Speaker
Janusz Malka
(DESY)
Description
Data in which a proton is tagged along the beampipe after the primary
interaction represents the cleanest way to measure diffraction. Data from
both H1 and ZEUS collaborations on inclusive diffractive deep inelastic
scattering, with a tagged proton, have been combined. Inclusive
diffractive deep inelastic scattering can be considered as the exchange of
a colourless object and is amenable to QCD fits in which the structure of
this object, sometimes called a Pomeron, is determined. Given such
processes are expected to factorise, such a Pomeron structure can be used
to predict the rates of jet production in e.g. diffractive photoproduction.
The comparison of jet data with the predictions of next-to-leading order
QCD are discussed in the context of factorising breaking. Another way to
study diffraction is through the production of vector mesons which is also
characterised by a colourless exchange with the proton which in lowest
order QCD is realised as a colourless gluon pair. Therefore consideration
of the dependence of the $J/\psi$ cross section on the photon-proton
centre-of-mass energy is related to the rise of the square of the gluon
density towards low values of Bjorken $x$. Comparisons of HERA data with
such theories and other data are presented.
Primary authors
Matthew Wing
(UCL)
Stefan Schmitt
(Deutsches Elektronen-Synchrotron (DE))
