Reaction processes in muon catalyzed fusion ($\mu \mathrm{CF}$), ${\left(dt\mu \right)}_{J=v=0}\to \alpha +n+\mu +17.6\mathrm{MeV}$ or ${\left(\alpha \mu \right)}_{nl}+n+17.6\mathrm{MeV}$ in a deuterium-tritium (D-T) mixture were comprehensively studied by Kamimura, Kino, and Yamashita [Phys. Rev. C 107, 034607 (2023)] by solving the $dt\mu \text{−}\alpha n\mu$ coupled channel (CC) Schrödinger equation under a boundary condition where the muonic molecule ${\left(dt\mu \right)}_{J=v=0}$ was set as the initial state and the outgoing wave was in the $\alpha n\mu$ channel. We approximate this CC framework and propose a considerably more tractable model using the $T$-matrix method based on the Lippmann-Schwinger equation. Nuclear interactions adopted in the $T$-matrix model are determined by reproducing the cross section of the reaction $d+t\to \alpha +n+17.6\mathrm{MeV}$ at low energies. The cross section of the strong-coupling rearrangement reaction is presented in a simple closed form based on our new model. This $T$-matrix model has reproduced most of the calculated results on the above $\mu \mathrm{CF}$ reaction reported by Kamimura et al. (2023) and is applicable to other $\mu \mathrm{CF}$ systems such as $\left(dd\mu \right), \left(tt\mu \right), {\left(dt\mu \right)}^{*}, {\left(dd\mu \right)}^{*}$.

Recent discussions about the origin of the so-called gallium anomaly have motivated a remeasurement of the half-life of ${}^{71}\mathrm{Ge}$. We have conducted three separate measurements using dedicated planar Ge detectors—one with ${}^{55}\mathrm{Fe}$ as a standard, one with ${}^{57}\mathrm{Co}$ as a standard, and one standalone ${}^{71}\mathrm{Ge}$ measurement. Our results yield a half-life of $11.468\pm 0.008$ days, which is consistent with, but significantly more precise than, the currently accepted value. With this experiment, the potential explanation of the gallium anomaly being due to an unexpectedly long ${}^{71}\mathrm{Ge}$ half-life has been ruled out, leaving the anomaly's origin as an open question.

Exact solutions to the equations of hydrodynamics provide valuable benchmark tests for numerical hydrodynamic codes and also provide useful insights into the nature of hydrodynamic flow. In this paper, we introduce two novel, closely related exact solutions with nontrivial rapidity dependence which are generalizations of the well-known Gubser flow solution to conformal hydrodynamics. We then use one of our solutions to explore the consequences of choosing between two different criteria for implementing the freeze-out process in fluid dynamical simulations of nuclear collisions: freeze-out at constant temperature vs freeze-out at constant Knudsen number. We find that, employing our exact solution, the differences between these freeze-out criteria are heavily influenced by the presence of strong collective flow. Our results highlight the importance of accurately describing the freeze-out process in collisions with large flow gradients, particularly in small systems.

We report on the first experimental measurements made at a magnetic confinement fusion device of the tritium(T)-tritium(T) reaction $\text{T}+\text{T}\to {}^4\mathrm{He}+2n$ indicating the presence of the intermediate two-body resonant reaction $\text{T}+\text{T}\to {}^5\mathrm{He}+n$. During the second deuterium-tritium campaign (DTE2) at the Joint European Torus, measurements of fusion plasmas with high tritium concentrations, $n_{\text{T}}/(n_{\text{T}}+n_{\text{D}})\approx 0.99$, heated with tritium neutral beam injection, were performed using the neutron time-of-flight (TOF) spectrometer TOFOR. We detect a peak in the neutron emission TOF spectrum consistent with the two-body resonant reaction. The TT neutron emission energy spectrum is modeled using an $R$-matrix framework where the distributions of the most likely model parameters given our experimental TOF data are determined utilizing a Markov chain Monte Carlo approach. We compare our best estimate of the $\text{T}+\text{T}$ neutron emission energy spectrum with results obtained at inertial confinement fusion experiments at the OMEGA facility and find a spectral shape that is consistent with the energy dependency in the neutron spectrum observed at OMEGA.

A new data set for the helicity-dependent differential cross section of the single-meson photoproduction reaction $\gamma p\to p{\pi }^0$ was obtained for the photon energy interval 150–400 MeV. The experiment was performed at the A2 tagged photon facility of the Mainz Microtron MAMI using a circularly polarized photon beam and a longitudinally polarized proton target. The reaction products were detected with the large-acceptance Crystal Ball and TAPS calorimeters covering 97% of the full solid angle. These new results, obtained with a fine energy and polar angle binning, greatly increase both the existing quantity and quality of the data available for this observable. A moment analysis, based on a finite expansion in Legendre polynomials, was applied to these data by using a bootstrap-based fitting method to correctly account for their systematic uncertainties. From the resulting decomposition of the differential cross sections, the $E2/M1$ ratio for the $N\to \mathrm{\Delta }\left(1232\right)$ transition was determined to be $[-2.38\pm 0.16(\mathrm{stat}.+\mathrm{sys}.)\pm 0.10\text{(model)}]\%$. Combining this value with previous results also allowed us to evaluate the most precise available estimate of the $E2/M1$ ratio to be used for all further reference and model comparisons.

We present a comprehensive reevaluation of the $ft$ values in superallowed nuclear $\beta$ decays crucial for the precise determination of $V_{ud}$ and low-energy tests of the electroweak standard model. It consists of the first, fully data-driven analysis of the nuclear $\beta$ decay form factor, that utilizes isospin relations to connect the nuclear charged weak distribution to the measurable charge distributions. This prescription supersedes previous shell-model estimations, and allows for a rigorous quantification of theory uncertainties in $f$ which is absent in the existing literature. Our new evaluation shows an overall downward shift of the central values of $f$ at the level of 0.01%.

Neutron transmission experiments can offer a new type of highly sensitive search for time-reversal invariance violating (TRIV) effects in nucleon-nucleon interactions via the same enhancement mechanism observed for large parity violating (PV) effects in neutron-induced compound nuclear processes. In these compound processes, the TRIV cross section is given as the product of the PV cross section, a spin factor $\kappa$, and a ratio of TRIV and PV matrix elements. We determined $\kappa$ to be $0.59\pm 0.05$ for ${}^{139}\mathrm{La}+n$ using both $(n,\gamma )$ spectroscopy and ($\vec{n}+{}^{139}\overrightarrow{\mathrm{La}}$) transmission. This result quantifies for the first time the high sensitivity of the ${}^{139}\mathrm{La}$ 0.75-eV $p$-wave resonance in a future search for effects of $P$-odd/$T$-odd interactions in ($\vec{n}+{}^{139}\overrightarrow{\mathrm{La}}$) forward transmission.

We calculate the ${}^{16}\mathrm{O}$ spectral function by combining coupled-cluster theory with a Gaussian integral transform and by expanding the integral kernel in terms of Chebyshev polynomials to allow for a quantification of the theoretical uncertainties. We perform an analysis of the spectral function and employ it to predict lepton-nucleus scattering. Our results well describe the ${}^{16}\mathrm{O}$ electron-scattering data in the quasielastic peak for momentum transfers $\left|\mathbf{q}\right|⪆500$ MeV and electron energies up to 1.2 GeV, extending, therefore, the so-called first-principles approach to lepton-nucleus cross sections well into the relativistic regime. To prove the applicability of this method to neutrino-nucleus cross sections, we implement our ${}^{16}\mathrm{O}$ spectral functions in the nuwro Monte Carlo event generator and provide a comparison with recently published T2K neutrino data.

We adapt the proton-neutron finite-amplitude method, which in its original form is an efficient implementation of the Skyrme quasiparticle random phase approximation, to include the coupling of quasiparticles to like-particle phonons. The approach allows us to add beyond-quasiparticle random-phase approximation correlations to computations of Gamow-Teller strength and $\beta$-decay rates in deformed nuclei for the first time. We test the approach in several deformed isotopes for which measured strength distributions are available. The additional correlations dramatically improve agreement with the data, and will lead to improved global $\beta$-decay rates.

Examination of high-resolution, experimental fusion excitation functions for ${}^{16,17,18}\mathrm{O}+{}^{12}\mathrm{C}$ reveals a remarkable irregular behavior that is rooted in the structure of both the colliding nuclei and the quasimolecular composite system. The impact of the $\ell$-dependent fusion barriers is assessed using a time-dependent Hartree-Fock model, viewed as a mean-field reference. Barrier penetrabilities, taken directly from a density-constrained calculation, provide a significantly improved description of the experimental data as compared to the standard Hill-Wheeler approach. The remaining deviations between the parameter-free theoretical mean-field predictions and experimental fusion cross sections are exposed and discussed.

Scattering experiments with three free nucleons in the ingoing channel are extremely challenging in terrestrial laboratories. Recently, the ALICE Collaboration successfully measured the scattering of three protons indirectly, by using the femtoscopy method in high-energy proton-proton collisions at the Large Hadron Collider. In order to establish a connection with current and future measurements of femtoscopic three-particle correlation functions, we analyze the scenarios involving $nnn$ and $ppp$ systems using the hyperspherical adiabatic basis. The correlation function is a convolution of the source function and the corresponding scattering wave function. The finite size of the source allows for the use of the free scattering wave function in most of the adiabatic channels except the lowest ones. The scattering wave function has been computed using two different potential models: ($i$) a spin-dependent Gaussian potential with parameters fixed to reproduce the scattering length and effective range and ($ii$) the Argonne $v_{18}$ nucleon-nucleon interaction. Moreover, in the case of three protons, the Coulomb interaction has been considered in its hypercentral form. The results presented here have to be considered as a first step in the description of three-particle correlation functions using the hyperspherical adiabatic basis, opening the door to the investigation of other systems, such as the $pp\mathrm{\Lambda }$ system. For completeness, the comparison with the measurement by the ALICE Collaboration is shown assuming different values of the source radius.

The astrophysical origin for the chemical elements between the first and second $r$-process peaks is a matter of intense debate, with a number of nucleosynthesis processes at explosive stellar environments possibly contributing to their production. Reliable data on the trends of neutron separation energies of neutron-rich isotopes are required to model neutron-capture processes that would produce these elements. Masses of ${}^{104}\mathrm{Y}$, ${}^{106}\mathrm{Zr}$, ${}^{112}\mathrm{Mo}$, and ${}^{115}\mathrm{Tc}$ have been measured with the time-of-flight-magnetic-rigidity $\left(\mathrm{ToF}\text{−}B\rho \right)$ technique at the National Superconducting Cyclotron Laboratory at Michigan State University. The experiment is the first application of the $\mathrm{ToF}\text{−}B\rho$ technique at the S800 spectrograph that reached the mass region relevant to heavy-element nucleosynthesis. The two-neutron separation energy deduced from the measured masses exhibits a smooth trend consistent with the theoretical predictions within the range of experimental uncertainty, indicating that there is no sudden shape transition in these isotopes as hinted at by previous data.

Project 8 has developed a novel technique, cyclotron radiation emission spectroscopy (CRES), for direct neutrino mass measurements. A CRES-based experiment on the beta spectrum of tritium has been carried out in a small-volume apparatus. We provide a detailed account of the experiment, focusing on systematic effects and analysis techniques. In a Bayesian (frequentist) analysis, we measure the tritium endpoint as $18{553}_{-19}^{+18}$ ($18{548}_{-19}^{+19}$) eV and set upper limits of 155 (152) eV (90% C.L.) on the neutrino mass. No background events are observed beyond the endpoint in 82 days of running. We also demonstrate an energy resolution of $1.66\pm 0.19\mathrm{eV}$ in a resolution-optimized magnetic trap configuration by measuring ${}^{83\mathrm{m}}\mathrm{Kr}17.8$-keV internal-conversion electrons. These measurements establish CRES as a low-background, high-resolution technique with the potential to advance neutrino mass sensitivity.

We perform a first-principles calculation of optical potentials for nucleon elastic scattering off medium-mass isotopes. Fully based on a saturating chiral Hamiltonian, the optical potentials are derived by folding nuclear density distributions computed with ab initio self-consistent Green's function theory with a nucleon-nucleon $t$ matrix computed with a consistent chiral interaction. The dependence on the folding interaction as well as the convergence of the target densities are investigated. Numerical results are presented and discussed for differential cross sections and analyzing powers, with focus on elastic proton scattering off calcium and nickel isotopes. Our optical potentials generally show a remarkable agreement with the available experimental data for laboratory energies in the range 65–200 MeV. We study the evolution of the scattering observables with increasing proton-neutron asymmetry by computing theoretical predictions of the cross section and analyzing power over the calcium and nickel isotopic chains.

Deciphering the conditions under which neutron captures occur in the Universe to synthesize heavy elements is an endeavor pursued since the 1950s, but has proved elusive up to now due to the experimental difficulty of generating the extreme neutron fluxes required. It has been evoked that laser-driven (pulsed) neutron sources could produce neutron beams with characteristics suitable to achieve nucleosynthesis in the laboratory. In this scheme, the laser first generates an ultra-high-current, high-energy proton beam, which is subsequently converted into a dense neutron beam. Here we model, in a self-consistent manner, the transport of laser-accelerated protons through the neutron converter, the subsequent neutron generation and propagation, and finally the neutron capture reactions in gold (${}^{197}\mathrm{Au}$), chosen as an illustrative example. Using the parameters of present-day available lasers, as well as of those foreseeable in the near future, we find that the final yield of the isotopes containing two more neutrons than the seed nuclei is negligible. Our investigation highlights that the areal density of the laser-driven neutron source is a critical quantity and that it would have to be increased by several orders of magnitude over the current state of the art in order to offer realistic prospects for laser-based generation of neutron-rich isotopes.

The development of emulators for the evaluation of many-body observables has gained increasing attention over the last years. In particular the framework of eigenvector continuation (EC) has been identified as a powerful tool when the Hamiltonian admits for a parametric dependence. By training the emulator on a set of training data the many-body solution for arbitrary parameter values can be robustly predicted in many cases. Furthermore, it can be used to resum perturbative expansions that otherwise diverge. In this work, we apply EC to the pairing Hamiltonian and show that EC-resummed perturbation theory is in qualitative agreement with the exact solution and that EC-based emulators robustly predict the ground-state energy once the training data are chosen appropriately. In particular the phase transition from the normal to the superfluid regime is quantitatively predicted using a very low number of training points.

The microscopic framework of time-dependent covariant density functional theory is applied to a systematic study of ternary quasifission in collisions of pairs of ${}^{238}\mathrm{U}$ nuclei. It is shown that the inclusion of octupole degree of freedom in the case of head-to-head collisions extends the energy window in which ternary quasifission occurs, and greatly enhances the number of nucleons contained in a middle fragment. Dynamical pairing correlations, included here in the time-dependent Bardeen-Cooper-Schrieffer approximation, prevent the occurrence of ternary quasifission in head-to-head collisions, and have an effect on the location of the energy window in which a middle fragment is formed in tail-to-tail collisions. In the latter case, as well as for tail-to-side collisions, the formation of very heavy neutron-rich systems in certain energy intervals is predicted.

In this paper, we re-examine one of the most promising candidates for determining the neutrino mass scale—the unique first forbidden $\beta$ transition from ${}^{187}\mathrm{Re}(5/2^{+}$) to ${}^{187}\mathrm{Os}(1/2^{-})$. With the lowest-known ground-state to ground-state $Q$ value for a $\beta$ transition at 2.4709 keV, rhenium's $\beta$ decay can offer insights into the neutrino mass scale puzzle. However, understanding its electron spectrum is a complex task. Besides involving a mixture of $s_{1/2}$-state and $p_{3/2}$-state electrons, the rhenium $\beta$ spectrum could be strongly influenced by various atomic corrections. In addition to our previous paper [R. Dvornický, K. Muto, F. Šimkovic, and A. Faessler, Phys. Rev. C 83, 045502 (2011)], we have incorporated finite nuclear size, diffuse nuclear surface, screening, and exchange corrections into the rhenium $\beta$ decay model. We have accounted for the last two effects within the framework of the Dirac-Hartree-Fock-Slater self-consistent method. We have discovered that both screening and exchange effects significantly alter the partial decay rates for the $s_{1/2}$- and $p_{3/2}$-state emission channels, while still maintaining the experimentally confirmed dominance of the $p_{3/2}$-state emission. The ratio between the respective decay rates has been found to be approximately ${10}^4$. When compared to the other corrections, the exchange effect stands out due to the modification it induces in the spectrum shape. We demonstrate that calculations with and without the exchange effect lead to entirely different shape factors for the decay spectrum. Finally, we illustrate that to preserve the linearity of the Kurie plot, it is essential to include the exchange correction in its definition. We conclude that atomic effects, especially the exchange effect, should be taken into account in current and future investigations of the neutrino mass scale from $\beta$ decays.

Background: The triple-alpha process is a vital reaction in nuclear astrophysics, characterized by two consecutive reactions [$2\alpha \leftrightarrows {}^8\mathrm{Be}(\alpha ,\gamma ){}^{12}\mathrm{C}$] that drive carbon formation. The second reaction occurs through the Hoyle state, a 7.65 MeV excited state in ${}^{12}\mathrm{C}$ with $J^{\pi }=0^{+}$. The rate of the process depends on the radiative width, which can be determined by measuring the branching ratio for electromagnetic decay. Recent measurements by Kibédi et al. conflicted with the adopted value and resulted in a significant increase of nearly 50% in this branching ratio, directly affecting the triple-alpha reaction.

Purpose: This work aims to utilize charged-particle spectroscopy with magnetic selection as a means to accurately measure the total radiative branching ratio (${\mathrm{\Gamma }}_{\mathrm{rad}}/\mathrm{\Gamma }$) of the Hoyle state in ${}^{12}\mathrm{C}$.

Methods: The Hoyle state in ${}^{12}\mathrm{C}$ was populated via ${}^{12}\mathrm{C}(\alpha ,{\alpha }^{\prime }){}^{12}{\mathrm{C}}^{*}$ inelastic scattering. The scattered $\alpha$-particles were detected using a $\mathrm{\Delta }E-E$ telescope, while the recoiled ${}^{12}\mathrm{C}$ ions were identified in a magnetic spectrometer.

Results: A radiative branching ratio value of ${\mathrm{\Gamma }}_{\mathrm{rad}}/\mathrm{\Gamma }\times {10}^4=4.0\pm 0.3\left(\mathrm{stat}.\right)\pm 0.16\left(\mathrm{syst}.\right)$ was obtained.

Conclusions: The radiative branching ratio for the Hoyle state obtained in this work is in agreement with the original adopted value. Our result suggests that the proton-$\gamma -\gamma$ spectroscopy result reported by Kibédi et al. may be excluded.

Interference terms between monopole and quadrupole Coulomb form factors that contribute to the cross section of electron scattering from polarized nuclei are studied within the plane wave Born approximation. By experimentally exploring the effect of this nuclear response, valuable insights into the sign of the quadrupole deformation can be obtained. The nuclear structure is evaluated numerically using a self-consistent deformed Hartree-Fock approximation with Skyrme effective interactions and accounting for pairing correlations. To illustrate the practical applicability, several examples of odd-$A$ nuclei with different spins and deformations are examined. Comparison of unpolarized and polarized cross sections becomes a tool to discriminate between the oblate and prolate nature of the nuclear shape, providing a deeper understanding of the nuclear deformation.