Leading proton production in e ⁺ p collisions at HERA

Events with a final-state proton carrying a large fraction of the proton beam momentum, x _L >0.6, and the square of the transverse momentum p _T ² <0.5 GeV ² , have been studied in e ⁺ p collisions with the ZEUS detector at HERA. Data with different photon virtualities were used: Q ² <0.02 GeV ² , 0.1<Q ² <0.74 GeV ² and 3<Q ² <254 GeV ² , corresponding to integrated luminosities of 0.9, 1.85 and 3.38 pb ^-1 . The cross sections are given as a function of x _L , p _T ² , Q ² and the Bjorken scaling variable, x. The ratio of the cross section for leading proton production to the inclusive e ⁺ p cross section shows only a mild dependence on Q ² and on x. In the region 0.6<x _L <0.97, the relative yield of protons is only a weak function of x _L .