Abstract
The phenomenon of hard diffraction is presented. The discussion includes: the present understanding of the process, experimental techniques, past measurements performed at the SPS, HERA and Tevatron colliders, the first LHC data and prospects for new results.
Highlights
Diffractive interaction is a process that is governed by strong forces, but in which no quantum numbers are transferred
The simplest of them is the elastic scattering, where the final state consists of the same particles as the initial state – both particles stay intact
In the Regge theory diffractive interactions are governed by the exchange of the pomeron trajectory, which intercept is close to unity and which is responsible for the growth of the total cross sections with the centre-of-mass energy
Summary
Diffractive interaction is a process that is governed by strong forces, but in which no quantum numbers are transferred. In central diffraction both particles stay intact, but the final state consists of additional particles. In the Regge theory diffractive interactions are governed by the exchange of the pomeron trajectory, which intercept is close to unity and which is responsible for the growth of the total cross sections with the centre-of-mass energy. In the quantum chromodynamics the pomeron can be described in the leading order as an exchange of two gluons in a color-signet state. At small t values (t is the four-momentum transfer squared and the cross section for diffractive processes is steeply falling with t) the strong coupling constant is not small enough to justify neglecting higher-order diagrams. The pomeron should be thought of rather as an exchange of a gluon ladder
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