International Journal of Modern Physics A

I give a brief introduction to diffraction in lepton–hadron and hadron–hadron collisions, the subject of this special issue of the International Journal of Modern Physics A.

The measurements of diffractive dijet and open charm electron–proton cross-sections in deep-inelastic scattering (DIS) and photoproduction at HERA are discussed with an emphasis on possible quantum chromodynamics (QCD) factorization breaking.

We present a summary of results from studies of diffraction at the Fermilab Tevatron collider by the D0 experiment. These include the elastic scattering measurement and studies of dijet exclusive production using Run II data. A brief description of Run I results is also given.

We present a reference review of diffractive results from CDF for collisions at , 630, 1800, and 1960 GeV at the Tevatron, published in 19 PRL/PRD papers from 1994 to 2012. Both soft and hard diffractive results are included for single and/or double dissociation, central diffraction or double Pomeron exchange (where both the proton and antiproton remain intact), multi-gap diffraction (a combination of single and double dissociation), elastic scattering, and the total cross-section, which through the optical theorem is related to the imaginary part of the forward elastic scattering amplitude. In each review, we include the comparisons made by CDF with theoretical predictions.

We study the behavior of elastic and diffractive proton dissociation cross sections at high energy. First, we describe what would be expected to be observed at the Large Hadron Collider (LHC) based on conventional Regge theory. We emphasize the tension between these expectations and the recent LHC measurements, and we discuss the possibilty to modify the classic Reggeon Field Theory (RFT) in a physically-motivated way so as to accommodate the tendencies observed at the LHC. As a result, we show that we are able to achieve a "global" description of the wide variety of high energy elastic and diffractive data that are presently available, particularly from the LHC experiments. The model is based on only one pomeron pole, but includes multi-pomeron interactions and, significantly, includes the transverse momentum dependence of intermediate partons as a function of their rapidity, which provides the rapidity dependence of the multi-pomeron vertices. We give predictions for diffractive observables at LHC, and higher, energies.

In this review we present our model which is an example of the self-consistent approach that incorporates our theoretical understanding of long distance physics, based both on N = 4 SYM for strong coupling and on the matching with the perturbative QCD approach. We demonstrate how important and decisive the LHC data were on strong interactions which led us to a set of the phenomenological parameters that fully confirmed our theoretical expectations, and produced a new picture of the strong interaction at high energy. We also show how far we have come towards creating a framework for the description of minimal bias events for high energy scattering without generating Monte Carlo codes.

In 1970, on purely theoretical grounds, all total hadronic total cross-sections were predicted to increase without limit for higher and higher energies. This was contrary to the conventional belief at that time. In 1978, an accurate phenomenological model was formulated for the case of proton–proton and antiproton-proton interactions. The parameters for this model were slightly improved in 1984 using the additional available experimental data. Since then, for 30 years these parameters have not changed. This development, including especially the difficult task of formulating this phenomenological model and the comparison of the predictions of this model with later experimental results, is summarized.

This paper reviews measurements of the total proton–proton cross-section at 7 TeV and 8 TeV by the ATLAS and TOTEM collaboration at the LHC. Similarities and differences between the two experiments are discussed. Some results on soft diffraction are also reviewed. The paper ends with a discussion of prospects and future plans of both experiments.

We present some physics topics that will allow us to constrain the Pomeron structure at the LHC in terms of gluon and quark densities using the dijet and γ+jet events and tagged protons in AFP (ATLAS) and CMS-TOTEM. We also discuss the possibility to test the BFKL dynamics using jet-gap-jet events.

We comment on the nonperturbative nature of the total cross-section in pp scattering and on the importance of the survival probability for the understanding of diffractive final states in pp scattering.

A brief summary is reported on measurements of soft and hard diffractive processes by the ATLAS, CMS and TOTEM collaborations at a center of mass energy of 7 TeV.

Recent CMS results on diffraction are presented. These include the measurements of the soft diffractive cross sections, of the forward rapidity gap cross section, of the diffractive dijet cross section, the measurement of a large rapidity gap in W and Z boson events and the measurement of the pseudorapidity distribution of charged particles in a single diffractive enhanced sample. This last measurement is the first common result of the CMS and TOTEM collaborations. Some prospects of common CMS-TOTEM data taking are also discussed.

We review some selected results within the Durham model of central exclusive production. We present a detailed discussion of this theoretical approach for modeling exclusive processes and we briefly review some of its phenomenological applications.

We present possible measurements on forward physics and diffraction that can be accomplished at the LHC.