  The CMS experiment at the LHC includes a hybrid silicon pixel detector for
the reconstruction of charged tracks and of the interaction vertices. The
barrel region consists of n-in-n sensors with 100X150 um^2 cell size processed
on diffusion oxygenated float zone silicon. A biasing grid is implemented and
pixel isolation is achieved with the moderated p-spray technique. An extensive
test program was carried out on the H2 beam line of the CERN SPS. In this paper
we describe the sensor layout, the beam test setup and the results obtained
with both irradiated and non-irradiated prototype devices. Measurements of
charge collection, hit detection efficiency, Lorentz angle and spatial
resolution are presented.
