arXiv subjects

Egle Tomasi-Gustafsson

Publications and source records attributed to Egle Tomasi-Gustafsson.

57 records · Page 4Linked to original sources

arXiv2000

Relevant polarization observables for the study of the Roper resonance with hadronic probes

The purpose of this contribution is to stress the great importance of polarization observables for the study of nucleon resonances, in particular in the case of deuteron and proton probes. Polarization observables play a unique role in signing the reaction mechanism and bring new information in the microscopic description of baryon resonances. We will calculate the relevant polarization observables, for $p+d$- and $p+α$-collisions, in case of inclusive reactions and for some selected exclusive channels.

nucl-th↗

arXiv2000

The $η_cγγ^*$ transition form factor in the decay $η_c\to γ\ell^+\ell^-$ and in the crossed channels $γe^-\to η_c e^- $ and $e^+e^-\toη_cγ

The Dalitz distribution and the effective mass spectrum of the lepton pair produced in the decay $η_c\to γ\ell^+ \ell^-$, as well as the differential cross sections for the crossed channels $γe^-\to η_c e^- $ and $e^+ e^-\to η_c γ$, are calculated in terms of the sole electromagnetic transition form factor for the vertex $η_c\toγγ^*$, where $γ^*$ is a virtual photon with a space-like (for $γe^- \to η_c e^- $) or a time-like (for $e^+ e^-\to η_c γ$ and $η_c\toγ\ell^+\ell^-$) four-momentum. Explicit parametrisations of the transition form factor are found in two different approaches, namely in Vector Dominance Model and in a QCD-inspired consideration on the basis of the process $c \bar{c}\to γ\ell^+ \ell^-$, with zero relative three-momentum of the annihilating quarks.

hep-ph↗

arXiv2000

Electroproduction of pseudoscalar mesons on the deuteron

A general analysis of polarization phenomena for coherent meson electroproduction on deuterons, $e+ d\to e+ d +P^0$, where $P^0$ is a pseudoscalar $π^0$ or $η$-meson, is presented. The spin structure of the electromagnetic current for $P^0$-production at threshold is parametrized in terms of specific (inelastic) threshold electromagnetic form factors which depend on the momentum transfer squared and the effective mass of the produced hadronic system. We give expressions for the structure functions of the reaction $e+\vec{d}\to e +d+ P^0$ (where the deuteron target is polarized) in terms of these threshold form factors. The spin and isospin structures of the $γ^{*}+d\to d+P^0$ amplitudes (where $γ^*$ is a virtual photon) is established in the framework of the impulse approximation and relationships between meson electroproduction on deuterons and on nucleons are given. The reaction of $π^0$ electroproduction on deuterons is investigated in detail both at threshold and in the region of $Δ$-isobar excitation, using the effective Lagrangian approach for the calculation of the amplitudes of the elementary process $γ^*+N\to N+π$. Special attention is devoted to the analysis of all standard contributions to the exclusive cross section for $d(e,eπ^0)d$, which are functions of the momentum transfer square, $k^2$, of the excitation energy of the produced hadrons and of the pion production angle, in a region of relatively large momentum transfer. The sensitivity of these contributions to different parametrizations of the $γ^*πω$ form factor as well as to the choice of $NN-$potential is discussed.

hep-ph↗