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

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 correspondingto 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 pT ≥ 20 GeV and pseudorapidity |η| ≤ 4.4, and at least one having pT ≥ 42.5 GeV, the contribution of hard double-parton scattering is estimated to be fDPS = 0.092 +0.005 −0.011 (stat.) +0.033 −0.037 (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, σeff, was determined to be σeff = 14.9+1.2−1.0
(stat.) +5.1−3.8 (syst.) mb. This result is consistent within the quoted uncertainties with previous measurements of σeff,
performed at centre-of-mass energies between 63 GeV and 8 TeV using various final states, and it corresponds to 21+7−6% 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.