Abstract
Recent CMS results on forward physics and diffraction are reviewed. The differential diffractive cross section is measured as a function of ξ = M 2 X / S in the region dominated by single dissociation (SD) and double dissociation (DD), where M X is the mass of one of the two final-state hadronic systems separated by the largest rapidity gap in the event. The total SD and DD cross sections are extracted. The observation of a hard color-singlet exchange process in events with a large rapidity gap between two leading jets (jet-gap-jet) is reported. The fraction of jet-gap-jet to all dijet events is measured as a function of the second leading jet transverse momentum and the size of the pseudorapidity gap. The measured fractions are compared with predictions as well as Tevatron data.
Highlights
Diffractive interactions account for about a quarter of the total inelastic proton-proton cross section at high energies
An large rapidity gap (LRG) is presumed to be mediated by a color-singlet exchange (CSE)
Measurements of diffractive processes at the LHC provide valuable input to phenomenological mo√dels, as these cross sections cannot be calculated within perturbative QCD, and extrapolations in s from lower energies vary depending on model parameters
Summary
Diffractive interactions account for about a quarter of the total inelastic proton-proton cross section at high energies These interactions are characterized by at least one large rapidity gap (LRG) that is not suppressed exponentially. Measurements of diffractive processes at the LHC provide valuable input to phenomenological mo√dels, as these cross sections cannot be calculated within perturbative QCD, and extrapolations in s from lower energies vary depending on model parameters. Another interesting and related area of research is the study of events with a LRG between two jets at high transverse momentum pT. Tracker detectors very close to the beamline and sharing collision point with CMS, presents a unique future opportunity to extend the studies discussed here
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