Résumé du preprint DAPNIA-03-28

Hard diffraction and the nature of the Pomeron
J. Lamouroux,R. Peschanski,C. Royon,L. Schoeffel
We ask the question whether  the quark and gluon distributions in the Pomeron
obtained from QCD fits to hard diffraction processes at HERA can be
dynamically generated  from a state made of {\\it valence-like}  gluons and sea
quarks as input. By a method combining {\\it backward}   $Q^2$-evolution for data
exploration  and {\\it forward}  $Q^2$-evolution for a best fit determination, we
find that  the diffractive structure functions  published by the H1
collaboration at HERA  can be  described by a  simple {\\it
valence-like} input at an initial scale of order  $\\mu^2 \\sim 2.3-2.7\\ GeV^2$.
The parton number sum rules at the initial scale  $\\mu^2$ for the H1 fit gives
$2.1\\pm .1\\pm .1$ and
$.13\\pm .01 \\pm .02$ for gluon and sea quarks respectively, corresponding to  an
initial Pomeron  state made of  (almost) only two gluons. It has    flat
gluon  density leading to a  plausible interpretation in terms of a
gluonium state.


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