By using the theoretical approaches that describe well the available data on $t$-integrated coherent photoproduction of light and heavy vector mesons in Pb-Pb ultraperipheral collisions (UPCs) at the Large Hadron Collider (LHC) in Run 1, we calculate the momentum transfer distributions for this process for $\rho$ and $J/\psi$ vector mesons in the kinematics of Run 2 at the LHC. We demonstrate that nuclear shadowing not only suppresses the absolute value of the cross sections but also shifts the momentum transfer distributions toward smaller values of the momentum transfer $\left|t\right|$. This result can be interpreted as a broadening in the impact parameter space of the effective nucleon density in nuclei by 14% in the case of $\rho$ and the nuclear gluon distribution by 5%–11% in the case of $J/\psi$.

During the late stages of gravitational core-collapse of massive stars, extreme isospin asymmetries are reached within the core. Due to the lack of microscopic calculations of electron-capture (EC) rates for all relevant nuclei, in general simple analytic parametrizations are employed. We study here several extensions of these parametrizations, allowing for a temperature, electron density, and isospin dependence as well as for odd-even effects. The latter extra degrees of freedom considerably improve the agreement with large-scale microscopic rate calculations. We find, in particular, that the isospin dependence leads to a significant reduction of the global EC rates during core collapse with respect to fiducial results, where rates optimized on calculations of stable $fp$-shell nuclei are used. Our results indicate that systematic microscopic calculations and experimental measurements in the $N\approx 50$ neutron-rich region are desirable for realistic simulations of the core collapse.

Nucleon transfer reactions in deuteron-deuteron collisions at energies above the three- and four-body breakup threshold are described using exact four-body equations for transition operators that are solved in the momentum-space framework. Differential cross sections, analyzing powers, polarizations, and spin transfer coefficients are obtained using realistic two-nucleon potentials and including the Coulomb repulsion between protons. Overall good agreement between predictions and experimental data is found. Most remarkable discrepancies are seen around the minima of the differential cross section at higher energies and in the outgoing nucleon polarization at lower energies.

A new method to solve the Dirac equation on a 3D lattice is proposed, in which the variational collapse problem is avoided by the inverse Hamiltonian method and the fermion doubling problem is avoided by performing spatial derivatives in momentum space with the help of the discrete Fourier transform, i.e., the spectral method. This method is demonstrated in solving the Dirac equation for a given spherical potential in a 3D lattice space. In comparison with the results obtained by the shooting method, the differences in single-particle energy are smaller than ${10}^{-4}$ MeV, and the densities are almost identical, which demonstrates the high accuracy of the present method. The results obtained by applying this method without any modification to solve the Dirac equations for an axial-deformed, nonaxial-deformed, and octupole-deformed potential are provided and discussed.

The suppression of $\mathrm{{\rm Y}}$ mesons in the hot quark-gluon plasma (QGP) versus reduced feed-down is investigated in UU collisions at energies currently available at the BNL Relativistic Heavy Ion Collider and PbPb collisions at energies available at the CERN Large Hadron Collider. Our centrality- and $p_{\text{T}}$-dependent model encompasses screening, collisional damping, and gluodissociation in the QGP. For $\mathrm{{\rm Y}}\left(1S\right)$ it is in agreement with data from both STAR and CMS collaborations provided the relativistic Doppler effect and the reduced feed-down from the $\mathrm{{\rm Y}}\left(nS\right)$ and ${\chi }_{\mathrm{b}}\left(nP\right)$ states are properly considered. At both energies, most of the $\mathrm{{\rm Y}}\left(1S\right)$ suppression is found to be due to reduced feed-down, whereas most of the $\mathrm{{\rm Y}}\left(2S\right)$ suppression is caused by hot-medium effects. The importance of the latter increases with energy. The $p_{\text{T}}$ dependence is flat due to the relativistic Doppler effect and reduced feed-down. We predict the $\mathrm{{\rm Y}}\left(1S\right)$ suppression in PbPb at $\sqrt{s_{NN}}=5.02TeV$.

The ${\beta }^{-}$ decay of ${}^{34}\mathrm{Mg}$ was used to study the ${}^{34}\mathrm{Al}$ nucleus through $\gamma$ spectroscopy at the Isotope Separator On-Line facility of CERN. Previous studies identified two $\beta$-decaying states in ${}^{34}\mathrm{Al}$ having spin-parity assignments $J^{\pi }=4^{-}$ dominated by the normal configuration $\pi {\left(d_{5/2}\right)}^{-1}\otimes \nu \left(f_{7/2}\right)$ and $J^{\pi }=1^{+}$ by the intruder configuration $\pi {\left(d_{5/2}\right)}^{-1}\otimes \nu {\left(d_{3/2}\right)}^{-1}{\left(f_{7/2}\right)}^2$. Their unknown ordering and relative energy have been the subject of debate for the placement of ${}^{34}\mathrm{Al}$ inside or outside the $N=20$ “island of inversion.” We report here that the $1^{+}$ intruder lies only 46.6 keV above the $4^{-}$ ground state. In addition, a new half-life of $T_{1/2}=44.9\left(4\right)\mathrm{ms}$, that is twice as long as the previously measured 20(10) ms, has been determined for ${}^{34}\mathrm{Mg}$. Large-scale shell-model calculations with the recently developed sdpf-u-mix interaction are compared with the new data and used to interpret the mechanisms at play at the very border of the $N=20$ island of inversion.

Lifetimes of the $4_1^{+}$ states in ${}^{62,64}\mathrm{Fe}$ and the $11/2_1^{-}$ states in ${}^{61,63}\mathrm{Co}$ and ${}^{59}\mathrm{Mn}$ were measured at the Grand Accélérateur National d'Ions Lourds (GANIL) facility by using the Advanced Gamma Tracking Array (AGATA) and the large-acceptance variable mode spectrometer (VAMOS++). The states were populated through multinucleon transfer reactions with a ${}^{238}\mathrm{U}$ beam impinging on a ${}^{64}\mathrm{Ni}$ target, and lifetimes in the picosecond range were measured by using the recoil distance Doppler shift method. The data show an increase of collectivity in the iron isotopes approaching $N=40$. The reduction of the subshell gap between the $\nu 2p_{1/2}$ and $\nu 1g_{9/2}$ orbitals leads to an increased population of the quasi-SU(3) pair $\left(\nu 1g_{9/2},\nu 2d_{5/2}\right)$, which causes an increase in quadrupole collectivity. This is not observed for the cobalt isotopes with $N<40$ for which the neutron subshell gap is larger due to the repulsive monopole component of the tensor nucleon-nucleon interaction. The extracted experimental $B\left(E2\right)$ values are compared with large-scale shell-model calculations and with beyond-mean-field calculations with the Gogny D1S interaction. A good agreement between calculations and experimental values is found, and the results demonstrate in particular the spectroscopic quality of the Lenzi, Nowacki, Poves, and Sieja (LNPS) shell-model interaction.

Background: Non-compound-nucleus fission in the preactinide region has been an active area of investigation in the recent past. Based on the measurements of fission-fragment mass distributions in the fission of ${}^{202}\mathrm{Po}$, populated by reactions with varying entrance channel mass asymmetry, the onset of non-compound-nucleus fission was proposed to be around $Z_p{Z}_t\sim 1000$ [Phys. Rev. C 77, 024606 (2008)], where $Z_p$ and $Z_t$ are the projectile and target proton numbers, respectively.

Purpose: The present paper is aimed at the measurement of cross sections and spin distributions of evaporation residues in the ${}^{28}\mathrm{Si}+{}^{176}\mathrm{Yb}$ reaction ($Z_p{Z}_t=980$) to investigate the fusion hindrance which, in turn, would give information about the contribution from non-compound-nucleus fission in this reaction.

Method: Evaporation-residue cross sections were measured in the beam energy range of 129–166 MeV using the hybrid recoil mass analyzer (HYRA) operated in the gas-filled mode. Evaporation-residue cross sections were also measured by the recoil catcher technique followed by off-line $\gamma$-ray spectrometry at few intermediate energies. $\gamma$-ray multiplicities of evaporation residues were measured to infer about their spin distribution. The measurements were carried out using NaI(Tl) detector-based 4π-spin spectrometer from the Tata Institute of Fundamental Research, Mumbai, coupled to the HYRA.

Results: Evaporation-residue cross sections were significantly lower compared to those calculated using the statistical model code pace2 [Phys. Rev. C 21, 230 (1980)] with the coupled-channel fusion model code ccfus [Comput. Phys. Commun. 46, 187 (1987)] at beam energies close to the entrance channel Coulomb barrier. At higher beam energies, experimental cross sections were close to those predicted by the model. Average $\gamma$-ray multiplicities or angular momentum values of evaporation residues were in agreement with the calculations of the code ccfus + pace2 within the experimental uncertainties at all the beam energies.

Conclusions: Deviation of evaporation-residue cross sections from the "fusion + statistical model" predictions at beam energies close to the entrance channel Coulomb barrier indicates fusion hindrance at these beam energies which would lead to non-compound-nucleus fission. However, reasonable agreement of average angular momentum values of evaporation residues at these beam energies with those calculated using the coupled-channel fusion model with the statistical model codes ccfus + pace2 suggests that fusion suppression at beam energies close to the entrance channel Coulomb barrier where populated $l$ waves are low is not $l$ dependent.

We have studied elliptic flow $\left(v_2\right)$ of $\varphi$ mesons in the framework of a multiphase transport (AMPT) model at CERN Large Hadron Collider (LHC) energy. In the realms of AMPT model we observe that $\varphi$ mesons at intermediate transverse momentum $\left(p_T\right)$ deviate from the previously observed [at the BNL Relativistic Heavy Ion Collider (RHIC)] particle type grouping of $v_2$ according to the number of quark content, i.e, baryons and mesons. Recent results from the ALICE Collaboration have shown that $\varphi$ meson and proton $v_2$ has a similar trend, possibly indicating that particle type grouping might be due to the mass of the particles and not the quark content. A stronger radial boost at LHC compared to RHIC seems to offer a consistent explanation to such observation. However, recalling that $\varphi$ mesons decouple from the hadronic medium before additional radial flow is built up in the hadronic phase, a similar pattern in $\varphi$ meson and proton $v_2$ may not be due to radial flow alone. Our study reveals that models incorporating $\varphi$-meson production from $K\overline{K}$ fusion in the hadronic rescattering phase also predict a comparable magnitude of $\varphi$ meson and proton $v_2$ particularly in the intermediate region of $p_T$. Whereas, $v_2$ of $\varphi$ mesons created in the partonic phase is in agreement with quark-coalescence motivated baryon-meson grouping of hadron $v_2$. This observation seems to provide a plausible alternative interpretation for the apparent mass-like behavior of $\varphi$-meson $v_2$. We have also observed a violation of hydrodynamical mass ordering between proton and $\varphi$ meson $v_2$ further supporting that $\varphi$ mesons are negligibly affected by the collective radial flow in the hadronic phase due to the small in-medium hadronic interaction cross sections.

The Dalitz decay ${\pi }^0\to e^{+}{e}^{-}\gamma$ has been measured in the $\gamma p\to {\pi }^{0}p$ reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value obtained for the slope parameter of the ${\pi }^0$ electromagnetic transition form factor, $a_{\pi }=0.030\pm 0.{010}_{\mathrm{tot}}$, is in agreement with existing measurements of this decay and with recent theoretical calculations. The uncertainty obtained in the value of $a_{\pi }$ is lower than in previous results based on the ${\pi }^0\to e^{+}{e}^{-}\gamma$ decay.

The triton point charge radius is calculated to next-to-next-to-leading order (NNLO) in pionless effective field theory $(\mathrm{EFT}\left(\pi /\right))$, yielding a prediction of $1.14\pm 0.19$ fm (leading order), $1.59\pm 0.08$ fm (next-to leading order), and $1.62\pm 0.03$ fm (NNLO) in agreement with the current experimental extraction of $1.5978\pm 0.040$ fm [Angeli and Marinova, At. Data Nucl. Data Tables 99, 69 (2013)]. The error at NNLO is due to cutoff variation ($\sim 1\%$) within a reasonable range of calculated cutoffs and from a $\mathrm{EFT}\left(\pi /\right)$ error estimate ($\sim 1.5\%$). In addition new techniques are introduced to add perturbative corrections to bound- and scattering state calculations for short-range effective field theories, but with a focus on their use in $\mathrm{EFT}\left(\pi /\right)$.

Low-lying excited states in ${}^{38,40}\mathrm{P}$ have been identified in the $\beta$ decay of $T_z=+5,+6, {}^{38,40}\mathrm{Si}$. Based on the allowed nature of the Gamow-Teller (GT) decay observed, these states are assigned spin and parity of $1^{+}$ and are core-excited 1p1h intruder states with a parity opposite to the ground state. The occurrence of intruder states at low energies highlights the importance of pairing and quadrupole correlation energies in lowering the intruder states despite the $N=20$ shell gap. Configuration interaction shell model calculations with the state-of-art SDPF-MU effective interaction were performed to understand the structure of these 1p1h states in the even-$A$ phosphorus isotopes. States in ${}^{40}\mathrm{P}$ with $N=25$ were found to have very complex configurations involving all the $fp$ orbitals leading to deformed states as seen in neutron-rich nuclei with $N\approx 28$. The calculated GT matrix elements for the $\beta$ decay highlight the dominance of the decay of the core neutrons rather than the valence neutrons.

In the present work, I investigate the influence of neutron mass reduction due to magnetic field on the equation of state of neutron matter using the lowest-order constraint variational (LOCV) method with the $A{V}_{18}$ potential.

The distorted-wave Born approximation formalism for the description of the $(e,e^{\prime }\gamma )$ reaction, in which emitted photons and scattered electrons are simultaneously detected, is outlined. Both the Coulomb and the magnetic scattering are fully taken into account. The influence of electron bremsstrahlung is estimated within the plane-wave Born approximation. Recoil effects are also discussed. The formalism is applied for the low-energy $(e,e^{\prime }\gamma ){}^{92}\mathrm{Zr}$ reaction with excitation of the first collective ($2_1^{+}$) and mixed-symmetry ($2_2^{+}$) states. The corresponding transition charge and current densities are taken from a random-phase approximation (RPA) calculation within the quasiparticle phonon model. It is shown, by this example, in which way the magnetic subshell population of the excited state influences the angular distribution of the decay photon. For these quadrupole excitations the influence of magnetic scattering is only prominent at the backmost scattering angles, where a clear distinction of the photon pattern pertaining to the two states is predicted.

Resonances play critical roles in the formation of many physical phenomena, and many techniques have been developed for the exploration of resonances. In a recent letter [Phys. Rev. Lett. 117, 062502 (2016)], we proposed a new method for probing single-particle resonances by solving the Dirac equation in complex momentum representation for spherical nuclei. Here, we develop the theoretical formalism of this method for deformed nuclei. We elaborate numerical details and calculate the bound and resonant states in ${}^{37}\mathrm{Mg}$. The results are compared with those from the coordinate representation calculations with a satisfactory agreement. In particular, the present method can expose clearly the resonant states in a complex momentum plane and determine precisely the resonance parameters for not only narrow resonances but also broad resonances that were difficult to obtain before.

Comparison of hydrodynamic and “hybrid” $\text{hydrodynamics}+\text{transport}$ calculations with heavy-ion data inevitably requires the conversion of the fluid to particles. For dissipative fluids the conversion is ambiguous without additional theory input complementing hydrodynamics. We obtain self-consistent shear viscous phase-space corrections from linearized Boltzmann transport theory for a gas of hadrons. These corrections depend on the particle species, and incorporating them in Cooper–Frye freeze-out affects identified particle observables. For example, with additive quark model cross sections, proton elliptic flow is larger than pion elliptic flow at moderately high $p_T$ in $\text{Au}+\text{Au}$ collisions at the BNL Relativistic Heavy Ion Collider. This is in contrast to Cooper–Frye freeze-out with the commonly used “democratic Grad” ansatz that assumes no species dependence. Various analytic and numerical results are also presented for massless and massive two-component mixtures to better elucidate how species dependence arises. For convenient inclusion in pure hydrodynamic and hybrid calculations, Appendix G contains self-consistent viscous corrections for each species both in tabulated and parametrized form.

In chiral effective field theory the leading order (LO) nucleon-nucleon potential includes two contact terms, in the two spin channels $S=0,1$, and the one-pion-exchange potential. When the pion degrees of freedom are integrated out, as in the pionless effective field theory, the LO potential includes two contact terms only. In the three-nucleon system, the pionless theory includes a three-nucleon contact term interaction at LO whereas the chiral effective theory does not. Accordingly arbitrary differences could be observed in the LO description of three- and four-nucleon binding energies. We analyze the two theories at LO and conclude that a three-nucleon contact term is necessary at this order in both theories. In turn this implies that subleading three-nucleon contact terms should be promoted to lower orders. Furthermore, this analysis shows that one single low-energy constant might be sufficient to explain the large values of the singlet and triplet scattering lengths.

Background:The discovery of neutrinoless double-$\beta$ ($0\nu \beta \beta$) decay would demonstrate the nature of neutrinos, have profound implications for our understanding of matter-antimatter mystery, and solve the mass hierarchy problem of neutrinos. The calculations for the nuclear matrix elements $M^{0\nu }$ of $0\nu \beta \beta$ decay are crucial for the interpretation of this process.

Purpose: We study the effects of relativity and nucleon-nucleon short-range correlations on the nuclear matrix elements $M^{0\nu }$ by assuming the mechanism of exchanging light or heavy neutrinos for the $0\nu \beta \beta$ decay.

Methods:The nuclear matrix elements $M^{0\nu }$ are calculated within the framework of covariant density functional theory, where the beyond-mean-field correlations are included in the nuclear wave functions by configuration mixing of both angular-momentum and particle-number projected quadrupole deformed mean-field states.

Results: The nuclear matrix elements $M^{0\nu }$ are obtained for ten $0\nu \beta \beta$-decay candidate nuclei. The impact of relativity is illustrated by adopting relativistic or nonrelativistic decay operators. The effects of short-range correlations are evaluated.

Conclusions: The effects of relativity and short-range correlations play an important role in the mechanism of exchanging heavy neutrinos though the influences are marginal for light neutrinos. Combining the nuclear matrix elements $M^{0\nu }$ with the observed lower limits on the $0\nu \beta \beta$-decay half-lives, the predicted strongest limits on the effective masses are $|\langle m_{\nu }\rangle |<0.06\mathrm{eV}$ for light neutrinos and $|\langle m_{{\nu }_h}^{-1}\rangle {|}^{-1}>3.065\times {10}^8\mathrm{GeV}$ for heavy neutrinos.

The contribution of the two-phonon configurations to the ground state of ${}^4\mathrm{He}$ and ${}^{16}\mathrm{O}$ is evaluated nonperturbatively using a Hartree-Fock basis within an equation-of-motion phonon method using a nucleon-nucleon optimized chiral potential. Convergence properties of energies and root-mean-square radii versus the harmonic oscillator frequency and space dimensions are investigated. The comparison with the second-order perturbation theory calculations shows that the higher-order terms have an appreciable repulsive effect and yield too-small binding energies and nuclear radii. It is argued that four-phonon configurations, through their strong coupling to two phonons, may provide most of the attractive contribution necessary for filling the gap between theoretical and experimental quantities. Possible strategies for accomplishing such a challenging task are discussed.