Fusion cross sections have been measured for the asymmetric system ${}^{16}\mathrm{O}+{}^{165}\mathrm{Ho}$ at energies near and deep below the Coulomb barrier with an aim to investigate the occurrence of fusion hindrance for the system. Cross sections down to $\approx 700$ nb have been measured using the off-beam $\gamma$-ray technique. The fusion cross sections have been compared with the coupled channel calculations. The energy onset of fusion hindrance appears to occur at $E_{\mathrm{c}.\mathrm{m}.}=57\pm 0.85$ MeV, where a deviation in the slope of the experimental logarithmic derivative compared to that of coupled channel calculations has been observed. This is in agreement with the value obtained from the touching point configuration of the adiabatic model.

Rotational bands built on single quasiproton excitations in ${}^{127}\mathrm{Cs}$ have been investigated using the ${}^{121}\mathrm{Sb}({}^{12}\mathrm{C},\alpha 2n$) reaction and the ROSPHERE detector array at IFIN-HH, Bucharest. The lifetimes in the yrast negative-parity band based on the proton in $h_{11/2}$ orbital have been measured by applying the Doppler-shift attenuation method. The lifetime of the ${7/2}^{+}$ 273-keV state, member of the rotational band associated with the proton $g_{7/2}$ orbital, has been determined as $\tau$ = 1.22(5) ns by the fast timing technique. The experimental data were compared with the calculations performed using the quasiparticle plus triaxial rotor model and deformation parameters ${\epsilon }_2$ and $\gamma$ have been derived for the positive- and negative-parity structures. Evidence for triaxial nuclear shapes in the states described by the proton $h_{11/2}$ orbital was provided by both signature splitting and $B(E2,\mathrm{\Delta }J=2)$ transition strengths.

The formation of continuum neutron distribution in ${}^7\mathrm{Li}(p,n)$ has been identified as due to the coupling of the ${}^7\mathrm{Be}$ breakup levels to the final state of the reaction. The continuum neutron spectra produced by the ${}^7\mathrm{Li}(p,n)$ reaction has been estimated by measuring the double differential cross sections for continuum and resonant breakup of ${}^7\mathrm{Be}$, through the ${}^7\mathrm{Li}(p,n){}^7\mathrm{Be}^{*}$ reaction at 21 MeV of proton energy. The breakup contributions from continuum and $5/2^{-}$, $7/2^{-}$ states of ${}^7\mathrm{Be}$ have been identified. The measured double differential cross sections have been reproduced through continuum-discretized coupled channel-coupled reaction channel calculations. The cross sections were projected to neutron spectrum using the Monte Carlo approach and validated using experimentally measured ${}^3\mathrm{He}$ gated neutron spectra. ${}^7\mathrm{Li}(p,n)$ neutron spectrum at 20 MeV incident proton energy measured by McNaughton et al. [Nucl. Instrum. Methods 130, 555 (1975)] has been reproduced by adapting estimated model parameters for the reaction.

We propose a method to increase both the neutron storage time and the precision of its lifetime measurements by at least tenfold. The storage of ultracold neutrons (UCN) in material traps now provides the most accurate measurements of neutron lifetime and is used in many other experiments. The precision of these measurements is limited by the interaction of UCN with the trap walls. We show that covering trap walls with liquid helium may strongly decrease the UCN losses from material traps. ${}^4\mathrm{He}$ does not absorb neutrons at all. Superfluid He covers the trap walls as a thin film, $\approx 10$ nm thick, due to the van der Waals attraction. However, this He film on a flat wall is too thin to protect the UCN from their absorption inside a trap material. By combining the van der Waals attraction with capillary effects we show that surface roughness may increase the thickness of this film much beyond the neutron penetration depth, $\approx 33\mathrm{nm}$. Using liquid He for UCN storage requires low temperature, $T<0.5$ K, to avoid neutron interaction with He vapor, while the neutron losses because of the interaction with surface waves are small and can be accounted for using their linear temperature dependence.

We closely investigate $NN$ potentials based upon the $\mathrm{\Delta }$-full version of chiral effective-field-theory. We find that recently constructed $NN$ potentials of this kind, which (when applied together with three-nucleon forces) were presented as predicting accurate binding energies and radii for a range of nuclei from $A=16$ to $A=132$ and providing accurate equations of state for nuclear matter, yield a ${\chi }^2/\mathrm{datum}$ of 60 for the reproduction of the $pp$ data below 100 MeV laboratory energy. This ${\chi }^2$ is more than three times what the Hamada-Johnston potential of the year of 1962 achieved already some 60 years ago. We perceive this historical fact as concerning in view of the current emphasis on precision. We are able to trace the very large ${\chi }^2$ as well as the apparent success of the potentials in nuclear structure to unrealistic predictions for $P$-wave states, in which the $\mathrm{\Delta }$-full next-to-next-to-leading order (NNLO) potentials are off by up to 40 times the NNLO truncation errors. In fact, we show that the worse the description of the $P$-wave states, the better the predictions in nuclear structure. Thus, these potentials cannot be seen as the solution to the outstanding problems in current microscopic nuclear structure physics.

The occupancies and vacancies of the valence neutron orbitals across the stable tin isotopic chain from $112\le A\le 124$ have been determined. These were inferred from the cross sections of neutron-adding and -removing reactions. In each case, the reactions were chosen to have good angular-momentum matching for transfer to the low- and high-$\ell$ orbitals present in this valence space. These new data are compared to older systematic studies. The effective single-neutron energies are determined by combining information from energy centroids determined from the adding and removing reactions. Two of the five orbitals are nearly degenerate, below $N=64$, and approximately 2 MeV more bound than the other three, which are also degenerate.

Reactions involving weakly bound nuclei, both stable and radioactive, especially at energies near the Coulomb barrier remain at the forefront as topics to be understood, both experimentally and theoretically. Of special interest is the interplay between complete fusion, breakup, and direct reactions for these cases and the complete understanding of their influence on fusion, which arises because of the bottleneck in experimentally identifying complete fusion events. In this work we address this issue by measuring individual residue cross sections in the interaction of ${}^{6,7}\mathrm{Li}$ on a thin ${}^{58}\mathrm{Ni}$ target at energies around the barrier. Comparison with statistical model calculations and coupled reaction calculations allowed us to delineate the reaction products into those arising from complete fusion and those from direct transfer. At energies below the barrier where cross section enhancement is found to occur, the contribution of transfer channels to the total cross section is found to be large and had to be accounted for before assessing the enhancement above the one-dimensional barrier penetration predictions.

We suggest an extension to isospin asymmetric matter of the quarkyonic model from McLerran and Reddy [Phys. Rev. Lett. 122, 122701 (2019)]. This extension allows us to construct the $\beta$ equilibrium between quarks, nucleons, and leptons. The concept of quarkyonic matter originates from the large number of color limit for which nucleons have the correct degrees of freedom near the Fermi surface—reflecting the confining forces—while deep inside the Fermi sea quarks appear naturally. In isospin-asymmetric matter, we suggest to implement this concept within a global isoscalar relation between the shell gaps differentiating the nucleon and the quark sectors. In addition, we impose the conservation of the isospin-flavor asymmetry for the nucleon and the quark components. Within this model, several quarkyonic stars are constructed on top of the SLy4 model for the nucleon sector, producing a bump in the sound speed. As a consequence, quarkyonic stars are systematically bigger and have a larger maximum mass than the associated neutron stars. This model also predicts a lower proton fraction at $\beta$ equilibrium, which potentially quenches fast cooling in massive compact stars.

Proton decays of ${}^{10}\mathrm{N}$ states have been investigated with the invariant-mass technique using data from two reactions. In the first experiment, ${}^{10}\mathrm{N}$ states were created via multinucleon knockout from a fast ${}^{13}\mathrm{O}$ beam. The second experiment involved proton pickup from a ${}^9\mathrm{Be}$ target to a fast ${}^9\mathrm{C}$ beam. Both data sets produce similar distributions with a peak centered at a decay energy of 2.8 MeV and a width of $\approx 2.5$ MeV. This result is consistent with a previous study using a multinucleon transfer reaction which was originally fit with an $\ell =0$ resonance but later interpreted as an $\ell =1$ resonance. This later interpretation is affirmed as the proton pickup reaction should favor $\ell =1$. This strength is located near the predicted energies of two $\ell =1$ resonances in calculations using complex scaling and the Gamow shell model. The multinucleon knockout data also show excess strength below the main peak which is interpreted as contributions from one or more $\ell =0$ resonances.

We study the ability of variational approaches based on self-consistent mean-field and beyond-mean-field methods to reproduce exact energies and electromagnetic properties of the nuclei defined within the $sd$-shell valence space using the nontrivial USD Hamiltonian. In particular, Hartree-Fock-Bogoliubov (HFB), variation after particle-number projection (VAPNP), and projected generator coordinate methods (PGCM) are compared to exact solutions obtained by the full diagonalization of the Hamiltonian. We analyze the role played by the proton-neutron $\left(pn\right)$ mixing as well as the quadrupole and pairing degrees of freedom (including both isoscalar and isovector channels) in the description of the spectra of even-even, even-odd, and odd-odd nuclei in the whole $sd$ shell.

This work presents a microscopic study of dissipation in fission dynamical evolutions with the time-dependent Hartree-$\mathrm{Fock}+\mathrm{BCS}$ method in terms of energy dependence and pairing dependence. The friction coefficients and dissipation energies are extracted by mapping the symmetric fission process of ${}^{258}\mathrm{Fm}$ into a classical equation of motion. Density-constrained calculations are used to obtain the dynamical potential. The obtained friction coefficients have a strong dependence of deformations, and averagely match the coefficients adopted in statistical models. The dissipation indeed increase with increasing initial excitation energies or with decreasing pairing strengths. It is also shown that dissipations play a significant role in the final stage of scission. The demonstrated characteristics of dissipations will be valuable for calibrations of various fission models.

Using the EPOS3 model with the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model to describe the hadronic phase, we study the production of short-lived hadronic resonances and the modification of their yields and $p_{\mathrm{T}}$ spectra in $p\text{−}\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=$ 5.02 TeV. High-multiplicity $p\text{−}\mathrm{Pb}$ collisions exhibit similar behavior to midperipheral Pb-Pb collisions at LHC energies, and we find indications of a short-lived hadronic phase in $p\text{−}\mathrm{Pb}$ collisions that can modify resonance yields and $p_{\mathrm{T}}$ spectra through scattering processes. The evolution of resonance production is investigated as a function of the system size, which is related to the lifetime of the hadronic phase in order to study the onset and evolution of scattering effects in $p\text{−}\mathrm{Pb}$ collisions. We also study hadron production separately in the core and corona parts of these collisions and explore how this division affects the total particle yields as the system size increases.

The relative importance of neutron transfer and breakup process in a reaction around Coulomb barrier energies has been studied for the ${}^7\mathrm{Li}+{}^{124}\mathrm{Sn}$ system. Coupled channel calculations have been performed to understand the one neutron stripping and pickup cross sections along with the breakup in the ${}^7\mathrm{Li}+{}^{124}\mathrm{Sn}$ system. The systematics of one and two neutron stripping and pickup cross sections with a ${}^7\mathrm{Li}$ projectile on several targets show an approximate universal behavior, which has been explained by a simple model based on barrier penetration. Complete reaction mechanism have been studied by comparing the reaction cross sections with the measured total fusion and one neutron transfer cross sections.

The collective evolution of produced matter in heavy-ion collisions is effectively described by hydrodynamics from time scales greater than the inverse of the temperature, $\tau \gtrsim 1/T$. In the context of the Gubser solution, I show that the hydrodynamization condition $\tau T\gtrsim 1$ is translated into an allowed domain in the spatial system size and the final multiplicity for hydrodynamics applicability. It turns out that the flow measurements in $p\text{−}p$ collisions are inside the domain of validity. I predict that by approaching the boundaries of the allowed domain the hydrodynamic response to the initial ellipticity changes its sign. I follow a rather model-independent approach for the initial state where, instead of modeling the initial energy density of individual events, the initial system size and ellipticity event-by-event fluctuation are modeled. The model, initial state $\mathrm{fluctuation}+\mathrm{Gubser}$ solution$+$Cooper-Frye freeze-out, describes the multiplicity and transverse momentum dependence of two-point and four-point correlation functions ($c_2\left\{2\right\}$ and $c_2\left\{4\right\}$) in an accurate agreement with $p\text{−}p$ collision experimental measurements. In particular, the sign of the four-point correlation function is the same as the observation, which failed to be described correctly in previous studies. I also predict a signal for the sign change in the hydrodynamic response that can be inspected in future experimental measurements of two-point and four-point correlation functions at lower multiplicities.

We consider a plasma of massless particles undergoing Bjorken expansion, mimicking the matter created in ultrarelativistic heavy ion collisions. We study the transition to hydrodynamics using kinetic theory in the relaxation time approximation. By allowing the relaxation time to depend on time, we can monitor the speed of the transition from the collisionless regime to hydrodynamics. By using a special set of moments of the momentum distribution, we reduce the kinetic equation to a coupled mode problem which encompasses all versions of second-order viscous hydrodynamics for Bjorken flows. This coupled mode problem is analyzed first using techniques of linear algebra. Then we transform this two-mode problem into a single nonlinear differential equation and proceed to a fixed point analysis. We identify an attractor solution as the particular solution of this nonlinear equation that joins two fixed points: one corresponding to the collisionless, early time regime, the other corresponding to late time hydrodynamics. We exploit the analytic solution of this equation in order to test several approximations and to identify generic features of the transition to hydrodynamics. We argue that extending the accuracy of hydrodynamics to early time, i.e., to the region of large gradients, amounts essentially to improve the accuracy of the location of the collisionless fixed point. This is demonstrated by showing that a simple renormalization of a second-order transport coefficient puts the free streaming fixed point at the right location, and allows us to reproduce accurately the full solution of the kinetic equation within second-order viscous hydrodynamics, even in regimes far from local equilibrium.

The even-even Ti isotopic chain, from $A=42$ to 70, has been studied within the nuclear shell-model framework by employing an effective Hamiltonian which is derived by way of many-body perturbation theory from a chiral potential with two- and three-body forces, and includes three-body contributions which account for Pauli principle violations in nuclei with more than two valence particles. We consider ${}^{40}\mathrm{Ca}$ as a closed core and a model space spanned by the neutron and proton $0f1p$ orbitals with the addition of the $0g_{9/2}$ orbital for neutrons. Calculated two-neutron separation energies and excitation energies of the yrast $2^{+}$ states are reported and compared with the experimental data, which are available up to ${}^{62}\mathrm{Ti}$. The present study intends to investigate the effects of the adopted effective interactions on the evolution of the shell structure.

Excited states of the neutron-rich ${}^{89}\mathrm{Br}$ have been observed for the first time. They were populated in cold-neutron induced fission of ${}^{235}\mathrm{U}$ at the PF1B facility of the Institut Laue-Langevin, Grenoble. The measurement of $\gamma$ radiation following fission has been performed using the EXILL array of Ge detectors. The observed level structure looks similar to the yrast level structure of ${}^{87}\mathrm{Br}$. Large valence space shell model calculations performed for ${}^{89}\mathrm{Br}$ confirmed this similarity. Comparison of the observed $\pi g_{9/2}$ band with the results of the shell model calculations provides information on the evolution of collectivity in this region.

The production cross section of prompt ${\mathrm{\Lambda }}_c^{+}$ charm baryons was measured with the ALICE detector at the LHC at midrapidity in proton-proton ($pp$) and proton-lead ($p\text{–Pb}$) collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$. The ${\mathrm{\Lambda }}_c^{+}$ and $\overline{\mathrm{\Lambda }}{}_c^{-}$ baryons were reconstructed in the hadronic decay channels ${\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+}$ and ${\mathrm{\Lambda }}_c^{+}\to p{K}_S^0$ and respective charge conjugates. The measured differential cross sections as a function of transverse momentum ($p_T$) and the $p_T$-integrated ${\mathrm{\Lambda }}_c^{+}$ production cross section in $pp$ and in $p\text{–Pb}$ collisions are presented. The ${\mathrm{\Lambda }}_c^{+}$ nuclear modification factor ($R_{p\mathrm{Pb}}$), calculated from the cross sections in $pp$ and in $p\text{–Pb}$ collisions, is presented and compared with the $R_{p\mathrm{Pb}}$ of $D$ mesons. The ${\mathrm{\Lambda }}_c^{+}/D^0$ ratio is also presented and compared with the light-flavor baryon-to-meson ratios $p/\pi$ and $\mathrm{\Lambda }/K_S^0$, and measurements from other LHC experiments. The results are compared to predictions from model calculations and Monte Carlo event generators.