Nuclear Theory·nucl-th

Friday·November 18, 2016

6 papers—6 primary·0 cross-listed

01
[Submitted on 17 Nov 2016]
Two-Photon-Exchange Effects and $Δ (1232)$ Deformation
Hai-Qing Zhou🇨🇳 · Shin Nan Yang🇹🇼
The two-photon-exchange (TPE) contribution in $e p \to e p π^{0}$ with $W = M_{Δ}$ and small $Q^{2}$ is calculated and its corrections to the ratios of electromagnetic transition form factors $R_{E M} = E_{1 +}^{(3/2)} / M_{1 +}^{(3/2)}$ and $R_{S M} = S_{1 +}^{(3/2)} / M_{1 +}^{(3/2)}$ , are analysed. A simple hadronic model is used to estimate the TPE amplitude. Two phenomenological models, MAID2007 and SAID, are used to approximate the full $e p \to e p π^{0}$ cross sections which contain both the TPE and the one-photon-exchange (OPE) contributions. The genuine the OPE amplitude is then extracted from an integral equation by iteration. We find that the TPE contribution is not sensitive to whether MAID or SAID is used as input in the region with $Q^{2} < 2$ GeV $^{2}$ . It gives small correction to $R_{E M}$ while for $R_{S M}$ , the correction is about -10\% at small $ϵ$ and about $1%$ at large $ϵ$ for $Q^{2} \approx 2.5$ GeV $^{2}$ . The large correction from TPE at small $ϵ$ must be included in the analysis to get a reliable extraction of $R_{S M}$ .
Comments:
Talk given at Conference:C16-07-25
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1611.05536 [pdf]
JPS Conf.Proc.(2017)·13 citations
02
[Submitted on 17 Nov 2016]
New Results for Ultraperipheral Heavy Ion Collisions
Antoni Szczurek🇵🇱 · Mariola Klusek-Gawenda🇵🇱 · Piotr Lebiedowicz🇵🇱 · Wolfgang Schäfer🇵🇱
We discuss diphoton semi(exclusive) production in ultraperipheral $P b P b$ collisions at energy of $s_{N N} =$ 5.5 TeV (LHC). The nuclear calculations are based on equivalent photon approximation in the impact parameter space. The cross sections for elementary $γ γ \to γ γ$ subprocess are calculated including three different mechanisms: box diagrams with leptons and quarks in the loops, a VDM-Regge contribution with virtual intermediate hadronic excitations of the photons and the two-gluon exchange contribution (formally three-loops). We got relatively high cross sections in $P b P b$ collisions. This opens a possibility to study the $γ γ \to γ γ$ (quasi)elastic scattering at the LHC. We find that the cross section for elastic $γ γ$ scattering could be measured in the lead-lead collisions for the diphoton invariant mass up to $W_{γ γ} \approx 15 - 20$ GeV. We identify region(s) of phase space where the two-gluon exchange contribution becomes important ingredient compared to box and nonperturbative VDM-Regge mechanisms. We discuss also first results concerning production of two $e^{+} e^{-}$ pairs in UPCs of heavy ions. We considered only double scattering mechanism.
Comments:
invited talk by A. Szczurek at the international workshop Diffraction 2016, Santa Tecla, Sicily, Italy, September 2-7, 2016, 6 pages, 7 figures, 1 table. arXiv admin note: substantial text overlap with arXiv:1610.08546, arXiv:1606.09038
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1611.05601 [pdf]
AIP Conf.Proc.(2017)·2 citations
03
[Submitted on 17 Nov 2016]
Relativistic Effects and Three-Nucleon Forces in Nuclear Matter and Nuclei
Herbert Müther🇩🇪 · Francesca Sammarruca🇺🇸 · Zhongyu Ma🇨🇳
We review a large body of predictions obtained within the framework of relativistic meson theory together with the Dirac-Brueckner-Hartree-Fock approach to nuclear matter and finite nuclei. The success of this method has been largely related to its ability to take into account important three-body effects. Therefore, the overarching theme of this article is the interpretation of the so-called "Dirac effects" as an effective three-nucleon force. We address the equation of state of isospin symmetric and asymmetric nucleonic matter and related issues, ranging from proton and neutron density distributions to momentum distributions and short-range correlations. A central part of the discussion is devoted to the optical model potential for nucleon-nucleus scattering. We also take the opportunity to explore similarities and differences with predictions based on the increasingly popular chiral effective field theory.
Comments:
44 pages, 20 figures, review
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1611.05621 [pdf]
IJMPE(2017)·21 citations
04
[Submitted on 17 Nov 2016]
Separable Representation of Multichannel Nucleon-Nucleus Optical Potentials
Linda Hlophe · Charlotte Elster
One important ingredient for many applications of nuclear physics to astrophysics, nuclear energy, and stockpile stewardship are cross sections for reactions of neutrons with rare isotopes. Since direct measurements are often not feasible, indirect methods, e.g. (d,p) reactions, should be used. Those (d,p) reactions may be viewed as three-body reactions and described with Faddeev techniques. Faddeev equations in momentum space have a long tradition of utilizing separable interactions in order to arrive at sets of coupled integral equations in one variable. Optical potentials representing the effective interactions in the neutron (proton) nucleus subsystem are usually non-Hermitian as well as energy-dependent. Including excitations of the nucleus in the calculation requires a multichannel optical potential. The purpose of this paper is to introduce a separable, energy-dependent multichannel representation of complex, energy-dependent optical potentials that contain excitations of the nucleus and that fulfill reciprocity exactly. Momentum space Lippmann-Schwinger integral equations are solved with standard techniques to obtain the form factors for the separable representation. Starting from energy-dependent multichannel optical potentials for neutron and proton scattering from $^{12}$ C, separable representations based on a generalization of the Ernst-Shakin-Thaler (EST) scheme are constructed which fulfill reciprocity exactly. Applications to n $+^{12}$ C and p $+^{12}$ C scattering are investigated for energies from 0 to 50~MeV.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1611.05734 [pdf]
PRC(2017)·5 citations
05
[Submitted on 17 Nov 2016]
Squeezed back-to-back correlations of $ϕϕ$ in Au+Au and d+Au collisions at the Relativistic Heavy Ion Collider energies
Yong Zhang🇨🇳 · Wei-Ning Zhang🇨🇳
We investigate the squeezed back-to-back correlations (BBC) of $ϕϕ$ , caused by the mass modification of the particles in the source medium, in the heavy-ion collisions of Au+Au and d+Au at the Relativistic Heavy Ion Collider (RHIC) energies. The BBC functions are calculated using the modified masses extracted from experimental data and the source space-time distributions provided by the viscous hydrodynamic code VISH2+1. Our investigations indicate that the BBC of $ϕϕ$ may perhaps be observed in the collisions of d+Au and the peripheral collisions of Au+Au at the RHIC. We suggest to measure the BBC experimentally for understanding the mass modifications of the $ϕ$ meson in the collisions.
Comments:
10 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1611.05770 [pdf]
1 citation
06
[Submitted on 17 Nov 2016]
Monte Carlo Glauber wounded nucleon model with meson cloud
B.G. Zakharov🇷🇺
We study the effect of the nucleon meson cloud on predictions of the Monte Carlo Glauber wounded nucleon model for $AA$ , $p A$ , and $pp$ collisions. From the analysis of the data on the charged multiplicity density in $AA$ collisions we find that the meson-baryon Fock component reduces the required fraction of binary collisions by a factor of $\sim 2$ for Au+Au collisions at $s = 0.2$ TeV and $\sim 1.5$ for Pb+Pb collisions at $s = 2.76$ TeV. For central $AA$ collisions the meson cloud can increase the multiplicity density by $\sim 16 - 18$ \%. We give predictions for the midrapidity charged multiplicity density in Pb+Pb collisions at $s = 5.02$ TeV for the future LHC run 2. We find that the meson cloud has a weak effect on the centrality dependence of the ellipticity $ϵ_{2}$ in $AA$ collisions. For collisions of the deformed uranium nuclei at $s = 0.2$ TeV we find that the meson cloud may improve somewhat agreement with the data on the dependence of the elliptic flow on the charged multiplicity for very small centralities defined via the ZDCs signals. We find that the meson cloud may lead to a noticeable reduction of $ϵ_{2}$ and the size of the fireball in $p A$ and $pp$ collisions.
Comments:
17 pages, 13 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1611.05825 [pdf]
J.Exp.Theor.Phys.(2017)·13 citations

Affiliations

first authorsco-authorsvia INSPIRE

Two-Photon-Exchange Effects and Δ(1232) Deformation

New Results for Ultraperipheral Heavy Ion Collisions

Relativistic Effects and Three-Nucleon Forces in Nuclear Matter and Nuclei

Separable Representation of Multichannel Nucleon-Nucleus Optical Potentials

Squeezed back-to-back correlations of ϕϕ in Au+Au and d+Au collisions at the Relativistic Heavy Ion Collider energies

Monte Carlo Glauber wounded nucleon model with meson cloud

Affiliations

Two-Photon-Exchange Effects and $Δ (1232)$ Deformation

Squeezed back-to-back correlations of $ϕϕ$ in Au+Au and d+Au collisions at the Relativistic Heavy Ion Collider energies