  We present measurements and calculations of the trap loss rate for laser
cooled Rb atoms confined in either a magneto-optic or a magnetic quadrupole
trap when exposed to a room temperature background gas of Ar. We study the loss
rate as a function of trap depth and find that copious glancing elastic
collisions, which occur in the so-called quantum-diffractive regime and impart
very little energy to the trapped atoms, result in significant differences in
the loss rate for the MOT compared to a pure magnetic trap due solely to the
difference in potential depth. This finding highlights the importance of
knowing the trap depth when attempting to infer the total collision cross
section from measurements of trap loss rates. Moreover, this variation of trap
loss rate with trap depth can be used to extract information about the
differential cross section.
