Transversity of Quarks and Nucleons in Sidis and Drell Yan

One of the persistent challenges confronting the QCD parton model is the explanation of the significant azimuthal and single spin asymmetries that emerge in inclusive and semi-inclusive processes . Going beyond the collinear approximation in PQCD recent progress has been achieved in characterizing these asymmetries in terms of absorptive scattering . Such asymmetries involve time-reversal-odd (T -odd) transverse momentum dependent (TMD) distribution and fragmentation functions . They are indicative of correlations between transverse momentum of quarks and or hadrons, and the transverse spin of the reacting particles . In SIDIS for unpolarized target sT · (P × k⊥), depicts a correlation of transverse quark polarization with the proton’s momentum and the intrinsic quark momentum in an unpolarized nucleon while sT · (p × P h⊥), corresponds to that of a fragmenting quark’s polarization with quark and transverse pion momentum, P h⊥. These correlations enter the unpolarized cross-section convoluted with h1 13 and the Collins fragmentation function H 1 . This cos 2φ asymmetry is not suppressed by 1/Q where Q represents the hard QCD scale. Model estimates of absorptive scattering have led to color gauge invariant 8,14,15 definitions of unsubtracted 16,17 transverse momentum dependent distribution and fragmentation functions. h1 is projected from the correlation function for TMD distribution functions Φ(k, P ), 12 ∫