Nuclear Theory·nucl-th

Friday·February 12, 2016

8 papers—6 primary·2 cross-listed

01
Toward a consistent evolution of the quark-gluon plasma and heavy quarks
Marlene Nahrgang🇺🇸 · Jörg Aichelin🇫🇷 · Pol Bernard Gossiaux🇫🇷 · Klaus Werner🇫🇷
Heavy-quark observables in ultrarelativistic heavy-ion collisions, like the nuclear modification factor and the elliptic flow, give insight into the mechanisms of high-momentum suppression and low-momentum thermalization of heavy quarks. Here, we present a global study of these two observables within a coupled approach of the heavy-quark propagation in a realistic fluid dynamical medium, MC@sHQ+EPOS2, and compare to experimental data from RHIC and LHC experiments. The heavy quarks scatter elastically and inelastically with the quasiparticles of the quark-gluon plasma (QGP), which are represented consistently with the underlying equation of state. We examine two scenarios: first, we interpret the lattice QCD equation of state as a sum of partonic and hadronic contributions, and second, as a gas of massive partonic quasiparticles. It is observed that independent of their momentum the energy loss of heavy quarks depends strongly on how the lattice QCD equation of state is translated into degrees of freedom of the QGP.
nucl-thhep-phPRC(2016)·36 citations
02
Asymptotic normalization coefficients for $^{7} Be + p \to^{8} B$ from the peripheral $^{7} Be$ ( $d$ , $n$ ) $^{8} B$ reaction and their astrophysical application
O. Tojiboev · R. Yarmukhamedov · S. V. Artemov · S. B. Sakuta
The proton transfer $^{7} Be$ ( $d$ , $n$ ) $^{8} B$ reaction at the energy of 4.5 MeV (c.m.) has been analysed within the modified DWBA. New estimates and their uncertainties are obtained for values of the asymptotic normalization coefficients for $p +^{7} Be \to^{8} B$ , the astrophysical $S_{17} (0)$ factor and the s-wave $p +^{7} Be$ scattering lengths.
nucl-thPRC(2016)·13 citations
03
Role of electronic shell in the double beta decay
E. G. Drukarev🇷🇺 · M. Ya. Amusia🇮🇱 · L. V. Chernysheva🇷🇺
We demonstrate that the limiting energy available for ejected electrons in double beta decay is diminished by about 400 eV due to inelastic processes in the electronic shell.
nucl-thhep-exPRC(2016)·4 citations
04
Calculation of Energy Spectrum of 12C Isotope by Relativistic Cluster model
Nafiseh Roshanbakht · Mohammad Reza Shojaei
In this paper, we have calculated the energy spectrum of 12C isotope by cluster model. The experimental results show that the "Hoyle" state at 7.65 MeV in 12C isotope has a well-developed three-alpha structure. Hence, we select a three-body system and for interaction between the clusters we use modified Yukawa potential plus coulomb potential. Then, we solve the relativistic Klein-Gordon equation using Nikiforov-Uvarov method to calculate the energy spectrum. Finally, the calculated results are compared with the experimental data. The results show that the isotope 12C should be considered as consisting of three-alpha cluster and the modified Yukawa potential is adaptable for cluster interactions.
nucl-thPramana(2016)·5 citations
05
Event-by-event hydrodynamics $+$ jet energy loss: A solution to the $R_{AA} \otimes v_{2}$ puzzle
Jacquelyn Noronha-Hostler (Houston U.)🇺🇸 · Barbara Betz (Frankfurt U.)🇩🇪 · Jorge Noronha (Sao Paulo U.)🇧🇷 · Miklos Gyulassy (LBNL, NSD and Columbia U. and CCNU, Wuhan, Inst. Part. Phys.)🇺🇸
High $p_{T} > 10$ GeV elliptic flow, which is experimentally measured via the correlation between soft and hard hadrons, receives competing contributions from event-by-event fluctuations of the low $p_{T}$ elliptic flow and event plane angle fluctuations in the soft sector. In this paper, a proper account of these event-by-event fluctuations in the soft sector, modeled via viscous hydrodynamics, is combined with a jet energy loss model to reveal that the positive contribution from low $p_{T}$ $v_{2}$ fluctuations overwhelms the negative contributions from event plane fluctuations. This leads to an enhancement of high $p_{T} > 10$ GeV elliptic flow in comparison to previous calculations and provides a natural solution to the decade long high $p_{T}$ $R_{AA} \otimes v_{2}$ puzzle. We also present the first theoretical calculation of high $p_{T}$ $v_{3}$ , which is shown to be compatible with current LHC data. Furthermore, we discuss how short wavelength jet-medium physics can be deconvoluted from the physics of soft, bulk event-by-event flow observables using event shape engineering techniques.
nucl-thhep-phnucl-exPRL(2016)·140 citations
06
From QCD to Physical Resonances
Daniel R. Bolton🇺🇸 · Raúl A. Briceño🇺🇸 · David J. Wilson🇬🇧
In this talk, we present the first chiral extrapolation of a resonant scattering amplitude obtained from lattice QCD. Finite-volume spectra, determined by the Hadron Spectrum Collaboration at $m_{π} = 236$ MeV, for the isotriplet $π π$ channel are analyzed using the Lüscher method to determine the infinite-volume scattering amplitude. Unitarized Chiral Perturbation Theory is then used to extrapolate the scattering amplitude to the physical light quark masses. The viability of this procedure is demonstrated by its agreement with the experimentally determined scattering phase shift up to center-of-mass energies of 1.2 GeV. Finally, we analytically continue the amplitude to the complex plane to obtain the $ρ$ -pole at $[755 (2) (1) (_{02}^{20}) - \frac{i}{2} 129 (3) (1) (_{1}^{7})]$ MeV.
nucl-thhep-latAIP Conf.Proc.(2016)·1 citation
07
Existence of the critical endpoint in the vector meson extended linear sigma model
Peter Kovács🇭🇺 · Zsolt Szép🇭🇺 · György Wolf🇭🇺
The chiral phase transition of the strongly interacting matter is investigated at nonzero temperature and baryon chemical potential mu_B within an extended (2+1) flavor Polyakov constituent quark-meson model which incorporates the effect of the vector and axial vector mesons. The effect of the fermionic vacuum and thermal fluctuations computed from the grand potential of the model is taken into account in the curvature masses of the scalar and pseudoscalar mesons. The parameters of the model are determined by comparing masses and tree-level decay widths with experimental values in a chi^2-minimization procedure which selects between various possible assignments of scalar nonet states to physical particles. We examine the restoration of the chiral symmetry by monitoring the temperature evolution of condensates and the chiral partners' masses and of the mixing angles for the pseudoscalar eta-eta' and the corresponding scalar complex. We calculate the pressure and various thermodynamical observables derived from it and compare them to the continuum extrapolated lattice results of the Wuppertal-Budapest collaboration. We study the T-mu_B phase diagram of the model and find that a critical end point exists for parameters of the model, which give acceptable values of chi^2.
↳ hep-phnucl-thPRD(2016)·110 citations
08
Improved empirical parametrizations of the $γ^{*} N \to Δ (1232)$ and $γ^{*} N \to N (1520)$ helicity amplitudes and the Siegert's theorem
G. Ramalho🇧🇷
In the nucleon electroexcitation reactions, $γ^{*} N \to R$ , where $R$ is a nucleon resonance ( $N^{*}$ ), the electric amplitude $E$ , and the longitudinal amplitude $S_{1/2}$ , are related by $E \propto \frac{ω}{∣ q ∣} S_{1/2}$ , at the pseudo-threshold limit ( $∣ q ∣ \to 0$ ), where $ω$ and $∣ q ∣$ are respectively the energy and the magnitude of three-momentum of the photon. The previous relation is usually refereed as the Siegert's theorem. The form of the electric amplitude, defined in terms of the transverse amplitudes $A_{1/2}$ and $A_{3/2}$ , and the explicit coefficients of the relation, depend on the angular momentum and parity ( $J^{P}$ ) of the resonance $R$ . The Siegert's theorem is the consequence of the structure of the electromagnetic transition current, which induces constraints between the electromagnetic form factors in the pseudo-threshold limit. In the present work, we study the implications of the Siegert's theorem for the $γ^{*} N \to Δ (1232)$ and $γ^{*} N \to N (1520)$ transitions. For the $γ^{*} N \to N (1520)$ transition, in addition to the relation between electric amplitude and longitudinal amplitude, we obtain also a relation between the two transverse amplitudes: $A_{1/2} = A_{3/2} / 3$ , at the pseudo-threshold. % The constraints at the pseudo-threshold are tested for the MAID2007 parametrizations of the reactions under discussion. New parametrizations for the amplitudes $A_{1/2}$ , $A_{3/2}$ and $S_{1/2}$ , for the $γ^{*} N \to Δ (1232)$ and $γ^{*} N \to N (1520)$ transitions, valid for small and large $Q^{2}$ , are proposed. The new parametrizations are consistent with both: the pseudo-threshold constraints (Siegert's theorem) and the empirical data.
↳ hep-phhep-exnucl-exnucl-thPRD(2016)·30 citations

Affiliations

first authorsco-authorsvia INSPIRE