Abstract
The cross section for dijet production in pp collisions at sqrt(s) = 7 TeV is presented as a function of xi, a variable that approximates the fractional momentum loss of the scattered proton in single-diffractive events. The analysis is based on an integrated luminosity of 2.7 inverse nanobarns collected with the CMS detector at the LHC at low instantaneous luminosities, and uses events with jet transverse momentum of at least 20 GeV. The dijet cross section results are compared to the predictions of diffractive and nondiffractive models. The low-xi data show a significant contribution from diffractive dijet production, observed for the first time at the LHC. The associated rapidity gap survival probability is estimated.
Highlights
A significant fraction of the total inelastic proton-proton cross section at high energies is attributed to diffractive processes, characterized by the presence of a large rapidity region Áy with no hadrons, usually called ‘‘rapidity gap’’ [rapidity is defined as y 1⁄4 ð1=2Þ ln1⁄2ðE þ pZÞ=ðE À pZÞ, where E and pZ are the energy and longitudinal momentum of the final-state particle, respectively]
The forward part of the hadron calorimeter, HF, consists of steel absorbers and embedded radiation-hard quartz fibers, which provide a fast collection of Cherenkov light
The remaining pileup background was estimated with minimum-bias Monte Carlo (MC) samples (PYTHIA6 Z1 and PYTHIA8; see section) and was found to be less than 2%
Summary
A significant fraction of the total inelastic proton-proton cross section at high energies is attributed to diffractive processes, characterized by the presence of a large rapidity region Áy with no hadrons, usually called ‘‘rapidity gap’’ [rapidity is defined as y 1⁄4 ð1=2Þ ln1⁄2ðE þ pZÞ=ðE À pZÞ, where E and pZ are the energy and longitudinal momentum of the final-state particle, respectively]. Diffraction with a hard scale has been studied in protonantiproton (pp") and electron-proton (ep) collisions at CERN [2], Fermilab [3,4,5,6], and DESY [7,8,9,10] Such hard diffractive processes can be described in terms of the convolution of diffractive parton distribution functions (dPDFs) and hard scattering cross sections, which are calculable in pQCD. In this approach, the pomeron is treated as a color-singlet combination of partons with the vacuum quantum numbers.
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