Paper detail

Study of the photon remnant in resolved photoproduction at HERA

Photoproduction at HERA is studied in $ep$ collisions, with the ZEUS detector, for $γp$ centre-of-mass energies ranging from 130-270 GeV. A sample of events with two high-$p_T$ jets ($p_T > 6$ GeV, $η<1.6$) and a third cluster in the approximate direction of the electron beam is isolated using a clustering algorithm. These events are mostly due to resolved photoproduction. The third cluster is identified as the photon remnant. Its properties, such as the transverse and longitudinal energy flows around the axis of the cluster, are consistent with those commonly attributed to jets, and in particular with those found for the two jets in these events. The mean value of the photon remnant $p_T$ with respect to the beam axis is measured to be $2.1 \pm 0.2$ GeV, which demonstrates substantial mean transverse momenta for the photon remnant.