Nuclear Theory·nucl-th

Friday·January 1, 2016

11 papers—3 primary·8 cross-listed

01
Finite amplitude method applied to giant dipole resonance in heavy rare-earth nuclei
Tomohiro Oishi · Markus Kortelainen · Nobuo Hinohara
Background: The quasiparticle random phase approximation (QRPA), within the framework of the nuclear density functional theory (DFT), has been a standard tool to access the collective excitations of the atomic nuclei. Recently, finite amplitude method (FAM) has been developed, in order to perform the QRPA calculations efficiently without any truncation on the two-quasiparticle model space. Purpose: We discuss the nuclear giant dipole resonance (GDR) in heavy rare-earth isotopes, for which the conventional matrix diagonalization of the QRPA is numerically demanding. A role of the Thomas-Reiche-Kuhn (TRK) sum rule enhancement factor, connected to the isovector effective mass, is also investigated. Methods: The electric dipole photoabsorption cross section was calculated within a parallelized FAM-QRPA scheme. We employed the Skyrme energy density functional self-consistently in the DFT calculation for the ground states and FAM-QRPA calculation for the excitations. Results: The mean GDR frequency and width are mostly reproduced with the FAM-QRPA, when compared to experimental data, although some deficiency is observed with isotopes heavier than erbium. A role of the TRK enhancement factor in actual GDR strength is clearly shown: its increment leads to a shift of the GDR strength to higher-energy region, without a significant change in the transition amplitudes. Conclusions: The newly developed FAM-QRPA scheme shows a remarkable efficiency, which enables to perform systematic analysis of GDR for heavy rare-earth nuclei. Theoretical deficiency of photoabsorption cross section could not be improved by only adjusting the TRK enhancement factor, suggesting the necessity of beyond the self-consistent QRPA approach, and/or a more systematic optimization of the EDF parameters.
nucl-thPRC(2016)·44 citations
02
High temperature Bose-Einstein condensation
Viktor V. Begun🇵🇱
The indications of a possible pion condensation at the LHC are summarized. The condensation is predicted by the non-equilibrium hadronization model for 2.76 TeV Pb+Pb collisions at the LHC. The model solves the proton/pion puzzle and reproduces the low $p_{T}$ enhancement of the pion spectra, as well as the spectra of protons and antiprotons, charged kaons, $K_{S}^{0}$ , $K^{*} (892)^{0}$ and $ϕ (1020)$ . The obtained parameters allow to estimate the amount of pion condensate on the level of 5\% from the total number of pions at the LHC. The condensate is located at $p_{T} < 250$ MeV.
nucl-thhep-phEPJ Web Conf.(2016)·4 citations
03
The Constant-Sound-Speed parameterization for NJL models of quark matter in hybrid stars
Ignacio F. Ranea-Sandoval🇦🇷 · Sophia Han🇺🇸 · Milva G. Orsaria🇦🇷 · Gustavo A. Contrera🇦🇷 · Fridolin Weber🇺🇸 · Mark G. Alford🇺🇸
The discovery of pulsars as heavy as 2 solar masses has led astrophysicists to rethink the core compositions of neutron stars, ruling out many models for the nuclear equations of state (EoS). We explore the hybrid stars that occur when hadronic matter is treated in a relativistic mean-field approximation and quark matter is modeled by three-flavor local and non-local Nambu Jona-Lasinio (NJL) models with repulsive vector interactions. The NJL models typically yield equations of state that feature a first order transition to quark matter. Assuming that the quark-hadron surface tension is high enough to disfavour mixed phases, and restricting to EoSes that allow stars to reach 2 solar masses, we find that the appearance of the quark matter core either destabilizes the star immediately (this is typical for non-local NJL models) or leads to a very short hybrid star branch in the mass-radius relation (this is typical for local NJL models). Using the Constant-Sound-Speed parametrization we can see that the reason for the near-absence of hybrid stars is that the transition pressure is fairly high and the transition is strongly first order.
nucl-thastro-ph.SRPRC(2016)·72 citations
04
Non-perturbative collisional energy loss of heavy quarks in quark-gluon plasma
Nikolai Kochelev🇷🇺 · Hee-Jung Lee🇰🇷 · Yongseok Oh🇰🇷 · Baiyang Zhang🇨🇳 · Pengming Zhang🇨🇳
We suggest a new mechanism for the energy loss of fast heavy quarks in quark-gluon plasma. This mechanism is based on pion production caused by the anomalous chromomagnetic quark-gluon-pion interaction induced by strong topological fluctuations of the gluon fields represented by instantons. We found that this mechanism gives a considerable contribution to the collisional energy loss of a heavy quark in quark-gluon plasma, which shows a nontrivial role of nonperturbative phenomena in strongly interacting quark-gluon plasma.
↳ hep-phhep-exnucl-exnucl-thPRC(2016)·5 citations
05
Indications for a critical point in the phase diagram for hot and dense nuclear matter
Roy A. Lacey (Depts. of Chemistry and Physics, Stony Brook University)🇺🇸
Two-pion interferometry measurements are studied for a broad range of collision centralities in Au+Au (Root_s = 7.7 - 200 GeV) and Pb+Pb (Root_s = 2.76 TeV) collisions. They indicate non-monotonic excitation functions for the Gaussian emission source radii difference [(R_out)^2 - (R_side)^2], suggestive of reaction trajectories which spend a fair amount of time near a "soft point" in the equation of state (EOS) that coincides with the critical end point (CEP). A Finite-Size Scaling (FSS) analysis of these excitation functions, provides further validation tests for the CEP. It also indicates a second order phase transition at the CEP, and the values T^{cep} ~ 165 MeV and mu_B^{cep} ~ 95 MeV for its location in the (T, mu_B)-plane of the phase diagram. The static critical exponents (nu ~ 0.66 and gamma ~ 1.2) extracted via the same FSS analysis, place this CEP in the 3D Ising model universality class. A Dynamic Finite-Size Scaling analysis of the excitation functions, gives the estimate z ~ 0.87 for the dynamic critical exponent, suggesting that the associated critical expansion dynamics is dominated by the hydrodynamic sound mode.
↳ nucl-exhep-exnucl-thNPA(2016)·14 citations
06
Exploring the QCD Phase Structure with Beam Energy Scan in Heavy-ion Collisions
Xiaofeng Luo🇨🇳
Beam energy scan programs in heavy-ion collisions aim to explore the QCD phase structure at high baryon density. Sensitive observables are applied to probe the signatures of the QCD phase transition and critical point in heavy-ion collisions at RHIC and SPS. Intriguing structures, such as dip, peak and oscillation, have been observed in the energy dependence of various observables. In this paper, an overview is given and corresponding physics implications will be discussed for the experimental highlights from the beam energy scan programs at the STAR, PHENIX and NA61/SHINE experiments. Furthermore, the beam energy scan phase II at RHIC (2019-2020) and other future experimental facilities for studying the physics at low energies will be also discussed.
↳ nucl-exhep-exhep-latnucl-thNPA(2016)·147 citations
07
Centrality dependence of forward $J / ψ$ suppression in high energy proton-nucleus collisions
B. Ducloué🇫🇮 · T. Lappi🇫🇮 · H. Mäntysaari🇺🇸
The production of forward $J / ψ$ mesons in proton-nucleus collisions can provide important information on gluon saturation. In a previous work we studied this process in the Color Glass Condensate framework, describing the target using a dipole cross section fitted to HERA inclusive data and extrapolated to the case of a nuclear target using the optical Glauber model. In this work we study the centrality dependence of the nuclear suppression in this model and compare our results with recent LHC data for this observable.
↳ hep-phnucl-thNPA(2016)·0 citations
08
$η$ and $η^{'}$ decays into lepton pairs
Pere Masjuan🇩🇪 · Pablo Sanchez-Puertas🇩🇪
In this work, we calculate the branching ratios for the $η (η^{'}) \to ℓ ˉ ℓ$ decays, where $ℓ = e, μ$ . These processes have tiny rates in the standard model due to spin flip, loop, and electromagnetic suppression, for what they could be sensitive to New Physics effects. In order to provide a reliable input for the Standard Model, we exploit the general analytical properties of the amplitude. For that purpose, we invoke the machinery of Canterbury approximants, which provides a systematic description of the underlying hadronic physics in a data-driven fashion. Given the current experimental discrepancies, we discuss in detail the role of the resonant region and comment on the reliability of $χ$ PT calculations. Finally, we discuss the kind of new physics which we think would be relevant to account for them.
↳ hep-phhep-exnucl-thJHEP(2016)·59 citations
09
Charm hadrons above $T_{c}$
Swagato Mukherjee🇺🇸 · P. Petreczky🇺🇸 · S. Sharma🇺🇸
From the analysis of the lattice data on fluctuations and correlations of charm we conclude that open charm meson and baryon-like excitations exist above the QCD crossover temperature, and in fact are the dominant degrees of freedom for thermodynamics in the vicinity of the transition. Charm quarks become the dominant charm degrees of freedom only for temperatures T>200 MeV.
↳ hep-phhep-latnucl-thNPA(2016)·0 citations
10
Measurements of $D_{S}^{\pm}$ -meson production in Au+Au collisions at $s_{N N}$ = 200 GeV in STAR
Md. Nasim (for the STAR collaboration)🇺🇸
We present the first measurement of the nuclear modification factor $R_{AA}$ and elliptic flow $v_{2}$ of $D_{s}$ in Au+Au collisions at $s_{N N}$ = 200 GeV with the STAR detector. These results have been compared with those of other open charm mesons and strange mesons to determine how the (possibly) strangeness equilibrated partonic matter affects the $D_{s}$ meson production. We find that the nuclear modification factor of $D_{S}$ are systematically higher than unity and $D^{0}$ $R_{AA}$ . The ratio $D_{s} / D^{0}$ is shown as a function of transverse momentum for the 10-40 $%$ most central Au+Au collisions and compared with that in $p + p$ collisions obtained from PYTHIA. It is also compared with that in Pb-Pb collisions at 2.76 TeV by the ALICE experiment. Our measurement indicates a hint of enhancement of $D_{S}$ production in Au+Au collisions with respect to $p + p$ collisions as compared to non-strange $D$ mesons.
↳ nucl-exhep-exnucl-thNPA(2016)·4 citations
11
Thermalization of mini-jets in a quark-gluon plasma
Edmond Iancu🇫🇷 · Bin Wu🇫🇷
We present the complete physical picture for the evolution of a high-energy jet propagating through a weakly-coupled quark-gluon plasma (QGP) by analytical and numerical investigation of thermalization of the soft components of the jet. Our results support the following physical picture: the leading particle emits a significant number of mini-jets which promptly evolve via multiple branching and thus degrade into a myriad of soft gluons, with energies of the order of the medium temperature $T$ . Via elastic collisions with the medium constituents, these soft gluons relax to local thermal equilibrium with the plasma over a time scale which is considerably shorter than the typical lifetime of the mini-jet. The thermalized gluons form a tail which lags behind the hard components of the jet. Together with the background QGP, they behave hydrodynamically.
↳ hep-phhep-exnucl-exnucl-thNPA(2016)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE