Nuclear Theory·nucl-th

Thursday·September 10, 2015

9 papers—3 primary·6 cross-listed

01
Impressions of the Meson Spectrum: Hybrids & Exotics, present and future
M.R. Pennington🇺🇸
It has long been expected that the spectrum of hadrons in QCD would be far richer and extensive than experiment has so far revealed. While there have been experimental hints of this richness for some time, it is really only in the last few years that dramatic progress has been seen in the exploration both experimentally and in calculations on the lattice. Precision studies enabled by new technology both with detectors and high performance computations are converging on an understanding of the spectrum in strong coupling QCD. These methodologies are laying the foundation for a decade of potential discovery that electro and photoproduction experiments at Jefferson Lab, which when combined with key results on $B$ and charmonium decays from both $e^{+} e^{-}$ and $pp$ colliders, should turn mere impressions of the light meson spectrum into a high definition picture.
nucl-thhep-phEPJ Web Conf.(2016)·4 citations
02
Generalized Second-Order Thomas-Fermi Method for Superfluid Fermi Systems
J.C. Pei🇨🇳 · Na Fei🇨🇳 · Y.N. Zhang🇨🇳 · P. Schuck🇫🇷
Using the $ℏ$ -expansion of the Green's function of the Hartree-Fock-Bogoliubov equation, we extend the second-order Thomas-Fermi approximation to generalized superfluid Fermi systems by including the density-dependent effective mass and the spin-orbit potential. We first implement and examine the full correction terms over different energy intervals of the quasiparticle spectra in calculations of finite nuclei. Final applications of this generalized Thomas-Fermi method are intended for various inhomogeneous superfluid Fermi systems.
nucl-thcond-mat.quant-gasPRC(2015)·4 citations
03
Estimation of 2p2h effect on Gamow-Teller transition with Second Tamm-Dancoff-Approximation
Futoshi Minato
Two-particle two-hole (2p2h) effect on the Gamow-Teller (GT) transition for neutron-rich nuclei is studied by the second Tamm-Dancoff approximation (STDA) with the Skyrme interaction. Unstable $^{24}$ O and $^{34}$ Si, and stable $^{48}$ Ca nuclei are chosen to study the quenching and fragmentation of the GT strengths. Correlation of the 2p2h configurations causes $20$ \% quenching and downward shift of GT giant resonances (GTGRs). The residual interaction changing relative angular momentum, appeared in the tensor force part, gives a meaningful effect to the GT strength distributions. In this work, $17$ to $26$ \% of the total GT strengths are brought to high energy region above GTGRs. In particular, the tensor force brings strengths to high energy more than $50$ MeV. STDA calculation within a small model space for 2p2h configuration is also performed and experimental data of $^{48}$ Ca is reproduced reasonably.
nucl-thPRC(2016)·16 citations
04
Towards an improved understanding of $η \to γ^{*} γ^{*}$
S. Holz🇩🇪 · J. Plenter🇩🇪 · C. W. Xiao🇩🇪 · T. Dato🇩🇪 · C. Hanhart🇩🇪 · B. Kubis🇩🇪 · U.-G. Meißner🇩🇪 · A. Wirzba🇩🇪
We argue that high-quality data on the reaction $e^{+} e^{-} \to π^{+} π^{-} η$ will allow one to determine the doubly-virtual form factor $η \to γ^{*} γ^{*}$ in a model-independent way with controlled accuracy. This is an important step towards a reliable evaluation of the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon. When analyzing the existing data for $e^{+} e^{-} \to π^{+} π^{-} η$ for total energies squared $k^{2} > 1 GeV^{2}$ , we demonstrate that the effect of the $a_{2}$ meson provides a natural breaking mechanism for the commonly employed factorization ansatz in the doubly-virtual form factor $F_{η γ^{*} γ^{*}} (q^{2}, k^{2})$ . However, better data are needed to draw firm conclusions.
↳ hep-phhep-exnucl-thEPJC(2021)·88 citations
05
Relativistic Mean-Field Models with Scaled Hadron Masses and Couplings: Hyperons and Maximum Neutron Star Mass
K.A. Maslov🇷🇺 · E.E. Kolomeitsev🇸🇰 · D.N. Voskresensky🇷🇺
An equation of state of cold nuclear matter with an arbitrary isotopic composition is studied within a relativistic mean-field approach with hadron masses and coupling constants depending self-consistently on the scalar mean-field. All hadron masses decrease universally with the scalar field growth, whereas meson-nucleon coupling constants can vary differently. More specifically we focus on two modifications of the KVOR model studied previously. One extension of the model (KVORcut) demonstrates that the equation of state stiffens if the increase of the scalar-field magnitude with the density is bounded from above at some value for baryon densities above the saturation nuclear density. This can be realized if the nucleon vector-meson coupling constant changes rapidly as a function of the scalar field slightly above the desired value. The other version of the model (MKVOR) utilizes a smaller value of the nucleon effective mass at the nuclear saturation density and a saturation of the scalar field in the isospin asymmetric matter induced by a strong variation of the nucleon isovector-meson coupling constant as function of the scalar field. A possibility of hyperonization of the matter in neutron star interiors is incorporated. Our equations of state fulfill majority of known empirical constraints including the pressure-density constraint from heavy-ion collisions, direct Urca constraint, gravitational-baryon mass constraint for the pulsar J0737-3039B, and the constraint on the maximum mass of the neutron stars.
↳ astro-ph.HEnucl-thNPA(2016)·58 citations
06
Anisotropic flow fluctuations in hydro-inspired freeze-out model for relativistic heavy ion collisions
L.V. Bravina🇳🇴 · E.S. Fotina🇷🇺 · V.L. Korotkikh🇷🇺 · I.P. Lokhtin🇷🇺 · L.V. Malinina🇷🇺 · E.N. Nazarova🇷🇺 · S.V. Petrushanko🇷🇺 · A.M. Snigirev🇷🇺 · E.E. Zabrodin🇷🇺
The LHC data on event-by-event harmonic flow coefficients measured in PbPb collisions at center-of-mass energy 2.76 TeV per nucleon pair are analyzed and interpreted within the HYDJET++ model. To compare the model results with the experimental data the unfolding procedure is employed. The essentially dynamical origin of the flow fluctuations in hydro-inspired freeze-out approach has been established. It is shown that the simple modification of the model via introducing the distribution over spatial anisotropy parameters permits HYDJET++ to reproduce both elliptic and triangular flow fluctuations and related to it eccentricity fluctuations of the initial state at the LHC energy.
↳ hep-phnucl-thEPJC(2015)·31 citations
07
Pinning down QCD-matter shear viscosity in ultrarelativistic heavy-ion collisions via EbyE fluctuations using pQCD + saturation + hydrodynamics
K. J. Eskola🇫🇮 · H. Niemi🇩🇪 · R. Paatelainen🇪🇸
We introduce an event-by-event pQCD + saturation + hydro ("EKRT") framework for high-energy heavy-ion collisions, where we compute the produced fluctuating QCD-matter energy densities from next-to-leading order (NLO) perturbative QCD (pQCD) using saturation to control soft particle production, and describe the space-time evolution of the QCD matter with viscous hydrodynamics, event by event (EbyE). We compare the computed centrality dependence of hadronic multiplicities, p_T spectra and flow coefficients v_n against LHC and RHIC data. We compare also the computed EbyE probability distributions of relative fluctuations of v_n, as well as correlations of 2 and 3 event-plane angles, with LHC data. Our systematic multi-energy and -observable analysis not only tests the initial state calculation and applicability of hydrodynamics, but also makes it possible to constrain the temperature dependence of the shear viscosity-to-entropy ratio, eta/s(T), of QCD matter in its different phases. Remarkably, we can describe all these different flow observables and correlations consistently with eta/s(T) that is independent of the collision energy.
↳ hep-phnucl-thNucl.Part.Phys.Proc.(2016)·5 citations
08
Nuclear PDF constraints from p+Pb collisions at the LHC
Ilkka Helenius🇸🇪 · Hannu Paukkunen🇫🇮 · Kari J. Eskola🇫🇮
As the current nuclear PDF analyses are mainly constrained by fixed-target Drell-Yan and deeply inelastic scattering data only the quark nuclear modifications at fairly large $x$ values are in a good control. Inclusive pion production in d+Au collisions at RHIC provides some constraints for gluons but due to the limited kinematic reach of the data the gluon modifications remain uncertain especially at small values of $x$ . In this talk, we discuss how the existing data from p+Pb collisions at the LHC can improve the nuclear PDF fits and which measurements would be sensitive to the small- $x$ gluons. In particular, we consider inclusive hadron production, compare this to direct photons, and show estimates of the effect of CMS dijet measurements to the uncertainty of nuclear gluon distributions.
↳ hep-phnucl-thPoS(2015)·8 citations
09
The cooling of the Cassiopeia A neutron star as a probe of a triplet neutron pairing in the core
Lev B. Leinson
The observed rapid cooling of the Cassiopeia A neutron star (Cas A NS) can be interpreted as being triggered by the onset of neutron superfluidity in the core of the star, causing enhanced neutrino emission from neutron Cooper pair breaking and formation (PBF). This provides a unique possibility for probing the neutron condensate in the core. Using consistent neutron star core and crust equation of state and composition, I explore the sensitivity of this interpretation to the phase state of the triplet superfluid condensate. Modeling cooling within an expected range of neutron star masses and envelope compositions, I found that the fast cooling of the Cas A NS can not be explained by the PBF processes in the conventional $^{3}$ P $_{2}$ condensate with $m_{j} = 0$ .
↳ astro-ph.HEastro-ph.SRnucl-th2 citations

Affiliations

first authorsco-authorsvia INSPIRE