The extraction of the bare triple - Pomeron vertex ; a crucial ingredient for diffraction

The triple-Pomeron coupling lies at the heart of the predictions for high energy diffractive processes. We explain why the existing determinations, which use single-particle inclusive hadronic data a+ b → a+Y , underestimate the value of the bare coupling, due to the neglect of soft rescattering which populates the rapidity gaps. We describe how data for the process γ+ p → J/ψ+Y can be used to give a much more reliable estimate of the bare coupling. We use the existing, fragmentary, J/ψ data from HERA to show that the triple-Pomeron coupling is probably about 3 times larger than the previous determinations. We emphasize the importance of an explicit measurement of the mass spectrum of the Y system which accompanies J/ψ production at HERA. The consequences for ultra high energy cosmic ray showers are mentioned. The triple-Pomeron coupling is a crucial ingredient for understanding diffraction. The value and the t-dependence of the vertex determine the asymptotic high energy behaviour of total cross sections and the cross section of diffractive dissociation. Moreover, in turn, the calculation of the rapidity gap survival factors, S, for diffractive processes depend on the properties of the triple-Pomeron vertex. The factor S depends on the particular diffractive process, as well as the values of its kinematic variables, and is found to be of size from about 0.01 to 1. An example of an analysis of soft high energy hadronic scattering, with the consequent calculation of the S factors, and their relation to the triple-Pomeron vertex can be found in [1]. The existing determinations of the vertex, which were made many years ago, were based on the analyses of the cross sections for single particle hadronic inclusive processes a + b → c+ Y, (1) See, for example, [2], or the review [3]