Recent diffractive structure function measurements in deep inelastic scattering (DIS) by
the H1 and ZEUS experiments at HERA are reviewed. In neutral current (NC) DIS, precise
measurements have been made of diffraction, $ep \\to eXY$, the signature of which is a
large rapidity gap (LRG) between the hadronic system $X$ and the proton or one of its
low-mass excited states $Y$. New results on charged current (CC) DIS are also presented.
They are identified in a CC DIS sample by a large rapidity gap, corresponding to a diffractive
process $ep \\to \\nu XY$ with a $W$ boson exchange. Moreover, within the framework of
QCD hard scattering factorisation in DIS, all these data provide constraints on the diffractive
parton distribution functions of the proton and predict a large gluon content. For example,
the resulting gluon distribution, extracted from the H1 measurements, carries an integrated
fraction of about 70% of the exchanged momentum. Note that these functions are crucial
inputs for the calculations of diffractive dijet or charm production in DIS. These parton
distribution functions may also be applicable to hadron-hadron scattering provided that an
additional rapidity gap survival probability is taken into account.
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