  We present a measurement of the shapes of b-jets using 300 pb-1 of data
obtained with the upgraded Collider Detector at Fermilab (CDF II) in p pbar
collisions at center of mass energy sqrt{s}=1.96 TeV. This measurement covers a
wide transverse momentum range, from 52 to 300 GeV/c. Samples of heavy-flavor
enhanced jets together with inclusive jets are used to extract the average
shapes of b-jets. The b-jets are expected to be broader than inclusive jets.
Moreover, b-jets containing a single b-quark are expected to be narrower than
those containing a b bbar pair from gluon splitting. The measured b-jet shapes
are found to be significantly broader than expected from the PYTHIA and HERWIG
Monte Carlo simulations. This effect may arise from an underestimation of the
fraction of b-jets originating from gluon splitting in these simulations.
