Measurement of the $t$ distribution in diffractive photoproduction at HERA

Abstract.

Photon diffractive dissociation, $\gamma p \rightarrow Xp$, has been studied at HERA with the ZEUS detector using $ep$ interactions where the virtuality $Q^2$ of the exchanged photon is smaller than 0.02 GeV$^2$. The squared four-momentum $t$ exchanged at the proton vertex was determined in the range $0.073< |t| < 0.40$ GeV$^2$ by measuring the scattered proton in the ZEUS Leading Proton Spectrometer. In the photon-proton centre-of-mass energy interval $176 < W < 225$ GeV and for masses of the dissociated photon system $4 < M_X < 32$ GeV, the $t$ distribution has an exponential shape, $dN/d|t| \propto \exp{(-b|t|)}$, with a slope parameter $b=6.8 \pm 0.9$ (stat.)$^{+1.2}_{-1.1}$ (syst.) GeV$^{-2}$.