Showing papers in "Physical Review C in 2013"

Combined analysis of all three phases of solar neutrino data from the Sudbury Neutrino Observatory

Abstract: We report results from a combined analysis of solar neutrino data from all phases of the Sudbury Neutrino Observatory. By exploiting particle identification information obtained from the proportional counters installed during the third phase, this analysis improved background rejection in that phase of the experiment. The combined analysis resulted in a total flux of active neutrino flavors from 8B decays in the Sun of (5.25 \pm 0.16(stat.)+0.11-0.13(syst.))\times10^6 cm^{-2}s^{-1}. A two-flavor neutrino oscillation analysis yielded \Deltam^2_{21} = (5.6^{+1.9}_{-1.4})\times10^{-5} eV^2 and tan^2{\theta}_{12}= 0.427^{+0.033}_{-0.029}. A three-flavor neutrino oscillation analysis combining this result with results of all other solar neutrino experiments and the KamLAND experiment yielded \Deltam^2_{21} = (7.41^{+0.21}_{-0.19})\times10^{-5} eV^2, tan^2{\theta}_{12} = 0.446^{+0.030}_{-0.029}, and sin^2{\theta}_{13} =(2.5^{+1.8}_{-1.5})\times10^{-2}. This implied an upper bound of sin^2{\theta}_{13} < 0.053 at the 95% confidence level (C.L.).

New potentialities of the Liège intranuclear cascade model for reactions induced by nucleons and light charged particles

Abstract: The new version (incl4.6) of the Li\`ege intranuclear cascade (INC) model for the description of spallation reactions is presented in detail. Compared to the standard version (incl4.2), it incorporates several new features, the most important of which are: (i) the inclusion of cluster production through a dynamical phase space coalescence model, (ii) the Coulomb deflection for entering and outgoing charged particles, (iii) the improvement of the treatment of Pauli blocking and of soft collisions, (iv) the introduction of experimental threshold values for the emission of particles, (v) the improvement of pion dynamics, (vi) a detailed procedure for the treatment of light-cluster-induced reactions taking care of the effects of binding energy of the nucleons inside the incident cluster and of the possible fusion reaction at low energy. Performances of the new model concerning nucleon-induced reactions are illustrated by a comparison with experimental data covering total reaction cross sections, neutron, proton, pion, and composite double-differential cross-sections, neutron multiplicities, residue mass and charge distributions, and residue recoil velocity distributions. Whenever necessary, the incl4.6 model is coupled to the ABLA07 de-excitation model and the respective merits of the two models are then tentatively disentangled. Good agreement is generally obtained in the 200 MeV to 2 GeV range. Below 200 MeV and down to a few tens of MeV, the total reaction cross section is well reproduced and differential cross sections are reasonably well described. The model is also tested for light-ion induced reactions at low energy, below 100 MeV incident energy per nucleon. Beyond presenting the update of the incl4.2 model, attention has been paid to applications of the new model to three topics for which some particular aspects are discussed for the first time. The first topic is the production of clusters heavier than alpha particle. It is shown that the energy spectra of these produced clusters are consistent with coalescence. The second topic regards the longitudinal residue recoil velocity and its fluctuations. Excellent results are obtained for these quantities. It addition, it is shown that the distributions of these quantities display typical random-walk characteristics, at least for not-too-large mass losses. They are interpreted as a direct consequence of the independence of successive binary collisions occurring during the cascade process. The last topic concerns the total reaction cross section and the residue-production cross sections for low-energy incident light ions. It is shown that our new model can give a rather satisfactory account of these cross sections, offering so an alternative to fusion models and the advantage of a single model for the progressive change from fusion to pre-equilibrium mechanisms.

0νββ and 2νββ nuclear matrix elements, quasiparticle random-phase approximation, and isospin symmetry restoration

Abstract: Within the quasiparticle random-phase approximation (QRPA) we achieve partial restoration of the isospin symmetry and hence fulfillment of the requirement that the 2νββ Fermi matrix element M^(2ν)_F vanishes, as it should, unlike in the previous version of the method. This is accomplished by separating the renormalization parameter g_pp of the particle-particle proton-neutron interaction into isovector and isoscalar parts. The isovector parameter g^(T=1)_(pp) needs to be chosen to be essentially equal to the pairing constant g_pair, so no new parameter is needed. For the 0νββ decay the Fermi matrix element M^(0ν)_F is substantially reduced, while the full matrix element M^(0ν) is reduced by ≈10%. We argue that this more consistent approach should be used from now on in the proton-neutron QRPA and in analogous methods

Further explorations of Skyrme-Hartree-Fock-Bogoliubov mass formulas. XIII. The 2012 atomic mass evaluation and the symmetry coefficient

Abstract: Our family of three Hartree-Fock-Bogoliubov (HFB) mass models, labeled BSk19, BSk20, and BSk21, is here extended by (a) refitting to the 2012 Atomic Mass Evaluation (AME), and (b) varying the symmetry coefficient $J$. Five new models, labeled BSk22 to BSk26, along with their mass tables, HFB-22 to HFB-26, respectively, are presented. These models are characterized by unconventional Skyrme forces containing ${t}_{4}$ and ${t}_{5}$ terms, i.e., density-dependent generalizations of the usual ${t}_{1}$ and ${t}_{2}$ terms, respectively. Highly realistic contact pairing forces are used. The Skyrme forces are constrained to fit realistic equations of state of neutron matter stiff enough to support the massive neutron stars PSR J1614$\ensuremath{-}$2230 and PSR J0348+0432. Unphysical spin and spin-isospin instabilities of homogeneous nuclear matter, including the transition to a polarized state in neutron-star matter, are eliminated with the new forces. The best fits to the new database of 2353 nuclei are found for models BSk24 ($J=30$ MeV) and BSk25 ($J=29$ MeV), for which the root-mean square (rms) deviations are 0.55 and 0.54 MeV, respectively. Despite the larger database this is even better than the rms deviation of 0.58 MeV that we found with our fits to the 2003 AME. With $J=32$ MeV the rms deviation rises to 0.63 MeV. The neutron-skin thicknesses derived from antiproton scattering are shown to be consistent with the conclusions that we have drawn from masses.

Nuclear matrix elements for double- β decay

Abstract: Background: Direct determination of the neutrino mass through double-$\ensuremath{\beta}$ decay is at the present time one of the most important areas of experimental and theoretical research in nuclear and particle physicsPurpose: We calculate nuclear matrix elements for the extraction of the average neutrino mass in neutrinoless double-$\ensuremath{\beta}$ decayMethods: The microscopic interacting boson model (IBM-2) is usedResults: Nuclear matrix elements in the closure approximation are calculated for ${}^{48}$Ca, ${}^{76}$Ge, ${}^{82}$Se, ${}^{96}$Zr, ${}^{100}$Mo, ${}^{110}$Pd, ${}^{116}$Cd, ${}^{124}$Sn, ${}^{128}$Te, ${}^{130}$Te, ${}^{148}$Nd, ${}^{150}$Nd, ${}^{154}$Sm, ${}^{160}$Gd, and ${}^{198}$Pt decayConclusions: Realistic predictions for the expected half-lives in neutrinoless double-$\ensuremath{\beta}$ decay with light and heavy neutrino exchange in terms of neutrino masses are made and limits are set from current experiments

Measurement of the elliptic anisotropy of charged particles produced in PbPb collisions at √sNN=2.76 TeV

Abstract: The anisotropy of the azimuthal distributions of charged particles produced in √s_(NN)=2.76 TeV PbPb collisions is studied with the CMS experiment at the LHC. The elliptic anisotropy parameter, v_2, defined as the second coefficient in a Fourier expansion of the particle invariant yields, is extracted using the event-plane method, two- and four-particle cumulants, and Lee-Yang zeros. The anisotropy is presented as a function of transverse momentum (p_T), pseudorapidity (η) over a broad kinematic range, 0.3

Initial-state geometry and the role of hydrodynamics in proton-proton, proton-nucleus, and deuteron-nucleus collisions

Abstract: We apply the successful Monte Carlo Glauber and IP-Glasma initial-state models of heavy-ion collisions to the much smaller size systems produced in proton-proton, proton-nucleus, and deuteron-nucleus collisions. We observe a significantly greater sensitivity of the initial-state geometry to details of multiparticle production in these models compared to nucleus-nucleus collisions. In particular, we find that the size of the system produced in $p+A$ collisions is very similar to the one produced in $p+p$ collisions and predict comparable Hanbury-Brown-Twiss radii in the absence of flow in both systems. Differences in the eccentricities computed in the models are large, while differences among the generated flow coefficients ${v}_{2}$ and ${v}_{3}$ are smaller. For a large number of participants in proton-lead collisions, the ${v}_{2}$ generated in the IP-Glasma model is comparable to the value obtained in proton-proton collisions. Viscous corrections to flow are large over characteristic lifetimes in the smaller size systems. In contrast, viscous contributions are significantly diminished over the longer space-time evolution of a heavy-ion collision.

Heavy-quark dynamics and hadronization in ultrarelativistic heavy-ion collisions: Collisional versus radiative energy loss

Abstract: We study the dynamics of energy loss and flow of heavy quarks produced in ultrarelativistic heavy-ion collisions within the framework of a Langevin equation coupled to a ($2+1$)-dimensional viscous hydrodynamic model that simulates the spacetime evolution of the produced hot and dense QCD matter. The classical Langevin approach is improved such that, apart from quasielastic scatterings, radiative energy loss is incorporated by treating gluon radiation as an additional force term. The hadronization of emitted heavy quarks is simulated via a hybrid fragmentation plus recombination model. Our calculation shows significant contribution from gluon radiation to heavy quark energy loss at high energies, and we find the recombination mechanism is important for heavy flavor meson production at intermediate energies. We present numerical results for the nuclear modification and elliptic flow of $D$ mesons, which are consistent with measurements at both the CERN Large Hadron Collider (LHC) and the BNL Relativistic Heavy-Ion Collider (RHIC); predictions for $B$ mesons are also provided.

Event-by-event distributions of azimuthal asymmetries in ultrarelativistic heavy-ion collisions

Abstract: Relativistic dissipative fluid dynamics is a common tool to describe the space-time evolution of the strongly interacting matter created in ultrarelativistic heavy-ion collisions. For a proper comparison to experimental data, fluid-dynamical calculations have to be performed on an event-by-event basis. Therefore, fluid dynamics should be able to reproduce, not only the event-averaged momentum anisotropies, 〈vn〉, but also their distributions. In this paper, we investigate the event-by-event distributions of the initial-state and momentum anisotropies en and vn, and their correlations. We demonstrate that the event-by-event distributions of relative vn fluctuations are almost equal to the event-by-event distributions of corresponding en fluctuations, allowing experimental determination of the relative anisotropy fluctuations of the initial state. Furthermore, the correlation c(v2,v4) turns out to be sensitive to the viscosity of the fluid providing an additional constraint to the properties of the strongly interacting matter.

Collective dynamics in high-energy proton-nucleus collisions

Abstract: We analyze the proton-lead collisions at the CERN Large Hadron Collider energy of $\sqrt{{s}_{NN}}=5.02$ TeV in the three-stage approach, previously used to successfully describe the relativistic $A$-$A$ collisions. The approach consists of the early phase, modeled with the Glauber model, the event-by-event viscous 3+1 dimensional (3+1 D) relativistic hydrodynamics, and the statistical hadronization at freeze-out. We show that features typical of collective dynamics, such as the harmonic flow and the ridge structures in the two-particle correlations in relative azimuth and pseudorapidity, may be naturally explained in our framework. In the proton-nucleus system the harmonic flow is generated from an initially event-by-event deformed system and is entirely due to these initial fluctuations. Notably, fluctuations of strength of the initial Glauber sources which yield the observed distribution of hadron multiplicities and, at the same time, lead to correct values of the elliptic flow coefficients both from the two- and four-particle cumulant method, as measured by the ATLAS collaboration. The azimuthally asymmetric flow is not modified significantly when changing the viscosity coefficient, the initial time for the collective expansion, or the initial size of the fireball. The results present an estimate of the collective component in the two-particle correlations measured experimentally. We demonstrate that the harmonic flow coefficients can be experimentally measured with methods based on large rapidity gaps which reduce some of the other sources of correlations.

Nucleon resonances within a dynamical coupled-channels model of $\pi N$ and $\gamma N$ reactions

Abstract: The nucleon resonances are investigated within a dynamical coupled-channels model of $\ensuremath{\pi}N$ and $\ensuremath{\gamma}N$ reactions up to the invariant mass $W=2$ GeV. The meson-baryon ($MB$) channels included in the calculations are $MB=$ $\ensuremath{\pi}N$, $\ensuremath{\eta}N$, $K\ensuremath{\Lambda}$, $K\ensuremath{\Sigma}$, and $\ensuremath{\pi}\ensuremath{\pi}N$ that has $\ensuremath{\pi}\ensuremath{\Delta}$, $\ensuremath{\rho}N$, and $\ensuremath{\sigma}N$ resonant components. The meson-baryon amplitudes ${T}_{{M}^{\ensuremath{'}}{B}^{\ensuremath{'}},MB}(W)$ are calculated from solving a set of coupled-channels integral equations defined by an interaction Hamiltonian consisting of (a) meson-exchange interactions ${v}_{{M}^{\ensuremath{'}}{B}^{\ensuremath{'}},MB}$ derived from phenomenological Lagrangian and (b) vertex interactions ${N}^{*}\ensuremath{\rightarrow}MB$ for describing the transition of a bare excited nucleon state ${N}^{*}$ to a meson-baryon channel $MB$. The parameters of ${v}_{{M}^{\ensuremath{'}}{B}^{\ensuremath{'}},MB}$ are mainly constrained by the fit to the data of $\ensuremath{\pi}N\ensuremath{\rightarrow}\ensuremath{\pi}N$ in the low-energy region up to $W=1.4$ GeV. The bare masses of ${N}^{*}$ and the ${N}^{*}\ensuremath{\rightarrow}MB$ parameters are then determined in simultaneous fits to the data of $\ensuremath{\pi}N\ensuremath{\rightarrow}\ensuremath{\pi}N$ up to $W=2.3$ GeV and those of $\ensuremath{\pi}N\ensuremath{\rightarrow}\ensuremath{\eta}N,K\ensuremath{\Lambda},K\ensuremath{\Sigma}$ and $\ensuremath{\gamma}N\ensuremath{\rightarrow}\ensuremath{\pi}N,\ensuremath{\eta}N,K\ensuremath{\Lambda},K\ensuremath{\Sigma}$ up to $W=2.1$ GeV. The pole positions and residues of nucleon resonances are extracted by analytically continuing the meson-baryon amplitudes ${T}_{{M}^{\ensuremath{'}}{B}^{\ensuremath{'}},MB}(W)$ to the complex Riemann energy surface. From the extracted residues, we have determined the ${N}^{*}\ensuremath{\rightarrow}\ensuremath{\pi}N,\ensuremath{\gamma}N,\ensuremath{\eta}N,K\ensuremath{\Lambda},K\ensuremath{\Sigma}$ transition amplitudes at resonance poles. We compare the resonance pole positions from our analysis with those given by the Particle Data Group and the recent coupled-channels analyses by the J\"ulich and Bonn-Gatchina groups. Four results agree well only for the first ${N}^{*}$ in each spin-parity-isospin $({J}^{P},I)$ channel. For higher mass states, the number of states and their resonance positions from four results do not agree well. We discuss the possible sources of the discrepancies and the need of additional data from new hadron facilities such as the Japan Proton Accelerator Research Complex.

Time and space dependence of the electromagnetic field in relativistic heavy-ion collisions

Abstract: Exact analytical solution for the space-time evolution of electromagnetic field in electrically conducting nuclear matter produced in heavy-ion collisions is discussed. It is argued that the parameter that controls the strength of the matter effect on the field evolution is $\ensuremath{\sigma}\ensuremath{\gamma}b$, where $\ensuremath{\sigma}$ is electrical conductivity, $\ensuremath{\gamma}$ is the Lorentz boost-factor, and $b$ is the characteristic transverse size of the matter. When this parameter is of the order 1 or larger, which is the case at the Relativistic Heavy Ion Collider and the Large Hadron Collider, the space-time dependence of the electromagnetic field completely differs from that in vacuum.

Neutron matter from chiral effective field theory interactions

Abstract: The neutron-matter equation of state constrains the properties of many physical systems over a wide density range and can be studied systematically using chiral effective field theory (EFT). In chiral EFT, all many-body forces among neutrons are predicted to next-to-next-to-next-to-leading order (N${}^{3}$LO). We present details and additional results of the first complete N${}^{3}$LO calculation of the neutron-matter energy, which includes the subleading three-nucleon as well as the leading four-nucleon forces, and provides theoretical uncertainties. In addition, we discuss the impact of our results for astrophysics: for the supernova equation of state, the symmetry energy and its density derivative, and for the structure of neutron stars. Finally, we give a first estimate for the size of the N${}^{3}$LO many-body contributions to the energy of symmetric nuclear matter, which shows that their inclusion will be important in nuclear structure calculations.

Λ polarization in peripheral heavy ion collisions

Abstract: We predict the polarization of $\ensuremath{\Lambda}$ and $\overline{\ensuremath{\Lambda}}$ hyperons in peripheral heavy ion collisions at ultrarelativistic energy, based on the assumption of local thermodynamical equilibrium at the freeze-out. The polarization vector is proportional to the curl of the inverse temperature four-vector field and its length, of the order of percents, is maximal for a particle with moderately high momentum lying on the reaction plane. A selective measurement of these particles could make $\ensuremath{\Lambda}$ polarization detectable.

Bulk viscosity effects in event-by-event relativistic hydrodynamics

Abstract: Bulk viscosity effects on the collective flow harmonics in heavy-ion collisions are investigated, on an event-by-event basis, using a newly developed 2+1 Lagrangian hydrodynamic code named v-usphydro, which implements the smoothed particle hydrodynamics algorithm for viscous hydrodynamics. A new formula for the bulk viscous corrections present in the distribution function at freeze-out is derived, starting from the Boltzmann equation for multi-hadron species. Bulk viscosity is shown to enhance the collective flow Fourier coefficients from ${v}_{2}({p}_{T})$ to ${v}_{5}({p}_{T})$ when ${p}_{T}\ensuremath{\sim}1$--2.5 GeV, even when the bulk viscosity to entropy density ratio, $\ensuremath{\zeta}/s$, is significantly smaller than $1/(4\ensuremath{\pi})$.

In-medium similarity renormalization group with chiral two- plus three-nucleon interactions

Abstract: We use the recently proposed in-medium similarity renormalization group (IM-SRG) to carry out a systematic study of closed-shell nuclei up to ${}^{56}\mathrm{Ni}$, based on chiral two- plus three-nucleon interactions. We analyze the capabilities of the IM-SRG by comparing our results for the ground-state energy to coupled cluster calculations, as well as to quasiexact results from the importance-truncated no-core shell model. Using chiral two- plus three-nucleon Hamiltonians whose resolution scales are lowered by free-space SRG evolution, we obtain good agreement with experimental binding energies in ${}^{4}\mathrm{He}$ and the closed-shell oxygen isotopes, while the calcium and nickel isotopes are somewhat overbound.

Testing viscous and anisotropic hydrodynamics in an exactly solvable case

Abstract: We exactly solve the one-dimensional boost-invariant Boltzmann equation in the relaxation time approximation for arbitrary shear viscosity. The results are compared with the predictions of viscous and anisotropic hydrodynamics. Studying different non-equilibrium cases and comparing the exact kinetic-theory results to the second-order viscous hydrodynamics results we find that recent formulations of second-order viscous hydrodynamics agree better with the exact solution than the standard Israel-Stewart approach. Additionally, we find that, given the appropriate connection between the kinetic and anisotropic hydrodynamics relaxation times, anisotropic hydrodynamics provides a very good approximation to the exact relaxation time approximation solution.

Baryon number conservation and the cumulants of the net proton distribution

Abstract: We discuss the modification of the cumulants of the net baryon and net proton distributions due to the global conservation of baryon number in heavy-ion collisions. Corresponding probability distributions and their cumulants are derived analytically. We show that the conservation of baryon number results in a substantial decrease of higher order cumulants. Based on our studies, we propose an observable that is insensitive to the modifications due to baryon number conservation.

Large-scale calculations of the double- β decay of 76 Ge , 130 Te , 136 Xe , and 150 Nd in the deformed self-consistent Skyrme quasiparticle random-phase approximation

Abstract: We use the axially deformed Skyrme quasiparticle random-phase approximation (QRPA) together with the ${\mathrm{SkM}}^{*}$ energy-density functional, both as originally presented and with the time-odd part adjusted to reproduce the Gamow-Teller resonance energy in ${}^{208}\mathrm{Pb}$, to calculate the matrix elements that govern the neutrinoless double-$\ensuremath{\beta}$ decay of ${}^{76}\mathrm{Ge},\phantom{\rule{0.28em}{0ex}}{}^{130}\mathrm{Te},\phantom{\rule{0.28em}{0ex}}{}^{136}\mathrm{Xe}$, and ${}^{150}\mathrm{Nd}$. Our matrix elements in ${}^{130}\mathrm{Te}$ and ${}^{136}\mathrm{Xe}$ are significantly smaller than those of previous QRPA calculations, primarily because of the difference in pairing or deformation between the initial and the final nuclei. In ${}^{76}\mathrm{Ge}$ and ${}^{150}\mathrm{Nd}$, our results are similar to those of less computationally intensive QRPA calculations. We suspect the ${}^{76}\mathrm{Ge}$ result, however, because we are forced to use a spherical ground state, even though our mean-field theory indicates a deformed minimum.

Spectra and ratios of identified particles in Au+Au and d+Au collisions at √sNN=200 GeV

Abstract: The transverse momentum (p(T)) spectra and ratios of identified charged hadrons (pi(+/-), K-+/-, p, (p) over bar) produced in root s(NN) = 200 GeV Au + Au and d + Au collisions are reported in five different centrality classes for each collision species. The measurements of pions and protons are reported up to p(T) = 6 GeV/c (5 GeV/c), and the measurements of kaons are reported up to p(T) = 4 GeV/c (3.5 GeV/c) in Au + Au (d + Au) collisions. In the intermediate p(T) region, between 2 and 5 GeV/c, a significant enhancement of baryon-to-meson ratios compared to those measured in p + p collisions is observed. This enhancement is present in both Au + Au and d + Au collisions and increases as the collisions become more central. We compare a class of peripheral Au + Au collisions with a class of central d + Au collisions which have a comparable number of participating nucleons and binary nucleon-nucleon collisions. The p(T)-dependent particle ratios for these classes display a remarkable similarity, which is then discussed.

Meson-baryon reactions with strangeness -1 within a chiral framework

Abstract: We study meson-baryon scattering with strangeness --1 in unitary chiral perturbation theory. Ten coupled channels are considered in our work, namely, ${\ensuremath{\pi}}^{0}\ensuremath{\Lambda}$, ${\ensuremath{\pi}}^{0}{\ensuremath{\Sigma}}^{0}$, ${\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\Sigma}}^{+}$, ${\ensuremath{\pi}}^{+}{\ensuremath{\Sigma}}^{\ensuremath{-}}$, ${K}^{\ensuremath{-}}p$, ${\overline{K}}^{0}n$, $\ensuremath{\eta}\ensuremath{\Lambda}$, $\ensuremath{\eta}{\ensuremath{\Sigma}}^{0}$, ${K}^{0}{\ensuremath{\Xi}}^{0}$, and ${K}^{+}{\ensuremath{\Xi}}^{\ensuremath{-}}$. A large amount of experimental data are analyzed, including the recent precise measurement by the SIDDHARTA Collaboration of the energy shift and width of the $1s$ state of kaonic hydrogen. This leads to a strong constraint on the free parameters in our theory and of the resulting meson-baryon scattering amplitudes. We also analyze the uncertainty that stems by using several different strategies to perform the fits to data. It is found that large uncertainties in the subthreshold extrapolation of the ${K}^{\ensuremath{-}}p$ scattering amplitude arise by either employing only one common weak pseudoscalar decay constant or distinguishing between ${f}_{\ensuremath{\pi}}$, ${f}_{K}$, and ${f}_{\ensuremath{\eta}}$. However, in both cases a good reproduction of experimental data is obtained. We also discuss the pole content of the resulting $S$-wave amplitudes, particularly in connection with the two-pole structure of the $\ensuremath{\Lambda}(1405)$ resonance.

Neutral pion production with respect to centrality and reaction plane in Au+Au collisions at √sNN=200 GeV

Abstract: The PHENIX experiment has measured the production of pi(0)s in Au + Au collisions at root S-NN = 200 GeV. The new data offer a fourfold increase in recorded luminosity, providing higher precision and a larger reach in transverse momentum, p(T), to 20 GeV/c. The production ratio of eta/pi(0) is 0.46 +/- 0.01(stat) +/- 0.05(syst), constant with p(T) and collision centrality. The observed ratio is consistent with earlier measurements, as well as with the p + p and d + Au values. pi(0) are suppressed by a factor of 5, as in earlier findings. However, with the improved statistical precision a small but significant rise of the nuclear modification factor R-AA vs p(T), with a slope of 0.0106 +/-(0.0034)(0.0029) (Gev/c)(-1), is discernible in central collisions. A phenomenological extraction of the average fractional parton energy loss shows a decrease with increasing p(T). To study the path-length dependence of suppression, the pi(0) yield is measured at different angles with respect to the event plane; a strong azimuthal dependence of the pi(0) R-AA is observed. The data are compared to theoretical models of parton energy loss as a function of the path length L in the medium. Models based on perturbative quantum chromodynamics are insufficient to describe the data, while a hybrid model utilizing pQCD for the hard interactions and anti-de-Sitter space/conformal field theory (AdS/CFT) for the soft interactions is consistent with the data. DOI: 10.1103/PhysRevC.87.034911

Time-dependent Hartree-Fock calculations for multinucleon transfer processes in 40,48 Ca+ 124 Sn, 40 Ca+ 208 Pb, and 58 Ni+ 208 Pb reactions

Abstract: Multinucleon transfer processes in heavy-ion reactions at energies slightly above the Coulomb barrier are investigated in a fully microscopic framework of the time-dependent Hartree-Fock (TDHF) theory. Transfer probabilities are calculated from the TDHF wave function after collision using the projection operator method which has recently been proposed by Simenel (C. Simenel, Phys. Rev. Lett. 105, 192701 (2010)). We show results of the TDHF calculations for transfer cross sections of the reactions of $^{40,48}$Ca+$^{124}$Sn at $E_{lab}=$ 170, 174 MeV, $^{40}$Ca+$^{208}$Pb at $E_{lab}=$ 235, 249 MeV, and $^{58}$Ni+$^{208}$Pb at $E_{lab}=$ 328.4 MeV, for which measurements are available. We find the transfer processes show different behaviors depending on the $N/Z$ ratios of the projectile and the target, and the product of the charge numbers, $Z_P Z_T$. When the projectile and the target have different $N/Z$ ratios, fast transfer processes of a few nucleons towards the charge equilibrium of the initial system occur in reactions at large impact parameters. As the impact parameter decreases, a neck formation is responsible for the transfer. A number of nucleons are transferred by the neck breaking when two nuclei dissociate, leading to transfers of protons and neutrons in the same direction. Comparing cross sections by theory and measurements, we find the TDHF theory describes the transfer cross sections of a few nucleons reasonably. As the number of transferred nucleons increases, the agreement becomes less accurate. The TDHF calculation overestimates transfer cross sections accompanying a large number of neutrons when more than one proton are transferred. Comparing our results with those by other theories, we find the TDHF calculations give qualitatively similar results to those of direct reaction models such as GRAZING and Complex WKB.

Ab initio Gorkov-Green's function calculations of open-shell nuclei

Abstract: We present results from a new ab initio method that uses the self-consistent Gorkov-Green's function theory to address truly open-shell systems. The formalism has been recently worked out up to second order and is implemented here in nuclei on the basis of realistic nuclear forces. Benchmark calculations indicate that the method is in agreement with other ab initio approaches in doubly closed shell ${}^{40}$Ca and ${}^{48}$Ca. We find good convergence of the results with respect to the basis size in ${}^{44}$Ca and ${}^{74}$Ni and discuss quantities of experimental interest including ground-state energies, pairing gaps, and particle addition and removal spectroscopy. These results demonstrate that the Gorkov method is a valid alternative to multireference approaches for tackling degenerate or near-degenerate quantum systems. In particular, it increases the number of mid-mass nuclei accessible in an ab initio fashion from a few tens to a few hundred.

High transverse momentum quarkonium production and dissociation in heavy ion collisions

Abstract: We calculate the yields of quarkonia in heavy ion collisions at RHIC and the LHC as a function of their transverse momentum. Based upon non-relativistic quantum chromodynamics, our results include both color-singlet and color-octet contributions and feed-down effects from excited states. In reactions with ultra-relativistic nuclei, we focus on the consistent implementation of dynamically calculated nuclear matter effects, such as coherent power corrections, cold nuclear matter energy loss, and the Cronin effect in the initial state. In the final state, we consider radiative energy loss for the color-octet state and collisional dissociation of quarkonia as they traverse through the QGP. Theoretical results are presented for J/psi and Upsilon and compared to experimental data where applicable. At RHIC, a good description of the high-pT J/psi modification observed in central Cu+Cu and Au+Au collisions can be achieved within the model uncertainties. We find that measurements of J/psi yields in proton-nucleus reactions are needed to constrain the magnitude of cold nuclear matter effects. At the LHC, a good description of the experimental data can be achieved only in mid-central and peripheral Pb+Pb collisions. The large five-fold suppression of prompt J/psi in the most central nuclear reactions may indicate for the first time possible thermal effects at the level of the quarkonium wavefunction at large transverse momenta.

Electric dipole polarizability in 208 Pb: Insights from the droplet model

Abstract: We study the electric dipole polarizability αD in 208Pb based on the predictions of a large and representative set of relativistic and nonrelativistic nuclear mean-field models. We adopt the droplet model as a guide to better understand the correlations between αD and other isovector observables. Insights from the droplet model suggest that the product of αD and the nuclear symmetry energy at saturation density J is much better correlated with the neutron skin thickness Δrnp of 208Pb than the polarizability alone. Correlations of αDJ with Δrnp and with the symmetry energy slope parameter L suggest that αDJ is a strong isovector indicator. Hence, we explore the possibility of constraining the isovector sector of the nuclear energy density functional by comparing our theoretical predictions against measurements of both αD and the parity-violating asymmetry in 208Pb. We find that the recent experimental determination of αD in 208Pb in combination with the range for the symmetry energy at saturation density J=[31±(2)est] MeV suggests Δrnp(208Pb)=0.165±(0.009)expt±(0.013)theor±(0.021)est fm and L=43±(6)expt±(8)theor±(12)est MeV.

Spontaneous fission modes and lifetimes of superheavy elements in the nuclear density functional theory

Abstract: Background: The reactions with the neutron-rich ${}^{48}\mathrm{Ca}$ beam and actinide targets resulted in the detection of new superheavy (SH) nuclides with $Z=104--118$. The unambiguous identification of the new isotopes, however, still poses a problem because their $\ensuremath{\alpha}$-decay chains terminate by spontaneous fission (SF) before reaching the known region of the nuclear chart. The understanding of the competition between $\ensuremath{\alpha}$-decay and SF channels in SH nuclei is, therefore, of crucial importance for our ability to map the SH region and to assess its extent.Purpose: We perform self-consistent calculations of the competing decay modes of even-even SH isotopes with $108\ensuremath{\le}Z\ensuremath{\le}126$ and $148\ensuremath{\le}N\ensuremath{\le}188$.Methods: We use the state-of-the-art computational framework based on self-consistent symmetry-unrestricted nuclear density functional theory capable of describing the competition between nuclear attraction and electrostatic repulsion. We apply the SkM* Skyrme energy density functional. The collective mass tensor of the fissioning superfluid nucleus is computed by means of the cranking approximation to the adiabatic time-dependent Hartree-Fock-Bogoliubov (HFB) approach. This paper constitutes a systematic self-consistent study of spontaneous fission in the SH region, carried out at a full HFB level, that simultaneously takes into account both triaxiality and reflection asymmetry.Results: Breaking axial symmetry and parity turns out to be crucial for a realistic estimate of collective action; it results in lowering SF lifetimes by more than 7 orders of magnitude in some cases. We predict two competing SF modes: reflection symmetric modes and reflection asymmetric modes.Conclusions: The shortest-lived SH isotopes decay by SF; they are expected to lie in a narrow corridor formed by ${}^{280}\mathrm{Hs}$, ${}^{284}\mathrm{Fl}$, and ${}_{118}^{284}\mathrm{Uuo}$ that separates the regions of SH nuclei synthesized in ``cold-fusion'' and ``hot-fusion'' reactions. The region of long-lived SH nuclei is expected to be centered on ${}^{294}\mathrm{Ds}$ with a total half-life of $\ensuremath{\sim}1.5\phantom{\rule{0.28em}{0ex}}\mathrm{days}$. Our survey provides a solid benchmark for the future improvements of self-consistent SF calculations in the region of SH nuclei.

Volume Fluctuations and Higher Order Cumulants of the Net Baryon Number

Abstract: We consider the effect of volume fluctuations on cumulants of the net baryon number. Based on a general formalism, we derive universal expressions for the net baryon number cumulants in the presence of volume fluctuations with an arbitrary probability distribution. The relevance of these fluctuations for the baryon-number cumulants and in particular for the ratios of cumulants is assessed in the Polyakov loop extended quark-meson model within the functional renormalization group. We show that the baryon number cumulants are generally enhanced by volume fluctuations and that the critical behavior of higher-order cumulants may be modified significantly.

Interpretation of the X(3872) as a charmonium state plus an extra component due to the coupling to the meson-meson continuum

Abstract: We present a quark model calculation of the charmonium spectrum with self-energy corrections due to the coupling to the meson-meson continuum. The bare masses used in the calculation are computed within the relativized quark model by Godfrey and Isgur. The strong decay widths of $3S$, $2P$, $1D$, and $2D$ $c\overline{c}$ states are also calculated, to set the values of the ${}^{3}{P}_{0}$ pair-creation model's parameters we use to compute the vertex functions of the loop integrals. Finally, the nature of the $X(3872)$ resonance is analyzed and the main possibilities ($c\overline{c}$ state or $D{\overline{D}}^{*}$ molecule) are discussed. According to our results, the $X(3872)$ is compatible with the meson ${\ensuremath{\chi}}_{c1}(2P)$, with ${J}^{\mathrm{PC}}={1}^{++}$, and is thus interpreted as a $c\overline{c}$ core plus higher Fock components due to the coupling to the meson-meson continuum. These ${J}^{\mathrm{PC}}={1}^{++}$ quantum numbers are in agreement with the experimental results found by the LHCb collaboration. In our view, the $X(3872)$'s mass is lower than the quark model's predictions because of self-energy shifts.

Hartree-Fock-Bogoliubov nuclear mass model with 0.50 MeV accuracy based on standard forms of Skyrme and pairing functionals

Abstract: We present a new Hartree-Fock-Bogoliubov nuclear mass model based on standard forms of Skyrme and pairing functionals, which corresponds to the most accurate mass model we ever achieved within the framework of the nuclear energy density functional theory. Our new mass model is characterized by a model standard deviation ${\ensuremath{\sigma}}_{\mathrm{mod}}=0.500$ MeV with respect to essentially all the 2353 available mass data for nuclei with neutron and proton numbers larger than 8. At the same time, the underlying Skyrme functional yields a realistic description of infinite homogeneous nuclear matter properties, as determined by realistic calculations and by experiments; these include in particular the incompressibility coefficient, the pressure in charge-symmetric nuclear matter, the neutron-proton effective mass splitting, the stability against spin and spin-isospin fluctuations, as well as the neutron-matter equation of state.