Studies of 4-jet production in proton-proton collisions at √s = 7 TeV

Abstract

Measurements of the differential cross sections for the production of exactly four jets in proton-proton collisions are presented as a function of the transverse momentum pT and pseudorapidity eta, together with the correlations in azimuthal angle and the pT balance among the jets. The data sample was collected in 2010 at a center-of-mass energy of 7 TeV with the CMS detector at the LHC, with an integrated luminosity of 36 inverse pb. The cross section for exactly 4 jets, with 2 hard jets of pT > 50 GeV each, together with 2 jets of pT > 20 GeV each, within |eta|< 4.7 is measured to be sigma = 330 +/- 5 (stat) +/- 45 (syst.) nb. It is found that fixed-order matrix element calculations including parton showers describe the measured differential cross sections in some regions of phase space only, and that adding contributions from double parton scattering brings the Monte Carlo predictions closer to the data.

Figures

Figure 1. Differential cross sections as a function of the jet transverse momenta pT (left) and pseudorapidity eta (right) compared to predictions of POWHEG, MADGRAPH, SHERPA, and PYTHIA8. Scale factors of 10^6, 10^4 and 10^2 are applied to the measurement of the leading, subleading and third jet, respectively. The yellow band represents the total uncertainty, including the statistical and systematic components added in quadrature.

Figure 2. Ratios of predictions of POWHEG, MADGRAPH, SHERPA, PYTHIA8 and HERWIG++ to data as a function of the jet transverse momenta pT (Left) and pseudorapidity eta (Right) for each specific jet. The yellow band represents the total uncertainty, including the statistical and systematic components added in quadrature.

Figure 3. Normalized differential cross sections as a function of the difference in azimuthal angle Deltaphi_soft (left), Delta^rel_soft pT (middle), and DeltaS (right) compared to the predictions of POWHEG, MADGRAPH, SHERPA, PYTHIA8 and HERWIG++. A comparison with the POWHEG predictions interfaced with the parton shower PYTHIA6 tune Z2' without MPI is also shown. The lower panel shows the ratios of the predictions to the data. The yellow band represents the total uncertainty, including the statistical and systematic components added in quadrature. Systematic uncertanties in the normalized cross sections are smaller than the ones in the absolute cross sections, since they are not affected by the migration effects from outside the selected phase space.