Nuclear Theory·nucl-th

Tuesday·October 27, 2020

16 papers—6 primary·10 cross-listed

07
[Submitted on 24 Oct 2020] (cross-list from nucl-ex)
Investigating High-Energy Proton-Induced Reactions on Spherical Nuclei: Implications for the Pre-Equilibrium Exciton Model
Morgan B. Fox (1) · Andrew S. Voyles (1 and 2) · Jonathan T. Morrell (1) · Lee A. Bernstein (1 and 2) · Amanda M. Lewis (1) · Arjan J. Koning (3) · Jon C. Batchelder (1) · Eva R. Birnbaum (4) · Cathy S. Cutler (5) · Dmitri G. Medvedev (5) · Francois M. Nortier (4) · Ellen M. O'Brien (4) · Christiaan Vermeulen (4) ((1) Department of Nuclear Engineering, University of California, Berkeley (2) Lawrence Berkeley National Laboratory (3) International Atomic Energy Agency (4) Los Alamos National Laboratory (5) Brookhaven National Laboratory)
A number of accelerator-based isotope production facilities utilize 100- to 200-MeV proton beams due to the high production rates enabled by high-intensity beam capabilities and the greater diversity of isotope production brought on by the long range of high-energy protons. However, nuclear reaction modeling at these energies can be challenging because of the interplay between different reaction modes and a lack of existing guiding cross section data. A Tri-lab collaboration has been formed among the Lawrence Berkeley, Los Alamos, and Brookhaven National Laboratories to address these complexities by characterizing charged-particle nuclear reactions relevant to the production of established and novel radioisotopes. In the inaugural collaboration experiments, stacked-targets of niobium foils were irradiated at the Brookhaven Linac Isotope Producer (E $_{p}$ =200 MeV) and the Los Alamos Isotope Production Facility (E $_{p}$ =100 MeV) to measure $^{93}$ Nb(p,x) cross sections between 50 and 200 MeV. The measured cross-section results were compared with literature data as well as the default calculations of the nuclear model codes TALYS, CoH, EMPIRE, and ALICE. We developed a standardized procedure that determines the reaction model parameters that best reproduce the most prominent reaction channels in a physically justifiable manner. The primary focus of the procedure was to determine the best parametrization for the pre-equilibrium two-component exciton model. This modeling study revealed a trend toward a relative decrease for internal transition rates at intermediate proton energies (E $_{p}$ =20-60 MeV) in the current exciton model as compared to the default values. The results of this work are instrumental for the planning, execution, and analysis essential to isotope production.
Comments:
37 pages, 62 figures. Revised version, published in Physical Review C
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2010.12790 [pdf]
PRC(2021)·20 citations
08
[Submitted on 25 Oct 2020] (cross-list from hep-ph)
Chiral symmetry breaking and chemical equilibrium in a heavy-ion collisions
Sourendu Gupta🇮🇳 · Jajati K. Nayak🇮🇳 · Sushant K. Singh🇮🇳
We examine the thermalization of an ensemble of the octet of pseudoscalar mesons, in the isospin symmetric limit, whose interactions are constrained through chiral symmetry, unitarity, and measurements. The reaction amplitudes generate all resonances up to masses of about 2 GeV, with twelve input parameters, namely f_pi, three masses, and eight low energy constants (LECs) of chiral perturbation theory. In linear response theory, we find that matter takes an extremely long time to thermalize. These long relaxation times are directly related to the fact that these mesons are pseudo-Goldstone bosons of chiral symmetry breaking. This result indicates that fireballs created with zero baryon number in heavy-ion collisions will drop out of chemical equilibrium once they enter the chiral symmetry broken phase.
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
2010.13044 [pdf]
PRD(2021)·4 citations
09
[Submitted on 25 Oct 2020] (cross-list from hep-ph)
Vector mesons spectrum in a medium with a chiral imbalance induced by the vacuum of fermions
Vladimir Kovalenko🇷🇺 · Alexander Andrianov🇷🇺 · Vladimir Andrianov🇷🇺
The properties of the light vector mesons in the presence of local parity breaking medium with a chiral imbalance are considered in the vector-meson dominance model. Applying the finite lowest-order radiatively induced local effective Lagrangian, initially developed for the QED, for the vector $ρ$ and $ω$ mesons, we obtained the mass spectrum as a function of momentum and chiral chemical potential $μ_{5}$ . We showed that in addition to the Chern-Simons term, splitting the transverse polarisations of the mesons, there is another radiatively induced contribution that becomes important at momentum and $μ_{5}$ around a few hundred MeV.
Comments:
6 pages, 2 figures, talk given at The 5th international conference on particle physics and astrophysics (ICPPA-2020), 5-9 October 2020, Moscow, Russia (Online)
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2010.13238 [pdf]
J.Phys.Conf.Ser.(2020)·4 citations
10
[Submitted on 26 Oct 2020] (cross-list from hep-ph)
Wigner functions and quantum kinetic theory of polarized photons
Koichi Hattori🇯🇵 · Yoshimasa Hidaka🇯🇵 · Naoki Yamamoto🇯🇵 · Di-Lun Yang🇯🇵
We derive the Wigner functions of polarized photons in the Coulomb gauge with the $ℏ$ expansion applied to quantum field theory, and identify side-jump effects for massless photons. We also discuss the photonic chiral vortical effect for the Chern-Simons current and zilch vortical effect for the zilch current in local thermal equilibrium as a consistency check for our formalism. The results are found to be in agreement with those obtained from different approaches. Moreover, using the real-time formalism, we construct the quantum kinetic theory (QKT) for polarized photons. By further adopting a specific power counting scheme for the distribution functions, we provide a more succinct form of an effective QKT. This photonic QKT involves quantum corrections associated with self-energy gradients in the collision term, which are analogous to the side-jump corrections pertinent to spin-orbit interactions in the chiral kinetic theory for massless fermions. The same theoretical framework can also be directly applied to weakly coupled gluons in the absence of background color fields.
Comments:
25 pages, no figures, minor revisions, journal version in JHEP
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE); cond-mat.other (cond-mat.other); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
2010.13368 [pdf]
JHEP(2021)·53 citations
11
[Submitted on 26 Oct 2020] (cross-list from hep-lat)
Distribution of Energy-Momentum Tensor around a Static Quark in the Deconfined Phase of SU(3) Yang-Mills Theory
Ryosuke Yanagihara🇯🇵 · Masakiyo Kitazawa🇯🇵 · Masayuki Asakawa🇯🇵 · Tetsuo Hatsuda🇯🇵
Energy momentum tensor (EMT) characterizes the response of the vacuum as well as the thermal medium under the color electromagnetic fields. We define the EMT by means of the gradient flow formalism and study its spatial distribution around a static quark in the deconfined phase of SU(3) Yang-Mills theory on the lattice. Although no significant difference can be seen between the EMT distributions in the radial and transverse directions except for the sign, the temporal component is substantially different from the spatial ones near the critical temperature $T_{c}$ . This is in contrast to the prediction of the leading-order thermal perturbation theory. The lattice data of the EMT distribution also indicate the thermal screening at long distance and the perturbative behavior at short distance.
Comments:
12 pages, 12 figures
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2010.13465 [pdf]
PRD(2020)·14 citations
12
[Submitted on 26 Oct 2020] (cross-list from hep-ph)
Kinetic and Chemical Equilibration of Quark-Gluon Plasma
Xiaojian Du🇩🇪 · Sören Schlichting🇩🇪
We solve a leading-order QCD kinetic theory with light quarks and gluon degrees of freedom to study the non-equilibrium dynamics of the quark-gluon plasma (QGP). By including both elastic and inelastic scatterings for quarks and gluon, the model is proficient to describe kinetic and chemical equilibration of the QGP, and thus connects the initial (semi-) hard production of partons at early times with the hydrodynamic description of a near-thermalized quark-gluon plasma after the first fm/c of the collision. Within this approach, we investigate the time scales and mechanisms for kinetic and chemical equilibration of the QGP at zero and non-zero net-baryon density and elaborate on the connections to jet quenching physics and hydrodynamics.
Comments:
5 pages, 10 figures; Proceeding on 10th International Conference on Hard and Electromagnetic Probes of High Energy Nuclear Collisions (Hard Probe 2020) (Austin, TX, USA), May 31- June 5, 2020
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2010.13488 [pdf]
PoS(2021)·1 citation
13
[Submitted on 26 Oct 2020] (cross-list from hep-ph)
Di-lepton production from a single photon in strong magnetic fields: Vacuum dichroism
Koichi Hattori🇯🇵 · Hidetoshi Taya🇯🇵 · Shinsuke Yoshida🇨🇳
We study di-lepton production from a single photon in the presence of a strong constant magnetic field. By the use of the Ritus-basis formalism, we analytically evaluate the photon--to--di-lepton conversion vertex with fully taking into account the non-perturbative interactions between the produced fermions and the strong magnetic field. We show that the di-lepton spectrum becomes anisotropic with respect to the magnetic-field direction and depends on the photon polarization as a manifestation of the vacuum dichroism in a strong magnetic field. According to the energy conservation in the presence of the Landau quantization, not only the transverse momentum of the produced fermions but also the longitudinal momentum is discretized, and the di-lepton spectrum exhibits spike structures as functions of the incident photon energy and the magnetic field strength. We also show that the di-lepton production is strictly prohibited for massless fermions in the lowest Landau levels as an analogue of the so-called helicity suppression.
Comments:
Minor improvements, Refs added in ver. 2; Notations improved, extended discussions added in outlook, published version
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
2010.13492 [pdf]
JHEP(2021)·41 citations
14
[Submitted on 26 Oct 2020] (cross-list from hep-ph)
Condensates and pressure of two-flavor chiral perturbation theory at nonzero isospin and temperature
Prabal Adhikari🇺🇸 · Jens O. Andersen🇳🇴 · Martin A. Mojahed🇳🇴
We consider two-flavor chiral perturbation theory ( $χ$ PT) at finite isospin chemical potential $μ_{I}$ and finite temperature $T$ . We calculate the effective potential and the quark and pion condensates as functions of $T$ and $μ_{I}$ to next-to-leading order in the low-energy expansion in the presence of a pionic source. We map out the phase diagram in the $μ_{I}$ -- $T$ plane. Numerically, we find that the transition to the pion-condensed phase is second order in the region of validity of $χ$ PT, which is in agreement with model calculations and lattice simulations. Finally, we calculate the pressure to two-loop order in the symmetric phase for nonzero $μ_{I}$ and find that $χ$ PT seems to be converging very well.
Comments:
11 pages and 6 figures, LaTeX; typos corrected, references added
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2010.13655 [pdf]
EPJC(2021)·25 citations
15
[Submitted on 26 Oct 2020] (cross-list from hep-ph)
QGP modification to single inclusive jets in a calibrated transport model
Weiyao Ke🇺🇸 · Xin-Nian Wang🇺🇸
We study inclusive jet suppression and modifications in the quark-gluon plasma (QGP) with a transport-based model. The model includes vacuum-like parton shower evolution at high-virtuality, a linearized transport for jet-medium interactions, and a simple ansatz for the jet-induced hydrodynamic response of the medium. Model parameters are calibrated to nuclear modification factors for inclusive hadron $R_{AA}^{h}$ and single inclusive jets $R_{AA}^{j}$ with cone size $R = 0.4$ in 0-10% central Au-Au and Pb-Pb collisions measured at the RHIC and LHC. The calibrated model consistently describes the cone-size dependent $R_{AA}^{j} (R)$ , modifications to inclusive jet fragmentation functions and jet shape. We discuss the origin of these modifications by analyzing the medium-induced jet energy flow in this model and elucidate the interplay of hard parton evolution and jet-induced medium response. In particular, we demonstrate that the excess of soft hadrons at $p_{T} \sim 2$ GeV/ $c$ in jet fragmentation function and jet shape at large $r = Δ η^{2} + Δ ϕ^{2}$ are consequences of both soft medium-induced gluon radiation and jet-induced medium excitation.
Comments:
48 pages, 20 figures, prepared for submission
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2010.13680 [pdf]
JHEP(2021)·73 citations
16
[Submitted on 26 Oct 2020] (cross-list from hep-ph)
Systematizing and addressing theory uncertainties of unitarization with the Inverse Amplitude Method
Alexandre Salas-Bernárdez🇪🇸 · Felipe J. Llanes-Estrada🇪🇸 · Juan Escudero-Pedrosa (Univ. Complutense Madrid)🇪🇸 · Jose Antonio Oller (Univ. Murcia)🇪🇸
Effective Field Theories (EFTs) constructed as derivative expansions in powers of momentum, in the spirit of Chiral Perturbation Theory (ChPT), are a controllable approximation to strong dynamics as long as the energy of the interacting particles remains small, as they do not respect exact elastic unitarity. This limits their predictive power towards new physics at a higher scale if small separations from the Standard Model are found at the LHC or elsewhere. Unitarized chiral perturbation theory techniques have been devised to extend the reach of the EFT to regimes where partial waves are saturating unitarity, but their uncertainties have hitherto not been addressed thoroughly. Here we take one of the best known of them, the Inverse Amplitude Method (IAM), and carefully following its derivation, we quantify the uncertainty introduced at each step. We compare its hadron ChPT and its electroweak sector Higgs EFT applications. We find that the relative theoretical uncertainty of the IAM at the mass of the first resonance encountered in a partial-wave is of the same order in the counting as the starting uncertainty of the EFT at near-threshold energies, so that its unitarized extension should \textit{a priori} be expected to be reasonably successful. This is so provided a check for zeroes of the partial wave amplitude is carried out and, if they appear near the resonance region, we show how to modify adequately the IAM to take them into account.
Comments:
Revised version, 47 pages in SciPost format, with 13 captioned figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2010.13709 [pdf]
SciPost Phys.(2021)·29 citations

Affiliations

first authorsco-authorsvia INSPIRE