Sj. Brodsky et al., THE REGGEON TRAJECTORY IN EXCLUSIVE AND INCLUSIVE LARGE MOMENTUM-TRANSFER REACTIONS, Physics letters. Section B, 318(1), 1993, pp. 203-211
A fundamental prediction of perturbative QCD is that the Reggeon traje
ctories alpha(rho) (t) and alpha(A2) (t) governing charge exchange rea
ctions at high energies s much greater than -t must monotonically appr
oach zero at large spacelike momentum transfers. The asymptotic predic
tion lim-t-->infinity alpha(R)(t) = 0 reflects the fact that a weakly
interacting quark-antiquark pair is exchanged in the t-channel. Howeve
r, measurements of the inclusive processes pi-p --> pi0X at s congruen
t-to 300 GeV2 and 8 GeV2 > -t > 2 GeV2 indicate that the effective rho
trajectory becomes negative at large -t. We resolve the apparent cont
radiction between the perturbative QCD predictions and the experimenta
l data by showing that the hard QCD part of the trajectory is weakly c
oupled and that its contribution will be hidden until much higher ener
gy. We also show that Reggeon contributions to exclusive and inclusive
mesonic exchange hadron reactions can be systematically studied in pe
rturbative QCD. In particular, the Reggeon contributions to the reacti
on pi-p --> pi0X and pi-p --> pi0n is discussed in detail.