2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/48358As confirmed by some recent LEP data on phi, K^* and D^*0 production, final state interactions in quark fragmentation may give origin to non-zero values of the off-diagonal element rho_{1,-1} of the helicity density matrix of vector mesons produced in e^+ e^- annihilations: we give estimates for rho_{1,-1} of vector mesons with a large x_E and collinear with the parent jet, relating its size and sign to the associated hard constituent dynamics. We mention possible non-zero values of rho_{1,-1} in several other processes.3 pages, LaTeX, no figures, uses sprocl.sty. Talk delivered by F. Murgia at the XIII International Symposium on High Energy Spin Physics (SPIN98), September 8-12, 1998, Protvino, RussiaHigh Energy Physics - Phenomenologytext