  We report measurements of Upsilon meson production in p+p, d+Au, and Au+Au
collisions using the STAR detector at RHIC. We compare the Upsilon yield to the
measured cross section in p+p collisions in order to quantify any modifications
of the yield in cold nuclear matter using d+Au data and in hot nuclear matter
using Au+Au data separated into three centrality classes. Our p+p measurement
is based on three times the statistics of our previous result. We obtain a
nuclear modification factor for Upsilon(1S+2S+3S) in the rapidity range |y|<1
in d+Au collisions of R_dAu = 0.79 +/- 0.24 (stat.) +/- 0.03 (sys.) +/- 0.10
(pp sys.). A comparison with models including shadowing and initial state
parton energy loss indicates the presence of additional cold-nuclear matter
suppression. Similarly, in the top 10% most-central Au+Au collisions, we
measure a nuclear modification factor of R_AA=0.49 +/- 0.1 (stat.) +/- 0.02
(sys.) +/- 0.06 (pp sys.), which is a larger suppression factor than that seen
in cold nuclear matter. Our results are consistent with complete suppression of
excited-state Upsilon mesons in Au+Au collisions. The additional suppression in
Au+Au is consistent with the level expected in model calculations that include
the presence of a hot, deconfined Quark-Gluon Plasma. However, understanding
the suppression seen in d+Au is still needed before any definitive statements
about the nature of the suppression in Au+Au can be made.
