Recently studies of the differential nature of the flow angle fluctuations, known as event plane angular decorrelation, indicated that measurements that assume a common symmetry plane may need to consider the flow angle fluctuations effect. Using the hijing and ampt models, it is shown that the flow angle fluctuations measurements, obtained with the two- and three-subevents correlation method, could have significant nonflow effects associated with long- and short-range nonflow correlations. The current study demonstrates the four-subevents cumulant methods' ability to reduce the nonflow effects. It is further argued that the measurements using the four-subevents correlation method can be used to provide accurate quantification of the differential flow angle fluctuations.

Using covariant density functional theory with the DDME2 functional and labeling single-particle energy orbitals by Nilsson quantum numbers, a search for particle-hole (p-h) excitations connected to the appearance of shape coexistence is performed for $Z=38$ to 84. Islands of shape coexistence are found near the magic numbers $Z=82$ and $Z=50$, restricted in regions around the relevant neutron midshells $N=104$ and $N=66$, respectively, in accordance with the well-accepted p-h interpretation of shape coexistence in these regions, which we call neutron-induced shape coexistence, since the neutrons act as elevators creating holes in the proton orbitals. Similar but smaller islands of shape coexistence are found near $N=90$ and $N=60$, restricted in regions around the relevant proton midshells $Z=66$ and $Z=39$, respectively, related to p-h excitations across the three-dimensional isotropic harmonic-oscillator magic numbers $N=112$ and $N=70$, which correspond to the beginning of the participation of the opposite parity orbitals $1i_{13/2}$ and $1h_{11/2}$, respectively, to the onset of deformation. We call this case proton-induced shape coexistence, since the protons act as elevators creating holes in the neutron orbitals, thus offering a possible microscopic mechanism for the appearance of shape coexistence in these regions. In the region around $N=40$, $Z=40$, an island is located on which both neutron p-h excitations and proton p-h excitations are present.

Background: Photon strength functions are an important ingredient in calculations relevant for the nucleosynthesis of heavy elements. The relation to the photoabsorption cross section allows to experimentally constrain photon strength functions by investigating the photoresponse of atomic nuclei.

Purpose: We determine the photoresponse of ${}^{66}\mathrm{Zn}$ in the energy region of 5.6 MeV to 9.9 MeV and analyze the contribution of the 'elastic' decay channel back to the ground state. In addition, for the elastic channel electric and magnetic dipole transitions were separated.

Methods: Nuclear resonance fluorescence experiments were performed using a linearly polarized quasi-monoenergetic photon beam at the High Intensity $\gamma$-ray Source. Photon beam energies from 5.6 to 9.9 MeV with an energy spread of about 3% were selected in steps of 200–300 keV. Two high purity germanium detectors were used for the subsequent $\gamma$-ray spectroscopy.

Results: Full photoabsorption cross sections are extracted from the data making use of the monoenergetic character of the photon beam. For the ground-state decay channel, the average contribution of electric and magnetic dipole strengths is disentangled. The average branching ratio back to the ground state is determined as well.

Conclusions: The new results indicate lower cross sections when compared to the values extracted from a former experiment using bremsstrahlung on ${}^{66}\mathrm{Zn}$. In the latter, the average branching ratio to the ground state is estimated from statistical-model calculations in order to analyze the data. Corresponding estimates from statistical-model calculations underestimate this branching ratio compared to the values extracted from the present analysis, which would partly explain the high cross sections determined from the bremsstrahlung data.

We investigate the effects of nonequilibrium dynamics in small colliding systems by comparing a nonequilibrium transport approach, Parton-Hadron-String Dynamics (PHSD), with a $(2+1)$-dimensional viscous hydrodynamic model, VISHNew. Focusing on $p+\mathrm{Pb}$ collisions at energies available at the Large Hadron Collider, we extract the initial conditions for the hydrodynamic model from PHSD, in order to reduce the impact of the early out-of-equilibrium dynamics and focus on the traces of nonequilibrium in the ensuing medium evolution. We find that in the transport approach quantities like energy density and bulk viscous pressure are highly inhomogeneous on the transverse plane during the whole evolution, whereas the hydrodynamic simulations dissolve more efficiently the initial spatial irregularities, still keeping a high degree of inhomogeneity due to the smaller size and lifetime of the medium produced in $p+\mathrm{Pb}$ collisions with respect to heavy-ion reactions. As a first step that will help to identify the impact of these nonequilibrium effects on final observables in proton-nucleus collisions, we perform an analysis of the transverse spherocity, an event-shape observable able to distinguish between jetty and isotropic configurations of transverse momenta. We found that the spherocity distribution in PHSD is slightly shifted towards the isotropic limit with respect to the hydrodynamic result. Even though this dissimilarity is partially due to the difference in the final charged particle production, it mainly comes from the different description within the two frameworks of the medium produced in small colliding systems. This finding supports the idea that multidifferential measurements, such as those based on event categorization according to multiplicity and spherocity, are useful to study final-state observables in ultrarelativistic proton-nucleus collisions.

The half-life of ${}^6\mathrm{He}$ has been measured using a low-energy radioactive beam implanted in an ${\mathrm{YAlO}}_3$ Ce-doped inorganic scintillator and recording decay events in a $4\pi$ geometry. Events were time-stamped with a digital data acquisition system enabling a reliable control of dead-time effects and detector gain variations. The result, $T_{1/2}=(807.25\pm 0.{16}_{\mathrm{stat}}\pm 0.{11}_{\mathrm{sys}}$) ms, provides the most precise value obtained so far and is consistent with the only previous measurement having a precision smaller than 0.1%. This resolves the long-standing discrepancy previously observed between two sets of measurements.

Bayesian model mixing (BMM) is a statistical technique that can be used to combine models that are predictive in different input domains into a composite distribution that has improved predictive power over the entire input space. We explore the application of BMM to the mixing of two expansions of a function of a coupling constant $g$ that are valid at small and large values of $g$ respectively. This type of problem is quite common in nuclear physics, where physical properties are straightforwardly calculable in strong and weak interaction limits or at low and high densities or momentum transfers, but difficult to calculate in between. Interpolation between these limits is often accomplished by a suitable interpolating function, e.g., Padé approximants, but it is then unclear how to quantify the uncertainty of the interpolant. We address this problem in the simple context of the partition function of zero-dimensional ${\varphi }^4$ theory, for which the (asymptotic) expansion at small $g$ and the (convergent) expansion at large $g$ are both known. We consider three mixing methods: linear mixture BMM, localized bivariate BMM, and localized multivariate BMM with Gaussian processes. We find that employing a Gaussian process in the intermediate region between the two predictive models leads to the best results of the three methods. The methods and validation strategies we present here should be generalizable to other nuclear physics settings.

Precise neutron-energy measurements are required to probe the nuclear structure effects of neutron-rich nuclei, where $\beta$-delayed neutron emission becomes a dominant decay mode. The Neutron dEtector with Xn Tracking (NEXT) array has been designed and constructed to measure $\beta$-delayed neutrons with better energy resolution. The new design localizes the neutron interaction position by optically segmenting the detector along the direction of the neutron flight path, reducing the associated uncertainties in the neutron time-of-flight measurements. This significantly improves the energy resolution without losing the necessary detection efficiency. The proof-of-principle and efficiency measurements showed promising results. This article details the implementation of the neutron tracking capability of NEXT array in time-of-flight measurements.

Lifetimes of low-energy states in the semimagic nucleus ${}^{211}\mathrm{At}$ were measured employing the recoil-distance Doppler shift and the Doppler-shift attenuation methods. The deduced transition probabilities are compared to two shell-model calculations, one using the modified Kuo-Herling interaction in a multi-$j$ model space and the other using a semiempirical interaction for protons confined to the single-$j 0h_{9/2}$ orbital. The Kuo-Herling calculations overestimates some of the ground-state transition probabilities, possibly due to contributions not included in the calculated ground-state wave function of ${}^{211}\mathrm{At}$. A strong underestimation of the $E2$ strengths involving the $7/2_1^{-}$ state is also observed. Therefore, a modification of a single two-body matrix element of the Kuo-Herling interaction is introduced which improves the agreement with the experimental data significantly. The calculations in the single-$j$ approximation agree very well with the measured transition probabilities, indicating that seniority can be regarded as a good quantum number in ${}^{211}\mathrm{At}$.

We present a detailed theoretical investigation of proton emission from ${}^{140}\mathrm{Ho}$ within the nonadiabatic quasiparticle approach. The calculated proton emission half-life reproduces well the measured data. The importance of triaxiality and of the residual $np$ interaction are studied. The ground state spin and parity of ${}^{139}\mathrm{Dy}$ (daughter) and ${}^{140}\mathrm{Ho}$ (parent) are ascertained unambiguously as $7/2^{+}$ and $3^{-}$, respectively, by analyzing the rotational energies, half-lives, and branching ratios.

To explain the production of light nuclei in heavy-ion collisions at extreme energies, we focus on the deuteron case. A Gibbs ensemble at chemical freeze-out is a prerequisite to investigate the nonequilibrium evolution of the expanding fireball. Quantum statistical approaches allow us to describe correlations including bound-state formation in the strongly interacting and hot system. We consider the virial approach to evaluate proton-neutron correlations. In generalization of the treatment of protons in pionic matter (pion-proton puzzle), the influence of the pion environment on deuteron-like correlations is evaluated using data for the pion-deuteron scattering phase shifts. Calculated yields for deuteron production are compared with those observed at the LHC.

Quark-gluon plasma (QGP) tomography aims to constrain the parameters characterizing the properties and evolution of QGP formed in heavy-ion collisions, by exploiting low- and high-$p_{\perp }$ theory and data. Higher-order harmonics $v_n$ ($n>2$) are an important—but seldom explored—part of this approach. However, to take full advantage of them, several issues have to be addressed: (i) consistency of different methods for calculating $v_n$, (ii) importance of event-by-event fluctuations to high-$p_{\perp }{R}_{AA}$ and $v_2$ predictions, and (iii) sensitivity of higher harmonics to the initial state of fluid-dynamical evolution. We obtain that (i) several methods for calculating harmonics are compatible with each other, (ii) event-by-event calculations are important in mid-central collisions, and (iii) various initializations of the evolution of the medium lead to quantitatively and qualitatively different predictions, likely to be distinguished by future measurements. We also find that the present high-$p_{\perp }{v}_4$ data cannot be reproduced using initial states for fluid-dynamical evolution given by state-of-the-art models. We call this discrepancy the high-$p_{\perp }{v}_4$ puzzle at the Large Hadron Collider.

Nuclear excitation cross section of ${}^{229}\mathrm{Th}$ from the ground state to the low-lying isomeric state via inelastic electron scattering is calculated, on the level of Dirac distorted wave Born approximation. With electron energies below 100 eV, inelastic scattering is very efficient in the isomeric excitation, yielding excitation cross sections on the order of ${10}^{-27}$ to ${10}^{-26}{\mathrm{cm}}^2$. Systematic analyses are presented on elements affecting the excitation cross section, including the ion-core potential, the relativistic effect, the knowledge of the reduced nuclear transition probabilities, etc.

We investigate the role of different Skyrme forces (SIII, SkI4, and SAMi) in the ground state decay of various radioactive parent nuclei such as Ra, Th, U, and Pu. The daughters of these nuclei are either doubly magic ${}^{208}\mathrm{Pb}$ or a nearby isotope of Pb. Using spherical choice of cluster and daughter, calculations are performed within the framework of the preformed cluster model (PCM), where the preformation probability $P_0$ and penetration probability $P$ of decaying fragments are used to obtain the half-lives of cluster emission. The considered forces modify the barrier characteristics and consequently the penetration path, as the scattering potential at the first turning point of the barrier is lowest with the SkI4 force (lowest penetrability) and highest with the SIII force (highest penetrability). However, the preformation probability of decaying clusters is highest for the SkI4 force followed by SAMi and SIII Skyrme forces. To look for the possible role of the spin-orbit effect on the cluster radioactivity, the half-lives of emitted clusters are calculated with and without the inclusion of spin-orbit potential $V_J$. In addition, the $\alpha$-decay half live are also calculated to extract an inclusive picture of the dynamics involved.

Elastic and inelastic scattering angular distributions have been measured for the ${}^{11}\mathrm{B}+{}^{120}\mathrm{Sn}$ reaction at bombarding energies around the Coulomb barrier: $E_{Lab}=31.2$, 32.6, 34.7, and 37.2 MeV. Additionally, $1p$ stripping and pickup, and $1\alpha$ stripping yields have been observed in the spectra. Coupled-channel calculations have been performed in the context of the double-folding São Paulo potential. Overall, the theoretical results are in good agreement with the experimental elastic and inelastic scattering angular distributions.

Fission at low excitation energy is an ideal playground to probe the impact of nuclear structure on nuclear dynamics. While the importance of structural effects in the nascent fragments is well established in the (trans-)actinide region, the observation of asymmetric fission in several neutron-deficient pre-actinides can be explained by various mechanisms. To deepen our insight into that puzzle, an innovative approach based on inverse kinematics and an enhanced version of the VAMOS$++$ heavy-ion spectrometer was implemented at the GANIL facility, Caen. Fission of ${}^{178}\mathrm{Hg}$ was induced by fusion of ${}^{124}\mathrm{Xe}$ and ${}^{54}\mathrm{Fe}$. The two fragments were detected in coincidence using VAMOS$++$ supplemented with a new SEcond Detection arm. For the first time in the pre-actinide region, access to the pre-neutron mass and total kinetic energy distributions, and the simultaneous isotopic identification of one the fission fragment, was achieved. The present work describes the experimental approach, and discusses the pre-neutron observables in the context of an extended asymmetric-fission island located southwest of ${}^{208}\mathrm{Pb}$. A comparison with different models is performed, demonstrating the importance of this new asymmetric-fission island for elaborating on driving effects in fission.

We present a determination of optical potentials for ${}^{10}\mathrm{Be}$-nucleus collisions using the double-folding method to compute the real part and Kramers-Kronig dispersion relations to derive the imaginary part. As microscopic inputs we use chiral effective field theory nucleon-nucleon interactions at next-to-next-to-leading order combined with state-of-the-art nucleonic densities. With these potentials, we compute elastic-scattering cross sections for the exotic nucleus ${}^{10}\mathrm{Be}$ off various targets, and compare them to experiment. Without any fitting parameter, we obtain good agreement with data. For collisions on light targets, we observe significant uncertainty related to the short-range physics, whereas for heavy targets that uncertainty remains small.