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# Light Cone 2018

May 14 – 18, 2018
Jefferson Lab - CEBAF Center
US/Eastern timezone

## Pion off-shell electromagnetic form factors

May 15, 2018, 3:00 PM
20m
Auditorium (Jefferson Lab - CEBAF Center)

### Speaker

Dr Joao Pacheco de Melo (Laboratório de Fisica Teórica e Computacional, LFTC, UCS)

### Description

\documentclass[12pt]{article} \begin{document} \pagestyle{empty} Pion off-shell electromagnetic form factors J.~P.~B.~C.~de~Melo$^1$,~Tobias Frederico$^2$ and C.-R.~Ji$^3$ $^1$Laborat\'orio de F\'{\i}sica Te\'orica e Computacional-LFTC \newline Universidade Cruzeiro do Sul, 01506-000, S\~ao Paulo, Brazil \\ $^2$Departamento de F\'\i sica, Instituto Tecnol\'ogico de Aeron\'autica, Centro T\'ecnico Aeroespacial $^3$Department of Physics, North Carolina State University,~NCSU, USA \\ The light mesons, like pion, play special rules in try to understanting QCD, between another motivation, the pion is the Goldstone boson, and, is central to symmetry breaking and partial current conservation (PCAC). The most general way to take informations about the hadronic substructure, i.e.; in terms of the degrees of freedom from QCD, quarks and gluons, are the study of the electromagnetic form factors. The electromagnetic form factors play also, fundamental importance in order to studing processes involving hadrons and virtual photons. Because the pion have spin zero, and, with the time-reverse invariance, we need only one electromagnetic form factor to describe the pion. Still, general approaches about electromagnetic form factors for pseudoscalar particles, not take in account off-shell effects. But in order to be more consistent, and go beyond on-shell, the off-shell effects is need be included at the electromagnetic interactions. The possible on-shell effects, also appear in meson pion exchange current [1], because in that case, the exchanged pion is not on-mass shell. The most general electromagnetic description for the pion, need two electromagnetic form factors, $F_1(q^2,t)$, and, $F_2(q^2,t)$, wich are related the Ward-Takahashi identity [2]. Ward-Takahashi identity was explore some years ago for the boson case in the reference [3] with the light-front approach. The electromagnetic off-shell form factors was been calculated for the boson bound state, and, in that work, is realized, the zero modes inclusion is crucial to preserve the Ward-Takahashi indentities with the Light-front Field Theory. However, microscopic model is not already made to incorpore off-shel effects at the vertex, and extract the off-shell form factors. In the present work, we explore the electromagnetic off-shell effects for the pion meson and extract the off-shell electromagnetic form factors, $F_1(q^2,t)$ and $F_2(q^2,t)$, from experimental electroproduction cross section data [4,5]. However, the extraction of the electromagnetic form factor with the reaction $^1H(e,e',\pi^+)n$, need some model for the $G_{\pi NN}(t)$ form factor, here, we explore some possibilities for this form factor. The differents models are explored, in order to see the power predictions for that models, with respect the pion observables, like, electromagnetic form factors, electromagnetic radius and, also, the pion electroweak decay constant. \\ References 1. F.Gross and D. O. Riska, Phys. Rev. C36, 1928 (1987). 2. Lewis H. Ryder, Quantum Field Theory, Cambridge University Press. 3. H. W. L. Naus, J. P. B. C. de Melo and T.Frederico, Few Body Syst. 24, 99 (1998). 4. H. P. Blok et al., [Jefferson Lab Collaboration], Phys. Rev. C78, 045202 (2008). 5. G. M. Huber et al., [Jefferson Lab Collaboration], Phys. Rev. C78, 045203 (2008). \end{document}

### Primary author

Dr Joao Pacheco de Melo (Laboratório de Fisica Teórica e Computacional, LFTC, UCS)

### Co-authors

Chueng R. Ji (North Carolina State University) Prof. Tobias Frederico (ITA - CTA)

 Slides