ANGULAR DECAY DISTRIBUTION OF LEPTONS FROM W-BOSONS AT NLO IN HADRONIC COLLISIONS

We propose the measurement of the angular decay distribution of leptons from W-production at high-q(T) in ppBAR collisions. The polar and azimuthal angles in the W rest frame can be reconstructed modulo a sign ambiguity in cos theta enabling the measurement of six out of nine helicity cross sections sigma(alpha) describing the most general decay distribution. We review the LO results of the nine helicity cross sections and present the results of complete O(alpha(s)2) next-to-leading (NLO) calculation of four parity conserving structure functions. We show that large deviations from the well-known (1 + cos theta)2 distribution valid at low-q(T) are expected already at moderate transverse W-momentum (q(T) is similar to 20 GeV). The measurement of the sign of the ''T-odd'' helicity cross sections will discriminate between V - A and V + A couplings of the W. We present detailed analytical formulas for all parton level cross sections and discuss the size of the NLO corrections for W+ production at the Tevatron collider. It is shown that the measurement of sigma(A) (originating from the parity violating part of the hadron tensor) provide clear constraints on the gluon structure function since it receives sizable contributions only from the qG initiated process.