In very high-energy collisions nuclei are practically transparent to each other but produce very hot nearly baryon-free matter in the so-called central rapidity region. The energy in the central rapidity region comes from the kinetic energy of the colliding nuclei. We calculate the energy and rapidity loss of the nuclei using the color glass condensate model. This model also predicts the excitation energy of the nuclear fragments. Using a space-time picture of the collision we calculate the baryon and energy densities of the receding baryonic fireballs. For central collisions of gold nuclei at the highest energy attainable at the Relativistic Heavy-Ion Collider, for example, we find baryon densities more than ten times that of atomic nuclei over a large volume.

Background: Projectile breakup can make a large contribution to reactions induced by projectiles with mass numbers 2, 3, and 4, yet there is no global model for it and no clear agreement on the details of the reaction mechanism.

Purpose: This project aims to develop a phenomenological model for light-projectile breakup that can guide the development of detailed theories and provide a useful tool for applied calculations.

Method: An extensive database of double-differential cross sections for the breakup of deuterons, ${}^3\mathrm{He}$ ions, and $\alpha$ particles was assembled from the literature and analyzed in a consistent way.

Results: Global systematics for the centroid energies, peak widths, and angular distributions of the breakup peaks have been extracted from the data. The dominant mechanism appears to be absorptive breakup, where the unobserved projectile fragment fuses with the target nucleus during the initial interaction. The global target-mass-number and incident-energy dependencies of the absorptive breakup cross section have also been determined, along with channel-specific normalization constants.

Conclusions: Results from the model generally agree with the original data after subtraction of a reasonable underlying continuum. Absorptive breakup can account for as much as 50%–60% of the total reaction cross section.

Based on the factorization formalism of nonrelativistic quantum chromodynamics (NRQCD), we calculate the production cross section for the charmonium [$J/\psi$, $\psi \left(2S\right)$, ${\chi }_{cJ}$, ${\eta }_c$, and $h_c$] and the bottomonium [$\mathrm{{\rm Y}}\left(nS\right)$, ${\chi }_{bJ}$, ${\eta }_b$, and $h_b$] produced by the hard photoproduction processes and fragmentation processes in relativistic heavy ion collisions. It is shown that the existing experimental data on heavy quarkonium production at the Large Hadron Collider (LHC) can be described in the framework of the NRQCD formalism, and the phenomenological values of matrix elements for color-singlet and color-octet components give the main contribution. The numerical results of photoproduction processes and fragmentation processes for the heavy quarkonium production become prominent in $p-p$ collisions and Pb-Pb collisions at LHC energies.

We show the effects of a triangle singularity mechanism for the $\gamma p\to K^{+}\mathrm{\Lambda }\left(1405\right)$ reaction. The mechanism has a $N^{*}$ resonance around 2030 MeV, which decays into $K^{*}\mathrm{\Sigma }$. The $K^{*}$ decays to $K^{+}\pi$, and the $\pi \mathrm{\Sigma }$ merge to form the $\mathrm{\Lambda }\left(1405\right)$. This mechanism produces a peak around $\sqrt{s}=2110$ MeV, and has its largest contribution around $\cos \theta =0$. The addition of this mechanism to other conventional ones leads to a good reproduction of $d\sigma /d\cos \theta$ and the integrated cross section around this energy, providing a solution to a problem encountered in previous theoretical models.

I construct a model of the inner crust of neutron stars using interactions from chiral effective field theory (EFT) in order to calculate its equation of state (EOS), shear properties, and the spectrum of crustal shear modes. I systematically study uncertainties associated with the nuclear physics input, the crust composition, and neutron entrainment, and estimate their impact on crustal shear properties and the shear-mode spectrum. I find that the uncertainties originate mainly in two sources: The neutron-matter EOS and neutron entrainment. I compare the spectrum of crustal shear modes to observed frequencies of quasiperiodic oscillations in the afterglow of giant $\gamma$-ray bursts and find that all of these frequencies could be described within uncertainties, which are, however, at present too sizable to infer neutron-star properties from observations.

We study the surface tension of highly magnetized three-flavor quark matter within the formalism of multiple reflection expansion. Quark matter is described as a mixture of free Fermi gases composed of quarks $u$, $d$, $s$ and electrons in chemical equilibrium under weak interactions. Due to the presence of strong magnetic fields the particles' transverse motion is quantized into Landau levels, and the surface tension has a different value in the parallel and transverse directions with respect to the magnetic field. We calculate the transverse and longitudinal surface tension for different values of the magnetic field and for quark-matter drops with different sizes, from a few fm to the bulk limit. For baryon number densities between 2 to 10 times the nuclear saturation density, the surface tension falls in the range of 2 to 20 $\mathrm{MeV}/{\mathrm{fm}}^2$. The largest contribution comes from strange quarks which have a surface tension an order of magnitude larger than the one for $u$ or $d$ quarks and more than two orders of magnitude larger than for electrons. Our results show that the total surface tension is quite insensitive to the size of the drop. We also find that the surface tensions in the transverse and parallel directions are almost unaffected by the magnetic field if $eB$ is below $\sim 5\times {10}^{-3}{\mathrm{GeV}}^2$. Nevertheless, for higher values of $eB$, there is a significant increase in the parallel surface tension and a significant decrease in the transverse one with respect to the unmagnetized case.

We present a microscopic model for electric monopole ($E0$) transition matrix elements by combining a configuration interaction model for orbital occupations with an energy-density functional model for the single-particle potential and radial wave functions. The configuration interaction model is used to constrain the orbital occupations for the diagonal and off-diagonal matrix elements. These are used in an energy-density functional calculation to obtain a self-consistent transition density. This density contains the valence contribution, as well as the polarization of the protons by the valence protons and neutrons. We show connections between $E0$ matrix elements and isomer and isotope shifts of the charge radius. The spin-orbit correction to the charge density is important in some cases. This model accounts for a large part of the data over a wide region of the nuclear chart. It also accounts for the shape of the observed electron scattering form factors. The results depend on the Skyrme parameters used for the energy-density functional and might be used to provide new constraints for them.

The advanced time-delayed $\gamma \gamma \left(t\right)$ method has been applied to determine half-lives of low-lying states in the $N=50$ isotones ${}^{94}\mathrm{Ru}$ and ${}^{96}\mathrm{Pd}$. The inferred experimental $E2$ strengths for the $4^{+}\to 2^{+}$ transitions in the two nuclei show a dramatic deviation with respect to the shell model predictions in the $(f_{5/2},p,g_{9/2})$ proton hole space in ${}^{100}\mathrm{Sn}$. The anomalous behavior can be ascribed to a breakdown of the seniority quantum number in the $\pi g_{9/2}^n$ configuration due to particle-hole excitations across the $N=Z=50$ shell as confirmed by large-scale shell model calculations.

The $\beta$ decay of the drip-line nucleus ${}^{20}\mathrm{Mg}$ gives important information on key astrophysical resonances in ${}^{20}\mathrm{Na}$, which are relevant to the onset of the rapid proton capture process. A detailed $\beta$-decay spectroscopic study of ${}^{20}\mathrm{Mg}$ was performed by a continuous-implantation method. A detection system was specially developed for charged-particle decay studies, giving improved spectroscopic information including the delayed proton energies, the half-life of ${}^{20}\mathrm{Mg}$, the excitation energies, the branching ratios, and the $logft$ values for the states in ${}^{20}\mathrm{Na}$ populated in the $\beta$ decay of ${}^{20}\mathrm{Mg}$. A new proton branch was observed and the corresponding excited state in ${}^{20}\mathrm{Na}$ was proposed. The large isospin asymmetry for the mirror decays of ${}^{20}\mathrm{Mg}$ and ${}^{20}\mathrm{O}$ was also well reproduced. To resolve the long-standing problem about the astrophysically interesting 2645 keV resonance in ${}^{20}\mathrm{Na}$ convincingly, a higher-statistics measurement may still be needed.

Background: For a long time, fission barriers of actinide nuclei have been mostly microscopically calculated for even-even fissioning systems. Calculations in the case of odd nuclei have been performed merely within a so-called equal-filling approximation (EFA) as opposed to an approach taking explicitly into account the time-reversal-breaking properties at the mean-field level—and for only one single-particle configuration.

Purpose: We study the dependence of the fission barriers on various relevant configurations (e.g., to evaluate the so-called specialization energy). In addition, we want to assess the relevance of the EFA approach as a function of the deformation, which has been already found for the ground-state deformation.

Methods: Calculations within the Hartree–Fock plus BCS approach with self-consistent particle blocking have been performed by using the ${\mathrm{SkM}}^{*}$ Skyrme effective interaction in the particle-hole channel and a seniority force in the particle-particle channel. Axial symmetry has been imposed throughout the whole fission path while the intrinsic parity symmetry has been allowed to be broken in the outer fission barrier region.

Results: Potential-energy curves have been determined for six different configurations in ${}^{235}\mathrm{U}$ and four in ${}^{239}\mathrm{Pu}$. Inner and outer fission barriers have been calculated along with some spectroscopic properties in the fission isomeric well. These results have been compared with available data. The influence of time-reversal-breaking mean fields on the solutions has been investigated.

Conclusions: A sizable configuration dependence of the fission barrier (width and height) has been demonstrated. A reasonable agreement with available systematic evaluations of fission-barrier heights has been found. The EFA approach has been validated at the large elongations occurring at the outer-barrier region.

The influence of pairing correlations on the neutron root mean square (rms) radius of nuclei is investigated in the framework of self-consistent Skyrme Hartree-Fock-Bogoliubov calculations. The continuum is treated appropriately by the Green's function techniques. As an example the nucleus ${}^{124}\mathrm{Zr}$ is treated for a varying strength of pairing correlations. We find that, as the pairing strength increases, the neutron rms radius first shrinks, reaches a minimum, and beyond this point it expands again. The shrinkage is due to the the so-called pairing antihalo effect, i.e., due to the decrease of the asymptotic density distribution with increasing pairing. However, in some cases, increasing pairing correlations can also lead to an expansion of the nucleus due to a growing occupation of so-called halo orbits, i.e., weakly bound states and resonances in the continuum with low-$\ell$ values. In this case, the neutron radii are extended just by the influence of pairing correlations, since these halo orbits cannot be occupied without pairing. The term “antihalo effect” is not justified in such cases. For a full understanding of this complicated interplay, self-consistent calculations are necessary.

The interaction potential energy of the three deformed fragments formed in fission of ${}^{252}\mathrm{Cf}$ is studied for various combinations of three-fragment fission. The lowest height of the potential energy ridge between three touching and separated deformed fragments is sought. The excitation energies of various three-deformed-fragment configurations, at the lowest barrier heights related to the yield of the corresponding configuration, are considered in detail. The most probable three-fragment fission configurations are discussed. The yields of various ternary fragments in fission of ${}^{250}\mathrm{Cf}$ agree well with available experimental data.

We study the Bose-Einstein condensation of a finite-size pion gas subject to the influence of a magnetic field. We find the expressions for the critical chemical potential and temperature for the onset of condensation. We show that for values of the external magnetic flux larger than the elemental flux, the critical temperature is larger than the one obtained by considering only finite-size effects. We use experimentally reported values of pion source sizes and multiplicities at Large Hadron Collider (LHC) energies to show that if the magnetic flux, produced initially in peripheral heavy-ion collisions, is at least partially preserved up to the hadronic phase, the combined finite-size and magnetic field effects give rise to a critical temperature above the kinetic freeze-out temperature. We discuss the implications for the evolution of the pion system created in relativistic heavy-ion collisions.

As is well known, spacelike proton form factors expressed in the Breit frame may be interpreted as the Fourier transform of static space distributions of electric charge and current. In particular, the electric form factor is simply the Fourier transform of the charge distribution $F\left(q\right)=\int e^{i\vec{q}·\vec{r}}\rho \left(r\right)d^{3}r$. We do not have an intuitive interpretation of the same level of simplicity for the proton timelike form factor appearing in the reactions $e^{+}{e}^{-}\leftrightarrow \overline{p}p$. However, one may suggest that, in the center-of-mass frame, where $q_{\mu }{x}^{\mu }=qt$, a timelike electric form factor is the Fourier transform $F\left(q\right)=\int e^{iqt}R\left(t\right)dt$ of a function $R\left(t\right)$ expressing how the electric properties of the forming (or annihilating) proton-antiproton pair evolve in time. Here we analyze in depth this idea and show that the functions $\rho \left(r\right)$ and $R\left(t\right)$ can be formally written as the time and space integrals of a unique correlation function depending on both time and space coordinates.

The isovector giant dipole resonance (IVGDR) $\gamma$ decay was measured in the compound nuclei ${}^{80}\mathrm{Zr}$ and ${}^{81}\mathrm{Rb}$ at an excitation energy of $E^{*}=54$ MeV. The fusion reaction ${}^{40}\mathrm{Ca}+{}^{40}\mathrm{Ca}$ at $E_{\mathrm{beam}}=136$ MeV was used to form the compound nucleus ${}^{80}\mathrm{Zr}$, while the reaction ${}^{37}\mathrm{Cl}+{}^{44}\mathrm{Ca}$ at $E_{\mathrm{beam}}=95$ MeV was used to form the compound nucleus ${}^{81}\mathrm{Rb}$ at the same excitation energy. The IVGDR parameters extracted from the analysis were compared with the ones found at higher excitation energy ($E^{*}=83$ MeV). The comparison allows one to observe two different nuclear mechanisms: (i) the IVGDR intrinsic width remains constant with the excitation energy in the nucleus ${}^{81}\mathrm{Rb}$; (ii) the isospin-violating spreading width (i.e., Coulomb spreading width) remains constant with the excitation energy in the nucleus ${}^{80}\mathrm{Zr}$. The experimental setup used for the $\gamma$-ray detection was composed by the AGATA demonstrator array coupled to the large-volume ${\mathrm{LaBr}}_3$:Ce detectors of the ${\mathrm{HECTOR}}^{+}$ array.

We use a three-body continuum discretized coupled channel (CDCC) model to investigate Coulomb and nuclear effects in breakup and reaction cross sections. The breakup of the projectile is simulated by a finite number of square integrable wave functions. First we show that the scattering matrices can be split in a nuclear term and in a Coulomb term. This decomposition is based on the Lippmann-Schwinger equation and requires the scattering wave functions. We present two different methods to separate both effects. Then, we apply this separation to breakup and reaction cross sections of ${}^7\mathrm{Li}+{}^{208}\mathrm{Pb}$. For breakup, we investigate various aspects, such as the role of the $\alpha +t$ continuum, the angular-momentum distribution, and the balance between Coulomb and nuclear effects. We show that there is a large ambiguity in defining the Coulomb and nuclear breakup cross sections, since both techniques, although providing the same total breakup cross sections, strongly differ for the individual components. We suggest a third method which could be efficiently used to address convergence problems at large angular momentum. For reaction cross sections, interference effects are smaller, and the nuclear contribution is dominant above the Coulomb barrier. We also draw attention to different definitions of the reaction cross section which exist in the literature and which may induce small, but significant, differences in the numerical values.

We study the strange vector meson ($K^{*},{\overline{K}}^{*}$) dynamics in relativistic heavy-ion collisions based on the microscopic parton-hadron-string dynamics (PHSD) transport approach which incorporates partonic and hadronic degrees of freedom, a phase transition from hadronic to partonic matter—quark-gluon-plasma (QGP)—and a dynamical hadronization of quarks and antiquarks as well as final hadronic interactions. We investigate the role of in-medium effects on the $K^{*},{\overline{K}}^{*}$ meson dynamics by employing Breit–Wigner spectral functions for the $K^{*}$ with self-energies obtained from a self-consistent coupled-channel $G$-matrix approach. Furthermore, we confront the PHSD calculations with experimental data for $p+p$, $\text{Cu}+\text{Cu}$, and $\text{Au}+\text{Au}$ collisions at energies up to $\sqrt{s_{NN}}=200$ GeV. Our analysis shows that, at relativistic energies, most of the final $K^{*}$ (observed experimentally) are produced during the late hadronic phase, dominantly by the $K+\pi \to K^{*}$ channel, such that the fraction of the $K^{*}$ from the QGP is small and can hardly be reconstructed from the final observables. The influence of the in-medium effects on the $K^{*}$ dynamics at energies typical of the BNL Relativistic Heavy Ion Collider is rather modest due to their dominant production at low baryon densities (but high meson densities); however, it increases with decreasing beam energy. Moreover, we find that the additional cut on the invariant-mass region of the $K^{*}$ further influences the shape and the height of the final spectra. This imposes severe constraints on the interpretation of the experimental results.

We analyze the data on cross sections and asymmetries for the $pd\to \eta {}^3\mathrm{He}$ reaction close to threshold and look for bound states of the $\eta {}^3\mathrm{He}$ system. Rather than parameterizing the scattering matrix, as is usually done, we develop a framework in which the $\eta {}^3\mathrm{He}$ optical potential is the key ingredient, and its strength, together with some production parameters, are fitted to the available experimental data. The relationship of the scattering matrix to the optical potential is established using the Bethe-Salpeter equation and the $\eta {}^3\mathrm{He}$ loop function incorporates the range of the interaction given by the empirical ${}^3\mathrm{He}$ density. We find a local Breit-Wigner form of the $\eta {}^3\mathrm{He}$ amplitude $T$ below threshold with a clear peak in ${\left|T\right|}^2$, which corresponds to an $\eta {}^3\mathrm{He}$ binding of about 0.3 MeV and a width of about 3 MeV. By fitting the potential we can also evaluate the $\eta {}^3\mathrm{He}$ scattering length, including its sign, thus resolving the ambiguity in the former analyses.

Partial-wave analysis of meson and photon-induced reactions is needed to enable the comparison of many theoretical approaches to data. In both energy-dependent and independent parametrizations of partial waves, the selection of the model amplitude is crucial. Principles of the $S$ matrix are implemented to a different degree in different approaches; but a many times overlooked aspect concerns the selection of undetermined coefficients and functional forms for fitting, leading to a minimal yet sufficient parametrization. We present an analysis of low-energy neutral pion photoproduction using the least absolute shrinkage and selection operator (LASSO) in combination with criteria from information theory and $K$-fold cross validation. These methods are not yet widely known in the analysis of excited hadrons but will become relevant in the era of precision spectroscopy. The principle is first illustrated with synthetic data; then, its feasibility for real data is demonstrated by analyzing the latest available measurements of differential cross sections ($d\sigma /d\mathrm{\Omega }$), photon-beam asymmetries ($\mathrm{\Sigma }$), and target asymmetry differential cross sections ($d{\sigma }_T/d\equiv Td\sigma /d\mathrm{\Omega }$) in the low-energy regime.

We introduce a new microscopic approach to calculate the dependence of fusion barriers and cross sections on isospin dynamics. The method is based on the time-dependent Hartree–Fock theory and the isoscalar and isovector properties of the energy density functional (EDF). The contribution to the fusion barriers originating from the isoscalar and isovector parts of the EDF is calculated. It is shown that, for nonsymmetric systems, the isovector dynamics influence the subbarrier fusion cross sections. For most systems this results in an enhancement of the subbarrier cross sections, while for others we observe differing degrees of hindrance. We use this approach to provide an explanation of recently measured fusion cross sections which show a enhancement at low $E_{\mathrm{c}.\mathrm{m}.}$ energies for the system ${}^{40}\mathrm{Ca}+{}^{132}\mathrm{Sn}$ as compared with the more neutron-rich system ${}^{48}\mathrm{Ca}+{}^{132}\mathrm{Sn}$ and discuss the dependence of subbarrier fusion cross sections on transfer.