An approach to the extraction of the two-photon exchange (TPE) correction from elastic $ep$ scattering data is presented. The cross-section, polarization transfer (PT), and charge asymmetry data are considered. It is assumed that the TPE correction to the PT data is negligible. The form factors and TPE correcting term are given by one multidimensional function approximated by the feedforward neural network (NN). To find a model-independent approximation, the Bayesian framework for the NNs is adapted. A large number of different parametrizations is considered. The most optimal model is indicated by the Bayesian algorithm. The obtained fit of the TPE correction behaves linearly in $\epsilon$ but it has a nontrivial $Q^2$ dependence. A strong dependence of the TPE fit on the choice of parametrization is observed.

We report a measurement of the neutrino-electron elastic scattering rate from ${}^8$B solar neutrinos based on a 123 kton-day exposure of KamLAND. The background-subtracted electron recoil rate, above a 5.5-MeV analysis threshold is 1.49 $\pm$ 0.14(stat) $\pm$ 0.17(syst) events per kton-day. Interpreted as due to a pure electron flavor flux with a ${}^8$B neutrino spectrum, this corresponds to a spectrum integrated flux of 2.77 $\pm$ 0.26(stat) $\pm$ 0.32(syst) $\times$10${}^6$ cm${}^{-2}$s${}^{-1}$. The analysis threshold is driven by ${}^{208}$Tl present in the liquid scintillator, and the main source of systematic uncertainty is due to background from cosmogenic ${}^{11}$Be. The measured rate is consistent with existing measurements and with standard solar model predictions which include matter-enhanced neutrino oscillation.

In this paper we study the residual proton-neutron interactions and make use of the systematics of these interactions to describe experimental data of nuclear masses and to predict some of the unknown masses. The odd-even effect staggering of the residual proton-neutron interaction between the last proton and the last neutron is found and argued in terms of pairing interactions. Two local mass relations, which work very accurately for masses of four neighboring nuclei, are discovered. The accuracy of our predicted masses for medium and heavy nuclei is competitive with that of the AME2003 extrapolations, with the virtue of simplicity.

I have analyzed reduced neutron widths (${\Gamma }_n^0$) for the subset of 1245 resonances in the nuclear data ensemble (NDE) for which they have been reported. Random matrix theory (RMT) predicts for the Gaussian orthogonal ensemble that these widths should follow a ${\chi }^2$ distribution having one degree of freedom ($\nu =1$)—the Porter Thomas distribution (PTD). Careful analysis of the ${\Gamma }_n^0$ values in the NDE rejects the validity of the PTD with a statistical significance of at least 99.97% ($\nu =0.801\pm 0.052$). This striking disagreement with the RMT prediction is most likely due to the inclusion of significant $p$-wave contamination to the supposedly pure $s$-wave NDE. When an energy-dependent threshold is used to remove the $p$-wave contamination, the PTD is still rejected with a statistical significance of at least 98.17% ($\nu =1.217\pm 0.092$). Furthermore, examination of the primary references for the NDE reveals that many resonances in most of the individual data sets were selected using methods derived from RMT. Therefore, using the full NDE data set to test RMT predictions seems highly questionable. These results cast very serious doubt on claims that the NDE represents a striking confirmation of RMT.

We report on the changes in mean square charge radii of unstable neon nuclei relative to the stable ${}^{20}$Ne, based on the measurement of optical isotope shifts. The studies were carried out using collinear laser spectroscopy on a fast beam of neutral neon atoms. High sensitivity on short-lived isotopes was achieved thanks to nonoptical detection based on optical pumping and state-selective collisional ionization, which was complemented by an accurate determination of the beam kinetic energy. The new results provide information on the structural changes in the sequence of neon isotopes all across the neutron $sd$ shell, ranging from the proton drip line nucleus and halo candidate ${}^{17}$Ne up to the neutron-rich ${}^{28}$Ne in the vicinity of the “island of inversion.” Within this range the charge radius is smallest for ${}^{24}$Ne with $N=14$ corresponding to the closure of the neutron $d_{5/2}$ shell, while it increases toward both neutron shell closures, $N=8$ and $N=20$. The general trend of the charge radii correlates well with the deformation effects which are known to be large for several neon isotopes. In the neutron-deficient isotopes, structural changes arise from the onset of proton-halo formation for ${}^{17}$Ne, shell closure in ${}^{18}$Ne, and clustering effects in ${}^{20,21}$Ne. On the neutron-rich side the transition to the island of inversion plays an important role, with the radii in the upper part of the $sd$ shell confirming the weakening of the $N=20$ magic number. The results add new information to the radii systematics of light nuclei where data are scarce because of the small contribution of nuclear-size effects to the isotope shifts which are dominated by the finite-mass effect.

A glasma flux-tube model has been proposed to explain strong elongation on pseudorapidity $\eta$ of the same-side two-dimensional (2D) peak in minimum-bias angular correlations from $\sqrt{s_{NN}}=200$ GeV Au-Au collisions. The same-side peak or “soft ridge” is said to arise from coupling of flux tubes to radial flow whereby gluons radiated transversely from flux tubes are boosted by radial flow to form a narrow structure or ridge on azimuth. In this study we test the theory conjecture by comparing measurements to predictions for particle production, spectra, and correlations from the glasma model and from conventional fragmentation processes. We conclude that the glasma model is contradicted by measured hadron yields, spectra, and correlations, whereas a two-component model of hadron production, including minimum-bias parton fragmentation, provides a quantitative description of most features of the data, although $\eta$ elongation of the same-side 2D peak remains undescribed.

The incoherent pion photoproduction reaction $\gamma d\to {\pi }^{-}pp$ is considered theoretically in a wide energy region $E_{th}\le E_{\gamma }\le 2700$ MeV. The model applied contains the impulse approximation as well as the $NN$ and $\pi N$ final-state-interaction (FSI) amplitudes. The aim of the paper is to study a reliable way for getting the information on elementary $\gamma n\to {\pi }^{-}p$ reaction cross sections beyond the impulse approximation for $\gamma d\to {\pi }^{-}pp$. For the elementary $\gamma N\to \pi N$, $NN\to NN$, and $\pi N\to \pi N$ amplitudes, the results of The George Washington University (GW) Data Analysis Center (DAC) are used. There are no additional theoretical constraints. The calculated cross sections $d\sigma /d\Omega (\gamma d\to {\pi }^{-}pp)$ are compared with existing data. The procedure used to extract information on the differential cross section $d\sigma /d\Omega (\gamma n\to {\pi }^{-}p)$ on the neutron from the deuteron data using the FSI correction factor $R$ is discussed. The calculations for $R$ versus ${\pi }^{-}p$ center-of-mass (CM) angle ${\theta }_1$ of the outgoing pion are performed at different photon-beam energies with kinematic cuts for a “quasifree” process $\gamma n\to {\pi }^{-}p$. The results show a sizable FSI effect $R\ne 1$ from the $S$-wave part of $pp$-FSI at small angles close to ${\theta }_1\sim 0$: this region narrows as the photon energy increases. At larger angles, the effect is small ($|R-1|\ll 1$) and agrees with estimations of FSI in the Glauber approach.

A formalism based on the complex-scaling method is developed for solving the few-particle scattering problem, in terms of bound state boundary conditions. Several applications are presented to demonstrate the efficiency of the method for computing the elastic and three-body breakup reactions in systems described by Hamiltonians which may include both short- and long-range interactions.

This paper gives a momentum-space representation of the Argonne V18 potential as an expansion in products of spin-isospin operators with scalar coefficient functions of the momentum transfer. Two representations of the scalar coefficient functions for the strong part of the interaction are given. One is as an expansion in an orthonormal basis of rational functions and the other as an expansion in Chebyshev polynomials on different intervals. Both provide practical and efficient representations for computing the momentum-space potential that do not require integration or interpolation. Programs based on both expansions are available as supplementary material. Analytic expressions are given for the scalar coefficient functions of the Fourier transform of the electromagnetic part of the Argonne V18. A simple method for computing the partial-wave projections of these interactions from the operator expressions is also given.

It is known that coupling an intrinsic excitation of integer spin and positive parity $I^{+}$ to a rotor having a degenerate set of states $L^{\pi }=0^{+},2^{+},4^{+},...,$ generates a series of $K$ bands. A given value of $I^{+}$ gives rise to several bands labeled by $K^{+}=0^{+},1^{+},2^{+},...,I^{+}$, that is, a total of ($I+1$) such bands, in the spectrum of the combined system. We discuss how a binary cluster model of an excited core orbited by a spinless cluster can approximate these conditions. A crucial point is that the radial wave functions of relative motion are very similar for low $L$, and their radial coupling integrals even more so, such that the wave functions play the model role of a common intrinsic state for the lowest excited states of the system. If the core has a $0^{+}$ ground state and a low-lying $2^{+}$ excited state, then lifting the degeneracy leads to a ground state $K^{+}=0^{+}$ band and low-lying excited $K^{+}=0^{+}$, $1^{+}$, and $2^{+}$ bands. Although these are all seen in light nuclei, the $K^{+}=1^{+}$ band is conspicuous by its apparent absence in heavy nuclei, and we urge experimental groups to reexamine their data for signs of it.

Starting from the Maxwell-Jüttner equilibrium distribution, we develop a relativistic lattice Boltzmann (LB) algorithm capable of handling ultrarelativistic systems with flat, but expanding, spacetimes. The algorithm is validated through simulations of a quark-gluon plasma, yielding excellent agreement with hydrodynamic simulations. The present scheme opens the possibility of transferring the recognized computational advantages of lattice kinetic theory to the context of both weakly and ultrarelativistic systems.

Focusing on four types of correlation plots, $R_{\mathrm{AA}}$ versus $v_2$, $R_{\mathrm{AA}}$ versus $I_{\mathrm{AA}}$, $I_{\mathrm{AA}}$ versus $v_2^{I_{\mathrm{AA}}}$, and $v_2$ versus $v_2^{I_{\mathrm{AA}}}$, we demonstrate how the centrality dependence of correlations between multiple jet quenching observables provide valuable insight into the energy loss mechanism in a quark-gluon plasma. In particular, we find that a qualitative energy loss model gives a good description of $R_{\mathrm{AA}}$ versus $v_2$ only when we take $\Delta E\sim l^3$ and a medium geometry generated by a model of the color glass condensate. This same $\Delta E\sim l^3$ model also qualitatively describes the trigger $p_T$ dependence of $R_{\mathrm{AA}}$ versus $I_{\mathrm{AA}}$ data and makes novel predictions for the centrality dependence for this $R_{\mathrm{AA}}$ versus $I_{\mathrm{AA}}$ correlation. Current data suggest, albeit with extremely large uncertainty, that $v_2^{I_{\mathrm{AA}}}\gg v_2$, a correlation that is difficult to reproduce in current energy loss models.

The parton and hadron cascade model PACIAE based on PYTHIA is utilized to systematically investigate strange particle production in $pp$ collisions at energies available at the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC). Globally speaking, the PACIAE results of the strange particle rapidity density at midrapidity and the transverse momentum distribution are better than those of PYTHIA (default) in comparison with STAR and ALICE experimental data. This may represent the importance of the parton and hadron rescatterings, as well as the reduction mechanism of strange quark suppression, added in the PACIAE model. The $K/\pi$ ratios as a function of reaction energy in $pp$ collisions from CERN Super Proton Synchrotron (SPS) to LHC energies are also analyzed in this paper.

The reactions ${}^{26}$Al${}^g$($p$,$$$\gamma$)${}^{27}$Si and ${}^{26}$Al${}^m$($p$,$$$\gamma$)${}^{27}$Si are important for influencing the galactic abundance of the cosmic $\gamma$-ray emitter ${}^{26}$Al${}^g$ and for the excess abundance of ${}^{26}$Mg found in presolar grains, respectively. Precise excitation energies and spin assignments of states from the ground state to the region of astrophysical interest in ${}^{27}$Si, including the identification and pairing of key astrophysical resonances with analog states in the mirror nucleus ${}^{27}$Al, are reported using $\gamma$ rays observed in the ${}^{12}$C + ${}^{16}$O fusion reaction. The detailed evolution of Coulomb energy differences between the states in ${}^{27}$Si and ${}^{27}$Al is explored, including the region above the astrophysical reaction thresholds.

We investigate the effects of strong magnetic fields on the equation of state of warm stellar matter as it may occur in a protoneutron star. Both neutrino-free and neutrino-trapped matter at a fixed entropy per baryon are analyzed. A relativistic mean-field nuclear model, including the possibility of hyperon formation, is considered. A density-dependent magnetic field with a magnitude of ${10}^{15}\mathrm{G}$ at the surface and not more than $3\times {10}^{18}\mathrm{G}$ at the center is considered. The magnetic field gives rise to a neutrino suppression, mainly at low densities, in matter with trapped neutrinos. It is shown that a hybrid protoneutron star will not evolve into a low-mass black hole if the magnetic field is strong enough and the magnetic field does not decay. However, the decay of the magnetic field after cooling may give rise to the formation of a low-mass black hole.

The ${\beta }^{+}$/EC decay of ${}^{180}$Tl and excited states in the daughter nucleus ${}^{180}$Hg have been investigated at the CERN On-Line Isotope Mass Separator (ISOLDE) facility. Many new low-lying energy levels were observed in ${}^{180}$Hg, of which the most significant are the 0${}_2^{+}$ at 419.6 keV and the 2${}_2^{+}$ at 601.3 keV. The former is the bandhead of an excited band in ${}^{180}$Hg assumed originally to be of prolate nature. From the $\beta$ feeding to the different states in ${}^{180}$Hg, the ground-state spin of ${}^{180}$Tl was deduced to be (4${}^{-}$,5${}^{-}$).

Excited states in ${}^{180}$Hg were populated using the ${}^{147}$Sm(${}^{36}$Ar,3n)${}^{180}$Hg reaction and studied by in-beam conversion-electron spectroscopy. Conversion electrons emitted at the target position were measured using the Silicon Array for Conversion Electron Detection (SACRED) spectrometer and tagged through the characteristic $\alpha$ decays of ${}^{180}$Hg detected in a position-sensitive silicon strip detector located at the focal plane of the gas-filled recoil separator Recoil Ion Transport Unit (RITU). Electron conversion of transitions previously assigned to ${}^{180}$Hg through in-beam $\gamma$-ray spectroscopy studies was identified up to the 10${}^{+}\to 8^{+}$ transition and the intensities of the conversion-electron transitions were found to be consistent with the previous multipolarity assignments. Evidence was also found for two highly converted transitions in ${}^{180}$Hg: a 167 keV transition is interpreted as the transition from the newly identified 2${}_2^{+}$ state at 601 keV to the 2${}_1^{+}$ state at 434 keV, while a 420 keV transition is assigned as the $E0$ decay from the 0${}^{+}$ bandhead of the prolate-deformed configuration to the weakly deformed ground state.

The Green-Kubo relation and fluctuation-dissipation theorem are employed to calculate the shear viscosity $\eta$ of a finite hot nucleus directly from the width and energy of the giant dipole resonance (GDR) of this nucleus. The ratio $\eta /s$ of shear viscosity $\eta$ to entropy density $s$ is extracted from the experimental systematics of the GDR in copper, tin, and lead isotopes at finite temperature $T$. These empirical results are then compared with the predictions by several independent models as well as with almost model-independent estimations. Based on these results, it is concluded that the ratio $\eta /s$ in medium and heavy nuclei decreases with increasing temperature $T$ to reach $\left(1.3\text{--}4\right)\times \hslash /\left(4\pi k_B\right)$ at $T=5\mathrm{MeV}$.

The cluster structure of ${}^9$Be has been investigated through high precision elastic scattering cross-section measurements of a ${}^9$Be $+$ ${}^{208}$Pb system at below barrier energies, $E=$ 24–34 MeV.The observed deviation from the Rutherford scattering can only be explained by an $n$ $+$ ${}^8$Be cluster description of ${}^9$Be, whereas the $\alpha$ $+$ ${}^5$He cluster picture fails to explain the measured data, indicating the dominance of the $n$ $+$ ${}^8$Be cluster structure of ${}^9$Be. In addition to sequential and direct breakup, the coupling effect of one neutron stripping on elastic scattering is significant even at 10 MeV below the barrier. The sensitivity of the high precision elastic scattering data to the cluster structure of ${}^9$Be has been demonstrated.

The evaporation residue (ER) cross sections for $3n$ and $4n$ evaporation channels in the ${}^{50}$Ti + ${}^{249}$Bk reaction leading the formation of ${}^{296}$119 and ${}^{295}$119 isotopes are evaluated by means of a modified fusion-by-diffusion model. In the model, the dynamic evolution from dinucleus to mononucleus is taken into account with the two-dimensional coupled Langenvin equations. The calculated maximum ER cross sections in 3$n$ and 4$n$ evaporation channels of the ${}^{50}$Ti + ${}^{249}$Bk reaction are $0.17$ and $0.57$ pb, respectively. The cross section of $0.57$ pb is close to the present experimental limit for the registration of the evaporation residual nuclei. Therefore, superheavy element 119 may be the most hopeful new element with $Z>118$ to be synthesized under somehow improved experimental conditions in the near future.