  We present a sample of 29 galaxy clusters from the XMM-LSS survey over an
area of some 5deg2 out to a redshift of z=1.05. The sample clusters, which
represent about half of the X-ray clusters identified in the region, follow
well defined X-ray selection criteria and are all spectroscopically confirmed.
For all clusters, we provide X-ray luminosities and temperatures as well as
masses. The cluster distribution peaks around z=0.3 and T =1.5 keV, half of the
objects being groups with a temperature below 2 keV. Our L-T(z) relation points
toward self-similar evolution, but does not exclude other physically plausible
models. Assuming that cluster scaling laws follow self-similar evolution, our
number density estimates up to z=1 are compatible with the predictions of the
concordance cosmology and with the findings of previous ROSAT surveys. Our well
monitored selection function allowed us to demonstrate that the inclusion of
selection effects is essential for the correct determination of the evolution
of the L-T relation, which may explain the contradictory results from previous
studies. Extensive simulations show that extending the survey area to 10deg2
has the potential to exclude the non-evolution hypothesis, but that constraints
on more refined ICM models will probably be limited by the large intrinsic
dispersion of the L-T relation. We further demonstrate that increasing the
dispersion in the scaling laws increases the number of detectable clusters,
hence generating further degeneracy [in addition to sigma8, Omega_m, L(M,z) and
T(M,z)] in the cosmological interpretation of the cluster number counts. We
provide useful empirical formulae for the cluster mass-flux and mass-count-rate
relations as well as a comparison between the XMM-LSS mass sensitivity and that
of forthcoming SZ surveys.
