In this article, we investigate the contribution of the high twist Feynman
diagrams to the large-pT​ pion production cross section in proton-proton
collisions and we present the general formulae for the high and leading twist
differential cross sections. The pion wave function where two non-trivial
Gegenbauer coefficients a2​ and a4​ have been extracted from the CLEO data,
two other pion model wave functions, P2​, P3​, the asymptotic and the
Chernyak-Zhitnitsky wave functions are used in the calculations. The results of
all the calculations reveal that the high twist cross sections, the ratios R,
r, the dependence transverse momentum pT​ and the rapidity y of pion in
the ΦCLEO​(x,Q2) wave function case is very close to the
Φasy​(x) asymptotic wave function case. It is shown that the high twist
contribution to the cross section depends on the choice of the meson wave
functions.Comment: 28 pages 18 figures RevTex