Nuclear Theory·nucl-th

Thursday·September 10, 2015

9 papers—3 primary·6 cross-listed

04
[Submitted on 7 Sept 2015] (cross-list from hep-ph)
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.
Comments:
15 pages, 10 figures; v2: major revision - author list extended, treatment of the left-hand cut corrected, discussion and references updated; v3: version published in EPJC
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1509.02194 [pdf]
EPJC(2021)·88 citations
05
[Submitted on 8 Sept 2015] (cross-list from astro-ph.HE)
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.
Comments:
59 pages, 27 figures, version accepted for publication
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
1509.02538 [pdf]
NPA(2016)·58 citations
06
[Submitted on 9 Sept 2015] (cross-list from hep-ph)
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.
Comments:
12 pages including 9 figures as EPS-files; prepared using LaTeX package for publication in the European Physical Journal C
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1509.02692 [pdf]
EPJC(2015)·31 citations
07
[Submitted on 9 Sept 2015] (cross-list from hep-ph)
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.
Comments:
5 pages, 4 figures, contributed talk by K.J.E. at the 7th International Conference on Hard and Electromagnetic Probes of High Energy Nuclear Collisions (Hard Probes 2015), Montreal, Canada, 29 June - 3 July, 2015
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1509.02767 [pdf]
Nucl.Part.Phys.Proc.(2016)·5 citations
08
[Submitted on 9 Sept 2015] (cross-list from hep-ph)
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.
Comments:
Talk presented at DIS2015 conference, April 27 - May 1, 2015, Southern Methodist University, Dallas, Texas. v2: updated reference list
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1509.02798 [pdf]
PoS(2015)·8 citations
09
[Submitted on 7 Sept 2015] (cross-list from astro-ph.HE)
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 $m_{j} = 0$ .
Comments:
This paper has been withdrawn by the author due to loss of relevance
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Theory (nucl-th)
arXiv:
1509.02827 [pdf]
2 citations

Affiliations

first authorsco-authorsvia INSPIRE

Towards an improved understanding of η→γ∗γ∗

Relativistic Mean-Field Models with Scaled Hadron Masses and Couplings: Hyperons and Maximum Neutron Star Mass

Anisotropic flow fluctuations in hydro-inspired freeze-out model for relativistic heavy ion collisions

Pinning down QCD-matter shear viscosity in ultrarelativistic heavy-ion collisions via EbyE fluctuations using pQCD + saturation + hydrodynamics

Nuclear PDF constraints from p+Pb collisions at the LHC

The cooling of the Cassiopeia A neutron star as a probe of a triplet neutron pairing in the core

Affiliations

Towards an improved understanding of $η \to γ^{} γ^{}$