Main Question or Discussion Point
A recent article on Proton/Lead collisions (http://physics.aps.org/articles/v8/61) used a graphic seen in earlier articles on Proton/Proton collisions (ie. http://arxiv.org/pdf/1206.0148v1.pdf). I understand the gray disks to represent protons just after the collision (flattened due to relativity at their high speeds), but I am not sure how to understand the colored bars. Appreciate insight anyone would have on this.