Proton Electromagnetic Form Factors in the Time-like Region through the Scan Technique

For over 100 y, scientists have investigated the properties of the proton, which is one of the most abundant components of visible matter in the universe. Nevertheless, researchers do not fully understand many details about its internal structure and dynamics. Time-like electromagnetic form factors are some of the observable quantities that can help us achieve a deeper understanding. In this review article, we present an overview of the current experimental status in this field, consisting of measurements of the time-like reactions e+e-& RARR;pp over bar and pp over bar & RARR;e(+)e(-) and future measurements of pp over bar & RARR;mu(+)mu(-.) The focus is put on recent high-precision results of the reaction e(+)e(-)& RARR;pp over bar that have been obtained after analyzing 688.5 pb-1 of data taken at the BESIII experiment. They are compared to and put into perspective with results from previous measurements in this channel. We discuss the channels pp over bar & RARR;e(+)e(-) and pp over bar & RARR;mu(+)mu(-) in terms of the few existing, as well as future measurements, which the PANDA experiment will perform. Finally, we review several new theoretical models and phenomenological approaches inspired by the BESIII high-precision results and then discuss their implications for a deeper understanding of the proton's structure and inner dynamics.