A boiling sea of quarks and gluons, including virtual ones—this is how we can imagine the main phase of high-energy proton collisions. It would seem that particles here have significantly more opportunities to evolve than when less numerous and much “better-behaved” secondary particles spread out from the collision point. However, data from the LHC accelerator prove that reality works differently, in a manner that is better described by an improved model of proton collisions.
A lot happens during high-energy proton-proton collisions. Protons are hadrons, i.e. clusters of partons—quarks and the gluons that bind them together. When protons collide with each other at sufficiently high energies, their quarks and gluons (including the virtual ones, which appear momentarily during interactions) enter into various complex interactions.
Only when they “cool down” do the quarks stick together to form new hadrons, which scatter from the collision area and are recorded in detectors. Intuition therefore suggests that the entropy of the produced hadrons—a quantity describing the number of states in which the particle system can find itself—should be different from that in the parton phase of the collision, when there are many interacting quarks and gluons, and the interactions appear at first glance to be as chaotic as they are dynamic.