Fri·Feb 5, 2016Friday·February 5, 2016

1. 01*

   Direct Evidence of Octupole Deformation in Neutron-Rich ${}^{144}$Ba

   B. Bucher🇺🇸 · S. Zhu🇨🇳 · C. Y. Wu🇺🇸 · R. V. F. Janssens🇺🇸 · D. Cline🇺🇸 · A. B. Hayes🇺🇸 · M. Albers🇺🇸 · A. D. Ayangeakaa🇺🇸 · P. A. Butler🇬🇧 · C. M. Campbell🇺🇸 · M. P. Carpenter🇺🇸 · C. J. Chiara🇺🇸 and 22 other authors

   The neutron-rich nucleus ${}^{144}$Ba ($t_{1/2}$=11.5 s) is expected to exhibit some of the strongest octupole correlations among nuclei with mass numbers $A$ less than 200. Until now, indirect evidence for such strong correlations has been inferred from observations such as enhanced $E1$ transitions and interleaving positive- and negative-parity levels in the ground-state band. In this experiment, the octupole strength was measured directly by sub-barrier, multi-step Coulomb excitation of a post-accelerated 650-MeV ${}^{144}$Ba beam on a 1.0-mg/cm${}^2$ ${}^{208}$Pb target. The measured value of the matrix element, $⟨3_1^{-}\Vert \mathcal{M}(E3)\Vert 0_1^{+}⟩=0.65{(}_{-23}^{+17})$ $e$b${}^{3/2}$, corresponds to a reduced $B(E3)$ transition probability of 48(${}_{-34}^{+25}$) W.u. This result represents an unambiguous determination of the octupole collectivity, is larger than any available theoretical prediction, and is consistent with octupole deformation.

   nucl-exPRL(2016)·170 citations
2. 02*

   Electromagnetic radiation as a probe of the initial state and of viscous dynamics in relativistic nuclear collisions

   Gojko Vujanovic🇺🇸 · Jean-François Paquet🇨🇦 · Gabriel S. Denicol🇨🇦 · Matthew Luzum🇪🇸 · Sangyong Jeon🇨🇦 · Charles Gale🇨🇦

   The penetrating nature of electromagnetic signals makes them suitable probes to explore the properties of the strongly-interacting medium created in relativistic nuclear collisions. We examine the effects of the initial conditions and shear relaxation time on the spectra and flow coefficients of electromagnetic probes, using an event-by-event 3+1D viscous hydrodynamic simulation (MUSIC).

   ↳ nucl-thhep-phnucl-exPRC(2016)·47 citations
3. 03*

   Coherent photoproduction of vector mesons in heavy ion ultraperipheral collisions: Update for run 2 at the CERN Large Hadron Collider

   V. Guzey🇷🇺 · E. Kryshen🇷🇺 · M. Zhalov (PNPI, Gatchina)🇷🇺

   We make predictions for the cross sections of coherent photoproduction of $\rho$, $\varphi$, $J/\psi$, $\psi (2S)$, and ${\rm Y}(1S)$ mesons in Pb-Pb ultraperipheral collisions (UPCs) at $\sqrt{s_{NN}}=5.02$ TeV in the kinematics of run 2 at the Large Hadron Collider extending the approaches successfully describing the available Pb-Pb UPC data at $\sqrt{s_{NN}}=2.76$ TeV. Our results illustrate the important roles of hadronic fluctuations of the photon and inelastic nuclear shadowing in photoproduction of light vector mesons on nuclei and the large leading twist nuclear gluon shadowing in photoproduction of quarkonia on nuclei. We show that the ratio of $\psi (2S)$ and $J/\psi$ photoproduction cross sections in Pb-Pb UPCs is largely determined by the ratio of these cross sections on the proton. We also argue that UPCs with electromagnetic excitations of the colliding ions followed by the forward neutron emission allows one to significantly increase the range of photon energies accessed in vector meson photoproduction on nuclei.

   ↳ nucl-thhep-phnucl-exPRC(2016)·108 citations
4. 04*

   Valence-quark distribution functions in the kaon and pion

   Chen Chen🇨🇳 · Lei Chang🇨🇳 · Craig D. Roberts🇺🇸 · Shaolong Wan🇨🇳 · Hong-Shi Zong🇨🇳

   We describe expressions for pion and kaon dressed-quark distribution functions that incorporate contributions from gluons which bind quarks into these mesons and hence overcome a flaw of the commonly used handbag approximation. The distributions therewith obtained are purely valence in character, ensuring that dressed-quarks carry all a meson's momentum at a characteristic hadronic scale and vanishing as $(1-x{)}^2$ when Bjorken-$x\to 1$. Comparing such distributions within the pion and kaon, it is apparent that the size of SU(3)-flavour symmetry breaking in meson parton distribution functions is modulated by the flavour dependence of dynamical chiral symmetry breaking. Corrections to these leading-order formulae may be divided into two classes, responsible for shifting dressed-quark momentum into glue and sea-quarks. Working with available empirical information, we build an algebraic framework that is capable of expressing the principal impact of both classes of corrections. This enables a realistic comparison with experiment which allows us to identify and highlight basic features of measurable pion and kaon valence-quark distributions. We find that whereas roughly two-thirds of the pion's light-front momentum is carried by valence dressed-quarks at a characteristic hadronic scale, this fraction rises to 95% in the kaon; evolving distributions with these features to a scale typical of available Drell-Yan data produces a kaon-to-pion ratio of u-quark distributions that is in agreement with the single existing data set; and predict a u-quark distribution within the pion that agrees with a modern reappraisal of $\pi N$ Drell-Yan data. Precise new data are essential in order to validate this reappraisal and because a single modest-quality measurement of the kaon-to-pion ratio cannot be considered definitive.

   ↳ nucl-thhep-exhep-lathep-ph+1PRD(2016)·124 citations
5. 05*

   Beam energy dependence of Hanbury-Brown-Twiss radii from a blast-wave model

   S. Zhang🇨🇳 · Y. G. Ma🇨🇳 · J. H. Chen🇨🇳 · C. Zhong🇨🇳

   The beam energy dependence of correlation lengths (the Hanbury-Brown-Twiss radii) is calculated by using a blast-wave model and the results are comparable with those from RHIC-STAR beam energy scan data as well as the LHC-ALICE measurements. A set of parameter for the blast-wave model as a function of beam energy under study are obtained by fit to the HBT radii at each energy point. The transverse momentum dependence of HBT radii is presented with the extracted parameters for Au + Au collision at $\sqrt{s_{NN}}=$ 200 GeV and for Pb+Pb collisions at 2.76 TeV. From our study one can learn that particle emission duration can not be ignored while calculating the HBT radii with the same parameters. And tuning kinetic freeze-out temperature in a range will result in system lifetime changing in the reverse direction as it is found in RHIC-STAR experiment measurements.

   ↳ nucl-thhep-phnucl-exAdv.High Energy Phys.(2016)·17 citations
6. 06*

   Low-energy hypernuclear spectra with microscopic particle-rotor model with relativistic point coupling hyperon-nucleon interaction

   H. Mei🇯🇵 · K. Hagino🇯🇵 · J.M. Yao🇺🇸 · T. Motoba🇯🇵

   We extend the microscopic particle-rotor model for hypernuclear low-lying states by including the derivative and tensor coupling terms in the point-coupling nucleon-$\Lambda$ particle ($N\Lambda$) interaction. Taking ${}_{\Lambda }^{13}$C as an example, we show that a good overall description for excitation spectra is achieved with four sets of effective $N\Lambda$ interaction. We find that the $\Lambda$ hyperon binding energy decreases monotonically with increasing the strengths of the high-order interaction terms. In particular, the tensor coupling term decreases the energy splitting between the first $1/2^{-}$ and $3/2^{-}$ states and increases the energy splitting between the first $3/2^{+}$ and $5/2^{+}$ states in ${}_{\Lambda }^{13}$C.

   ↳ nucl-thnucl-exPRC(2016)·16 citations
7. 07*

   Speed of Sound in Hadronic matter using Non-extensive Tsallis Statistics

   Arvind Khuntia🇮🇳 · Pragati Sahoo🇮🇳 · Prakhar Garg🇮🇳 · Raghunath Sahoo🇮🇳 · Jean Cleymans🇿🇦

   The speed of sound ($c_s$) is studied to understand the hydrodynamical evolution of the matter created in heavy-ion collisions. The quark-gluon plasma (QGP) formed in heavy-ion collisions evolves from an initial QGP to the hadronic phase via a possible mixed phase. Due to the system expansion in a first order phase transition scenario, the speed of sound reduces to zero as the specific heat diverges. We study the speed of sound for systems, which deviate from a thermalized Boltzmann distribution using non-extensive Tsallis statistics. In the present work, we calculate the speed of sound as a function of temperature for different $q$-values for a hadron resonance gas. We observe a similar mass cut-off behaviour in non-extensive case for $c_s^2$ by including heavier particles, as is observed in the case of a hadron resonance gas following equilibrium statistics. Also, we explicitly present that the temperature where the mass cut-off starts, varies with the $q$-parameter which hints at a relation between the degree of non-equilibrium and the limiting temperature of the system. It is shown that for values of $q$ above approximately 1.13 all criticality disappear in the speed of sound, i.e. the decrease in the value of the speed of sound, observed at lower values of $q$, disappears completely.

   ↳ hep-phnucl-exnucl-thEPJA(2016)·28 citations
8. 08*

   Thermal Charm and Charmonium Production in Quark Gluon Plasma

   Kai Zhou🇨🇳 · Zhengyu Chen🇨🇳 · Carsten Greiner🇩🇪 · Pengfei Zhuang🇨🇳

   We study the effect of thermal charm production on charmonium regeneration in high energy nuclear collisions. By solving the kinetic equations for charm quark and charmonium distributions in Pb+Pb collisions, we calculate the global and differential nuclear modification factors $R_{AA}(N_{part})$ and $RAA(p_t)$ for $J/\Psi$s. Due to the thermal charm production in hot medium, the charmonium production source changes from the initially created charm quarks at SPS, RHIC and LHC to the thermally produced charm quarks at Future Circular Collider (FCC), and the $J/\Psi$ suppression ($R_{AA}<1$) observed so far will be replaced by a strong enhancement ($R_{AA}>1$) at FCC at low transverse momentum.

   ↳ hep-phnucl-exnucl-thPLB(2016)·33 citations
9. 09*

   New Astrophysical Reaction Rate for the ${}^{12}\text{C}(\alpha ,\gamma {)}^{16}\text{O}$ Reaction

   Z. D. An🇨🇳 · Y. G. Ma🇨🇳 · G. T. Fan🇨🇳 · Y. J. Li · Z. P. Chen🇨🇳 · Y. Y. Sun🇨🇳

   A new astrophysical reaction rate for ${}^{12}$C($\alpha ,\gamma$)${}^{16}$O has been evaluated on the basis of a global R-matrix fitting to the available experimental data. The reaction rates of ${}^{12}$C($\alpha ,\gamma$)${}^{16}$O for stellar temperatures between 0.04 $\le$ $T_9$ $\le$ 10 are provided in a tabular form and by an analytical fitting expression. At $T_9$ = 0.2, the reaction rate is (7.83 $\pm$ 0.35)$\times 10^{15}$ $\mathrm{c}{\mathrm{m}}^3\mathrm{mo}{\mathrm{l}}^{-1}{\mathrm{s}}^{-1}$, where stellar helium burning occurs.

   ↳ nucl-thnucl-exApJL(2016)·7 citations
10. 10*

    Kinematic constrains on interacting nucleons in $Pb+Pb$ collisions at $\sqrt{s_{NN}}=2.76$ TeV within the HIJING code

    Khaled Abdel-Waged🇸🇦 · Nuha Felemban🇸🇦

    The kinematic constrains on interacting nucleons in Large Hadron Collider (LHC) heavy-ion collisions are investigated in the framework of the Heavy Ion Jet Interaction Generator (HIJING) code incorporated with a collective cascade recipe. The latter is used to implement energy-momentum conservation constrains on both primary and secondary interacting nucleons. It is found that the energy-momentum conservation constrains on the interacting nucleons affect the whole charged particle pseudo-rapidity density distribution $(\frac{d{N}_{ch}}{d\eta })$, at different centralities (from central (0-5\%) to peripheral (70-80\%) collisions), in Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV. In particular, the kinematic constrains on interacting nucleons are shown to reduce $(\frac{d{N}_{ch}}{d\eta })$ yield at mid-pseudorapidity $(|\eta |<2)$ in all centrality intervals, which is consistent with the LHC data. In addition, the model predicts an enhancement of the hadron production at $|\eta |>8$, which could be checked in future ALICE Zero Degree calorimeter. Such an enhancement is found to be mainly due to the interactions of protons at the spectator parts of the collision. This indicates that the kinematic constrains are important for a correct geometrical treatment of Pb+Pb collisions at LHC energies.

    ↳ nucl-thnucl-exPRC(2016)·4 citations
11. 11*

    Revealing transversity GPDs through the photoproduction of a photon and a $\rho$ meson

    R. Boussarie🇫🇷 · B. Pire🇫🇷 · L. Szymanowski🇵🇱 · S. Wallon🇫🇷

    Photoproduction of a pair of particles with large invariant mass is a natural extension of collinear QCD factorization theorems which have been much studied for deeply virtual Compton scattering and deeply virtual meson production. We discuss the production of a photon and a meson, where the wide angle Compton scattering on a meson subprocess factorizes from generalized parton distribution. We calculate at dominant twist and leading order in ${\alpha }_s$, the production cross-section of a transversely polarized $\rho$ meson which is sensitive to chiral-odd GPDs, and show that it may be measurable in near future JLab experiments.

    ↳ hep-phhep-exnucl-exnucl-thEPJ Web Conf.(2016)·8 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.