Abstract
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−→pp¯ and pp¯→e+e− and future measurements of pp¯→μ+μ−. The focus is put on recent high-precision results of the reaction e+e−→pp¯ 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¯→e+e− and pp¯→μ+μ− 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.
Highlights
The proton, along with its partner nucleon, the neutron, makes up more than 99.9% of the visible matter in the universe
The internal structure and dynamics of the proton, which originate from the strong interaction, has been the target of intense investigations over the past 100 y since the discovery of the proton
The comparison starts with the cross-section of the process e+e− ←→ ppin Section 4.1, which was determined by most experiments performing scan measurements of proton form factors (FFs)
Summary
The proton, along with its partner nucleon, the neutron, makes up more than 99.9% of the visible matter in the universe. The internal structure and dynamics of the proton, which originate from the strong interaction, has been the target of intense investigations over the past 100 y since the discovery of the proton. A detailed theoretical description of the internal proton structure and its constituents’ dynamics is made difficult by the non-perturbative nature of the underlying theory, quantum chromodynamics (QCD), within the energy regime of the nucleon. Precise knowledge of one of the most simple observables that parametrize the proton’s structure and dynamics, the electromagnetic (EM) form factors (FFs), is crucial for understanding the proton structure. These quantities provide a perfect testing ground for our understanding of QCD
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