"Studying the Transverse Spin Structure of the Proton at PHENIX"
Christine A. Aidala
Columbia University

The spin structure of the proton has revealed itself to be extremely
complex and is an area of ongoing research.  The Relativistic Heavy Ion
Collider (RHIC) at Brookhaven National Laboratory (BNL) inaugurated its
operation as the first polarized proton collider during the 2001-2002 run,
marking the beginning of a new era in the study of proton spin structure.

From the data collected in this run, the PHENIX experiment measured the
transverse single-spin asymmetry ($A_N$) for neutral pion and charged
hadron production at $x_F\sim$0.0 over a $p_T$ range of 0.5 to 5.0 GeV/$c$
at a center-of-mass energy ($\sqrt{s}$) of 200 GeV.  Interest in these
measurements arises from the observation of large ($\sim$30\%) transverse
single-spin asymmetries in pion production at forward angles by the E704
collaboration at Fermilab ($\sqrt{s}=19.4$~GeV), found by the STAR and
BRAHMS experiments to persist at RHIC energies, as well as single-spin,
azimuthal asymmetries observed recently in semi-inclusive deep-inelastic
scattering experiments.  Such large asymmetries were initially surprising
because at leading order, perturbative quantum chromodynamics predicted
only small effects.

Current PHENIX results for $A_N$ as well as prospectives for future
transverse spin measurements will be discussed.