Bridging Time-Like and Space-Like N* Form Factors

The study of electromagnetic transitions opens a window into the very nature of the strong interaction. And, indeed, such a study of how a ground-state nucleon transitions to an excited state, over a broad range of q2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$q^2$$\end{document}, will provide keen insight into the evolution of how dynamically-generated masses emerge from the asymptotically-free, nearly massless quarks of perturbative QCD as well as provide information on the ancillary effects from the meson–baryon cloud. The space-like (q2<0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$q^2<0$$\end{document}) region has been explored more intensively, particularly at JLab, but efforts have also begun in studying the time-like (q2>0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$q^2>0$$\end{document}) region at GSI. We are living in exciting times whereby near-future prospects exist in extracting high-quality data in both the space-like and time-like regimes (JLab12 and FAIR, for example). The recent ECT* workshop, entitled space-like and time-like electromagnetic baryonic transitions, brought together several disparate communities of experimentalists and theorists. The goal and purpose of this workshop was to make the very first steps towards a much needed consistent description spanning the two kinematical regimes in q2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$q^2$$\end{document}. The discussions included photoproduction measurements (ELSA, JLab, LEPS, and MAMI), wherein the q2=0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$q^2=0$$\end{document} point anchors the connection between space-like and time-like regions and meson-beam data (GSI and J-PARC) and amply complements the requisite information for baryon spectroscopy. This paper presents the outcomes from this ECT* workshop, space-like and time-like baryon electromagnetic transitions, held at the European Centre for Theoretical Studies in Nuclear Physics and Related Areas in Trento, Italy, May 8–12, 2017.