Nucleons in Heavy Ion Collisions Are Half as Big as Previously Expected

To understand quark-gluon plasma, theorists compare a sophisticated model to a large amount of experimental data. One of the parameters in this model is the size of the nucleons inside the two colliding lead nuclei. Low-energy experiments find a nucleon size of around 0.5 femtometers, while heavy ion experimental data have found a much larger nucleon size, of about 1 femtometers. A new analysis of heavy ion experimental data includes the experimentally measured reaction rate of lead-lead collisions to arrive at a nucleon size of 0.6 femtometers.