Nuclear Theory·nucl-th

Thursday·December 17, 2020

5 papers—2 primary·3 cross-listed

01
[Submitted on 16 Dec 2020]
Recent advances in the quantification of uncertainties in reaction theory
A.E. Lovell · F.M. Nunes · M. Catacora-Rios · G.B. King
Uncertainty quantification has become increasingly more prominent in nuclear physics over the past several years. In few-body reaction theory, there are four main sources that contribute to the uncertainties in the calculated observables: the effective potentials, approximations made to the few-body problem, structure functions, and degrees of freedom left out of the model space. In this work, we illustrate some of the features that can be obtained when modern statistical tools are applied in the context of nuclear reactions. This work consists of a summary of the progress that has been made in quantifying theoretical uncertainties in this domain, focusing primarily on those uncertainties coming from the effective optical potential as well as their propagation within various reaction theories. We use, as the central example, reactions on the doubly-magic stable nucleus $^{40}$ Ca, namely neutron and proton elastic scattering and single-nucleon transfer $^{40}$ Ca(d,p) $^{41}$ Ca. First, we show different optimization schemes used to constrain the optical potential from differential cross sections and other experimental constraints; we then discuss how these uncertainties propagate to the transfer cross section, comparing two reaction theories. We finish by laying out our future plans.
Comments:
28 pages, 7 figures, J Phys. G
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2012.09012 [pdf]
J.Phys.G(2020)·34 citations
02
[Submitted on 8 Dec 2020]
Determination of matter radius and neutron skin of $^{58}$ Ni from reaction cross section of proton+ $^{58}$ Ni scattering based on chiral $g$ -matrix model
Shingo Tagami · Maya Takechi · Jun Matsui · Tomotsugu Wakasa · Masanobu Yahiro
Background: Using the chiral (Kyushu) $g$ -matrix folding model with the densities calculated with Gogny-HFB (GHFB) with the angular momentum projection (AMP), we determined the central values of matter radius and neutron skin from the central values of reaction cross sections $σ_{R} (EXP)$ of p+ $^{40, 48}$ Ca and p+ $^{208}$ Pb scattering. As for p+ $^{58}$ Ni scattering, $σ_{R} (EXP)$ are available as a function of incident energy $E_{in}$ . Aim: Our aim is to determine matter radius $r_{m}$ and skin $r_{skin}$ for $^{58}$ Ni from the $σ_{R} (EXP)$ of p+ $^{58}$ Ni scattering by using the Kyushu $g$ -matrix folding model with the GHFB+AMP densities. Results: For p+ $^{58}$ Ni scattering, the Kyushu $g$ -matrix folding model with the GHFB+AMP densities reproduces $σ_{R} (EXP)$ in $8.8 \leq E_{in} \leq 81$ MeV. For $E_{in} = 81$ MeV, we define the factor $F$ as $F = σ_{R} (EXP) / σ_{R} (AMP) = 0.9775$ . The $F σ_{R} (AMP)$ be much the same as the center values of $σ_{R} (EXP)$ in $8.8 \leq E_{in} \leq 81$ MeV. We then determine $r_{m} (EXP)$ from the center values of $σ_{R} (EXP)$ , using $σ_{R} (EXP) = C r_{m}^{2} (EXP)$ with $C = r_{m}^{2} (AMP) / (F σ_{R} (AMP))$ . The $r_{m} (EXP)$ thus obtained are averaged over $E_{in}$ . The averaged value is $r_{m} (EXP) = 3.697$ fm. Eventually, we obtain $r_{skin} (EXP) = 0.023$ fm from $r_{m} = 3.697$ fm and $r_{p} (EXP) = 3.685$ fm of electron scattering.
Comments:
arXiv admin note: substantial text overlap with arXiv:2011.12235, arXiv:2012.01063
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2012.09146 [pdf]
0 citations
03
[Submitted on 15 Dec 2020] (cross-list from hep-ph)
Saturation effects in SIDIS at very forward rapidities
E. Iancu🇫🇷 · A.H. Mueller🇺🇸 · D.N. Triantafyllopoulos🇮🇹 · S.Y. Wei🇮🇹
Using the dipole picture for electron-nucleus deep inelastic scattering at small Bjorken $x$ , we study the effects of gluon saturation in the nuclear target on the cross-section for SIDIS (single inclusive hadron, or jet, production). We argue that the sensitivity of this process to gluon saturation can be enhanced by tagging on a hadron (or jet) which carries a large fraction $z ≃ 1$ of the longitudinal momentum of the virtual photon. This opens the possibility to study gluon saturation in relatively hard processes, where the virtuality $Q^{2}$ is (much) larger than the target saturation momentum $Q_{s}^{2}$ , but such that $z (1 - z) Q^{2} ≲ Q_{s}^{2}$ . Working in the limit $z (1 - z) Q^{2} ≪ Q_{s}^{2}$ , we predict new phenomena which would signal saturation in the SIDIS cross-section. For sufficiently low transverse momenta $k_{⊥} ≪ Q_{s}$ of the produced particle, the dominant contribution comes from elastic scattering in the black disk limit, which exposes the unintegrated quark distribution in the virtual photon. For larger momenta $k_{⊥} ≳ Q_{s}$ , inelastic collisions take the leading role. They explore gluon saturation via multiple scattering, leading to a Gaussian distribution in $k_{⊥}$ centred around $Q_{s}$ . When $z (1 - z) Q^{2} ≪ Q^{2}$ , this results in a Cronin peak in the nuclear modification factor (the $R_{p A}$ ratio) at moderate values of $x$ . With decreasing $x$ , this peak is washed out by the high-energy evolution and replaced by nuclear suppression ( $R_{p A} < 1$ ) up to large momenta $k_{⊥} ≫ Q_{s}$ . Still for $z (1 - z) Q^{2} ≪ Q_{s}^{2}$ , we also compute SIDIS cross-sections integrated over $k_{⊥}$ . We find that both elastic and inelastic scattering are controlled by the black disk limit, so they yield similar contributions, of zeroth order in the QCD coupling.
Comments:
53 pages, 13 figures, 6 appendices. New appendix on double-logarithmic corrections, 2 additional figures and minor corrections. Published in JHEP
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2012.08562 [pdf]
JHEP(2021)·29 citations
04
[Submitted on 16 Dec 2020] (cross-list from hep-ph)
Equilibration of the Quark-Gluon Plasma at finite net-baryon density in QCD kinetic theory
Xiaojian Du🇩🇪 · Sören Schlichting🇩🇪
We explore the out-of-equilibrium dynamics of the Quark-Gluon Plasma at zero and finite net-baryon density based on an effective kinetic theory of Quantum Chromo Dynamics (QCD). By investigating the isotropization of the longitudinal pressure, we determine the relevant time and temperature scales for the onset of viscous hydrodynamics, and quantify the dependence on the chemical composition of the QGP. By extrapolating our results to realistic coupling strength, we discuss phenomenological consequences regarding the role of the pre-equilibrium phase at different collision energies.
Comments:
7 pages, 3 figures, see our companion paper: Equilibration of weakly coupled QCD plasmas
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2012.09068 [pdf]
PRL(2021)·62 citations
05
[Submitted on 16 Dec 2020] (cross-list from hep-ph)
Equilibration of weakly coupled QCD plasmas
Xiaojian Du🇩🇪 · Sören Schlichting🇩🇪
We employ a non-equilibrium Quantum Chromodynamics (QCD) kinetic description to study the kinetic and chemical equilibration of the Quark-Gluon Plasma (QGP) at weak coupling. Based on our numerical framework, which explicitly includes all leading order processes involving light flavor degrees of freedom, we investigate the thermalization process of homogeneous and isotropic plasmas far-from equilibrium and determine the relevant time scales for kinetic and chemical equilibration. We further simulate the longitudinally expanding pre-equilibrium plasma created in ultrarelativistic heavy-ion collisions at zero and non-zero density of the conserved charges and study its microscopic and macroscopic evolution towards equilibrium.
Comments:
32+10 pages, 32 figures, also see our companion paper: Equilibration of the Quark-Gluon Plasma at finite net-baryon density in QCD kinetic theory
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2012.09079 [pdf]
PRD(2021)·63 citations

Affiliations

first authorsco-authorsvia INSPIRE

Recent advances in the quantification of uncertainties in reaction theory

Determination of matter radius and neutron skin of 58Ni from reaction cross section of proton+58Ni scattering based on chiral g-matrix model

Saturation effects in SIDIS at very forward rapidities

Equilibration of the Quark-Gluon Plasma at finite net-baryon density in QCD kinetic theory

Equilibration of weakly coupled QCD plasmas

Affiliations

Determination of matter radius and neutron skin of $^{58}$ Ni from reaction cross section of proton+ $^{58}$ Ni scattering based on chiral $g$ -matrix model