Study of hard double-parton scattering in four-jet events in pp collisions at √s=7 TeV with the ATLAS experiment

Abstract

Inclusive four-jet events produced in proton-proton collisions at a centre-of-mass energy of s=7 TeV are analysed for the presence of hard double-parton scattering using data corresponding to an integrated luminosity of 37.3 pb−1, collected with the ATLAS detector at the LHC. The contribution of hard double-parton scattering to the production of four-jet events is extracted using an artificial neural network, assuming that hard double-parton scattering can be approximated by an uncorrelated overlaying of dijet events. For events containing at least four jets with transverse momentum p<inf>T</inf> ≥ 20 GeV and pseudorapidity |η| ≤ 4.4, and at least one having p<inf>T</inf> ≥ 42.5 GeV, the contribution of hard double-parton scattering is estimated to be f<inf>DPS</inf> = 0.092<inf>− 0.011</inf> + 0.005(stat.)<inf>− 0.037</inf> + 0.033(syst.). After combining this measurement with those of the inclusive dijet and four-jet cross-sections in the appropriate phase space regions, the effective cross-section, σ<inf>eff</inf> , was determined to be σ<inf>eff</inf> = 14. 9<inf>− 1.0</inf> + 1.2(stat.)<inf>− 3.8</inf> + 5.1(syst.) mb. This result is consistent within the quoted uncertainties with previous measurements of σ<inf>eff</inf> , performed at centre-of-mass energies between 63 GeV and 8 TeV using various final states, and it corresponds to 21<inf>− 6</inf> + 7 % of the total inelastic cross-section measured at s=7 TeV. The distributions of the observables sensitive to the contribution of hard double-parton scattering, corrected for detector effects, are also provided.[Figure not available: see fulltext.] © 2016 Elsevier B.V., All rights reserved.