Nuclear Theory·nucl-th

Thursday·March 26, 2015

13 papers—6 primary·7 cross-listed

01
Sub-threshold $ϕ$ and $Ξ^{-}$ production by high mass resonances with UrQMD
Jan Steinheimer🇩🇪 · Marcus Bleicher🇩🇪
We present a possible explanation for the deep sub-threshold, $ϕ$ and $Ξ^{-}$ production yields measured with the HADES experiment in Ar+KCl reactions at $E_{lab} = 1.76$ A GeV and present predictions for Au+Au reactions at $E_{lab} = 1.23$ A GeV. To explain the surprisingly high yields of $ϕ$ and $Ξ^{-}$ hadrons we propose new decay channels for high mass baryon resonances. These new decay channels are constrained by elementary $p + p \to p + p + ϕ$ cross sections, and $Ξ^{-}$ production in p+Nb. Based on the fits to the elementary reactions one obtains a satisfactorily description of $ϕ$ and $Ξ^{-}$ production in deep sub-threshold Ar+KCl reactions as well as the observed nuclear transparency ratio in proton induced $ϕ$ production in cold nuclear matter. The results implicate that no new medium effects are required to describe the rare strange particle production data in low energy nuclear collisions.
nucl-thnucl-exJ.Phys.G(2016)·74 citations
02
Effects of the Inverse Square Potential on Nucleon-Nucleon Elastic Scattering in the Bethe-Salpeter Equation
Susumu Kinpara🇯🇵
Bethe-Salpeter equation is applied to nucleon-nucleon elastic scattering at the intermediate energy. The differential cross section and the polarization are calculated in terms of the phase shift analysis method using the two-body potential derived from the Bethe-Salpeter equation. The lowest-order Born approximation for the K-matrix is corrected by including the inverse square part of the potential.
nucl-th1 citation
03
Recent results from the UrQMD hybrid model for heavy ion collisions
Marcus Bleicher🇩🇪 · Stephan Endres🇩🇪 · Jan Steinheimer🇩🇪 · Hendrik van Hees🇩🇪
These proceedings present recent results from transport-hydrodynamics-hybrid models for heavy ion collisions at relativistic energies. The main focus is on the absorption of (anti-)protons in the hadronic afterburner stage of the reaction, di-lepton production at SPS and heavy quark dynamics.
nucl-th3 citations
04
Hydrodynamic modeling of pseudorapidity flow correlations in relativistic heavy-ion collisions and the torque effect
Piotr Bozek🇵🇱 · Wojciech Broniowski🇵🇱 · Adam Olszewski🇵🇱
We analyze correlations between the event-plane angles in different intervals of pseudorapidity within the 3+1-dimensional viscous hydrodynamics with the Glauber-model initial conditions. As predicted earlier, the fluctuations in the particle production mechanism in the earliest stage, together with asymmetry of the emission profiles in pseudorapidity from the forward- and backward going wounded nucleons, lead to the torque effect, namely, decorrelation of the event-plane angles in distant pseudorapidity bins. We use two- or three-bin measures of correlation functions to quantify the effect, with the latter compared to the recent data from the CMS collaboration. We find a sizable torque effect, with magnitude larger at RHIC than at the LHC.
nucl-thhep-phnucl-exPRC(2015)·31 citations
05
Vector interaction enhanced bag model for astrophysical applications
Thomas Klahn🇵🇱 · Tobias Fischer🇵🇱
For quark matter studies in astrophysics the thermodynamic bag model (tdBAG) has been widely used. Despite its success it fails to account for various phenomena expected from Quantum-Chromo-Dynamics (QCD). We suggest a straightforward extension of tdBAG in order to take the dynamical breaking of chiral symmetry and the influence of vector interactions explicitly into account. As for tdBAG the model mimics confinement in a phenomenological approach. It is based on an analysis of the Nambu--Jona-Lasinio (NJL) model at finite density. Furthermore, we demonstrate how NJL and bag models in this regime follow from the more general and QCD based framework of Dyson-Schwinger (DS) equations in medium by assuming a simple gluon contact interaction. Based on our simple and novel model, we construct quark hadron hybrid equations of state (EoS) and study systematically chiral and deconfinement phase transitions, the appearance of $s$ -quarks and the role of vector interaction. We further study these aspects for matter in beta-equilibrium at zero temperature, with particular focus on the current ~2 solar masses maximum mass constraint for neutron stars. Our approach indicates that the currently only theoretical evidence for the hypothesis of stable strange matter is an artifact of tdBAG and results from neglecting the dynamical breaking of chiral symmetry.
nucl-thastro-ph.HEhep-phApJ(2015)·152 citations
06
Nonconformal viscous anisotropic hydrodynamics
Dennis Bazow🇺🇸 · Ulrich W. Heinz🇺🇸 · Mauricio Martinez🇺🇸
We generalize the derivation of viscous anisotropic hydrodynamics from kinetic theory to allow for non-zero particle masses. The macroscopic theory is obtained by taking moments of the Boltzmann equation after expanding the distribution function around a spheroidally deformed local momentum distribution whose form has been generalized by the addition of a scalar field that accounts non-perturbatively (i.e. already at leading order) for bulk viscous effects. Hydrodynamic equations for the parameters of the leading-order distribution function and for the residual (next-to-leading order) dissipative flows are obtained from the three lowest moments of the Boltzmann equation. The approach is tested for a system undergoing (0+1)-dimensional boost-invariant expansion for which the exact solution of the Boltzmann equation in relaxation time approximation is known. Nonconformal viscous anisotropic hydrodynamics is shown to approximate this exact solution more accurately than any other known hydrodynamic approximation.
nucl-thhep-phPRC(2015)·60 citations
07
Tetraquark Cusp Effects from Diquark Pair Production
Samuel H. Blitz🇺🇸 · Richard F. Lebed🇺🇸
We present the first study of the cusp effect (the movement of resonant poles due to the proximity of multiparticle thresholds) caused by the creation of diquark-antidiquark pairs. The cusp profile for such states is obtained from constituent counting rules. We compare the effectiveness of diquark cusps in moving resonant poles with that from a phenomenological form commonly used for meson-pair creation, and find that mesons tend to be more effective at lower energies $(e.g.$ , the $K K$ threshold), while diquarks tend to be more effective at the charm [ $X (3872)$ ] scales and above.
↳ hep-phnucl-thPRD(2015)·29 citations
08
Revisiting Scalar Glueballs
Hai-Yang Cheng🇹🇼 · Chun-Khiang Chua🇹🇼 · Keh-Fei Liu🇺🇸
It is commonly believed that the lowest-lying scalar glueball lies somewhere in the isosinglet scalar mesons $f_{0} (1370), f_{0} (1500)$ and $f_{0} (1710)$ denoted generically by $f_{0}$ . In this work we consider lattice calculations and experimental data to infer the glue and $q q ˉ$ components of $f_{0}$ . These include the calculations of the scalar glueball masses in quenched and unquenched lattice QCD, measurements of the radiative decays $J / ψ \to γ f_{0}$ , the ratio of $f_{0}$ decays to $π π$ and $K K ˉ$ , the ratio of $J / ψ$ decays to $f_{0} (1710) ω$ and $f_{0} (1710) ϕ$ , the $f_{0}$ contributions to $B_{s} \to J / ψ π^{+} π^{-}$ , and the near mass degeneracy of $a_{0} (1450)$ and $K_{0}^{*} (1430)$ . All analyses suggest the prominent glueball nature of $f_{0} (1710)$ and the flavor octet structure of $f_{0} (1500)$ .
↳ hep-phhep-exhep-latnucl-thPRD(2015)·56 citations
09
Bosonic and fermionic Weinberg-Joos (j,0)+ (0,j) states of arbitrary spins as Lorentz-tensors or tensor-spinors and second order theory
E. G. Delgado Acosta🇲🇽 · V.M. Banda Guzman🇲🇽 · M. Kirchbach🇲🇽
We propose a general method for the description of arbitrary single spin-j states transforming according to (j,0)+(0,j) carrier spaces of the Lorentz algebra in terms of Lorentz-tensors for bosons, and tensor-spinors for fermions, and by means of second order Lagrangians. The method allows to avoid the cumbersome matrix calculus and higher \partial^{2j} order wave equations inherent to the Weinberg-Joos approach. We start with reducible Lorentz-tensor (tensor-spinor) representation spaces hosting one sole (j,0)+(0,j) irreducible sector and design there a representation reduction algorithm based on one of the Casimir invariants of the Lorentz algebra. This algorithm allows us to separate neatly the pure spin-j sector of interest from the rest, while preserving the separate Lorentz- and Dirac indexes. However, the Lorentz invariants are momentum independent and do not provide wave equations. Genuine wave equations are obtained by conditioning the Lorentz-tensors under consideration to satisfy the Klein-Gordon equation. In so doing, one always ends up with wave equations and associated Lagrangians that are second order in the momenta. Specifically, a spin-3/2 particle transforming as (3/2,0)+ (0,3/2) is comfortably described by a second order Lagrangian in the basis of the totally antisymmetric Lorentz tensor-spinor of second rank, \Psi_[ \mu\nu]. Moreover, the particle is shown to propagate causally within an electromagnetic background. In our study of (3/2,0)+(0,3/2) as part of \Psi_[\mu\nu] we reproduce the electromagnetic multipole moments known from the Weinberg-Joos theory. We also find a Compton differential cross section that satisfies unitarity in forward direction. The suggested tensor calculus presents itself very computer friendly with respect to the symbolic software FeynCalc.
↳ hep-phnucl-thEPJA(2015)·22 citations
10
Gluon Transport Equation with Effective Mass and Dynamical Onset of Bose-Einstein Condensation
Jean-Paul Blaizot🇫🇷 · Yin Jiang🇺🇸 · Jinfeng Liao🇺🇸
We study the transport equation describing a dense system of gluons, in the small scattering angle approximation, taking into account medium-generated effective masses of the gluons. We focus on the case of overpopulated systems that are driven to Bose-Einstein condensation on their way to thermalization. The presence of a mass modifies the dispersion relation of the gluon, as compared to the massless case, but it is shown that this does not change qualitatively the scaling behavior in the vicinity of the onset.
↳ hep-phcond-mat.quant-gashep-thnucl-thNPA(2016)·11 citations
11
Gluon Transport Equations with Condensate in the Small Angle Approximation
Jean-Paul Blaizot🇫🇷 · Jinfeng Liao🇺🇸
We derive the set of kinetic equations that control the evolution of gluons in the presence of a condensate. We show that the dominant singularities remain logarithmic when the scattering involves particles in the condensate. This allows us to define a consistent small angle approximation.
↳ hep-phcond-mat.quant-gashep-thnucl-thNPA(2016)·9 citations
12
Optimising the neutron environment of Radiation Portal Monitors: a computational optimisation study
Mark R. Gilbert · Zamir Ghani · Lee W. Packer
Efficient and reliable detection of radiological or nuclear threats is a crucial part of national and international efforts to prevent terrorist activities. Radiation Portal Monitors (RPMs), which are deployed worldwide, are intended to interdict smuggled fissile material by detecting emissions of neutrons and gamma rays. However, considering the range and variety of threat sources, vehicular and shielding scenarios, and that only a small signature is present, it is important that the design of the RPMs allows these signatures to be accurately differentiated from the environmental background. Using Monte-Carlo neutron-transport simulations of a model helium-3 detector system we have conducted a parameter study to identify the optimum combination of detector shielding and collimation that maximises the sensitivity of RPMs. These structures, which could be simply and cost-effectively added to existing RPMs, can improve the detector response by more than a factor of two relative to an unmodified, bare design. Furthermore, optimisation of the air gap surrounding the helium tubes also improves detector efficiency.
↳ physics.ins-detnucl-thNucl.Instrum.Meth.A(2015)·2 citations
13
Hydrodynamics Beyond the Gradient Expansion: Resurgence and Resummation
Michal P. Heller🇨🇦 · Michal Spalinski🇵🇱
Consistent formulations of relativistic viscous hydrodynamics involve short lived modes, leading to asymptotic rather than convergent gradient expansions. In this Letter we consider the Mueller-Israel-Stewart theory applied to a longitudinally expanding quark-gluon plasma system and identify hydrodynamics as a universal attractor without invoking the gradient expansion. We give strong evidence for the existence of this attractor and then show that it can be recovered from the divergent gradient expansion by Borel summation. This requires careful accounting for the short-lived modes which leads to an intricate mathematical structure known from the theory of resurgence.
↳ hep-thhep-phnucl-thphysics.flu-dynPRL(2015)·374 citations

Affiliations

first authorsco-authorsvia INSPIRE