Measurement of the z- and x-dependence of the Mean Transverse Momentum of Charged Hadrons, Charged Pions and K_s^0 at HERMES

The mean transverse momenta of hadrons, , produced in e^+ N deep inelastic scattering was studied as a function of the hadron energy fraction z and the Bjorken variable x. The statistical accuracy of the HERMES data permitted to observe at high z differences in between hadrons with positive and negative charges, h^+, h^- and K_s^0 for the first time. These differences can presumably be explained by the flavour dependence of the intrinsic transverse momentum distributions of quarks in the initial nucleon.