Nuclear Theory·nucl-th

Friday·November 10, 2017

10 papers—6 primary·4 cross-listed

01
[Submitted on 8 Nov 2017]
Structure of the nucleon's low-lying excitations
Chen Chen🇧🇷 · Bruno El-Bennich🇧🇷 · Craig D. Roberts🇺🇸 · Sebastian M. Schmidt🇩🇪 · Jorge Segovia🇪🇸 · Shaolong Wan🇨🇳
A continuum approach to the three valence-quark bound-state problem in quantum field theory is used to perform a comparative study of the four lightest $(I = 1/2, J^{P} = 1/ 2^{\pm})$ baryon isospin-doublets in order to elucidate their structural similarities and differences. Such analyses predict the presence of nonpointlike, electromagnetically-active quark-quark (diquark) correlations within all baryons; and in these doublets, isoscalar-scalar, isovector-pseudovector, isoscalar-pseudoscalar, and vector diquarks can all play a role. In the two lightest $(1/2, 1/ 2^{+})$ doublets, however, scalar and pseudovector diquarks are overwhelmingly dominant. The associated rest-frame wave functions are largely $S$ -wave in nature; and the first excited state in this $1/ 2^{+}$ channel has the appearance of a radial excitation of the ground state. The two lightest $(1/2, 1/ 2^{-})$ doublets fit a different picture: accurate estimates of their masses are obtained by retaining only pseudovector diquarks; in their rest frames, the amplitudes describing their dressed-quark cores contain roughly equal fractions of even- and odd-parity diquarks; and the associated wave functions are predominantly $P$ -wave in nature, but possess measurable $S$ -wave components. Moreover, the first excited state in each negative-parity channel has little of the appearance of a radial excitation. In quantum field theory, all differences between positive- and negative-parity channels must owe to chiral symmetry breaking, which is overwhelmingly dynamical in the light-quark sector. Consequently, experiments that can validate the contrasts drawn herein between the structure of the four lightest $(1/2, 1/ 2^{\pm})$ doublets will prove valuable in testing links between emergent mass generation and observable phenomena and, plausibly, thereby revealing dynamical features of confinement.
Comments:
13 pages, 6 figures, 1 table
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1711.03142 [pdf]
PRD(2018)·69 citations
02
[Submitted on 9 Nov 2017]
$T$ -matrix Approach to Quark-Gluon Plasma
Shuai Y.F. Liu🇺🇸 · Ralf Rapp🇺🇸
A selfconsistent thermodynamic $T$ -matrix approach is deployed to study the microscopic properties of the quark-gluon plasma (QGP), encompassing both light- and heavy-parton degrees of freedom in a unified framework. The starting point is a relativistic effective Hamiltonian with a universal color force. The input in-medium potential is quantitatively constrained by computing the heavy-quark (HQ) free energy from the static $T$ -matrix and fitting it to pertinent lattice-QCD (lQCD) data. The corresponding $T$ -matrix is then applied to compute the equation of state (EoS) of the QGP in a two-particle irreducible formalism including the full off-shell properties of the selfconsistent single-parton spectral functions and their two-body interaction. In particular, the skeleton diagram functional is fully resummed to account for emerging bound and scattering states as the critical temperature is approached from above. We find that the solution satisfying three sets of lQCD data (EoS, HQ free energy and quarkonium correlator ratios) is not unique. As limiting cases we discuss a weakly-coupled solution (WCS) which features color-potentials close to the free energy, relatively sharp quasiparticle spectral functions and weak hadronic resonances near $T_{c}$ , and a strongly-coupled solution (SCS) with a strong color potential (much larger than the free energy) resulting in broad non-quasiparticle parton spectral functions and strong hadronic resonance states which dominate the EoS when approaching $T_{c}$ .
Comments:
30 pages, 14 figures; version published in Phys. Rev. C; comments added to introduction and conclusion
Subjects:
Nuclear Theory (nucl-th); Quantum Gases (cond-mat.quant-gas); High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1711.03282 [pdf]
PRC(2018)·94 citations
03
[Submitted on 9 Nov 2017]
Longitudinal decorrelation measures of flow magnitude and event-plane angles in ultra-relativistic nuclear collisions
Piotr Bozek🇵🇱 · Wojciech Broniowski🇵🇱
We discuss the forward-backward correlations of harmonic flow in Pb+Pb collisions at the CERN Large Hadron Collider (LHC), applying standard multibin measures, as well as proposed here new measures. We illustrate the methods with hydrodynamic model simulations based on event-by-event initial conditions from the wounded quark model with asymmetric rapidity emission profiles. Within the model we examine independently the event-plane angle and the flow magnitude decorrelations. We find specific hierarchy between various flow decorrelation measures and confirm certain factorization relations. We find qualitative agreement of the model and the data from the ATLAS and CMS Collaborations.
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1711.03325 [pdf]
PRC(2018)·57 citations
04
[Submitted on 9 Nov 2017]
Dynamical and many-body correlation effects in the kinetic energy spectra of isotopes produced in nuclear multifragmentation
S.R. Souza · R. Donangelo · M.B. Tsang · W.G. Lynch
The properties of the kinetic energy spectra of light isotopes produced in the breakup of a nuclear source and during the deexcitation of its products are examined. The initial stage, at which the hot fragments are created, is modeled by the Statistical Multifragmentation Model, whereas the Weisskopf-Ewing evaporation treatment is adopted to describe the subsequent fragment deexcita- tion, as they follow their classical trajectories dictated by the Coulomb repulsion among them. The energy spectra obtained are compared to available experimental data. The influence of the fusion cross-section entering into the evaporation treatment is investigated and its influence on the qual- itative aspects of the energy spectra turns out to be small. Although these aspects can be fairly well described by the model, the underlying physics associated with the quantitative discrepancies remains to be understood.
Comments:
7 pages, 4 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1711.03347 [pdf]
PRC(2018)·6 citations
05
[Submitted on 8 Nov 2017]
Directed flow in heavy-ion collisions and its implications for astrophysics
Yuri B. Ivanov🇷🇺
Analysis of directed flow ( $v_{1}$ ) of protons, antiprotons and pions in heavy-ion collisions is performed in the range of collision energies $s_{N N}$ = 2.7--39 GeV. Simulations have been done within a three-fluid model employing a purely hadronic equation of state (EoS) and two versions of the EoS with deconfinement transitions: a first-order phase transition and a smooth crossover transition. The crossover EoS is unambiguously preferable for the description of experimental data at lower collision energies $s_{N N} \leq$ 20 GeV. However, at higher collision energies $s_{N N} \geq$ 20 GeV the purely hadronic EoS again becomes advantageous. This indicates that the deconfinement EoS in the quark-gluon sector should be stiffer at high baryon densities than those used in the calculation. The latter finding is in agreement with that discussed in astrophysics in connection with existence of hybrid stars with masses up to about two solar masses.
Comments:
7 pages, 3 figures. Contribution to Proceedings of the Conference "Compact Stars in the QCD Phase Diagram VI", Dubna, Sept. 26-29, 2017. arXiv admin note: substantial text overlap with arXiv:1601.03902
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1711.03461 [pdf]
Universe(2017)·6 citations
06
[Submitted on 8 Nov 2017]
Electromagnetic transition form factors of the Roper resonance in baryon chiral perturbation theory
Mishiko Gelenava🇬🇪
We consider the electromagnetic transition form factors of the Roper resonance in the framework of an effective field theory of pions, nucleons and delta and Roper resonances as explicit degrees of freedom. Due to the lack experimental data in the region of applicability of low energy effective field theory we fit available free coupling constants and compare obtained results compare to the predictions of a theoretical model.
Comments:
arXiv admin note: text overlap with arXiv:1606.04873 by other authors
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1711.03494 [pdf]
EPJA(2018)·7 citations
07
[Submitted on 8 Nov 2017] (cross-list from hep-ph)
Probing the time structure of the quark-gluon plasma with top quarks
Liliana Apolinário🇵🇹 · José Guilherme Milhano🇵🇹 · Gavin P. Salam🇨🇭 · Carlos A. Salgado🇪🇸
The tiny droplets of Quark Gluon Plasma (QGP) created in high-energy nuclear collisions experience fast expansion and cooling with a lifetime of a few $fm / c$ . Despite the information provided by probes such as jet quenching and quarkonium suppression, and the excellent description by hydrodynamical models, direct access to the time evolution of the system remains elusive. We point out that the study of hadronically-decaying $W$ bosons, notably in events with a top-antitop quark pair, can provide key novel insight, into the time structure of the QGP. This is because of a unique feature, namely a time delay between the moment of the collision and that when the $W$ -boson decay products start interacting with the medium. Furthermore, the length of the time delay can be constrained by selecting specific reconstructed top-quark momenta.
Comments:
v1: 5 pages and 5 figures, plus supplemental material. v2: Typos corrected, one reference added. v3: includes additional clarifications; version to be published in Phys.Rev.Lett
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1711.03105 [pdf]
PRL(2018)·90 citations
08
[Submitted on 9 Nov 2017] (cross-list from hep-lat)
More on heavy tetraquarks in lattice QCD at almost physical pion mass
Anthony Francis🇨🇦 · Renwick J. Hudspith🇨🇦 · Randy Lewis🇨🇦 · Kim Maltman🇬🇧
We report on our progress in studying exotic, heavy tetraquark states, $q q' Q ˉ Q ˉ'$ . Using publicly available dynamical $n_{f} = 2 + 1$ Wilson-Clover gauge configurations, generated by the PACS-CS collaboration, with pion masses $≃$ 164, 299 and 415 MeV, we extend our previous analysis to heavy quark components containing heavier than physical bottom quarks $Q ˉ Q ˉ' = b ˉ' b ˉ'$ or $Q ˉ Q ˉ' = b ˉ b ˉ'$ , charm and bottom quarks $c ˉ b ˉ$ and also only charm quarks $c ˉ c ˉ$ . Throughout we employ NRQCD and relativistic heavy quarks for the heavier than bottom, bottom and charm quarks. Using our previously established diquark-antidiquark and meson-meson operator basis we comment in particular on the dependence of the binding energy on the mass of the heavy quark component $Q ˉ Q ˉ$ , with heavy quarks ranging from $m_{Q} = 0.85 \dots 6.3 \cdot m_{b}$ . In the heavy flavor non-degenerate case, $Q ˉ Q ˉ'$ , and especially for the tetraquark channel $u d c ˉ b ˉ$ , we extend our work to utilize a $3 \times 3$ GEVP to study the ground and threshold states thereby enabling a clear identification of possible binding. Finally, we present initial work on the $Q ˉ Q ˉ' = c ˉ c ˉ$ system where a much larger operator basis is available in comparison to flavor combinations with NRQCD quarks.
Comments:
8 pages, 5 figures, proceedings contribution to "Lattice 2017. 35th International Symposium on Lattice Field Theory", 18th-24th June 2017, Granada, Spain
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1711.03380 [pdf]
EPJ Web Conf.(2018)·10 citations
09
[Submitted on 9 Nov 2017] (cross-list from nucl-ex)
Formation of $Σ π$ pairs in nuclear captures of K $^{-}$ mesons
Raffaele Del Grande🇮🇹 · Kristian Piscicchia🇮🇹 · Slawomir Wycech🇮🇹
The capture of K $^{-}$ mesons on nucleons bound in nuclei offer a chance to study the $Σ π$ pairs below the kinematic threshold of the $K ˉ$ N systems. Various hyperon-pion charged combination are presently under investigation by AMADEUS. These data allow to test both isospin 0 and 1 amplitudes giving the possibility to detect the structure of resonant $Λ$ (1405) state. Contrasted against similar electro-production data, it is possible to detect changes of $Λ$ (1405) in nuclear media. Expected spectra and their uncertainties are calculated.
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1711.03427 [pdf]
Acta Phys.Polon.B(2017)·15 citations
10
[Submitted on 9 Nov 2017] (cross-list from hep-ph)
Nonequilibrium quark production in the expanding QCD plasma
Naoto Tanji🇮🇹 · Juergen Berges🇩🇪
We perform real-time lattice simulations of nonequilibrium quark production in the longitudinally expanding QCD plasma. Starting from a highly occupied gluonic state with vacuum quark sector, we extract the time evolution of quark and gluon number densities per unit transverse area and rapidity. The total quark number shows after an initial rapid increase an almost linear growth with time. Remarkably, this growth rate appears to be consistent with a simple kinetic theory estimate involving only two-to-two scattering processes in small-angle approximation. This extends previous findings about the role of two-to-two scatterings for purely gluonic dynamics in accordance with the early stages of the bottom-up thermalization scenario.
Comments:
33 pages, 23 figures, published version
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1711.03445 [pdf]
PRD(2018)·24 citations

Affiliations

first authorsco-authorsvia INSPIRE