  An experiment (E497) is underway at TRIUMF to measure the angle-integrated,
parity violating longitudinal analyzing power, Az, in proton-proton elastic
scattering, to a precision of +/- 0.2 x 10^-7. The experiment uses a 221 MeV
longitudinally polarized proton beam incident on a 40 cm liquid hydrogen
target. The beam energy is carefully chosen so that the contribution to Az from
the J=0 parity mixed partial wave (1S0-3P0) integrates to zero over the
acceptance of the apparatus, leaving the experiment sensitive mainly (>95%) to
Az arising from the 3P2-1D2, J=2 wave. To minimize sources of systematic error,
the TRIUMF ion source and cyclotron parameters have been refined to the extent
that helicity correlated beam changes are at an extremely low level, and
specialized instrumentation on the E497 beamline is able to measure residual
helicity correlated modulations to a precision consistent with the goals of the
experiment. A data taking run in February-March, 1997 logged approximately 12%
of the desired data and produced a preliminary result, Az = (1.1 +/- 0.4 +/-
0.4) x 10^-7, where the error is statistical only.
