EPS Figure
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Illustration of the way PYTHIA models the "underlying event" in proton-antiproton collision by including multiple parton interactions. In adddition to the hard 2-to-2 parton-parton scattering with transverse momentum, PT(hard), sometimes there is a second "semi-hard" 2-to-2 parton-parton scattering that contributes particles to the "underlying event". (Return)