Stock Photo - 22 August 2020, Saxony, Leipzig: A test person of a large-scale experiment of the University Medicine Halle/Saale holds a concert ticket in her hand in front of the Arena Leipzig. Around 2200 visitors take part in the experiment entitled ""Restart-19"", in which the pop singer Tim Bendzko performs. The scientists want to use sensors and other aids to monitor their walking paths and fluorescent disinfectant is to make visible which surfaces are touched particularly often. The flight of aerosols - the smallest mixtures of particles that can carry the virus - will also be tracked. The aim is to develop a mathematical model that can be used to assess the risk of corona outbreak after a major event in a hall. Photo: Hendrik Schmidt/dpa-Zentralbild/ZB. - Leipzig/Saxony/Germany