CDF has recently measured a large number of double parton scatterings. The
observed value of σeff, the non perturbative parameter which
characterizes the process, is considerably smaller as compared with the naive
expectation. The small value of σeff is likely to be an indication of
the importance of the two-body parton correlations in the many-body parton
distributions of the proton.Comment: 8 pages, latex file, no figures, contributions to the proceedings of
the ISMD9