Nuclear Theory·nucl-th

Friday·December 1, 2017

8 papers—5 primary·3 cross-listed

01
[Submitted on 30 Nov 2017]
Examining nonextensive statistics in relativistic heavy-ion collisions
A. Simon🇩🇪 · G. Wolschin🇩🇪
We show in detailed numerical solutions of the nonlinear Fokker-Planck equation (FPE) which has been associated with nonextensive q-statistics that the available data on rapidity distributions for stopping in relativistic heavy-ion collisions cannot be reproduced with any permitted value of the nonextensivity parameter (1 < q < 1.5). This casts doubt on the nonextensivity concept that is widely used in relativistic heavy-ion physics.
Comments:
8 pages, 6 figures. Updated title, abstract, text and figures as published
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1711.11324 [pdf]
PRC(2018)·9 citations
02
[Submitted on 30 Nov 2017]
Fitting and selecting scattering data
Enrique Ruiz Arriola🇪🇸 · Jose Enrique Amaro🇪🇸 · Rodrigo Navarro Perez🇺🇸
The main purpose of scattering experiments is to unveil the underlying structure of the colliding particles and their interaction. Typically one measures scattering observables (cross sections and polarizations) at discrete angles and energies and mutually consistent data may validate or falsify proposed theories or models. However, the accumulation of data from different laboratories while potentially improves the statistical significance it may sometimes generate mutually inconsistent data as a side-effect. Thus, some decision has to be made on what are the maximal amount of data which are mutually compatible. We show elastic $π N$ and $N N$ scattering as prominent examples where this selection is called for. We discuss how it can be done in a self-consistent manner invoking a principle of maximal consensus of the database and with the help of a sufficiently flexible model involving a minimal number of theoretical assumptions. In the NN case this has become possible with a combination of long distance field theoretical constraints at the hadronic level such as pion exchanges and electromagnetic effects and a coarse graining of the unknown interaction over the shortest de Broglie wavelength being probed in the scattering process.
Comments:
7 pages, 5 figures, talk presented by ERA at XVII International Conference on Hadron Spectroscopy and Structure - Hadron2017, Salamanca, 25-29 September 2017
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1711.11338 [pdf]
PoS(2018)·3 citations
03
[Submitted on 30 Nov 2017]
Studies of mesic atoms and nuclei
Eliahu Friedman🇮🇱 · Avraham Gal🇮🇱 · Aleš Cieplý🇨🇿 · Jaroslava Hrtánková🇨🇿 · Jiří Mareš🇨🇿
$K^{-}$ mesons offer a unique setting where mesic atoms have been studied both experimentally and theoretically, thereby placing constraints on the possible existence and properties of meson-nuclear quasibound states. Here we review progress in this field made recently by the Jerusalem--Prague Collaboration using near-threshold $K^{-} N$ scattering amplitudes generated in several meson--baryon coupled channels models inspired by a chiral EFT approach. Our own procedure of handling subthreshold kinematics self consistently is used to transform these free-space energy dependent amplitudes to in-medium density dependent amplitudes from which $K^{-}$ optical potentials are derived. To fit the world data of kaonic atoms, these single-nucleon optical potentials are augmented by multi-nucleon terms. It is found that only two of the studied models reproduce also the single-nucleon absorption fractions available from old bubble chamber experiments. These two models are then checked for possible $K^{-}$ nuclear quasibound states, despite realizing that $K^{-}$ optical potentials are not constrained by kaonic atom data at densities exceeding half nuclear-matter density. We find that when such states exist, their widths are invariably above 100 MeV, forbiddingly large to allow observation. Multi-nucleon absorption is found to be substantial in this respect. This suggests that observable strongly bound $K^{-}$ mesons are limited to the very light systems, such as $K^{-} pp$ .
Comments:
presented by A. Gal at Hadron2017, Sept. 2017, Salamanca, Spain; prepared for Proceedings of Science
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1711.11371 [pdf]
PoS(2018)·4 citations
04
[Submitted on 30 Nov 2017]
Comprehensive Study of Observables in Compton Scattering on the Nucleon
Harald W. Griesshammer (George Washington U.)🇺🇸 · Judith A. McGovern (U. of Manchester)🇬🇧 · Daniel R. Phillips (Ohio U.)🇺🇸
We present an analysis of $13$ observables in Compton scattering on the proton. Cross sections, asymmetries with polarised beam and/or targets, and polarisation-transfer observables are investigated for energies up to the $Δ (1232)$ resonance to determine their sensitivity to the proton's dipole scalar and spin polarisabilities. The Chiral Effective Field Theory Compton amplitude we use is complete at N $^{4}$ LO, $O (e^{2} δ^{4})$ , for photon energies $ω \sim m_{π}$ , and so has an accuracy of a few per cent there. At photon energies in the resonance region it is complete at NLO, $O (e^{2} δ^{0})$ , and so its accuracy there is about $20$ \%. We find that for energies from pion-production threshold to about $250 MeV$ , multiple asymmetries have significant sensitivity to presently ill-determined combinations of proton spin polarisabilities. We also argue that the broad outcomes of this analysis will be replicated in complementary theoretical approaches, e.g., dispersion relations. Finally, we show that below the pion-production threshold, $6$ observables suffice to reconstruct the Compton amplitude, and above it $11$ are required. Although not necessary for polarisability extractions, this opens the possibility to perform "complete" Compton-scattering experiments. An interactive Mathematica notebook, including results for the neutron, is available from judith.mcgovern@manchester.ac.uk .
Comments:
75 pages LaTeX2e (pdflatex) including 37 figures as .pdf files using includegraphics; minor corrections. Text-identical to published version but including the Online Supplement. Higher-resolution figures are available at http://home.gwu.edu/~hgrie/Compton/one-N-comprehensive-observables-delta4.v2.0.high-resolution-figures.tgz
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1711.11546 [pdf]
EPJA(2018)·16 citations
05
[Submitted on 30 Nov 2017]
Non-perturbative Approach to Equation of State and Collective Modes of the QGP
Shuai Y.F. Liu🇺🇸 · Ralf Rapp🇺🇸
We discuss a non-perturbative $T$ -matrix approach to investigate the microscopic structure of the quark-gluon plasma (QGP). Utilizing an effective Hamiltonian which includes both light- and heavy-parton degrees of freedoms. The basic two-body interaction includes color-Coulomb and confining contributions in all available color channels, and is constrained by lattice-QCD data for the heavy-quark free energy. The in-medium $T$ -matrices and parton spectral functions are computed selfconsistently with full account of off-shell properties encoded in large scattering widths. We apply the $T$ -matrices to calculate the equation of state (EoS) for the QGP, including a ladder resummation of the Luttinger-Ward functional using a matrix-log technique to account for the dynamical formation of bound states. It turns out that the latter become the dominant degrees of freedom in the EoS at low QGP temperatures indicating a transition from parton to hadron degrees of freedom. The calculated spectral properties of one- and two-body states confirm this picture, where large parton scattering rates dissolve the parton quasiparticle structures while broad resonances start to form as the pseudocritical temperature is approached from above. Further calculations of transport coefficients reveal a small viscosity and heavy-quark diffusion coefficient.
Comments:
10 pages, 8 figures, proceedings of XLVII International Symposium on Multiparticle Dynamics (ISMD2017)
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1711.11559 [pdf]
EPJ Web Conf.(2018)·2 citations
06
[Submitted on 30 Nov 2017] (cross-list from hep-ph)
Prompt photon yield and $v_{2}$ coefficient from gluon fusion induced by magnetic field in heavy-ion collision
Jorge David Castaño-Yepes🇲🇽 · Alejandro Ayala🇿🇦 · C. A. Dominguez🇿🇦 · L. A. Hernández🇲🇽 · Saúl Hernández-Ortíz🇲🇽 · María Elena Tejeda-Yeomans🇲🇽
We compute the production of prompt photons and the $v_{2}$ harmonic coefficient in relativistic heavy-ion collisions induced by gluon fusion in the presence of an intense magnetic field, during the early stages of the reaction. The calculations take into account several parameters which are relevant to the description of the experimental transverse momentum distribution, and elliptic flow for RHIC and LHC energies. The main imput is the strength of the magnetic field which varies in magnitude from 1 to 3 times the pion mass squared, and allows the gluon fusion that otherwise is forbidden in the absence of the field. The high gluon occupation number and the value of the saturation scale also play an important role in our calculation, as well as a flow velocity and geometrical factors. Our results support the idea that the origin of at least some of the photon excess observed in heavy-ion experiments may arise from magnetic field induced processes, and gives a good description of the experimental data.
Comments:
6 pages, 2 figures, conference paper from ISMD 2017
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1711.11163 [pdf]
EPJ Web Conf.(2018)·0 citations
07
[Submitted on 30 Nov 2017] (cross-list from hep-ph)
Strange matter in compact stars
Thomas Klaehn🇺🇸 · David Blaschke🇷🇺
We discuss possible scenarios for the existence of strange matter in compact stars. The appearance of hyperons leads to a hyperon puzzle in ab-initio approaches based on effective baryon-baryon potentials but is not a severe problem in relativistic mean field models. In general, the puzzle can be resolved in a natural way if hadronic matter gets stiffened at supersaturation densities, an effect based on the quark Pauli quenching between hadrons. We explain the conflict between the necessity to implement dynamical chiral symmetry breaking into a model description and the conditions for the appearance of absolutely stable strange quark matter that require both, approximately masslessness of quarks and a mechanism of confinement. The role of strangeness in compact stars (hadronic or quark matter realizations) remains unsettled. It is not excluded that strangeness plays no role in compact stars at all. To answer the question whether the case of absolutely stable strange quark matter can be excluded on theoretical grounds requires an understanding of dense matter that we have not yet reached.
Comments:
8 pages, 1 figure, accepted for publication in Proceedings of "Strangeness in Quark Matter 2017", Utrecht (EPJ WoC)
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
1711.11260 [pdf]
EPJ Web Conf.(2018)·8 citations
08
[Submitted on 30 Nov 2017] (cross-list from hep-ph)
A Nakanishi-based model illustrating the covariant extension of the pion GPD overlap representation and its ambiguities
N. Chouika🇫🇷 · C. Mezrag🇮🇹 · H. Moutarde🇫🇷 · J. Rodríguez-Quintero🇪🇸
A systematic approach for the model building of Generalized Parton Distributions (GPDs), based on their overlap representation within the DGLAP kinematic region and a further covariant extension to the ERBL one, is applied to the valence-quark pion's case, using light-front wave functions inspired by the Nakanishi representation of the pion's Bethe-Salpeter amplitudes (BSA). This simple but fruitful pion's GPD model illustrates the general model building technique and, in addition, allows for the ambiguities related to the covariant extension, grounded on the Double Distribution (DD) representation, to be constrained by requiring a soft-pion theorem to be properly observed.
Comments:
8 pages, 4 figures, matches published version + typo correction
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1711.11548 [pdf]
PLB(2018)·58 citations

Affiliations

first authorsco-authorsvia INSPIRE