Observation of vertex factorisation breaking in central pp interactions

Central \pipi events produced in pp interactions are studied in terms of correlations between the outgoing protons. It is observed there is more $\rho^{0}$(770) and \fmeson production in reactions where the outgoing protons %fastest and slowest particles in the laboratory frame are on opposite sides of the beam. This effect is not attributable to the trigger or the experimental acceptance, and suggests that the vertices do not factorise.