  We study di-hadron correlations in proton-proton collisions at $\sqrt{s} =
200$ GeV and interpret experimental data in terms of a fragmentation width and
a momentum imbalance. A fragmentation width of $580 \pm 50$ GeV/c is obtained,
and the measured momentum imbalance gives an `intrinsic' transverse momentum
width of partons in the proton of $2.6 \pm 0.2$ GeV/c. Consequences to heavy
ion collisions are discussed.
