Background: Isospin mixing is an interesting feature of atomic nuclei that plays a crucial role in the astrophysical nuclear reactions. However, variational nuclear structure models cannot describe it in a straightforward manner.

Purpose: We propose a tractable method to describe isospin mixing within the framework of a generator coordinate method and demonstrate its usability.

Method: We generate basis wave functions by applying the Fermi transition operator to the wave functions of isobars. The superposition of these basis wave functions and variationally obtained wave functions quantitatively describes isospin mixing.

Results: We apply our method to ${}^{14}\mathrm{N}$ and show that it reasonably describes both $T=0$ and 1 states and their mixing. The energy spectrum and $E1$ transition strengths are compared with the experimental data.

Conclusion: The proposed method is effective in describing isospin mixing and is particularly useful for discussing of $\alpha$-capture reactions of $N=Z$ nuclei.

The competition between $\alpha$- and ${\beta }^{+}/\text{EC}$-decay modes is studied systematically in nuclei along the $\alpha$-decay chains following the synthesis of superheavy nuclei with $Z=119$ and $Z=120$. A microscopic approach based on deformed self-consistent Hartree-Fock mean-field calculations with Skyrme forces and pairing correlations is used to describe the ${\beta }^{+}$ and electron capture weak decays, whereas the $\alpha$ decay is estimated from existing phenomenological expressions. It is shown that $\alpha$ decay is in most cases the dominant decay mode, but interesting instances are identified where the half-lives are comparable, opening the possibility of new pathways towards more neutron-rich nuclei in this region.

The standard model of particle physics (SM), augmented with neutrino mixing, is either the complete theory of interactions of known particles at energies naturally accessible on earth, or very nearly so, with a Lagrangian symmetric under the global $\mathrm{SU}{\left(2\right)}_L\times \mathrm{SU}{\left(2\right)}_R$ symmetry of two-massless-quark QCD, spontaneously broken to $\mathrm{SU}{\left(2\right)}_{L+R}$. Using naive dimensional operator power counting that enables perturbation and truncation in inverse powers of ${\mathrm{\Lambda }}_{\chi SB}\approx 1\text{GeV}$, we show that, to $\mathcal{O}\left({\mathrm{\Lambda }}_{\chi SB}\right)$ and $\mathcal{O}\left({\mathrm{\Lambda }}_{\chi SB}^0\right)$, SU(2) chiral perturbation theory [SU(2)$\chi \mathrm{PT}$] of protons, neutrons, and pions admits a liquid phase, with energy required to increase or decrease the nucleon density. We further show that in the semiclassical approximation—i.e., quantum nucleons and classical pions—“pionless SU(2)$\chi$PT” emerges in that chiral liquid: soft static infrared Nambu-Goldstone-boson pions decouple from “static chiral nucleon liquids” (Static$\chi$NLs). This vastly simplifies the derivation of saturated nuclear matter (the infinite liquid phase) and of finite microscopic liquid drops (ground-state heavy nuclides). Static$\chi$NLs are made entirely of nucleons. They have even parity, total spin zero, even proton number $Z$, and even neutron number $N$. The nucleons are arranged so local expectation values for spin and momentum vanish. We derive the Static$\chi$NL effective Lagrangian from semiclassical SU(2)$\chi$PT$$symmetries to order ${\mathrm{\Lambda }}_{\chi SB}$ and ${\mathrm{\Lambda }}_{\chi SB}^0$, including all relativistic four-nucleon operators that survive Fierz rearrangement in the nonrelativistic limit and SU(2)$\chi$PT$$fermion exchange operators and isovector exchange operators which are important when $Z\ne N$. Mean-field Static$\chi$NL nontopological solitons are true solutions of SU(2)$\chi$PT$$semiclassical symmetries; e.g., they obey all conserved vector current (CVC) and partially conserved axial current (PCAC) conservation laws. They have zero internal and external pressure. The nuclear liquid-drop model and Bethe–von Weizsäcker semiempirical mass formula emerge—with correct nuclear density and saturation and asymmetry energies—in an explicit Thomas-Fermi construction.

We present results of a systematic study of the capture process through the barrier penetration model. The nucleus-nucleus interaction potential is calculated using the double-folding model (DFM) with the M3Y Paris $\mathit{NN}$ forces. The nucleon densities entering the model are generated from the experimental three-parameter Fermi charge densities. The DFM has been extended to the case of deformed target nuclei. It is shown that the density-dependent M3Y $\mathit{NN}$ forces with the finite range exchange part can be mimicked successfully by the zero-range density-independent forces. The latter option significantly reduces the required computer time. For the nucleon densities and target nuclei deformations, we employ the values from the commonly used data bases. Thus, we do not vary any parameters to reach a better agreement with the data. The resulting cross sections are compared with data for 20 reactions with the product of the charge numbers $Z_P{Z}_T$ ranging from 216 up to 2576. We discuss the opinion met in the literature that the M3Y $\mathit{NN}$ forces provide a poorer description of the capture cross sections in heavy-ion collisions in comparison to the $\mathit{NN}$ forces coming from the relativistic mean-field approach. Our calculations show that the M3Y $\mathit{NN}$ forces give an agreement with the data which is not perfect yet is not worse than the one resulting from the relativistic mean-field approach $\mathit{NN}$ forces.

To describe the fusion cross sections with a method that includes the superfluidity and to understand the impact of pairing on both the fusion barrier and cross sections, we propose a real-space particle- and pairing-density-constrained scheme of the time-dependent Hartree-Fock-Bogoliubov (TDHFB) method and a definition of TDHFB particle current. Using the Gogny-TDHFB code, this scheme is applied to investigate the fusion reactions of ${}^{40}\mathrm{Ca}+{}^{40}\mathrm{Ca}, {}^{40}\mathrm{Ca}+{}^{44}\mathrm{Ca}$, and ${}^{40}\mathrm{Ca}+{}^{48}\mathrm{Ca}$ by comparison. The results show that this density-constrained TDHFB scheme is reliable for analysis of the collision processes involved with superfluid nuclei.

There is a deep astrophysical interest in the structure of ${}^{19}\mathrm{F}$ states close to the $\alpha$-decay threshold. The nuclear structure of these states is important for understanding of the development of $\alpha$ clustering in the ${}^{20}\mathrm{Ne}$ region. Emergence of clustered states, and generally states that favor coupling to reaction channels near the corresponding decay thresholds, is currently of special interest in theoretical physics. We specify the parameters of broad low spin states in ${}^{19}\mathrm{F}$ near the $\alpha$-decay threshold and present a theoretical study of these states. The study is limited to $\ell =0$ and 1 relative partial wave resonances in the $\alpha +{}^{15}\mathrm{N}$ interaction close to the $\alpha$-decay threshold in ${}^{19}\mathrm{F}$. Excitation function for ${}^{15}\mathrm{N}(\alpha ,\alpha$) elastic scattering was measured by the TTIK method. These new data together with the old, high-energy resolution data, were analyzed using the $R$ matrix approach. ${}^{19}\mathrm{F}$ nuclear structure was calculated using configuration interaction methods with the recently developed effective interaction Hamiltonian. As a result, in this work we identify a series of $\alpha$ clustering resonances in ${}^{19}\mathrm{F}$ and assess the distribution of the clustering strength, which is of importance to questions of astrophysics and for theoretical understanding of many-body physics and emergence of clustering in loosely bound or unstable nuclei. Progress has been made in theoretical understanding of the origins of clustering and questions for future theoretical and experimental research are identified.

The nuclear structure of ${}^{19}\mathrm{F}$ and ${}^{19}\mathrm{Ne}$ is important for understanding of $\alpha$ clustering in the $A=20$ mass region and in questions related to astrophysics. However, the only high-resolution broad angular and energy range study of the ${}^{19}\mathrm{F}$ resonance structure in $\alpha +{}^{15}\mathrm{N}$ scattering was published over 60 years ago, and a detailed analysis of complex excitation functions of overlapping resonances with several decay channels was simply impossible at that time. We performed a modern $R$-matrix analysis of these old data to assign spins and specify resonant parameters of levels up to excitation energy of 8.2 MeV in ${}^{19}\mathrm{F}$. We successfully tested our $R$-matrix parameters in a fit of the recent data on $\alpha +{}^{15}\mathrm{N}$ obtained by thick target inverse kinematics (TTIK) method at 180 degrees. We used the new parameters for ${}^{19}\mathrm{F}$ to fit TTIK data for $\alpha +{}^{15}\mathrm{O}$, the mirror resonant reactions. The comparison of the data for isobaric mirror resonant reactions provides an interesting insight into the nuclear structure.

The beam energy dependence of the directed flow is a sensitive probe for the properties of strongly interacting matter. Hybrid models that simulate dense (core) and dilute (corona) parts of the system by combining the fluid dynamics and hadronic cascade model describe well the bulk observables, strangeness productions, and radial and elliptic flows in high-energy heavy-ion collisions in the high baryon density region. However, the beam energy dependence of the directed flow cannot be described in existing hybrid models. We focus on improving the corona part, i.e., the nonequilibrium evolution part of the system, by introducing the mean-field potentials into a hadronic cascade model. For this purpose, we consider different implementations of momentum-dependent hadronic mean fields in the relativistic quantum molecular dynamics (RQMD) framework. First, Lorentz scalar implementation of a Skyrme type potential is examined. Then, full implementation of the Skyrme type potential as a Lorentz vector in the RQMD approach is proposed. We find that scalar implementation of the Skyrme force is too weak to generate repulsion explaining observed data of sideward flows at $\sqrt{s_{NN}}<10$ GeV, while vector implementation gives collective flows compatible with the data for a wide range of beam energies $2.7<\sqrt{s_{NN}}<20$ GeV. We show that our approach reproduces the negative proton directed flow at $\sqrt{s_{NN}}>10$ GeV discovered by experiments. We discuss the dynamical generation mechanisms of the directed flow within a conventional hadronic mean field. A positive slope of proton directed flow is generated predominantly during compression stages of heavy-ion collisions by the strong repulsive interaction due to high baryon densities. In contrast, at the expansion stages of the collision, the negative directed flow is generated more strongly than the positive one by the tilted expansion and shadowing by the spectator matter. At lower collision energies $\sqrt{s_{NN}}<10$ GeV, the positive flow wins against the negative flow because of a long compression time. On the other hand, at higher energies $\sqrt{s_{NN}}>10$ GeV, negative flow wins because of shorter compression time and longer expansion time. A transition beam energy from positive to negative flow is highly sensitive to the strength of the interaction.

A new measurement of $\gamma$ decay from the states above the neutron threshold in ${}^{208}\mathrm{Pb}$ has been performed at Cyclotron Centre Bronowice in Kraków, Poland. The main goal of the experiment was to observe the $\gamma$ decay to the ground state from the isoscalar giant quadrupole resonance (ISGQR). To this day, the only published observation of this phenomenon dates back to the late 1980s, where $\gamma$ decay to the ground state branching ratio was reported. At variance with the existing measurement using inelastic scattering of ${}^{17}\mathrm{O}$, here proton inelastic scattering is employed. In particular, data were obtained for ${}^{208}\mathrm{Pb}(p,p^{\prime }\gamma )$ at 85 MeV beam energy, where $\gamma$ rays were measured for proton scattering angles $8.9^{\circ }$, $10.7^{\circ }$, $12.5^{\circ }$, and $14.3^{\circ }$. By applying a similar analysis method as in the previous experiment, the branching ratio of ISGQR gamma decay to the ground state was extracted from the data.

According to different theoretical studies, the next magicity for the proton number should occur at $Z=114$, 120, or 126 and for the neutron number $N=184$. Superheavy nuclei of interest for the forthcoming synthesis of the isotopes with $Z=119$, 120 are investigated. Many reactions have yet to be studied in order to find the possible incoming channels for the formation of $Z=120$. In this work, synthesis of superheavy element 120 in terms of the fission and quasifission cross sections via ${}^{64}\mathrm{Ni}+{}^{238}\mathrm{U}$ reaction is evaluated and discussed. We have explored the possibility of formation of $Z=120$ via ${}^{64}\mathrm{Ni}+{}^{238}\mathrm{U}$ reaction, using the experimental data from Kozulin , Phys. Lett. B 686, 227 (2010). Some experimental efforts have been made to synthesize ${}^{302}120$, via Ni-induced and Cr-induced reaction, i.e., ${}^{64}\mathrm{Ni}+{}^{238}\mathrm{U}$ reaction at five $E^{*}$'s (excitation energies) and the ${}^{54}\mathrm{Cr}+{}^{248}\mathrm{Cm}$ reaction at only one energy, respectively. In this work, we have studied the Ni-induced reaction at given energies by including higher multipole deformations ${\beta }_{\lambda i}$ $(\lambda =2,3,4$; $i=1,2)$, and compact orientations ${\theta }_{ci}$ using the coplanar degree of freedom $(\mathrm{\Phi }=0^{\circ })$ within the framework of the dynamical cluster-decay model (DCM). The neck-length parameter is the only one, which is fixed in reference to the observed data for fission cross section $\left({\sigma }_{\mathrm{ff}}\right)$ calculated for mass region $A/2\pm 20$, and quasifission cross section $\left({\sigma }_{\mathrm{qf}}\right)$ for the incoming channel of ${}^{64}\mathrm{Ni}+{}^{238}\mathrm{U}$ reaction. Our calculations for Ni-induced reaction have shown a good concurrence with the experimental data for quasifission and fission cross sections along with the DCM-calculated estimated and predicted cross sections for evaporation residues (ERs), which can be used for future references. Our results demonstrate the insignificant compound nucleus formation possibility $P_{\text{CN}}$ $(\ll 1)$ for $Z=120$ from Ni-induced reaction because of the very low order of evaporation residues; thus, this work is not supporting this incoming channel for the formation of $Z=120$.

We measured 135 cross sections of residual nuclei produced in fragmentation reactions of ${}^{12}\mathrm{C}, {}^{14}\mathrm{N}$, and ${}^{13-16,20,22}\mathrm{O}$ projectiles impinging on a carbon target at kinetic energies of near $400A$ MeV, most of them for the first time, with the $\mathrm{R}{}^3\mathrm{B}$/LAND setup at the GSI facility in Darmstadt (Germany). The use of this state-of-the-art experimental setup in combination with the inverse kinematics technique gave the full identification in atomic and mass numbers of fragmentation residues with a high precision. The cross sections of these residues were determined with uncertainties below $20\%$ for most of the cases. These data are compared to other previous measurements with stable isotopes and are also used to benchmark different model calculations.

This work studies the production of direct photons in relativistic nuclear collisions, along with the production of hadrons. Radiation from the very first instants to the final moments of the evolution is included. The hybrid model used here describes all stages of relativistic heavy-ion collisions. Chronologically, those are an initial state reflecting the collision of nuclei described within the color glass condensate effective theory; a pre-equilibrium phase based on nonequilibrium linear response; relativistic viscous hydrodynamics, and a hadronic afterburner. The effect of the pre-equilibrium phase on both photonic and hadronic observables is highlighted for the first time. The potential of photon observables—spectrum, differential elliptic, and triangular flow—to reveal the chemical equilibration time is studied. Finally, we consider “small collision systems,” including $\text{proton}+\text{nucleus}$ collisions and collisions of light nuclei, as probed by hadronic and electromagnetic observables. We demonstrate how photon production can signal the formation of quark-gluon plasma in such small systems.

We extract the shear stress tensor of nuclear matter in the hadronic phase in high energy nuclear collisions. We use a blast-wave parametrization of the final state of nuclear collisions, including nonequilibrium deformations of particle distributions due to shear stress in the Navier-Stokes approximation. We fit spectra and elliptic flow of identified hadrons for a variety of collision energies and impact parameters at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). The systems analyzed cover a temperature range from about 110 to 150 MeV and vary in their chemical potentials for stable hadrons. We then attempt to estimate the specific shear viscosity $\eta /s$ of nuclear matter for various temperatures and chemical potentials in the hadronic phase. We assign systematic uncertainties to our results. Using a recent systematic study of fluid dynamics pseudodata with the same blast-wave model [Z. Yang and R. J. Fries, arXiv:2007.11777], we apply a correction to the raw fit results which removes some biases typical for blast-wave fits. This work is complementary to efforts using viscous fluid dynamics to extract the specific shear viscosity of quark gluon plasma at higher temperatures. We put our work in context with existing theoretical calculations of the specific shear viscosity.

We study cluster and hypernuclei production in heavy-ion collisions at relativistic energies employing the parton-hadron-quantum-molecular-dynamics (PHQMD) approach, a microscopic $n$-body transport model based on the QMD propagation of the baryonic degrees of freedom with density dependent two-body potential interactions. All other ingredients of PHQMD, including the collision integral and the treatment of the quark-gluon plasma (QGP) phase, are adopted from the parton-hadron-string-dynamics (PHSD) approach. In PHQMD the cluster formation occurs dynamically, caused by the interactions. The clusters are recognized by the Minimum Spanning Tree (MST) algorithm. We present the PHQMD results for cluster and hypernuclei formation in comparison with the available experimental data at energies available at the Alternating Gradient Synchrotron, the Super Proton Synchrotron, and the Beam Energy Scan and fixed-target programs at the BNL Relativistic Heavy Ion Collider. We also provide predictions on cluster production for the upcoming experiments at the GSI Facility for Antiproton and Ion Research (FAIR) and the Nuclotron-based Ion Collider Facility (NICA). PHQMD allows one to study the time evolution of formed clusters and the origin of their production, which helps to understand how such weakly bound objects are formed and survive in the rather dense and hot environment created in heavy-ion collisions. It offers therefore an explanation of the “ice in the fire” puzzle.

Background: Energetic quarks in nuclear deep-inelastic scattering propagate through the nuclear medium. Processes that are believed to occur inside nuclei include quark energy loss through medium-stimulated gluon bremsstrahlung and intranuclear interactions of forming hadrons. More data are required to gain a more complete understanding of these effects.

Purpose: To test the theoretical models of parton transport and hadron formation, we compared their predictions for the nuclear and kinematic dependence of pion production in nuclei.

Methods: We have measured charged-pion production in semi-inclusive deep-inelastic scattering off D, C, Fe, and Pb using the CLAS detector and the CEBAF 5.014-GeV electron beam. We report results on the nuclear-to-deuterium multiplicity ratio for ${\pi }^{+}$ and ${\pi }^{-}$ as a function of energy transfer, four-momentum transfer, and pion energy fraction or transverse momentum—the first three-dimensional study of its kind.

Results: The ${\pi }^{+}$ multiplicity ratio is found to depend strongly on the pion fractional energy $z$ and reaches minimum values of $0.67\pm 0.03, 0.43\pm 0.02$, and $0.27\pm 0.01$ for the C, Fe, and Pb targets, respectively. The $z$ dependencies of the multiplicity ratios for ${\pi }^{+}$ and ${\pi }^{-}$ are equal within uncertainties for C and Fe targets but show differences at the level of $10\%$ for the Pb-target data. The results are qualitatively described by the GiBUU transport model, as well as with a model based on hadron absorption, but are in tension with calculations based on nuclear fragmentation functions.

Conclusions: These precise results will strongly constrain the kinematic and flavor dependence of nuclear effects in hadron production, probing an unexplored kinematic region. They will help to reveal how the nucleus reacts to a fast quark, thereby shedding light on its color structure and transport properties and on the mechanisms of the hadronization process.

Exclusive cross sections for the ${}^{43}\mathrm{P}(-1p){}^{42}\mathrm{Si}$ reaction to the lowest $0^{+}$ and $2^{+}$ states, measured at NSCL with GRETINA and the S800, are interpreted in terms of a two-level mixing (collective) model of oblate and prolate coexisting shapes. Using the formalism developed for deformed nuclei, we calculate the spectroscopic amplitudes and exclusive cross sections in the strong-coupling limit, where for ${}^{43}\mathrm{P}$ the schematic wave function includes the coupling of the Nilsson [211]$\frac{1}{2}$ proton orbit. Good agreement with the experimental data is obtained when the amplitude of the oblate configuration is $\gtrsim 80$%, suggesting that both nuclei are predominantly oblate, in line with theoretical expectations. Model predictions for excitation energies and electromagnetic observables, which could motivate further studies of both nuclei, are also presented.

Charge radius is one of the most fundamental properties of a nucleus. However, a precise description of the evolution of charge radii along an isotopic chain is highly nontrivial, as reinforced by recent experimental measurements. In this paper, we propose a novel approach which combines a three-parameter formula and a Bayesian neural network. We find that the novel approach can describe the charge radii of all $A\ge 40$ and $Z\ge 20$ nuclei with a root-mean-square deviation about 0.015 fm. In particular, the charge radii of the calcium isotopic chain are reproduced very well, including the parabolic behavior and strong odd-even staggerings. We further test the approach for the potassium isotopes and show that it can describe well the experimental data within uncertainties.

The present work aims to explore the effects of projectile breakup on fusion cross section at energies near the Coulomb barrier to well above it. The complete fusion cross section for the strongly bound non-$\alpha$-cluster projectile ${}^{14}\mathrm{N}$ in interaction with a ${}^{181}\mathrm{Ta}$ target was obtained by summing the experimentally measured channel-by-channel cross section data of evaporated residues. The obtained total fusion cross section was compared with the theoretical code ccfull and the results were found to be consistent with each other. Further, the experimental fusion function data on ${}^{181}\mathrm{Ta}$ target with ${}^{14}\mathrm{N}$ projectile were deduced and compared with those obtained for other strongly bound projectiles, viz., ${}^{12,13}\mathrm{C}$, ${}^{16}\mathrm{O}$, and ${}^{19}\mathrm{F}$, in order to get some systematics in fusion reactions. The analysis of experimental fusion functions was performed within the framework of a benchmark curve called the universal fusion function (UFF). A suppression of about 5–25% with respect to UFF was observed for the presently studied systems at energies above the Coulomb barrier, indicating that the suppression is essentially due to the prompt breakup of the projectiles and is a strong function of breakup threshold of projectiles. The magnitude of such suppression was found to be lower for ${}^{14}\mathrm{N}$ projectile as compared to other strongly bound projectiles. Moreover, an interesting exponential relation between the experimentally deduced suppression factor and the breakup threshold of the projectile was obtained.