Elastic meson nucleon and nucleon nucleon scattering: Models vs. all available data

We consider simple-pole descriptions of soft elastic scattering at small t and s, and allow for the presence of a hard pomeron. We have built and analyzed an exhaustive dataset and we show that simple poles provide an excellent description of the data in the region 0.5 GeV 2 < t < 0.1 GeV 2 , 6 GeV< p s <63 GeV. We show that new form factors have to be used, and get information on the trajectories of the soft and hard pomerons. Recently 1 , we have shown that a model that includes a hard pomeron reproduces very well (with � 2 /d.o.f. ≈ 0.95 or with confidence level CL=93%) total cross sections and the ratioof the real to imaginary parts of the forward scattering amplitude, while the description obtained from a soft pomeron is much less convincing 2 (� 2 /d.o.f. ≈ 1.07, CL=6%). We considered the full, standard set of forward data 3 for pp, ¯ pp, Kp, �p, p and , and showed that the description extends down to √ s = 5 GeV. The details of these results are presented in the contribution of J.R. Cudell to these pro- ceedings 4 . However, despite an excellent � 2 and the fact that the hard pomeron intercept is very close to what is observed in deeply inelastic scattering 5 and in photoproduction 6 , it is not entirely sure that it is present in soft scattering. Indeed, its couplings are small and its contribution is less than 10% for √ s < 100 GeV. Hence it is important to look for confirmation of its presence in other soft processes, and the obvious place to start from is elastic scattering. This analysis is briefly presented in this paper. 1. Scattering amplitudes. We parametrise all exchanges by simple poles, and limit ourselves to a region in s and t where these are dominant. The normalization of the amplitude A ab (s,t) that describes the elastic scattering of hadrons a and b is given by