Study of hard double-parton scattering in four-jet events in $pp$ collisions at $\sqrt{s}=7$ TeV with the ATLAS experiment

Abstract

Inclusive four-jet events produced in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=7$ 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 $p_{\mathrm{T}}\ge 20$ GeV and pseudorapidity $\eta \le 4.4$, and at least one having $p_{\mathrm{T}}\ge 42.5$ GeV, the contribution of hard double-parton scattering is estimated to be $f_{\mathrm{DPS}}=0.092_{-0.011}^{+0.005}(stat.{)}_{-0.037}^{+0.033}(syst.)$. After combining this measurement with those of the inclusive dijet and four-jet cross-sections in the appropriate phase space regions, the effective overlap area between the interacting protons, ${\sigma }_{\mathrm{eff}}$, was determined to be ${\sigma }_{\mathrm{eff}}=14.9_{-1.0}^{+1.2}(stat.{)}_{-3.8}^{+5.1}(syst.)$ mb. This result is consistent within the quoted uncertainties with previous measurements of ${\sigma }_{\mathrm{eff}}$, 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 $\sqrt{s}=7$ TeV. The distributions of the observables sensitive to the contribution of hard double-parton scattering, corrected for detector effects, are also provided.

32 pages plus author list + cover pages (50 pages total), 15 figures, 1 table, published in JHEP, All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2015-08/

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