A multiphase transport model is used to understand the origin of long-range collective azimuthal correlations in small-system collisions. To disentangle between collectivity associated with initial-state intrinsic momentum anisotropy and the collectivity arising as a final-state response to the collision geometry, we studied the development of collectivity in 5.02-TeV $p+\mathrm{Pb}$ collisions with both initial-state and final-state effects included. We find that the initial momentum anisotropy may not be fully isotropized through parton interactions, and the final-state partonic collectivity in general is correlated with both the initial momentum anisotropy and the shape of the collision geometry. The initial momentum anisotropy also influences the event-by-event fluctuation of collective flow. Therefore, the mere evidence of the geometry response of the collective flow cannot rule out the presence of large contributions from the initial state.

Lifetimes of excited states of the phosphorus isotopes ${}_{15}^{33,34,35,36}\mathrm{P}$ have been measured by using the differential recoil-distance method. The isotopes of phosphorus were populated in binary grazing reactions initiated by a beam of ${}^{36}\mathrm{S}$ ions of energy 225 MeV incident on a thin ${}^{208}\mathrm{Pb}$ target mounted in the Cologne plunger apparatus. The combination of the PRISMA magnetic spectrometer and an early implementation of the AGATA $\gamma$-ray tracking array was used to detect $\gamma$ rays in coincidence with projectile-like nuclear species. Lifetime measurements of populated states were made within the range from about 1 to 100 ps. The number of states for which lifetime measurements were possible was limited by statistics. For ${}^{33}\mathrm{P}$, lifetime limits were determined for the first $3/2^{+}$ and $5/2^{+}$ states at 1431 and 1848 keV, respectively; the results are compared with previous published lifetime values. The lifetime of the first $2^{+}$ state of ${}^{34}\mathrm{P}$ at 429 keV was determined and compared with earlier measurements. For ${}^{35}\mathrm{P}$, the states for which lifetimes, or lifetime limits, were determined were those at 2386, 3860, 4101, and 4493 keV, with $J^{\pi }$ values of $3/2^{+}$, $5/2^{+}$, $7/2_1^{-}$, and $7/2_2^{-}$, respectively. There have been no previous published lifetimes for states in this nucleus. A lifetime was measured for the stretched $\pi \left(1f_{7/2}\right)\otimes \nu \left(1f_{7/2}\right)J^{\pi }=\left(7^{+}\right)$ state of ${}^{36}\mathrm{P}$ at 5212 keV and a lifetime limit was established for the stretched $\pi \left(1{\mathrm{d}}_{3/2}\right)\otimes \nu \left(1f_{7/2}\right)J^{\pi }=\left(5^{-}\right)$ state at 2030 keV. There are no previously published lifetimes for states of ${}^{36}\mathrm{P}$. Measured lifetime values were compared with the results of state-of-the-art shell-model calculations based on the PSDPF effective interaction. In addition, measured branching ratios, published mixing ratios, and electromagnetic transition rates, where available, have been compared with shell-model values. In general, there is good agreement between experiment and the shell model; however there is evidence that the shell-model values of the $M1$ transition rates for the $3/2_1^{+}\to 1/2^{+}$ (ground state) and $5/2_1^{+}\to 3/2_1^{+}$ transitions in ${}^{33}\mathrm{P}$ underestimate the experimental values by a factor between 5 and 10. In ${}^{35}\mathrm{P}$ there are some disagreements between experimental and shell-model values of branching ratios for the first and second excited $7/2^{-}$ states. In particular, there is a serious disagreement for the decay characteristics of the second $7/2^{-}$ state at 4493 keV, for which the shell-model counterpart lies at 4754 keV. In this case, the shell-model competing electromagnetic decay branches are dominated by $E1$ and $M1$ transitions.

Delayed $\gamma$ rays from neutron-rich $A=97$ fission fragments were measured using the Lohengrin spectrometer at the high-flux reactor of the Institut Laue-Langevin in Grenoble. Several lifetimes of excited states in ${}^{97}\mathrm{Sr}$ were measured using the fast-timing technique. The nucleus ${}^{97}\mathrm{Sr}$ exhibits shape coexistence and is located exactly at the border of the spherical ($N\le 58$) and deformed ($N\ge 60$) ground-state deformation. It is of particular interest to study the shape-coexisting structures at the spherical-deformed border ($N=59$). The determined lifetimes within this work are compared to an interacting boson-fermion model calculation that is based on the microscopic energy density functional to provide a better understanding of the spherical-deformed border in strontium isotopes.

We utilize a nuclear shell model Hamiltonian with only two adjustable parameters to generate, for the first time, exact solutions for pairing correlations for light to medium-mass nuclei, including the challenging proton-neutron pairs, while also identifying the primary physics involved. In addition to single-particle energy and Coulomb potential terms, the shell model Hamiltonian consists of an isovector $T=1$ pairing interaction and an average proton-neutron isoscalar $T=0$ interaction, where the $T=0$ term describes the average interaction between nonpaired protons and neutrons. This Hamiltonian is exactly solvable, where, utilizing three to seven single-particle energy levels, we reproduce experimental data for $0^{+}$ state energies for isotopes with mass $A=10$ through $A=62$ exceptionally well including isotopes from He to Ge. Additionally, we isolate effects due to like-particle and proton-neutron pairing, provide estimates for the total and proton-neutron pairing gaps, and reproduce $N$ (neutron) = $Z$ (proton) irregularity. These results provide a further understanding for the key role of proton-neutron pairing correlations in nuclei, which is especially important for waiting-point nuclei on the $rp$ path of nucleosynthesis.

Fission fragment mass distributions of ${}^{234\text{–}240}\mathrm{U}$, ${}^{236\text{–}242}\mathrm{Np}$, and ${}^{238\text{–}244}\mathrm{Pu}$ are studied using the Langevin approach in the wide excitation energy range as $E^{*}=15\text{–}55\mathrm{MeV}$. In the present calculation, neutron emission before fission, so-called multichance fission, was introduced. The calculated results well demonstrated the experimental data, which shows the double-peak structure up to the highest excitation energies and the clear dependence on the initial fissioning nuclides. The trend is nicely correlated with the neutron binding energy of the compound nucleus that dominates the neutron emission probability before fission.

An innovative procedure to determine the mass-angle distribution of fragments from quasifission is proposed. It is based on the subtraction of the contribution from compound-nucleus fission from the experimental correlation spectrum which is in most cases a mixture of fusion-fission and quasifission. The former is calculated with a four-dimensional dynamical model of fission within the stochastic Langevin theory. The proposed approach is benchmarked using measurements for different entrance channels, ranging from below to above the onset of quasifission, all leading to the same ${}^{202}\mathrm{Po}$ composite system. The sensitivity of the procedure is evaluated. Its potential for isolating the fragment-mass and emission-angle information pertaining to the sole quasifission process is discussed.

The Regge features of elastic $K^{\pm }N\to K^{\pm }N$, and charge exchange $K^{-}p\to {\overline{K}}^{0}n$ and $K^{+}n\to K^{0}p$ reactions are described by using a combined analysis of all these channels at high momenta. Based on the meson exchanges in the $t$-channel with their decays to a $K\overline{K}$ pair allowed, the exchanges of $\rho \left(775\right)+\omega \left(782\right)$ are excluded in contrast to existing model calculations and the present paper follows a new scheme for the meson exchanges $a_0\left(980\right)+\varphi \left(1020\right)+f_2\left(1275\right)+a_2\left(1320\right)$ Reggeized for the forward elastic-scattering amplitude together with Pomeron. The charge exchange reactions are described by $a_0\left(980\right)+a_2\left(1320\right)$ exchanges in the $t$-channel. Dominance of the isoscalar $f_2$ and Pomeron exchanges beyond $P_{\mathrm{Lab}}\approx 3\mathrm{GeV}/c$ is shown in the elastic process. Both the isovector $a_0$ and $a_2$ exchanges in charge exchange reactions play the respective roles in the low- and high-momenta region. Differential and total cross sections are presented to compare with existing data. A discussion is given to the polarization of $K^{-}p\to K^{-}p$ at $P_{\mathrm{Lab}}=10\mathrm{GeV}/c$ and $K^{-}p\to {\overline{K}}^{0}n$ at $P_{\mathrm{Lab}}=8\mathrm{GeV}/c$.

Permutation groups are applied to analyze the symmetries of pentaquark states. All possible quark configurations of the color, flavor, spin, and spatial degrees of freedom are worked out in the language of permutation groups, and the corresponding wave functions are constructed systematically in the form of a Yamanouchi basis. The pentaquark spatial wave functions of various symmetries, which are derived in the harmonic-oscillator interaction, are applied as complete bases to evaluate the low-lying light $q^4\overline{q}$ pentaquark mass of all configurations, where the Cornell-like potential is employed.

Knowledge of the neutron capture of copper and cobalt isotopes is important for the understanding of abundances of the heavier elements produced via the weak $s$ process. There are considerable discrepancies for the ${}^{63}\mathrm{Cu}\left(n,\gamma \right){}^{64}\mathrm{Cu}$ and ${}^{65}\mathrm{Cu}\left(n,\gamma \right){}^{66}\mathrm{Cu}$ cross-section values in the literature. New measurements of these cross sections were performed at the SARAF phase I facility using a high-power quasi-Maxwellian neutron source produced by irradiation of the liquid-lithium target (LiLiT) with an intense continuous-wave proton beam. The cross sections were measured by counting the activity of the irradiated targets. The measurement allowed us to evaluate the ${}^{63}\mathrm{Cu}\left(n,\gamma \right){}^{64}\mathrm{Cu}$, ${}^{65}\mathrm{Cu}\left(n,\gamma \right){}^{66}\mathrm{Cu}$, and ${}^{59}\mathrm{Co}\left(n,\gamma \right){}^{60}\mathrm{Co}$ Maxwellian averaged cross sections at 30 keV, obtaining values of $70.4\pm 1.8_{\exp }\pm 2.4_{\mathrm{syst}}$, $26.8\pm 1.5_{\exp }\pm 1.0_{\mathrm{syst}}$, and $38.1\pm 0.9_{\exp }\pm 0.9_{\mathrm{syst}}\mathrm{mb}$, respectively. The results are compared with previous measurements in the literature.

New experimental data obtained from $\gamma$-ray tagged one-neutron and one-proton knockout from ${}^{55}\mathrm{Co}$ are presented. A candidate for the sought-after $T=1,T_z=0,J^{\pi }=6^{+}$ state in ${}^{54}\mathrm{Co}$ is proposed based on a comparison to the new data on ${}^{54}\mathrm{Fe}$, the corresponding observables predicted by large-scale-shell-model (LSSM) calculations in the full $fp$-model space employing charge-dependent contributions, and isospin-symmetry arguments. Furthermore, possible isospin-symmetry breaking in the $A=54$, $T=1$ triplet is studied by calculating the experimental $c$ coefficients of the isobaric mass multiplet equation (IMME) up to the maximum possible spin $J=6$ expected for the ${\left(1f_{7/2}\right)}^{-2}$ two-hole configuration relative to the doubly magic nucleus ${}^{56}\mathrm{Ni}$. The experimental quantities are compared to the theoretically predicted $c$ coefficients from LSSM calculations using two-body matrix elements obtained from a realistic chiral effective field theory potential at next-to-next-to-next-to-leading order (${\mathrm{N}}^3\mathrm{LO}$).

Precision measurements of slow neutron cross sections with atoms have several scientific applications. In particular, the $n\text{−}{}^4\mathrm{He}$ $s$-wave scattering length is important to know both for helping to constrain the nuclear three-body interaction and for the proper interpretation of several ongoing slow neutron experiments searching for other types of neutron-atom interactions. We present new measurements of the ratios of the neutron differential scattering cross sections of the noble gases He, Ar, Kr, and Xe to Ne. All gases used were of natural isotopic abundance. These measurements were performed using a recently developed neutron-scattering apparatus for gas samples located on a pulsed slow neutron beamline which was designed to search for possible exotic neutron-atom interactions and employs both neutron time of flight information and a position-sensitive neutron detector for scattering event reconstruction. We found agreement with the literature values of scattering cross sections inferred from Ar/Ne, Kr/Ne, and Xe/Ne differential cross-section ratios over the $q$ range of 1–7 ${\mathrm{nm}}^{-1}$. However, for the case of He/Ne we find that the cross section inferred differs by 11.3% ($7.6\sigma$) from previously reported values inferred from neutron phase-shift measurements, but is in reasonable agreement with values from other measurements. The very large discrepancy in the He/Ne ratio calls for a new precision measurement of the $n\text{−}{}^4\mathrm{He}$ scattering length using neutron interferometry.

Background: Measurements of exclusive meson production are a useful tool in the study of hadronic structure. In particular, one can discern the relevant degrees of freedom at different distance scales through these studies.

Purpose: To study the transition between nonperturbative and perturbative quantum chromodynamics as the square of four-momentum transfer to the struck proton, $-t$, is increased.

Method: Cross sections for the ${}^1\mathrm{H}(e,e^{\prime }{\pi }^{+})n$ reaction were measured over the $-t$ range of 0.272 to 2.127 ${\mathrm{GeV}}^2$ with limited azimuthal coverage at fixed beam energy of 4.709 GeV, $Q^2$ of 2.4 ${\mathrm{GeV}}^2$, and $W$ of 2.0 GeV at the Thomas Jefferson National Accelerator Facility (JLab) Hall C.

Results: The $-t$ dependence of the measured ${\pi }^{+}$ electroproduction cross section generally agrees with prior data from JLab Halls B and C. The data are consistent with a Regge amplitude-based theoretical model but show poor agreement with a generalized parton distribution–based model.

Conclusion: The agreement of cross sections with prior data implies small contribution from the interference terms, and the confirmation of the change in $t$ slopes between the low- and high-$-t$ regions previously observed in photoproduction indicates the changing nature of the electroproduction reaction in our kinematic regime.

The $\gamma n\to {\pi }^{0}n$ differential cross section evaluated for 27 energy bins span the photon-energy range 290–813 MeV ($W=1.195$–1.553 GeV) and the pion c.m. polar production angles, ranging from ${18}^{\circ }$ to ${162}^{\circ }$, making use of model-dependent nuclear corrections to extract ${\pi }^0$ production data on the neutron from measurements on the deuteron target. Additionally, the total photoabsorption cross section was measured. The tagged photon beam produced by the 883 MeV electron beam of the Mainz Microtron MAMI was used for the ${\pi }^0$-meson production. Our accumulation of $3.6\times {10}^6$ $\gamma n\to {\pi }^{0}n$ events allowed a detailed study of the reaction dynamics. Our data are in reasonable agreement with previous A2 measurements and extend them to lower energies. The data are compared with predictions of previous said, maid, and BnGa partial-wave analyses and to the latest said fit MA19 that included our data. Selected photon-decay amplitudes $N^{*}\to \gamma n$ at the resonance poles are determined for the first time.

The reduced transition probabilities $B\left(E2\right)$ and $B\left(M1\right)$ of the negative-parity yrast states of ${}^{126}\mathrm{I}$ were studied by measuring the lifetimes in picoseconds using the Doppler-shift attenuation method. We investigated the phenomena of signature splitting and inversion using the two quasiparticle-plus triaxial rotor model (PRM). The experimental result—a sharp decrease in the $B\left(E2\right)$ values at the signature inversion—indicated a shape change with a possible shift in the axis of rotation. We interpreted this observation as a change in the triaxiality parameter, with values $\gamma =-{10}^{\circ }$ (Lund convention) below the inversion and $\gamma ={25}^{\circ }$ above it and a constant value of axial deformation of $\beta \approx 0.15$. We also assigned the valence particle configuration—neutron in the $h_{11/2}$ orbital and proton predominantly in the $d_{5/2}$ orbital mixed with the $g_{7/2}$ orbital—from the PRM calculation. Furthermore, the calculation reproduced the overall observed behavior of the signature splitting and inversion reasonably well. The observed backbending at the rotational frequency of 0.47 MeV was due to neutron alignment consistent with the second band crossing from the quasiparticle Routhian diagram.

The rotational bands in the neutron-rich nuclei ${}^{153–157}\mathrm{Pm}$ are investigated by a particle-number-conserving method. The kinematic moments of inertia for the one-quasiparticle bands in odd-$A$ Pm isotopes ${}^{153,155,157}\mathrm{Pm}$ are reproduced quite well by the present calculation. By comparison between the experimental and calculated moments of inertia for the three two-quasiparticle bands in the odd-odd nuclei ${}^{154,156}\mathrm{Pm}$, their configurations and bandhead spins have been assigned properly. For the two-quasiparticle band in ${}^{154}\mathrm{Pm}$, the configuration is assigned as $\pi 5/2^{-}\left[532\right]\otimes \nu 3/2^{-}\left[521\right]$ ($K^{\pi }=4^{+}$) with the bandhead spin $I_0=4\hslash$. In ${}^{156}\mathrm{Pm}$, the same configuration and bandhead spin assignments have been made for the two-quasiparticle band with lower excitation energy. The configuration $\pi 5/2^{+}\left[413\right]\otimes \nu 5/2^{+}\left[642\right]$ ($K^{\pi }=5^{+}$) with the bandhead spin $I_0=5\hslash$ is assigned for that with higher excitation energy.

The effects of the Dirac sea of nucleons are investigated within a covariant model of the hadronic interaction. I extend the usual mean field approximation and present a procedure to deal with divergences which are proportional to polynomials on the magnetic field intensity. For this purpose a nucleon propagator is used which takes account of the full effect of the magnetic field as well as the presence of the anomalous magnetic moments of both protons and neutrons. I examine single-particle properties and bulk thermodynamical quantities and conclude that within a reasonable range of densities and magnetic intensities the effects found are moderate.

As for the dominant decay channel of superheavy nuclei, we have reshaped the crucial nuclear potential in the $\alpha$-decay process through the systematical analysis of available experimental decay data. Specifically, a Fermi-type renormalization factor brings us an effective $\alpha$-daughter potential so that we can obtain the decay energy and half-life on the same footing, which exactly corresponds to the stability of nuclei. During this procedure, the $\alpha$ preformation factor is related with the recalculated pairing and shell corrections. Besides the excellent agreement between theory and experiment for both the decay energy and the half-life, we extend the study to available short-lived nuclei in the superheavy-mass region as a predictive set. It is found that the present $\alpha$-core potential can figure out the decay scheme of these superheavy $\alpha$ emitters very well. Encouraged by this, it is expected that the following predictions on the heaviest nuclei can be valuable for discussing their robustness and shed some light on the “island of stability” plus the fundamental mass of unknown nuclides from a novel perspective.

Low-lying yrast states of ${}^{204}\mathrm{Po}$ and ${}^{206}\mathrm{Po}$ were investigated by the $\gamma –\gamma$ fast timing technique with ${\mathrm{LaBr}}_3$(Ce) detectors. Excited states of these nuclei were populated in the ${}^{197}\mathrm{Au}({}^{11}\mathrm{B},4n){}^{204}\mathrm{Po}$ and the ${}^{198}\mathrm{Pt}({}^{12}\mathrm{C},4n){}^{206}\mathrm{Po}$ fusion-evaporation reactions, respectively. The beams were delivered by the FN-Tandem accelerator at the University of Cologne. The lifetimes of the $4_1^{+}$ states of both nuclei were measured, along with an upper lifetime limit for the $2_1^{+}$ state of ${}^{204}\mathrm{Po}$. A comparison between the derived $B(E2;4_1^{+}\to 2_1^{+})$ values and results from simplified empirical two-state mixing calculations suggests that for the $4_1^{+}$ states of even-even polonium isotopes the transition from single-particle mode at $N=126$ to collective mode, when reducing the number of neutrons, occurs above $N=122$.