  We extend our analyses of the dark matter (DM) distribution in relaxed
clusters to the case of Abell 383, a luminous X-ray cluster at z=0.189 with a
dominant central galaxy and numerous strongly-lensed features. Following our
earlier papers, we combine strong and weak lensing constraints secured with
Hubble Space Telescope and Subaru imaging with the radial profile of the
stellar velocity dispersion of the central galaxy, essential for separating the
baryonic mass distribution in the cluster core. Hydrostatic mass estimates from
Chandra X-ray observations further constrain the solution. These combined
datasets provide nearly continuous constraints extending from 2 kpc to 1.5 Mpc
in radius, allowing stringent tests of results from recent numerical
simulations. Two key improvements in our data and its analysis make this the
most robust case yet for a shallow slope \beta of the DM density profile
\rho_DM ~ r^-\beta on small scales. First, following deep Keck spectroscopy, we
have secured the stellar velocity dispersion profile to a radius of 26 kpc for
the first time in a lensing cluster. Secondly, we improve our previous analysis
by adopting a triaxial DM distribution and axisymmetric dynamical models. We
demonstate that in this remarkably well-constrained system, the logarithmic
slope of the DM density at small radii is \beta < 1.0 (95% confidence). An
improved treatment of baryonic physics is necessary, but possibly insufficient,
to reconcile our observations with the recent results of high-resolution
simulations.
