  We study the mass distribution of a sample of 28 galaxy clusters using strong
and weak lensing observations. The clusters are selected via their strong
lensing properties as part of the Sloan Giant Arcs Survey (SGAS) from the Sloan
Digital Sky Survey (SDSS). Mass modelling of the strong lensing information
from the giant arcs is combined with weak lensing measurements from deep
Subaru/Suprime-cam images to primarily obtain robust constraints on the
concentration parameter and the shape of the mass distribution. We find that
the concentration c_vir is a steep function of the mass, c_vir \propto
M_vir^-0.59\pm0.12, with the value roughly consistent with the
lensing-bias-corrected theoretical expectation for high mass (10^15 h^-1 M_sun)
clusters. However, the observationally inferred concentration parameters appear
to be much higher at lower masses (10^14 h^-1 M_sun), possibly a consequence of
the modification to the inner density profiles provided by baryon cooling. The
steep mass-concentration relation is also supported from direct stacking
analysis of the tangential shear profiles. In addition, we explore the
two-dimensional shape of the projected mass distribution by stacking weak
lensing shear maps of individual clusters with prior information on the
position angle from strong lens modelling, and find significant evidence for a
large mean ellipticity with the best-fit value of e = 0.47 \pm 0.06 for the
mass distribution of the stacked sample. We find that the luminous cluster
member galaxy distribution traces the overall mass distribution very well,
although the distribution of fainter cluster galaxies appears to be more
extended than the total mass.
