Experimental Results on Diffraction

In single diffractive dissociation (SDD), pp → pX , one of the protons survives the interaction while the other dissociates in a hadronic system with invariant mass MX , separated from the first proton by a large rapidity interval devoid of particles. In the presence of a hard scale, such interactions may be regarded as the result of the exchange of a colourless object with vacuum quantum numbers (e.g. a pomeron) consisting of quarks and gluons. One further defines ξ = 1− P ′ L PL , the fractional longitudinal momentum loss of the surviving proton and t = (P −P ), the squared four-momentum exchange at the proton vertex, with P and P ′ the four-momenta of the initial and final state proton, respectively, measured in the initial state centre-of-mass frame.