Quark fragmentation and off-diagonal helicity density matrix elements   for vector meson production
  As 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. 
M. Anselmino (1), M. Bertini (1), F. Murgia (2), P. Quintairos (3)   ((1) University and INFN, Torino, Italy, (2) University...