First measurement of the deep-inelastic structure of proton diffraction

A measurement is presented, using data taken with the H1 detector at HERA, of the contribution of diffractive interactions to deep-inelastic electron-proton ( ep) scattering in the kinematic range 8.5 < Q 2 < 50GeV 2, 2.4 × 10 −4 < Bjorken- x < 0.0133, and 3.7 × 10 −4 < χ p < 0.043. The diffractive contribution to the proton structure function F 2( x, Q 2) is evaluated as a function of the appropriate deep-inelastic scattering variables χ p , Q 2, β (= χ χ p ) using a class of deep-inelastic ep scattering events with no hadronic energy flow in an interval of pseudo-rapidity adjacent to the proton beam direction. the dependence of this contribution on χ p is measured to be χ p − n with n = 1.19 ± 0.06 (stat.) ± 0.07 (syst.) independent of β and Q 2, which is consistent with both a diffractive interpretation and a factorisable ep diffractive cross section. A first measurement of the deep-inelastic structure of the pomeron in the form of the Q 2 and β dependences of a factorised structure function is presented. For all measured β, this structure function is observed to be consistent with scale invariance.