interference corridor. The resulting $S\left(300\mathrm{keV}\right)$ range is consistent with stellar-evolution models that produce low-spin, high-mass ($\approx 50-70M_{\odot }$) black holes. Overall, the Bayesian framework yields statistically robust posteriors for $S_{E1}$ and $S_{E2}$, quantifying correlations and uncertainties relevant for stellar modeling. This work links the microscopic subthreshold ANCs ($C_1,C_2,C_0$) to a macroscopic astrophysical outcome—the formation of massive, low-spin black holes—thereby connecting nuclear reaction experiments and theory with stellar evolution, black-hole demographics, and gravitational-wave observations.

Within nuclear density-functional theory, we calculated spectroscopic magnetic-dipole and electric-quadrupole moments for various quasiparticle configurations of odd-$N$, even-$Z, 83\le N\le 125$ nuclei ranging from gadolinium to osmium. By tagging the blocked quasiparticles with single-particle states of the semimagic dysprosium isotope, we efficiently computed 22 prolate and 22 oblate states for each of the 154 nuclei and tracked them across the entire major neutron shell. We compared this extensive set of theoretical results with experimental data for 82 states in the region. Breaking rotational, time-reversal, and signature symmetries, we aligned the intrinsic angular momenta along the axis of axial symmetry, thereby enabling full shape- and spin-self-consistent polarizations. The spectroscopic moments were then obtained by restoring rotational symmetry. We conducted a detailed analysis of the pattern of agreement and disagreement between theory and experiment in individual nuclei. For the magnetic-dipole moments, agreement with the data varies and is characterized by an overall average and rms deviation of $0.11{\mu }_N$ and $0.35{\mu }_N$, respectively. For the electric-quadrupole moments, a good corresponding agreement of 0.16 and 0.29 b was observed.

We study the evolution of fission modes across the Th isotopic chain using a microscopic framework combining the time-dependent generator coordinate method and finite-temperature covariant density-functional theory. Theoretical fission-fragment charge distributions agree well with experiments, and reveal a rapid symmetric-to-asymmetric transition from $A=222$ to 234. By analyzing the collective potential-energy surfaces and time evolution of collective probability density distributions, we demonstrate that this fission mode transition is strongly correlated with the rapidly deepening asymmetric fission valley—a phenomenon driven by the reduction of deformation energies of both the heavy and light fragments formed in the asymmetric fission valley. Further analysis attributes the decrease of light-fragment deformation energies to the onset of a coexisting large-deformed minimum in neutron-rich Kr and Sr isotopes (the dominant isotopes for light asymmetric peak), which arises from a deformed proton $Z=38$ shell closure near ${\beta }_2\approx 0.46$. Notably, we identify, for the first time, the pivotal role of the light fragment and its shape coexistence structure on the fission mode transition in Th isotopes in a fully microscopic framework.

The problem of the two-body nature of the mechanism in multinucleon transfer (MNT) process is very important, especially when it comes to the production of unknown isotopes. In this work, we conduct a comprehensive study on the correlations of multiple physical quantities in the MNT reaction ${}^{238}\mathrm{U} + {}^{238}\mathrm{U}$: colliding energy, kinetic energies of emitting fragments, impact parameter, proton/neutron transfer number, and scattering angle. Based on our discovered correlation behaviors, the emission properties of the ${}^{244}\mathrm{U}$ fragment are emphasized, which would contribute significantly to the production of the actinide nuclei near shell closure $N=152$.

Located just one neutron removed from doubly magic, stable ${}^{48}\mathrm{Ca}$, the adjacent isotope ${}^{47}\mathrm{Ca}$ has been studied extensively with neutron-removing transfer reactions and interpreted within a shell-model picture. Neutron-adding transfer reactions onto the stable ${}^{46}\mathrm{Ca}$, however, have not been performed in nearly 60 years and never with the aid of high-resolution $\gamma$-ray spectroscopy. Here, we report on the ${}^{12}\mathrm{C}({}^{46}\mathrm{Ca},{}^{47}\mathrm{Ca}+\gamma )X$ one-neutron pickup reaction from ${}^{12}\mathrm{C}$ onto ${}^{46}\mathrm{Ca}$ at more than 50 MeV/nucleon, a regime of orbital angular momentum mismatch that selectively populates ${}^{47}\mathrm{Ca}$ final states based on $\ell \ge 3$ neutron configurations. Newly observed excited states and $\gamma$-ray transitions are discussed in comparison to $fp$ shell-model calculations in a variety of configuration spaces. It is shown that the nature of the observed spectrum of final states can be well interpreted, albeit with a significant fragmentation of the $\nu 0f_{5/2}$ strength observed in the measurement that is not borne out in the structure calculations.