In this work, the $\gamma Z$-exchange contributions in the low-energy elastic parity-violating $ep$ scattering are discussed with the approximation $m_e=0$. By expanding the $\gamma pp$ and $Zpp$ interactions on the momentum of photon and considering both the leading-order and the next-to-leading order interactions, we calculate the amplitudes of the $\gamma Z$-exchange diagrams. After performing the loop integral, we expand the results in the low energy limit, and obtain the analytic expressions for the amplitudes. Numerical comparisons show that the analytic expressions are very close to the full results over a large region. We investigate the power behaviors of these contributions and find that some are enhanced by a kinematic factor in the low energy limit. Additionally, in some cases, the imaginary parts of the contributions from the next-to-leading-order interactions are at the same order as those from the leading-order interactions. Furthermore, the corresponding contributions to the physical observable quantity $A_{\text{PV}}$ are also discussed. Combining all the properties together, we conclude that these analytic expressions describe the leading-order contributions of all $\gamma Z$-exchange helicity amplitudes in the region with ${\alpha }_e\ll Q/M_N\sim \delta /M_N^2\ll 1$, where ${\alpha }_e$ is the fine structure constant, $M_N$ is the mass of proton, $Q$ and $\delta$ are the small quantities related to the momentum transfer and the center-of-mass energy.

We develop a kinetic approach to the production of light nuclei up to mass number $A⩽4$ in intermediate-energy heavy-ion collisions by including them as dynamic degrees of freedom. The conversions between nucleons and light nuclei during the collisions are incorporated dynamically via the breakup of light nuclei by a nucleon and their reverse reactions. We also include the Mott effect on light nuclei; i.e., a light nucleus will no longer be bound if the phase-space density of its surrounding nucleons is too large. With this kinetic approach, we obtain a reasonable description of the measured yields of light nuclei in central $\mathrm{Au}+\mathrm{Au}$ collisions at energies of $0.25A\mathrm{GeV}$–$1.0A\mathrm{GeV}$ by the FOPI Collaboration. Our study also indicates that the observed enhancement of the $\alpha$-particle yield at low incident energies can be attributed to a weaker Mott effect on the $\alpha$ particle, which makes it more difficult to dissolve in nuclear medium, as a result of its much larger binding energy.

Background: Understanding the dynamics of quasifission reactions for the pre-actinides and actinides is particularly important for choosing suitable target projectile combinations to synthesize of superheavy elements. Measurements of fission-fragment mass distributions by us in reactions populating the pre-actinides nuclei ${}^{200}\mathrm{Pb}$ showed no indication of the presence of quasifission, contrary to two recent claims from the state-of-the-art theoretical calculations that predicted noncompound nuclear reaction in these reactions.

Purpose: The purpose was to investigate the signature of noncompound nuclear fission, if any, in the fission of ${}^{225}\mathrm{Pa}$ populated via two different entrance channels ${}^{20}\mathrm{Ne}+{}^{205}\mathrm{Tl}$ and ${}^{16}\mathrm{O}+{}^{209}\mathrm{Bi}$.

Methods: Two position-sensitive multiwire proportional counters were placed at the folding angle to detect the fission fragments. Mass distributions were extracted from the measured time-of-flight differences and position information ($\theta ,\varphi$) of the fission fragments.

Results: The mass distributions for both reactions are found to be symmetric at all the measured energies up to the excitation energy of 110 MeV. The variation of the standard deviations of mass distributions increases smoothly with excitation energy. The theoretical calculation indicates a significant amount of quasifission in the mass asymmetric region in both reactions.

Conclusion: The measured fission-fragment mass distributions for the two reactions that populated the same compound nucleus, do not provide evidence of quasifission in the mass symmetric region.

The generation of angular momentum in fissioning nuclei is not well understood. The predictions of different models disagree, particularly concerning the correlation between the fragments' angular momenta. In this article, a time-dependent collective Hamiltonian model is proposed to treat the generation of the angular momentum in the fission fragments due to the quantum uncertainty principle as well as the dynamics of the collective wave function during and after scission. The model is constructed in the framework of the frozen Hartree-Fock approximation using a Skyrme energy functional to extract deformations of the fission fragments as well as the interactions in a derived collective Hamiltonian. The fission reactions studied are ${}^{240}\mathrm{Pu}\to {}^{132}\mathrm{Sn}+{}^{108}\mathrm{Ru}$ and ${}^{240}\mathrm{Pu}\to {}^{144}\mathrm{Ba}+{}^{96}\mathrm{Sr}$. The model can account for a large part of the angular momentum found in experimental data. The orientation of the angular momentum of each fragment is found to be mainly in the plane perpendicular to the fission axis, in agreement with the experiment. The magnitudes of the angular momenta in the two fragments are nearly uncorrelated, in agreement with the recent experimental data of Wilson et al. [Nature (London) 590, 566 (2021)]. Some of the conclusions of the traditional collective vibration model are supported by the present model but some are not. Surprisingly, it is found that the angular momenta of the fragments are slightly correlated positively as in a wriggling mode. It is also found that the presence of an octupole deformation in a fragment can significantly increase the generated angular momentum.

We study the properties of the hadron-hadron potentials and quark-antiquark potentials from the viewpoint of the channel coupling. We demonstrate that, for finite quark masses, the coupling to the two-hadron continuum induces the imaginary part of the quark-antiquark potential, in contrast to the string-breaking phenomena in the static limit. It is also shown that the elimination of the different degrees of freedom induces the nonlocality and energy dependence of the effective potentials. For the obtained nonlocal potentials, we apply two methods of the local approximation proposed previously, the formal derivative expansion and the derivative expansion in the HAL QCD method, by carefully examining the energy dependence of the potential. As an application, we construct a coupled-channel model of $c\overline{c}$ and $D^0{\overline{D}}^{*0}$ to describe $X\left(3872\right)$, and discuss the property of the effective $D^0{\overline{D}}^{*0}$ potentials. We confirm that the local approximation by the HAL QCD method works better than the formal derivative expansion also for the energy-dependent potential. At the same time, we show that, in the HAL QCD method, the resulting phase shift is sensitive to the choice of the wave function to construct the local potential when the system has a shallow bound state such as $X\left(3872\right)$.

We discuss the modification of the properties of the tetraquark-like $T_{cc}{\left(3875\right)}^{+}$ and $T_{\overline{c}\overline{c}}{\left(3875\right)}^{-}$ states in dense nuclear matter. We consider the $T_{cc}^{+}$ and $T_{\overline{c}\overline{c}}^{-}$ in vacuum as purely isoscalar $D^{*}D$ and $\overline{D}{}^{*}\overline{D} S$-wave bound states, respectively, dynamically generated from a heavy-quark effective interaction between the charmed mesons. We compute the $D, \overline{D}, D^{*}$, and $\overline{D}{}^{*}$ spectral functions embedded in a nuclear medium and use them to determine the corresponding $T_{cc}^{+}$ and $T_{\overline{c}\overline{c}}^{-}$ self-energies and spectral functions. We find important modifications of the $D^{*}D$ and $\overline{D}{}^{*}\overline{D}$ scattering amplitudes and of the pole position of these exotic states already for ${\rho }_0/2$, with ${\rho }_0$ the normal nuclear density. We also discuss the dependence of these results on the $D^{*}D$ ($\overline{D}{}^{*}\overline{D}$) molecular component in the $T_{cc}^{+}$ ($T_{\overline{c}\overline{c}}^{-}$) wave function. Owing to the different nature of the $D^{(*)}N$ and $\overline{D}{}^{(*)}N$ interactions, we find characteristic changes of the in-medium properties of the $T_{cc}{\left(3875\right)}^{+}$ and $T_{\overline{c}\overline{c}}{\left(3875\right)}^{-}$, which become increasingly visible as the density increases. The experimental confirmation of the found distinctive density pattern will give support to the existence of molecular components in these tetraquark-like states, since in the case they were mostly colorless compact quark structures ($cc\overline{\ell }\overline{\ell }$ and $\overline{c}\overline{c}\ell \ell$, with $\ell =u,d$), the density behaviors of the $T_{cc}{\left(3875\right)}^{+}$ and $T_{\overline{c}\overline{c}}{\left(3875\right)}^{-}$ nuclear medium spectral functions, though different, would not likely be the same as those found in this work for molecular scenarios. Finally, we perform similar analyses for the isoscalar $J^P=1^{+}$ heavy-quark spin symmetry partners of the $T_{cc}^{+}$ ($T_{cc}^{*+}$) and the $T_{\overline{c}\overline{c}}^{-}$ ($T_{\overline{c}\overline{c}}^{*-}$) by considering the $D^{*0}{D}^{*+}$ and $\overline{D}{}^{*0}{D}^{*-}$ scattering $T$ matrices.

We calculate the magnetic moments of light nuclei $(A<20)$ using the auxiliary field diffusion Monte Carlo method and local two- and three-nucleon forces with electromagnetic currents from chiral effective field theory. For all nuclei under consideration, we also calculate the ground-state energies and charge radii. We generally find a good agreement with experimental values for all of these observables. For the electromagnetic currents, we explore the impact of employing two different power counting schemes, and study theoretical uncertainties stemming from the truncation of the chiral expansion order by order for select nuclei within these two approaches. We find that it is crucial to employ consistent power counting schemes for interactions and currents to achieve a systematic order-by-order convergence.

The $A\approx 100$ mass region is of special interest due to a rapid shape transition, observed by going from neutron number 58 to 60, especially pronounced in the Zr isotopes, where ${}^{98}\mathrm{Zr}$ is weakly and ${}^{100}\mathrm{Zr}$ is strongly deformed. To further examine this intricate phenomenon, in this work lifetimes of low-lying excited states in the nuclei ${}^{99}\mathrm{Zr}$ and ${}^{99}\mathrm{Nb}$ were determined using fast-timing techniques and an experimental setup consisting of four ${\mathrm{LaBr}}_3\left(\mathrm{Ce}\right)$ detectors. Neutron rich $A=99$ fragments were produced in neutron induced fission and separated by the spectrometer LOHENGRIN at the Institut Laue-Langevin in Grenoble, France. Experimental values are compared to two different calculations in the framework of the interacting boson-fermion model and discussed in the context of shape coexistence.

We consider nonequilibrium evolution of non-Gaussian fluctuations within relativistic hydrodynamics relevant for the QCD critical point search in heavy-ion collision experiments. We rely on the hierarchy of relaxation timescales, which emerges in the hydrodynamic regime near the critical point, to focus on the slowest mode such as the fluctuations of specific entropy, whose equilibrium magnitude, non-Gaussianity, and typical relaxation time are increasing as the critical point is approached. We derive evolution equations for the non-Gaussian correlators of this diffusive mode in an arbitrary relativistic hydrodynamic flow. We compare with the simpler case of the stochastic diffusion on a static homogeneous background and identify terms which are specific to the case of the full hydrodynamics with pressure fluctuations and flow.

Using the recently developed “maximum entropy” (or “least biased”) distribution function to truncate the moment hierarchy arising from kinetic theory, we formulate a far-from-equilibrium macroscopic theory that provides the possibility of describing both free-streaming and hydrodynamic regimes of heavy-ion collisions within a single framework. Unlike traditional hydrodynamic theories that include viscous corrections to finite order, the present formulation incorporates contributions to all orders in shear and bulk inverse Reynolds numbers, allowing it to handle large dissipative fluxes. By considering flow profiles relevant for heavy-ion collisions (Bjorken and Gubser flows), we demonstrate that the present approach provides excellent agreement with underlying kinetic theory throughout the fluid's evolution and, especially, in far-off-equilibrium regimes where traditional hydrodynamics breaks down.

We demonstrate that proton and pion flow measurements in heavy-ion collisions at incident energies ranging from 1 to 20 GeV per nucleon in the fixed target frame can be used for an accurate determination of the symmetric nuclear matter equation of state at baryon densities equal 2–4 times nuclear saturation density $n_0$. We simulate $\mathrm{Au}+\mathrm{Au}$ collisions at these energies using a hadronic transport model with an adjustable vector mean-field potential dependent on baryon density $n_B$. We show that the mean field can be parametrized to reproduce a given density dependence of the speed of sound at zero temperature $c_s^2(n_B,T=0)$, which we vary independently in multiple density intervals to probe the differential sensitivity of heavy-ion observables to the equation of state at these specific densities. Recent flow data from the STAR experiment at the center-of-mass energies $\sqrt{s_{NN}}=\{3.0,4.5\}\mathrm{GeV}$ can be described by our model, and a Bayesian analysis of these data indicates a hard equation of state at $n_B\in (2,3)n_0$ and a possible phase transition at $n_B\in (3,4)n_0$. More data at $\sqrt{s_{NN}}=2–5\text{GeV}$, as well as a more thorough analysis of the model systematic uncertainties will be necessary for a more precise conclusion.

Long-range correlations for pairs of charged particles with two-particle angular correlations are studied in $pp$ at $\sqrt{\mathit{\text{s}}}=13$ TeV with various Monte Carlo generators. The correlation functions are constructed as functions of the relative azimuthal angle $\mathrm{\Delta }\phi$ and the pseudorapidity separation $\mathrm{\Delta }\eta$ for pairs of different particle species with the identified hadrons such as $\pi$, $K$, $p$, and $\mathrm{\Lambda }$ in wide $\mathrm{\Delta }\eta$ ranges. Fourier coefficients are extracted for the long-range correlations in several-multiplicity classes using a low-multiplicity template fit method. The method allows one to subtract the enhanced away-side jet fragments in high-multiplicity events with respect to low-multiplicity events. However, we found that due to a kinematic bias on jets and differing model implementation of flow and jet components, subtracting the nonflow contamination in small systems can bias the results. It is found that the pythia8 default model where the presence of the collective flow is not expected but the bias results in very large flow. Also extracting flow signal from the epos4 and pythia8 string shoving models is not possible because of the flow signal introduced in the low-multiplicity events. Only a multiphase transport string melting model among studied model calculations is free from this bias and shows a mass ordering at low $p_{\mathrm{T}}$ and particle type grouping in the intermediate-$p_{\mathrm{T}}$ range. This feature was first observed in large systems, but the mass ordering in small systems differs from that observed in large collision systems.

The inner crust of a cold, nonaccreting neutron star is composed of a lattice of nuclei coexisting with a sea of superfluid neutrons. The interaction between one of the nuclei and a vortex induced by the rotation of a pulsar is calculated microscopically, based on the axially deformed Hartree-Fock-Bogolyubov framework, using effective interactions. The present work extends and improves previous studies in four ways: (i) it allows for the axial deformation of protons induced by the large deformation of neutrons due to the appearance of vortices; (ii) it includes the effect of Coulomb exchange; (iii) it considers the possible effects of the screening of the pairing interaction; and (iv) it improves the numerical treatment. We also demonstrate that the binding energy of the nucleus-vortex system can be used as a proxy to the pinning energy of a vortex and discuss in which conditions this applies. From our results, we can estimate the mesoscopic pinning forces per unit length acting on vortices. We obtain values ranging between ${10}^{14}$ to ${10}^{16}$ dyn/cm, consistent with previous findings.

Nucleon effective masses in neutron-rich matter are studied with the relativistic Brueckner-Hartree-Fock (RBHF) theory in the full Dirac space. The neutron and proton effective masses for symmetric nuclear matter are 0.80 times rest mass, which agrees well with the empirical values. In neutron-rich matter, the effective mass of the neutron is found to be larger than that of the proton, and the neutron-proton effective mass splittings at the empirical saturation density are predicted as $0.187\alpha$ with $\alpha$ being the isospin asymmetry parameter. The result is compared to other ab initio calculations and is consistent with the constraints from the nuclear reaction and structure measurements, such as the nucleon-nucleus scattering, the giant resonances of ${}^{208}\mathrm{Pb}$, and the Hugenholtz–Van Hove theorem with systematics of nuclear symmetry energy and its slope. The predictions of the neutron-proton effective mass splitting from the RBHF theory in the full Dirac space might be helpful to constrain the isovector parameters in phenomenological density functionals.

There is overwhelmingly experimental evidence indicating that excited nuclear states are dominated by quasiparticle (qp) excitations, which form many-body configurations with broken nucleon-pairs from different orbitals. By taking these multi-qp states as building blocks for a shell-model basis, we propose a novel shell-model method for the calculation of nuclear level density (NLD) in deformed nuclei. The shell-model diagonalization with two-body residual interactions yields a large ensemble of eigenstates of angular momentum and parity. We demonstrate that NLD as a statistical quantity depends sensitively on the structure of deformed single-particle states. As the first example to introduce this method, we take a well-deformed rare-earth nucleus, ${}^{164}\mathrm{Dy}$, for which NLD has been studied extensively by the Oslo method. By a quantitative comparison with discrete levels from spectroscopic measurements, we show that while the pronounced stepwise structure in the low-energy NLD curve can be understood as the collective excitation and nucleon-pair breaking, the exponential growth of levels in the higher-energy NLD can be described by the combination of the broken-pair states, subject to the Pauli principle. According to the nature of NLD with increasing excitation, we divide the entire NLD curve into (1) collective regime, (2) pair-breaking regime, and (3) multi-qp regime. We discuss the formation mechanism and characteristic features of NLD for the three regimes. In addition, the parity dependence and angular-momentum dependence in NLD are investigated with a strong emphasis on the structure effect.

The production of electrons from beauty-hadron decays was measured at midrapidity in proton-proton ($pp$) and central Pb-Pb collisions at center-of-mass energy per nucleon-nucleon pair $\sqrt{s_{NN}}$ = 5.02 TeV, using the ALICE detector at the LHC. The cross section measured in $pp$ collisions in the transverse momentum interval $2<p_{\mathrm{T}}<8\mathrm{GeV}/c$ was compared with models based on perturbative quantum chromodynamics calculations. The yield in the 10% most central Pb-Pb collisions, measured in the interval $2<p_{\mathrm{T}}<26\mathrm{GeV}/c$, was used to compute the nuclear modification factor $R_{AA}$, extrapolating the $pp$ reference cross section to $p_{\mathrm{T}}$ larger than 8 $\mathrm{GeV}/c$. The measured $R_{AA}$ shows significant suppression of the yield of electrons from beauty-hadron decays at high $p_{\mathrm{T}}$ and does not show a significant dependence above $8\mathrm{GeV}/c$ within uncertainties. The results are described by several theoretical models based on different implementations of the interaction of heavy quarks with a quark-gluon plasma, which predict a smaller energy loss for beauty quarks compared to light and charm quarks.

Under the framework of the vector meson dominance model, the absolute scattering lengths of light vector mesons ($\varphi , \omega$, and $\rho$) with the deuteron are calculated from the cross sections of vector meson photoproduction off a deuteron. Additionally, a fitting function is used to predict the scattering lengths of the heavy vector mesons $J/\psi -d$ and $\mathrm{{\rm Y}}-d$. Based on these results, the distribution of the scattering lengths $|{\alpha }_{Vd}|$ between vector mesons and the deuteron is presented and compared with the scattering lengths $|{\alpha }_{Vp}|$ between vector mesons and the proton. It is found that as the mass of the vector meson increases, the scattering lengths $|{\alpha }_{Vd}|$ become closer to $|{\alpha }_{Vp}|$. In addition, the correlation analysis indicates a strong positive relationship between the scattering length and the vector meson radius with a high correlation coefficient. The implications of results are essential for improving our understanding of the interaction between hadron and nucleus.

The ${}^{25}\mathrm{Al}(p,\gamma )$ reaction has long been highlighted as a possible means to bypass the production of ${}^{26}\mathrm{Al}$ cosmic $\gamma$ rays in classical nova explosions. However, uncertainties in the properties of key resonant states in ${}^{26}\mathrm{Si}$ have hindered our ability to accurately model the influence of this reaction in such environments. We report on a detailed $\gamma$-ray spectroscopy study of ${}^{26}\mathrm{Si}$ and present evidence for the existence of a new, likely $\ell =1$, resonance in the ${}^{25}\mathrm{Al}$ $+$ $p$ system at $E_r=153.9\left(15\right)$ keV. This state is now expected to provide the dominant contribution to the ${}^{25}\mathrm{Al}(p,\gamma )$ stellar reaction rate over the temperature range, $T\approx 0.1-0.2$ GK. Despite a significant increase in the rate at low temperatures, we find that the final ejected abundance of ${}^{26}\mathrm{Al}$ from classical novae remains largely unaffected even if the reaction rate is artificially increased by a factor of 10. Based on new, galactic chemical evolution calculations, we estimate that the maximum contribution of novae to the observed galactic abundance of ${}^{26}\mathrm{Al}$ is $\approx 0.2M_{\odot }$. Finally, we briefly highlight the important role that super-asymptotic giant branch stars may play in the production of ${}^{26}\mathrm{Al}$.