The underlying event and fragmentation
  A good fit to the CDF underlying event is obtained in the multiple parton scattering picture using HERWIG, after modifying the cluster hadronization algorithm as suggested by our previous study and adopting a larger maximum cluster size. The number of scatters per event is generated simply as a Poisson distribution. If our picture is correct, the baryon yield should be enhanced in the underlying event. This effect may be studied by measuring the proton-to-pion ratio. 
K. Odagiri