FORWARD PHYSICS AT THE LHC; ELASTIC SCATTERING

摘要

The following effects in the nearly forward ("soft") region of the LHC are proposed to be investigated: At small the fine structure of the cone (Pomeron) should be scrutinized: (a) a break of the cone near t _0.1 GeV~2, due to the two-pion threshold, and required by t-channel unitarity, and (b) possible small-period oscillations between t = 0 and the dip region. In measuring the elastic pp scattering and total pp cross-section at the LHC, the experimentalists are urged to treat the total cross-section ___t, the ratio p of real to imaginary part of the forward scattering amplitude, the forward slope B and the luminosity G as free parameters, and to publish model-independent results on dN/dt.? Of extreme interest are the details of the expected diffraction minimum in the differen_tial cross-section. Its position, expected in the interval 0.4 < -t < 1 GeV~2 at the level of about 10~(-2) mb _¤GeV~(-2)-10~(-1) mb GeV~(-2), cannot be predicted unambiguously, and its depth, i.e. the ratio of d__/dt at the minimum to that at the subsequent maximum (about -t = 5 GeV~2, which is about 5) is of great importance. The expected slow-down with increasing of the shrinkage of the second cone (beyond the dip-bump), together with the transition from an exponential to a power decrease in -t, will be indicative of the transition from "soft" to "hard" physics. Explicit models are proposed to help in quantifying this transition. In a number of papers a limiting behavior, or saturation of the black disk limit (BDL), was predicted. This controversial phenomenon shows that the BDL may not be the ultimate limit, instead a transition from shadow to antishadow scattering may by typical of the LHC energy scale.