Emergence of jet dominance in γ p interactions at fixed-target energies

In Fermilab experiment E683 we have used a large solid angle calorimeter to study the production of hadronic events with large transverse energy in $\ensuremath{\gamma}p$ and $\ensuremath{\pi}p$ collisions at center-of-mass energies from 20 to 25 GeV. We observe a sudden shift in $\ensuremath{\gamma}p$ event topology with increasing transverse energy, indicative of the emergence of jet dominance. This is the first observation of such a shift in event topology in fixed-target interactions. $\ensuremath{\pi}p$ interactions in the same kinematic region and under identical triggering conditions exhibit only a slight shift in event topology.