TRANSVERSELY POLARIZED PARTON DENSITIES, THEIR EVOLUTION AND THEIR MEASUREMENT

The transverse spin asymmetry of a quark in a baryon and the linear polarization of a gluon in a vector meson are studied from the t-channel point of view. Using the Altarelli-Parisi approach, they are shown to obey independent evolution equations and to decrease with increasing Q2. We investigate the possibility to measure them at leading twist, to leading order in α and αs and without analyzing the final polarizations. This requires simultaneous polarization of the beam and the target; the observable effect is in the azimuthal distribution of the high PT particle or jet. Assuming a simple (quark+scalar diquark) model for the baryon, a large asymmetry is expected in p {Mathematical expression} Drell-Yan collisions, a smaller one in high PTpp collisions, from the interference term in the scattering of two identical quarks. © 1990 Springer-Verlag.