The slope of the proton-proton scattering amplitude at t = 0

A dispersion relation for the slope of a crossing symmetric amplitude is derived and applied in pp scattering at high energies and at t = 0. The crossing symmetric amplitude is extracted from the pp amplitude with reasonable assumptions on the crossing antisymmetric part. It is found that the slope of the imaginary part is almost equal to the slope of the modulus. The derivative of the real part is much smaller than that of the imaginary part and shows a zero at NAL energies.