Wed·Aug 6, 2014Wednesday·August 6, 2014

1. 01*

   Symmetry Energy of Nucleonic Matter With Tensor Correlations

   Or Hen🇮🇱 · Bao-An Li🇺🇸 · Wen-Jun Guo🇺🇸 · L.B. Weinstein🇺🇸 · Eli Piasetzky🇮🇱

   The nuclear symmetry energy (E_sym(\roh)) is a vital ingredient of our understanding of many processes, from heavy-ion collisions to neutron stars structure. While the total nuclear symmetry energy at nuclear saturation density (\rho_0) is relatively well determined, its value at supranuclear densities is not. The latter can be better constrained by separately examining its kinetic and potential terms and their density dependencies. The kinetic term of the symmetry energy, E_sym^kin(\rho_0), equals the difference in the per-nucleon kinetic energy between pure neutron matter (PNM) and symmetric nuclear matter (SNM), often calculated using a simple Fermi gas model. However, experiments show that tensor force induced short-range correlations (SRC) between proton-neutron pairs shift nucleons to high-momentum in SNM, but have almost no effect in PNM. We present an approximate analytical expression for E_sym^kin(\rho) of correlated nucleonic matter. In our model, E_sym^kin(\rho_0) = -10 MeV, which differs significantly from +12.5 MeV for the widely-used free Fermi gas model. This result is consistent with our analysis of recent data on the free proton-to-neutron ratios measured in intermediate energy nucleus-nucleus collisions as well as with microscopic many-body calculations, and previous phenomenological extractions. We then use our calculated E_sym^kin(\rho) in combination with the known total symmetry energy and its density dependence at saturation density to constrain the value and density dependence of the potential part and to extrapolate the total symmetry energy to supranuclear densities.

   nucl-exastro-ph.SRnucl-thPRC(2015)·133 citations
2. 02*

   Photonuclear production of vector mesons in ultra-peripheral Pb-Pb collisions at the LHC

   Joakim Nystrand (for the ALICE Collaboration)🇳🇴

   Vector mesons are copiously produced in ultra-peripheral nucleus-nucleus collisions. In these collisions, the nuclei are separated by impact parameters larger than the sum of the nuclear radii, and the interaction is mediated by the electromagnetic field. The interaction effectively corresponds to a photonuclear interaction between a photon, generated from the electromagnetic field of one of the nuclei, and the target nucleus. The ALICE Collaboration has previously published results on exclusive J/psi photoproduction at mid and forward rapidities in Pb-Pb collisions. The cross section for this process is a particularly good measure of the nuclear gluon distribution. In this talk, the latest results on exclusive production of light and heavy vector mesons from ALICE in Pb-Pb collisions will be presented.

   nucl-exhep-exNPA(2014)·11 citations
3. 03*

   Search for the 4He-eta bound state in dd->(4He-eta)_{bound}->3He n pi0 and dd->(4He-eta)_{bound}->3He p pi- reactions with the WASA-at-COSY facility

   M. Skurzok🇵🇱 · W. Krzemien🇵🇱 · P. Moskal🇵🇱

   In November 2010, the search for the 4He-{\eta} bound state was per formed with high statistics and high acceptance with the WASA-at-COSY facility using a ramped beam technique. The signature of eta - mesic nuclei is searched for in the measured excitation functions for the two reaction channels: dd ->3He n pi0 and dd ->3He p pi- near the eta production threshold. This report includes the description of the experimental method and the status of the data analysis.

   nucl-exEPJ Web Conf.(2014)·3 citations
4. 04*

   Charge-dependent anisotropic flow studies and the search for the Chiral Magnetic Wave in ALICE

   Ron Belmont (for the ALICE Collaboration)🇺🇸

   Theoretical calculations have shown the possibility of P-violating bubbles in the QCD vacuum, which in combination with the strong magnetic field created in off-central heavy-ion collisions lead to novel effects such as the Chiral Magnetic Effect (CME) and the Chiral Separation Effect (CSE). A coupling between the CME and the CSE produces a wave-like excitation called the Chiral Magnetic Wave (CMW). The CMW produces a quadrupole moment that always has the same sign and is therefore present in an average over events. In this talk we present a series of charge-dependent anisotropic flow measurements in Pb--Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV in ALICE, using two- and three-particle correlators with unidentified hadrons. The relation of these measurements to the search for the CMW is discussed.

   nucl-exnucl-thNPA(2014)·22 citations
5. 05*

   Fundamental Neutron Physics Beamline at the Spallation Neutron Source at ORNL

   N. Fomin🇺🇸 · G. L. Greene🇺🇸 · R. Allen · V. Cianciolo🇺🇸 · C. Crawford🇺🇸 · T. Ito · P. R. Huffman🇺🇸 · E. B. Iverson🇺🇸 · R. Mahurin🇨🇦 · W. M. Snow🇺🇸

   We describe the Fundamental Neutron Physics Beamline (FnPB) facility located at the Spallation Neutron Source at Oak Ridge National Laboratory. The FnPB was designed for the conduct of experiments that investigate scientific issues in nuclear physics, particle physics, astrophysics and cosmology using a pulsed slow neutron beam. We present a detailed description of the design philosophy, beamline components, and measured fluxes of the polychromatic and monochromatic beams.

   ↳ physics.ins-detnucl-exphysics.acc-phNucl.Instrum.Meth.A(2015)·37 citations
6. 06*

   Viscous hydrodynamics for strongly anisotropic expansion

   Ulrich W. Heinz🇺🇸 · Dennis Bazow (Ohio State Univ.)🇺🇸 · Michael Strickland (Kent State Univ.)🇺🇸

   A new formulation of second-order viscous hydrodynamics, based on an expansion around a locally anisotropic momentum distribution, is presented. It generalizes the previously developed formalism of anisotropic hydrodynamics (aHydro) to include a complete set of dissipative currents for which equations of motion are derived by solving the Boltzmann equation in the 14-moment approximation. By solving the vaHydro equations for a transversally homogeneous, longitudinally boost-invariant system ((0+1)-dimensional expansion) and comparing with the exact solution of the Boltzmann equation in relaxation-time approximation we show that vaHydro performs much better than all other known second-order viscous hydrodynamic approximations.

   ↳ nucl-thhep-phnucl-exNPA(2014)·10 citations
7. 07*

   Impact of the equation-of-state -- gravity degeneracy on constraining the nuclear symmetry energy from astrophysical observables

   Xiao-Tao He🇺🇸 · F. J. Fattoyev🇺🇸 · Bao-An Li🇺🇸 · W. G. Newton🇺🇸

   There is a degeneracy between the equation of state (EOS) of superdense neutron-rich nuclear matter and the strong-field gravity in understanding properties of neutron stars. While the EOS is still poorly known, there are also longstanding ambiguities in choosing General Relativity or alternative gravity theories in the not-so-well tested strong-field regime. Besides possible appearance of hyperons and new phases, the most uncertain part of the nucleonic EOS is currently the density dependence of nuclear symmetry energy. To provide information that may help break the EOS-gravity degeneracy, we investigate effects of symmetry energy within its uncertain range determined by terrestrial nuclear laboratory experiments on the gravitational binding energy and spacetime curvature of neutron stars within GR and the scalar-tensor (ST) theory of gravity. In particular, we focus on effects of the following parameters characterizing the EOS of neutron-rich nucleonic matter: (1) the incompressibility $K_0$ of symmetric nuclear matter, (2) the slope $L$ of symmetry energy at saturation density and (3) the high-density behavior of symmetry energy. We find that the variation of either the density slope $L$ or the high-density behavior of symmetry energy leads to large changes in both the binding energy and curvature of neutron stars while effects of varying the more constrained $K_0$ are negligibly small. The difference in predictions using the GR and the ST theory appears only for massive neutron stars, and is significantly smaller than the differences resulting from variations in the symmetry energy. We conclude that within the ST theory of gravity, the EOS-gravity degeneracy has been broken by the recent relativistic pulsar measurements, and that measurements of neutron star properties sensitive to the compactness constrain mainly the density dependence of the symmetry energy.

   ↳ nucl-thastro-ph.SRgr-qcnucl-exPRC(2015)·51 citations
8. 08*

   Experimental research on the THGEM-based thermal neutron detector

   Yang Lei🇨🇳 · Zhou Jian-Rong🇨🇳 · Sun Zhi-Jia🇨🇳 · Zhang Ying🇨🇳 · Huang Chao-Qiang🇨🇳 · Sun Guang-Ai🇨🇳 · Wang Yan-Feng🇨🇳 · Yang Gui-An🇨🇳 · Xu Hong🇨🇳 · Xie Yu-Guang🇨🇳 · Chen Yuan-Bo🇨🇳

   A new thermal neutron detector with the domestically produced THGEM (THick Gas Electron Multiplier) was developed as an alternative to 3He to meet the needs of the next generation of neutron facilities. One type of Au-coated THGEM was designed specifically for the neutron detection. A detector prototype had been developed and the preliminary experimental tests were presented, including the performance of the Au-coated THGEM working in the Ar/CO2 gas mixtures and the neutron imaging test with 252CF source, which would provide the reference of experimental data for the research in future.

   ↳ physics.ins-detnucl-ex1 citation
9. 09*

   Properties and significance of the surface dipole mode

   P. Papakonstantinou🇰🇷

   A strong isoscalar dipole resonance is known to be excited in a variety of nuclei, including isospin symmetric ones, at approximately 6-7 MeV. A series of theoretical studies and accumulating experimental evidence support an interpretation of the above dipole resonance as an elementary surface vibration. Obviously, such a mode is potentially as interesting as any collective excitation for a variety of reasons. In addition, though, it is found to account for the observed isoscalar segment of pygmy dipole strength. As discussed here, this has important implications for pygmy-strength interpretations and searches for genuine neutron-skin oscillations.

   ↳ nucl-thnucl-exJPS Conf.Proc.(2015)·3 citations
10. 10*

    Azimuthal Anisotropy Distributions in High-Energy Collisions

    Li Yan🇫🇷 · Jean-Yves Ollitrault🇫🇷 · Arthur M. Poskanzer🇺🇸

    Elliptic flow in ultrarelativistic heavy-ion collisions results from the hydrodynamic response to the spatial anisotropy of the initial density profile. A long-standing problem in the interpretation of flow data is that uncertainties in the initial anisotropy are mingled with uncertainties in the response. We argue that the non-Gaussianity of flow fluctuations in small systems can be used to disentangle the initial state from the response. We apply this method to recent measurements of anisotropic flow in Pb+Pb and p+Pb collisions at the LHC. The response coefficient is found to decrease mildly as the system becomes smaller. This mild decrease is consistent with a low value of the ratio of viscosity over entropy.

    ↳ nucl-thhep-phnucl-exPLB(2015)·53 citations
11. 11*

    Pion $p_T$ spectra in $p+p$ collisions as a function of $\sqrt{s}$ and event multiplicity

    P. Sett🇮🇳 · P. Shukla🇮🇳

    We study the charged pion transverse momentum ($p_T$) spectra in $p$+$p$ collisions as a function of collision energy $\sqrt{s}$ and event multiplicity using Tsallis distribution. This study gives an insight of the pion production process in $p+p$ collisions. The study covers pion spectra measured in $p+p$ collisions at SPS energies (6.27-17.27 GeV), RHIC energies (62.4 GeV and 200 GeV) and LHC energies (900 GeV, 2.76 TeV and 7 TeV). The Tsallis parameters have been obtained and parameterized as a function of $\sqrt{s}$. The study suggests that as we move to higher energy more and more hard processes contribute to the spectra. We also study the charged pion spectra for different event multiplicities in $p$+$p$ collisions for LHC energies using Tsallis distribution. The variation of the Tsallis parameters as a function of event multiplicity has been obtained and their behavior is found to be independent of collision energy.

    ↳ hep-phhep-exnucl-exnucl-thAdv.High Energy Phys.(2014)·7 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.