Hadronization in semi-inclusive deep-inelastic scattering on nuclei

A series of semi-inclusive deep-inelastic scattering measurements on deuterium, helium, neon, krypton, and xenon targets has been performed in order to study hadronization. The data were collected with the HERMES detector at the DESY laboratory using a 27.6 GeV positron or electron beam. Hadron multiplic- ities on nucleus A relative to those on the deuteron, R^h_A, are presented for various hadrons (π+,π−,π0,K+,K−,p, and p) as a function of the virtual-photon energy ν, the fraction z of this energy transferred to the hadron, the photon virtuality Q2, and the hadron transverse momentum squared p2t. The data reveal a systematic decrease of R^h_A with the mass number A for each hadron type h. Furthermore, R^h_A increases (decreases) with increasing values of ν (z), increases slightly with increasing Q2, and is almost independent of p2t, except at large values of p2t. For pions two-dimensional distributions also are presented. These indicate that the dependences of R^h_A on ν and z can largely be described as a dependence on a single variable Lc, which is a combination of ν and z. The dependence on Lc suggests in which kinematic conditions partonic and hadronic mechanisms may be dominant. The behaviour of R^h_A at large p2t constitutes tentative evidence for a partonic energy-loss mechanism. The A-dependence of R^h_A is investigated as a function of ν, z, and of Lc.