The diquark and elastic pion-proton scattering at high energies

Small momentum transfer elastic pion-proton cross-section at high energies is calculated assuming the proton is composed of two constituents, a quark and a diquark. We find that it is possible to fit very precisely the data when (i) the pion acts as a single entity (no constituent quark structure) and (ii) the diquark is rather large, comparable to the size of the proton.