An $\alpha$-decay model is proposed based on the pick-up mechanism in which the $\alpha$ cluster formation is conceptualized as a process of the valence nucleons above the Fermi surface continuously picking up those below the Fermi surface and forming the specific quantum states. The probability of achieving a configuration with two neutrons and two protons is defined as the preformation probability of $\alpha$ cluster. The predicted $\alpha$ preformation probability accurately reproduces the nuclear shell structure without any adjustable parameters. The motion equation of the preformed $\alpha$ cluster is approximately described by a harmonic oscillator potential together with a Coulomb barrier, and an explicit expression of the barrier penetration probability is then derived, with the depth parameter $V_0$ of the potential well and the Bohr-Sommerfeld quantization condition. The measured $\alpha$ decay half-lives of 190 even-even nuclei can be well described with a root-mean-square deviation of 0.32. The $\alpha$ decay half-lives of the isotopic chains with $Z=118$ and $Z=120$ are predicted and systematically compared with the results from some other models.

We study the soft electric dipole ($E1$) response of deformed halo nuclei ${}^{31}\mathrm{Ne}$ and ${}^{37}\mathrm{Mg}$ using a deformed Woods-Saxon potential, with the potential depth adjusted to reproduce empirical separation energy of the last neutron orbit, i.e., 150 keV for ${}^{31}\mathrm{Ne}$ and 220 keV for ${}^{37}\mathrm{Mg}$. The configuration dependence of the $E1$ strength near the neutron threshold is pointed out. The halo configurations $\left[321\right]3/2$ at ${\beta }_2=0.5$ and $\left[330\right]1/2$ at ${\beta }_2=0.24$ in ${}^{31}\mathrm{Ne}$ contain large amplitudes of halo $p$-shell orbits, which significantly enhance the threshold strength by several times compared to the non-halo configuration $\left[202\right]5/2$ at ${\beta }_2=0.32$. In ${}^{37}\mathrm{Mg}$, the last neutron configuration is assigned as $\left[321\right]1/2$ at a large deformation of ${\beta }_2=0.46$, which involves a halo $p$-shell configuration that significantly enhances the soft dipole strength. This enhancement is about 60% larger than that of the $\left[321\right]3/2$ configuration in ${}^{31}\mathrm{Ne}$ because of large $p$-shell probability in ${}^{37}\mathrm{Mg}$. Experimental confirmation of the soft dipole strength is highly desired to determine the deformation and the configuration of the last neutron orbits both in ${}^{31}\mathrm{Ne}$ and ${}^{37}\mathrm{Mg}$.

Quantum computing can potentially provide advantages for specific computational tasks. The simulation of fermionic systems is one such task that lends itself well to quantum computation, with applications in nuclear physics and electronic systems. Here we present work in which we use a variance minimization method to find the full spectrum of energy eigenvalues of the Lipkin-Meshkov-Glick model, an exactly solvable nuclear shell model type system. We perform these calculations using both quantum simulators and real quantum hardware accessed via IBM cloud-based quantum computers. Using these IBM quantum computers we are able to obtain all eigenvalues for the cases of three and seven fermions (nucleons) in the Lipkin-Meshkov-Glick model. We further show a simulated result for a realistic calculation of ${}^6\mathrm{Li}$ with a shell model interaction which performs equivalently to the Lipkin-Meshkov-Glick model.

Collisional heavy ion double-charge-exchange (DCE) reactions, induced by second-order nucleon-nucleon interactions, are shown to provide access to the two-body transition densities of the complementary DCE transitions in the interacting nuclei. Corresponding two-body operators are introduced, treating the second-order distorted wave reaction amplitude in the $s$-channel interaction form. The theoretical results are applied to the reaction ${}^{18}\mathrm{O}+{}^{76}\mathrm{Se}\to {}^{18}\mathrm{Ne}+{}^{76}\mathrm{Ge}$ at $T_{\mathrm{lab}}=270\mathrm{MeV}$, being ${}^{76}\mathrm{Ge}$ a candidate for neutrinoless double beta decay.

Deuteron evaporation was observed from the $N=Z$ compound nuclei ${}^{52}\mathrm{Fe}^{★}$, ${}^{56}\mathrm{Ni}^{★}$, and ${}^{64}\mathrm{Ge}^{★}$ in an experiment conducted at Argonne National Laboratory, USA. The experiment included a novel combination of two highly pixelated double-sided Si-strip detectors inside the Microball charged-particle detection array, allowing for unequivocal discrimination of evaporated deuterons from protons and $\alpha$ particles. In conjunction with the Gammasphere array, Neutron Shell, and additional ancillary detectors, decay paths into various residual nuclei were investigated. The study provides insights into the competition of deuteron vs proton-neutron evaporation as a function of available excitation energy and populated angular momentum. Results are interpreted using a statistical evaporation formalism for multiple subsequent particle emissions. The decisive factor in the comparison appears to be the available excitation energy in the residual system, with single nucleon evaporation preferred over deuteron evaporation for higher excitation energies.

Background: Near- and sub-barrier fusion reactions between doubly magic nuclei are important benchmarks for theoretical models to reproduce the experimental excitation functions. Here we consider the cases of ${}^{16}\mathrm{O}+{}^{16}\mathrm{O}, {}^{48}\mathrm{Ca}+{}^{48}\mathrm{Ca}$, and ${}^{16}\mathrm{O}+{}^{208}\mathrm{Pb}$, which have been measured previously, as well as ${}^{40}\mathrm{Ca}+{}^{90}\mathrm{Zr}$, even though $Z=40$ is not a major shell closure.

Purpose: We aim to perform a complete measurement of the excitation function of ${}^{16}\mathrm{O}+{}^{48}\mathrm{Ca}$, to investigate its behavior near and below the Coulomb barrier where no data are available. Qualitative considerations suggest that this case should follow a trend similar to the other doubly magic systems. However, this might be disproved by the experiment, due to the very large positive fusion Q value and/or to the possible existence of hindrance with a high energy threshold.

Methods: The experiment was performed at the XTU Tandem of Laboratori Nazionali di Legnaro INFN. 24–42 MeV ${}^{16}\mathrm{O}$ beams, with intensities up to 20 p nA, and ${}^{48}\mathrm{Ca}$ targets of $50\mu \mathrm{g}/{\mathrm{cm}}^2$ were used. The evaporation residues (ER) were detected by the electrostatic deflector setup PISOLO at forward angles, and identified by their energy and two independent times of flight, between the final Si detector and two microchannel plate (MCP) detectors.

Results: The clear separation of the evaporation residues in the $E$-ToF (time-of-flight) spectra allowed the excitation function to be measured down to ${\sigma }_{\mathrm{fus}}\sim 2\mu \mathrm{b}$. The results were compared with coupled-channels (CC) calculations using the Akyüz-Winther potential, and a small sub-barrier fusion enhancement was observed. We extracted the logarithmic derivative of the excitation function and the astrophysical $S$ factor, as well as the fusion barrier distribution where a single peak is observed, as predicted by the CC calculations. Comparing with other investigated doubly magic systems reveals an analogous behavior down to the lowest measured energies.

Conclusions: The $S$ factor develops a maximum vs energy, and the logarithmic derivative reaches the so-called $L_{\mathrm{CS}}$ value, at the rather high cross section $\simeq 0.8$ mb. This is evidence of the fusion hindrance phenomenon whose threshold follows the phenomenological systematics established for medium-light systems. A large positive $Q$ value for fusion does not play a role in the ${}^{16}\mathrm{O}+{}^{48}\mathrm{Ca}$ system. The CC model is able to reproduce the excitation function down to that point. At lower energies the fusion cross sections are consistent with the one-dimensional barrier tunneling limit. In the spirit of the adiabatic model, decreasing (and vanishing) coupling strengths reproduce the cross sections far below the barrier, while the hindrance model fails in that energy region.

Quantum mechanical invariance principles dictate the most general operator structure that can be present in the nucleon-nucleon (NN) interaction. Five independent operators appear in the on-shell NN amplitude together with five corresponding coefficient functions. The usual choice for these coefficient functions is known as the NN Wolfenstein amplitudes. We analyze the order-by-order convergence of each of the five NN Wolfenstein amplitudes predicted by a semilocal coordinate space potential implementation of chiral effective field theory ($\chi \mathrm{EFT}$). We do this at laboratory kinetic energies between 25 and 200 MeV for both neutron-proton and proton-proton scattering. Our analysis uses the Gaussian-process methods developed by the BUQEYE Collaboration to describe the contributions of each $\chi \mathrm{EFT}$ order, and so yields truncation uncertainties for each Wolfenstein amplitude that are correlated across scattering angles. We combine information on the size of different orders in the EFT to infer the $\chi \mathrm{EFT}$ breakdown scale for each amplitude, finding, on average, ${\mathrm{\Lambda }}_b$ between 750 and 800 MeV. With this choice of ${\mathrm{\Lambda }}_b$, the EFT truncation uncertainties cover both higher-order results and empirical Wolfenstein amplitudes well for all orders other than the leading order.

The $\beta$ decay of spin-polarized ${}^{31}\mathrm{Mg}$ has been measured at TRIUMF to investigate the nuclear structure of the daughter nucleus ${}^{31}\mathrm{Al}$, which has been thought to be located outside of the $N=20$ island of inversion. By taking advantage of the spatial asymmetries of the $\beta$-ray counts for the respective daughter levels, unambiguous spin-parity assignments of seven levels in ${}^{31}\mathrm{Al}$ were successfully made for the first time. The spin-parity assignments enabled level-by-level comparisons of the experimental levels with the large-scale shell-model calculation using the SDPF-M interaction. It was shown that the ${}^{31}\mathrm{Al}$ levels are categorized into three groups from the structure viewpoint: 0p0h configuration dominant states including the $5/2^{+}$ ground state, 2p2h dominant states, and states with competitive 0p0h and 2p2h configurations. Various structures in an excitation energy region below $\sim 5\text{−}\mathrm{MeV}$ excitation energy suggest competition between the spherical mean field and the nuclear correlation, as in the case of the border nucleus ${}^{30}\mathrm{Mg}$.

In open quantum many-body systems, the theoretical description of resonant states of many particles strongly coupled to the continuum can be challenging. Such states are commonplace in, for example, exotic nuclei and hadrons, and can reveal important information about the underlying forces at play in these systems. In this work, we demonstrate that the complex-augmented eigenvector continuation (CA-EC) method, originally formulated for the two-body problem with uniform complex scaling, can reliably perform bound-to-resonance extrapolations for genuine three-body resonances having no bound subsystems. We first establish that three-body bound-to-resonance extrapolations are possible by benchmarking different few-body approaches, and we provide arguments to explain how the extrapolation works in the many-body case. We furthermore pave the way towards scalable resonance extrapolations in many-body systems by showing that the CA-EC method also works in the Berggren basis, studying a realistic application using the Gamow shell model.

In this article, we study the production of hydrogen and helium isotopes in heavy-ion collisions in the incident energy range between 80 and 150 MeV/nucleon. We compare the inclusive multiplicities emitted in the transverse plane of the reaction with the predictions given by the thermal model. As a first step, we validate the choice of this approach to describe the experimental measurements. We also show that the transient states have to be explicitly taken into account for a good statistical description of the experimental multiplicities. From the thermodynamical parameter values obtained we complete the existing database built with the use of thermal-statistical models to reproduce particle production in the (ultra)relativistic-energy measurements. We then proposed a new constraint on the so-called “freeze-out” region in the temperature ($T$) versus baryonic chemical potential (${\mu }_B$) phase diagram of the quantum chromodynamics. These new results indicate that there is a common framework to describe the hadron production and nuclear clustering processes in heavy-ion collisions.

We theoretically investigate $\mathrm{\Lambda }$ production via a ($K^{-}$, ${\pi }^{-}$) reaction on a ${}^6\mathrm{Li}$ target, using the distorted-wave impulse approximation with a Fermi-averaged $K^{-}n\to {\pi }^{-}\mathrm{\Lambda }$ amplitude. We calculate $\mathrm{\Lambda }$ production spectra using the Green's function method for a ${}^5\mathrm{Li}$ nuclear core $+$ $\mathrm{\Lambda }$ system, employing a $\mathrm{\Lambda }$ folding-model potential based on the ${}^5\mathrm{Li}$ nuclear density, which is constructed from $\alpha \text{−}p$ and ${}^3\mathrm{He}\text{−}d$ cluster wave functions. The results show that the calculated spectrum, which includes $\mathrm{\Lambda }$ bound, resonance, and continuum states, agrees well with the experimental data from the ($K^{-}$, ${\pi }^{-}$) reaction at $p_{K^{-}}=790\mathrm{MeV}/c$ ($0^{\circ }$), where substitutional ${(0p,0p^{-1})}_{\mathrm{\Lambda }n}$ and ${(0s,0s^{-1})}_{\mathrm{\Lambda }n}$ configurations dominate in the near-recoilless reactions. A narrow peak corresponds to a high-lying excited state with spin-parity $J^P=1^{+}$ at $E_{\mathrm{\Lambda }}=13.8\mathrm{MeV}$ near the ${}^3\mathrm{He}+d+\mathrm{\Lambda }$ threshold, arising from interference effects between ${}^5\mathrm{Li}(3/2^{+})\otimes {\left(0s_{1/2}\right)}_{\mathrm{\Lambda }}$ and ${}^5\mathrm{Li}(1/2^{+})\otimes {\left(0s_{1/2}\right)}_{\mathrm{\Lambda }}$ components. This study offers a valuable framework for extracting essential information on the structure and production mechanisms of hypernuclear states from experimental data.

This paper presents the measurement of charged-hadron and identified-hadron ($K_{\mathrm{S}}^0, \mathrm{\Lambda }, {\mathrm{\Xi }}^{-}$) yields in photonuclear collisions using $1.7{\mathrm{nb}}^{-1}$ of $\sqrt{s_{NN}}=5.02\mathrm{TeV} \mathrm{Pb}+\mathrm{Pb}$ data collected in 2018 with the ATLAS detector at the Large Hadron Collider. Candidate photonuclear events are selected using a combination of tracking and calorimeter information, including the zero-degree calorimeter. The yields as a function of transverse momentum and rapidity are measured in these photonuclear collisions as a function of charged-particle multiplicity. These photonuclear results are compared with $0.1{\mathrm{nb}}^{-1}$ of $\sqrt{s_{NN}}=5.02\mathrm{TeV} p+\mathrm{Pb}$ data collected in 2016 by ATLAS using similar charged-particle multiplicity selections. These photonuclear measurements shed light on potential quark-gluon plasma formation in photonuclear collisions via observables sensitive to radial flow, enhanced baryon-to-meson ratios, and strangeness enhancement. The results are also compared with the Monte Carlo dpmjet-iii generator and hydrodynamic calculations to test whether such photonuclear collisions may produce small droplets of quark-gluon plasma that flow collectively.

An investigation of high-transverse-momentum (high-$p_T$) photon-triggered jets in proton-proton ($p\text{−}p$) and ion-ion ($A\text{−}A$) collisions at $\sqrt{s_{NN}}=0.2$ and $5.02\mathrm{TeV}$ is carried out, using the multistage description of in-medium jet evolution. Monte Carlo simulations of hard scattering and energy loss in heavy-ion collisions are performed using parameters tuned in a previous study of the nuclear modification factor ($R_{AA}$) for inclusive jets and high-$p_T$ hadrons. We obtain a good reproduction of the experimental data for photon-triggered jet $R_{AA}$, as measured by the ATLAS detector, the distribution of the ratio of jet to photon $p_T$ ($X_{J\gamma }$), measured by both CMS and ATLAS, and the photon-jet azimuthal correlation as measured by CMS. We obtain a moderate description of the photon-triggered jet $I_{AA}$, as measured by STAR. A noticeable improvement in the comparison is observed when one goes beyond prompt photons and includes bremsstrahlung and decay photons, revealing their significance in certain kinematic regions, particularly at $X_{J\gamma }>1$. Moreover, azimuthal angle correlations demonstrate a notable impact of bremsstrahlung photons on the distribution, emphasizing their role in accurately describing experimental results. This work highlights the success of the multistage model of jet modification to straightforwardly predict (this set of) photon-triggered jet observables. This comparison, along with the role played by bremsstrahlung photons, has important consequences on the inclusion of such observables in a future Bayesian analysis.

We investigate the fluctuations of the net-baryon number near the critical point of the liquid-gas phase transition. We use the parity doublet model in the mean-field approximation fixed to the zero-temperature properties of nuclear matter to account for critical behavior. We explicitly calculate the fluctuations of the net-proton and net-neutron numbers as well as their correlations in the isospin-symmetric matter. We focus on the qualitative properties and systematics of the first- to fourth-order susceptibilities and their ratios. We demonstrate that the fluctuations of net-proton number do not reflect the total net-baryon number fluctuations in the vicinity of the nuclear liquid-gas phase transition. We also study the behavior of the baryon and proton number factorial cumulants. We highlight the importance of the nontrivial correlations between protons and neutrons.

In the years 2020 to 2021, a high resolution in-beam $\gamma$-ray spectroscopy campaign took place at the Radio Isotope Beam Factory within the frame of the HiCARI project. An array composed of 12 composite Ge detectors of different types was put together by an international collaboration in order to address a variety of physics cases of interest, in many cases by measuring excited-state half-lives using Doppler-shift techniques. The analysis of the Doppler-shifted lineshapes observed for the 988-keV, $3/2^{-}\to 1/2^{-}$ and 1655-keV, $5/2^{+}\to 3/2^{+}$ spin-flip $M1$ transitions in ${}^{131}\mathrm{In}$ and ${}^{131}\mathrm{Sn}$, respectively, the 332-keV, $1/2^{+}\to 3/2^{+}l$-forbidden $M1$ transition in ${}^{131}\mathrm{Sn}$, as well as the 607-keV, $2_1^{+}\to 0_1^{+}$ decay in ${}^{136}\mathrm{Te}$ allowed to characterize this new detector array and to establish a valid analysis procedure. The extracted half-lives are compared to previously reported results as well as theoretical calculations.

Background: The description of weakly bound nuclei using deformed few-body models has proven to be crucial in the study of reactions involving certain exotic nuclei. However, the core+valence nucleons models face the challenge of applying the Pauli exclusion principle, since the factorization of the system does not allow complete antisymmetrization. Therefore, states occupied by core nucleons should be blocked for the valence nucleons.

Purpose: We aim to study the carbon isotopes ${}^{17}\mathrm{C}$ and ${}^{19}\mathrm{C}$ which are good examples of weakly bound exotic nuclei with significant deformation where the valence shell is partially filled. We will explore the effect of different methods of blocking occupied states in deformed two-body models.

Methods: The structure of ${}^{17}\mathrm{C}$ and ${}^{19}\mathrm{C}$ is described with deformed two-body models where a Nilsson Hamiltonian is constructed using antisymmetrized molecular dynamic calculations of the cores. Different methods of blocking occupied Nilsson states are considered using the Bardeen-Cooper-Schrieffer formalism: without blocking, total blocking, and partial blocking. The latter also takes into account pair correlations to some extent. These models are later used to study ${}^{16}\mathrm{C}(d,p){}^{17}\mathrm{C}$, ${}^{17}\mathrm{C}(p,d){}^{16}\mathrm{C}$, and ${}^{18}\mathrm{C}(d,p){}^{19}\mathrm{C}$ transfer reactions within the adiabatic distorted wave approximation. In the first case, the results are compared with experimental data.

Results: A good reproduction of the structure of ${}^{17}\mathrm{C}$ is found, significantly improving the agreement in the ${}^{16}\mathrm{C}(d,p){}^{17}\mathrm{C}$ reaction including blocking effects. The ${}^{19}\mathrm{C}$ spectrum is better reproduced considering blocking, in particular, the partial blocking method that considers the pairing interaction provides the best description.

Conclusions: Promising results are shown for the study of transfer reactions involving weakly bound exotic nuclei, by highlighting the effect of blocking occupied Nilsson states. We envision to extend the models to the study of breakup reactions and to newly discovered halo nuclei.

We investigate the formation of intermediate mass and light nuclei in the processes associated with expanding nuclear matter: It is demonstrated that this phenomenon can be explained within the statistical approach by applying the local equilibrium concept. The production of such nuclei can be realized in central collisions of heavy ions at intermediate energies. We subdivide the expanding nuclear system into several parts (primary clustering) consisting of nucleons which are close in phase space. The nucleation process takes place inside these primary clusters, and it can be described as their statistical decay in the coexistence region of the nuclear liquid-gas phase transition. Our model can explain simultaneously both the yield and energy of the produced nuclei that was not possible when we consider the global chemical equilibrium in the whole nuclear system.

In this work, the contributions from $\gamma W$ exchange in neutron $\beta$ decay are estimated at the amplitude level. Using a general form for the electromagnetic (EM) form factors (FFs) of the proton, the EM FFs of the neutron, and the weak FFs of the $Wnp$ interaction as inputs, we present analytical expressions for the inner part of the $\gamma W$-exchange amplitude under the forward angle limit. The differences and relations between our method and those used in the references are discussed. To compare our numerical results with those provided in the references, we consider three types of FFs as examples. The numerical results show that when the favored EM FFs are used, our result for the contribution from the Fermi part is consistent with those reported in the references, while our results for the Gamow-Teller parts are about 7% and 13% larger than those reported in L. Hayen, Phys. Rev. D 103, 113001 (2021).

Spectroscopic properties of the unnatural-parity states of ${}^{43}\mathrm{Ca}$ populated through the ${}^{27}\mathrm{Al}({}^{19}\mathrm{F},$ $2pn){}^{43}\mathrm{Ca}$ reaction at 68 MeV beam energy, have been investigated using the Indian National Gamma Array (INGA) facility. The level scheme has been extended up to the $J^{\pi }=25/2^{+}$, the band-terminating state corresponding to $\pi {\left(1d_{3/2}\right)}^{-1}{\left(1f_{7/2}\right)}^1\otimes \nu {\left(1f_{7/2}\right)}^3$ configuration, by adding two new levels and six new transitions to the existing level scheme. The spin-parity assignments for the observed levels were done by $R_{\text{DCO}}$, $R_{\text{ADO}}$, and linear polarization measurements. The multipole mixing ratios $\left(\delta \right)$ for most of the transitions were measured. Large basis shell-model calculations were carried out to explain the microscopic origin of observed levels. Interplay between single-particle and collective mode of excitations in the positive parity levels has also been discussed.