Nuclear Theory·nucl-th

Monday·June 22, 2015

9 papers—5 primary·4 cross-listed

06
[Submitted on 17 Jun 2015] (cross-list from hep-lat)
The Magnetic Structure of Light Nuclei from Lattice QCD
Emmanuel Chang🇺🇸 · William Detmold🇺🇸 · Kostas Orginos🇺🇸 · Assumpta Parreno🇪🇸 · Martin J. Savage🇺🇸 · Brian C. Tiburzi🇺🇸 · Silas R. Beane🇺🇸
Lattice QCD with background magnetic fields is used to calculate the magnetic moments and magnetic polarizabilities of the nucleons and of light nuclei with $A \leq 4$ , along with the cross-section for the $M 1$ transition $n p \to d γ$ , at the flavor SU(3)-symmetric point where the pion mass is $m_{π} \sim 806$ MeV. These magnetic properties are extracted from nucleon and nuclear energies in six uniform magnetic fields of varying strengths. The magnetic moments are presented in a recent Letter. For the charged states, the extraction of the polarizability requires careful treatment of Landau levels, which enter non-trivially in the method that is employed. The nucleon polarizabilities are found to be of similar magnitude to their physical values, with $β_{p} = 5.22 (+ 0.66/ - 0.45) (0.23) \times 1 0^{- 4}$ fm $^{3}$ and $β_{n} = 1.253 (+ 0.056/ - 0.067) (0.055) \times 1 0^{- 4}$ fm $^{3}$ , exhibiting a significant isovector component. The dineutron is bound at these heavy quark masses and its magnetic polarizability, $β_{nn} = 1.872 (+ 0.121/ - 0.113) (0.082) \times 1 0^{- 4}$ fm $^{3}$ differs significantly from twice that of the neutron. A linear combination of deuteron scalar and tensor polarizabilities is determined by the energies of the $j_{z} = \pm 1$ deuteron states, and is found to be $β_{d, \pm 1} = 4.4 (+ 1.6/ - 1.5) (0.2) \times 1 0^{- 4}$ fm $^{3}$ . The magnetic polarizabilities of the three-nucleon and four-nucleon systems are found to be positive and similar in size to those of the proton, $β_{^{3} He} = 5.4 (+ 2.2/ - 2.1) (0.2) \times 1 0^{- 4}$ fm $^{3}$ , $β_{^{3} H} = 2.6 (1.7) (0.1) \times 1 0^{- 4}$ fm $^{3}$ , $β_{^{4} He} = 3.4 (+ 2.0/ - 1.9) (0.2) \times 1 0^{- 4}$ fm $^{3}$ . Mixing between the $j_{z} = 0$ deuteron state and the spin-singlet $n p$ state induced by the background magnetic field is used to extract the short-distance two-nucleon counterterm, $L ˉ_{1}$ , of the pionless effective theory for $N N$ systems (equivalent to the meson-exchange current contribution in nuclear potential models), that dictates the cross-section for the $n p \to d γ$ process near threshold. Combined with previous determinations of NN scattering parameters, this enables an ab initio determination of the threshold cross-section at these unphysical masses.
Comments:
49 pages, 24 figures
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1506.05518 [pdf]
PRD(2015)·111 citations
07
[Submitted on 18 Jun 2015] (cross-list from hep-ph)
Proceedings of the Sixth International Workshop on Multiple Partonic Interactions at the Large Hadron Collider
R. Astalos🇸🇰 · S. Baranov🇷🇺 · P. Bartalini🇨🇳 · I. Belyaev🇷🇺 · Ch. Bierlich🇸🇪 · B. Blok🇮🇱 · A. Buckley🇬🇧 · F. A. Ceccopieri🇧🇪 · I. Cherednikov🇧🇪 · J. R. Christiansen🇸🇪 · D. Ciangottini🇨🇭 · M. Deak🇪🇸 and 45 other authors
Multiple Partonic Interactions are often crucial for interpreting results obtained at the Large Hadron Collider (LHC). The quest for a sound understanding of the dynamics behind MPI - particularly at this time when the LHC is due to start its "Run II" operations - has focused the aim of this workshop. MPI@LHC2014 concentrated mainly on the phenomenology of LHC measurements whilst keeping in perspective those results obtained at previous hadron colliders. The workshop has also debated some of the state-of-the-art theoretical considerations and the modeling of MPI in Monte Carlo event generators. The topics debated in the workshop included: Phenomenology of MPI processes and multiparton distributions; Considerations for the description of MPI in Quantum Chromodynamics (QCD); Measuring multiple partonic interactions; Experimental results on inelastic hadronic collisions: underlying event, minimum bias, forward energy flow; Monte Carlo generator development and tuning; Connections with low-x phenomena, diffraction, heavy-ion physics and cosmic rays. In a total of 57 plenary talks the workshop covered a wide range of experimental results, Monte Carlo development and tuning, phenomenology and dedicated measurements of MPI which were produced with data from the LHC's Run I. Recent progress of theoretical understanding of MPI in pp, pA and AA collisions as well as the role of MPI in diffraction and small-x physics were also covered. The workshop forstered close contact between the experimental and theoretical communities. It provided a setting to discuss many of the different aspects of MPI, eventually identifying them as a unifying concept between apparently different lines of research and evaluating their impact on the LHC physics programme.
Comments:
MPI@LHC 2014, 3 - 7 November 2014, Krakow, Poland, 81 pages
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1506.05829 [pdf]
40 citations
08
[Submitted on 19 Jun 2015] (cross-list from hep-ph)
Shear Viscosity of a Quark Plasma Near the Chiral Phase Transition
Çağlar Doğan🇹🇷
We calculate the shear viscosity $η$ of a quark plasma through the two-flavor Nambu-Jona-Lasinio (NJL) model in the chiral limit, at finite temperature $T$ , and baryon number chemical potential $μ_{B}$ . We solve the Boltzmann equation by using in the collision term cross sections that are correct to leading order in the coupling constant. We find the ratio of shear viscosity to entropy density above and slightly below the chiral transition temperature to vary from 1.5 to 13 times the conjectured lower bound of $(4 π)^{- 1}$ depending on the chemical potential to temperature ratio. Ratio of shear viscosity to entropy density is found to be a monotonically increasing function of the ratio of chemical potential to temperature for temperatures between 185 and 300 MeV.
Comments:
12 pages, 5 figures, 1 appendix
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1506.05881 [pdf]
0 citations
09
[Submitted on 19 Jun 2015] (cross-list from hep-ex)
Combination of Measurements of Inclusive Deep Inelastic $e^{\pm} p$ Scattering Cross Sections and QCD Analysis of HERA Data
H1 · ZEUS Collaborations
A combination is presented of all inclusive deep inelastic cross sections previously published by the H1 and ZEUS collaborations at HERA for neutral and charged current $e^{\pm} p$ scattering for zero beam polarisation. The data were taken at proton beam energies of 920, 820, 575 and 460 GeV and an electron beam energy of 27.5 GeV. The data correspond to an integrated luminosity of about 1 fb $^{- 1}$ and span six orders of magnitude in negative four-momentum-transfer squared, $Q^{2}$ , and Bjorken $x$ . The correlations of the systematic uncertainties were evaluated and taken into account for the combination. The combined cross sections were input to QCD analyses at leading order, next-to-leading order and at next-to-next-to-leading order, providing a new set of parton distribution functions, called HERAPDF2.0. In addition to the experimental uncertainties, model and parameterisation uncertainties were assessed for these parton distribution functions. Variants of HERAPDF2.0 with an alternative gluon parameterisation, HERAPDF2.0AG, and using fixed-flavour-number schemes, HERAPDF2.0FF, are presented. The analysis was extended by including HERA data on charm and jet production, resulting in the variant HERAPDF2.0Jets. The inclusion of jet-production cross sections made a simultaneous determination of these parton distributions and the strong coupling constant possible, resulting in $α_{s} (M_{Z}) = 0.1183 \pm 0.0009 (exp) \pm 0.0005 (model/parameterisation) \pm 0.0012 (hadronisation)_{- 0.0030}^{+ 0.0037} (scale)$ . An extraction of $x F_{3}^{γ Z}$ and results on electroweak unification and scaling violations are also presented.
Comments:
159 pages, 83 figures. Updated version as accepted for publication. Small corrections and reordering of tables
Subjects:
High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1506.06042 [pdf]
EPJC(2015)·1153 citations

Affiliations

first authorsco-authorsvia INSPIRE

The Magnetic Structure of Light Nuclei from Lattice QCD

Proceedings of the Sixth International Workshop on Multiple Partonic Interactions at the Large Hadron Collider

Shear Viscosity of a Quark Plasma Near the Chiral Phase Transition

Combination of Measurements of Inclusive Deep Inelastic e±p Scattering Cross Sections and QCD Analysis of HERA Data

Affiliations

Combination of Measurements of Inclusive Deep Inelastic $e^{\pm} p$ Scattering Cross Sections and QCD Analysis of HERA Data