Nuclear Theory·nucl-th

Monday·September 19, 2016

10 papers—5 primary·5 cross-listed

01
Updates to the p+p and A+A chemical freeze-out lines from the new experimental data
V. V. Begun🇵🇱 · V. Vovchenko🇩🇪 · M. I. Gorenstein🇩🇪
We show that the new data on mean multiplicities measured in p+p and A+A collisions together with the updated list of resonances lead to the significant changes of the obtained freeze-out lines. The new A+A line gives much smaller temperatures at high collision energies and agrees with the values obtained at the LHC. The newly obtained p+p line is much closer to the A+A line than previously expected, and even touches it in the region where the $K^{+} / π^{+}$ horn appears in the data. It indicates that the temperatures that will be obtained in the beam energy and system size scan by the NA61/SHINE Collaboration might be very close. However, our analysis shows that the chemical potentials could be very different for the same energies in A+A and p+p. It adds more puzzles to the set of surprising coincidences at the energies close to the possible onset of deconfinement.
nucl-thhep-exhep-phnucl-exJ.Phys.Conf.Ser.(2017)·12 citations
02
Vortex structure in superfluid color-flavor locked quark matter
Mark G. Alford🇺🇸 · S. Kumar Mallavarapu🇺🇸 · Tanmay Vachaspati🇺🇸 · Andreas Windisch🇺🇸
The core region of a neutron star may feature quark matter in the color-flavor- locked (CFL) phase. The CFL condensate breaks the baryon number symmetry, such that the phenomenon of superfluidity arises. If the core of the star is rotating, vortices will form in the superfluid, carrying the quanta of angular momentum. In a previous study we have solved the question of stability of these vortices, where we found numerical proof of a conjectured instability, according to which superfluid vortices will decay into an arrangement of so-called semi-superfluid fluxtubes. Here we report first results of an extension of our framework that allows us to study multi-vortex dynamics. This will in turn enable us to investigate the structure of semi-superfluid string lattices, which could be relevant to study pinning phenomena at the boundary of the core.
nucl-thastro-ph.HEEPJ Web Conf.(2016)·1 citation
03
The quark mean field model with pion and gluon corrections
Xueyong Xing🇨🇳 · Jinniu Hu🇨🇳 · Hong Shen🇨🇳
The properties of nuclear matter and finite nuclei are studied within the quark mean field (QMF) model by taking the effects of pion and gluon into account at the quark level. The nucleon is described as the combination of three constituent quarks confined by a harmonic oscillator potential. To satisfy the spirit of QCD theory, the contributions of pion and gluon on the nucleon structure are treated in second-order perturbation theory. For the nuclear many-body system, nucleons interact with each other by exchanging mesons between quarks. With different constituent quark mass, $m_{q}$ , we determine three parameter sets about the coupling constants between mesons and quarks, named as QMF-NK1, QMF-NK2, and QMF-NK3 by fitting the ground-state properties of several closed-shell nuclei. It is found that all of the three parameter sets can give satisfactory description on properties of nuclear matter and finite nuclei, meanwhile they can also predict the larger neutron star mass around $2.3 M_{⊙}$ without the hyperon degrees of freedom.
nucl-thPRC(2016)·13 citations
04
Linearly increasing radius of the light fragment during the spontaneous fission of $^{282}$ Cn
D. N. Poenaru · R. A. Gherghescu
In a previous article published in Phys. Rev. C 94 (2016) 014309 we have shown for the first time that the best dynamical trajectory during the deformation toward fission of the superheavy nucleus $^{286}$ Fl is a linearly increasing radius of the light fragment, $R_{2}$ . This macroscopic-microscopic result reminds us about the $α$ or cluster preformation at the nuclear surface, assumed already in 1928, and proved microscopically many times. This time we give more detailed arguments for the neighboring nucleus $^{282}$ Cn. Also similar figures are presented for heavy nuclei $^{240}$ Pu and $^{252}$ Cf. The deep minimum of total deformation energy near the surface is shown for the first time as a strong argument for cluster preformation.
nucl-thEPJA(2016)·11 citations
05
Cumulants and nonlinear response of high $p_{T}$ harmonic flow at $s_{N N} = 5.02$ TeV
Jacquelyn Noronha-Hostler🇩🇪 · Barbara Betz🇺🇸 · Miklos Gyulassy🇧🇷 · Matthew Luzum🇧🇷 · Jorge Noronha🇺🇸 · Israel Portillo🇺🇸 · Claudia Ratti🇺🇸
Event-by-event fluctuations caused by quantum mechanical fluctuations in the wave function of colliding nuclei in ultrarelativistic heavy ion collisions were recently shown to be necessary for the simultaneous description of $R_{AA}$ as well as the elliptic and triangular flow harmonics at high $p_{T}$ in PbPb collisions at the Large Hadron Collider. In fact, the presence of a finite triangular flow as well as cumulants of the flow harmonic distribution that differ from the mean are only possible when these event-by-event fluctuations are considered. In this paper we combine event-by-event viscous hydrodynamics and jet quenching to make predictions for high $p_{T}$ $R_{AA}$ , $v_{2} {2}$ , $v_{3} {2}$ , and $v_{2} {4}$ in PbPb collisions at $s_{N N} = 5.02$ TeV. With an order of magnitude larger statistics we find that high $p_{T}$ elliptic flow does not scale linearly with the soft elliptical flow, as originally thought, but has deviations from perfectly linear scaling. A new experimental observable, which involves the difference between the ratio of harmonic flow cumulants at high and low $p_{T}$ , is proposed to investigate the fluctuations of high $p_{T}$ flow harmonics and measure this nonlinear response. By varying the path length dependence of the energy loss and the viscosity of the evolving medium we find that $R_{AA} (p_{T})$ and $v_{2} {2} (p_{T})$ strongly depend on the choice for the path length dependence of the energy loss, which can be constrained using the new LHC run 2 data.
nucl-thhep-phnucl-exPRC(2017)·86 citations
06
Psi(2S) Production at the LHC
Xiaojian Du🇺🇸 · Ralf Rapp🇺🇸
We calculate the production of $ψ (2 S)$ and the pertinent double ratio of its nuclear modification factor ( $R_{AA}$ ) over that of the $J / ψ$ in Pb-Pb collisions at the LHC. Based on a transport model with temperature dependent reaction rates, a sequential regeneration pattern emerges: the larger $ψ (2 S)$ width, relative to the $J / ψ$ , around and below the critical temperature, implies that most of the $ψ (2 S)$ states are regenerated later in the evolution of the fireball. This has noticeable consequences for the transverse-momentum ( $p_{T}$ ) spectra of the regenerated charmonia. While the total yield of $ψ (2 S)$ meson remains smaller than those of $J / ψ$ 's, their harder $p_{T}$ spectra can produce a double ratio above unity for a $p_{T} > 3$ GeV cut, as applied by the CMS collaboration. A significant uncertainty in our calculations is associated with the values of the temperature where most of the $ψ (2 S)$ regeneration occurs, the quantitative temperature dependence of its inelastic width.
↳ hep-phnucl-thJ.Phys.Conf.Ser.(2017)·10 citations
07
$T$ -Matrix Approach to Strongly Coupled QGP
Shuai Y.F. Liu🇺🇸 · Ralf Rapp🇺🇸
Based on a thermodynamic $T$ -matrix approach we extract the potential $V$ between two static charges in the quark-gluon plasma (QGP) from fits to the pertinent lattice-QCD free energy. With suitable relativistic corrections we utilize this new potential to compute heavy-quark transport coefficients and compare the results to previous calculations using either $F$ or $U$ as potential. We then discuss a generalization of the $T$ -matrix re-summation to a "matrix $lo g$ " re-summation of $t$ -channel diagrams for the grand partition function of the QGP in the Luttinger-Ward skeleton diagram formalism. With $V$ as a non-perturbative driving kernel in the light-parton sector, we obtain the QGP equation of state from fits to lattice-QCD data. The resulting light-parton spectral functions are characterized by large thermal widths at small momenta, indicating the dissolution of quasi-particles in a strongly coupled QGP.
↳ hep-phnucl-thJ.Phys.Conf.Ser.(2017)·6 citations
08
Theory overview of Heavy Ion collisions
T. Lappi🇫🇮
This presentation discusses some recently active topics in the theoretical interpretation of high energy heavy ion collisions at the LHC and at RHIC. We argue that the standard paradigm for understanding the spacetime evolution of the bulk of the matter produced in the collision is provided by viscous relativistic hydrodynamics, which can be used to systematically extract properties of the QCD medium from experimental results. The initial conditions of this hydrodynamical evolution are increasingly well understood in terms of gluon saturation, and can be quantified using Classical Yang-Mills fields and QCD effective kinetic theory. Hard and electromagnetic probes of the plasma provide additional constraints. A particularly fascinating subject are high multiplicity proton-proton and proton-nucleus collisions, where some of the characteristics previously attributed to only nucleus-nucleus collisions have been observed.
↳ hep-phnucl-thPoS(2016)·3 citations
09
Photoproduction of a large invariant mass $γ ρ$ pair at small momentum transfer
R. Boussarie🇫🇷 · B. Pire🇫🇷 · L. Szymanowski🇵🇱 · S. Wallon🇫🇷
The collinear factorization framework allows to describe the exclusive photoproduction of a $γ ρ$ pair in the generalized Bjorken regime in terms of a perturbatively calculable coefficient function and universal generalized parton distributions. The kinematics are defined by a large invariant mass of the $γ ρ$ pair and a small transverse momentum of the final nucleon. We calculate the scattering amplitude at leading order in $α_{s}$ and the differential cross sections for the process where the $ρ -$ meson is either longitudinally or transversely polarized, in the kinematics of the near future Jlab experiments. Our estimate of the cross section demonstrates that this process is measurable at JLab 12-GeV.
↳ hep-phhep-exnucl-exnucl-thPoS(2016)·0 citations
10
Neutrino emissivities and bulk viscosity in neutral two-flavor quark matter
J. Berdermann🇩🇪 · D. Blaschke🇵🇱 · T. Fischer🇵🇱 · A. Kachanovich🇵🇱
We study thermodynamic and transport properties for the isotropic color-spin-locking (iso-CSL) phase of two-flavor superconducting quark matter under compact star constraints within a NJL-type chiral quark model. Chiral symmetry breaking and the phase transition to superconducting quark matter leads to a density dependent change of quark masses, chemical potentials and diquark gap. A self-consistent treatment of these physical quantities influences on the microscopic calculations of transport properties. We present results for the iso-CSL direct URCA emissivities and bulk viscosities, which fulfill the constraints on quark matter derived from cooling and rotational evolution of compact stars. We compare our results with the phenomenologically successful, but yet heuristic 2SC+X phase. We show that the microscopically founded iso-CSL phase can replace the purely phenomenological 2SC+X phase in modern simulations of the cooling evolution for compact stars with color superconducting quark matter interior.
↳ astro-ph.HEnucl-thPRD(2016)·17 citations

Affiliations

first authorsco-authorsvia INSPIRE