  Semi-inclusive pi+ electroproduction on protons has been measured with the
CLAS detector at Jefferson Lab. The measurement was performed on a
liquid-hydrogen target using a 5.75 GeV electron beam. The complete five-fold
differential cross sections were measured over a wide kinematic range including
the complete range of azimuthal angles between hadronic and leptonic planes,
phi, enabling us to separate the phi-dependent terms. Our measurements of
phi-independent term of the cross section at low Bjorken x were found to be in
fairly good agreement with pQCD calculations. Indeed, the conventional current
fragmentation calculation can account for almost all of the observed cross
section, even at small pi+ momentum. The measured center-of-momentum spectra
are in qualitative agreement with high energy data, which suggests a surprising
numerical similarity between the spectator diquark fragmentation in the present
reaction and the anti-quark fragmentation measured in e+e- collisions. We have
observed that the two phi-dependent terms of the cross section are small.
Within our precision the cos(2phi) term is compatible with zero, except for
low-z region, and the measured cos(phi) term is much smaller in magnitude than
the sum of the Cahn and Berger effects.
