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 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 f(DPS) = 0.092 [−0.011 +0.005](stat.) [−0.037 +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, σeff , was determined to be σeff = 14.9 [−1.0 +1.2](stat.) [−3.8 +5.1] (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 [−6 +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
Aaboud, M., Aad, G., Abbott, B., Abdallah, J., Abdinov, O., Abeloos, B., et al. (2016). Study of hard double-parton scattering in four-jet events in pp collisions at √s = 7 TeV with the ATLAS experiment. JOURNAL OF HIGH ENERGY PHYSICS, 11(110), 1-51 [10.1007/JHEP11(2016)110].