Higher Twist Effects in Proton-Proton Collisions
  In this article, we investigate the contribution of the high twist Feynman diagrams to the large-$p_T$ 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 $a_2$ and $a_4$ have been extracted from the CLEO data, two other pion model wave functions, $P_2$, $P_3$, 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 $p_T$ and the rapidity $y$ of pion in the $\Phi_{CLEO}(x,Q^2)$ wave function case is very close to the $\Phi_{asy}(x)$ 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. 
A. I. Ahmadov, I. Boztosun, R. Kh. Muradov, A. Soylu and E. A.   Dadashov