Study of the hard double-parton scattering contribution to inclusive four-lepton production in pp collisions at √s = 8 TeV with the ATLAS detector

The inclusive production of four isolated charged leptons in pp collisions is analysed for the presence of hard double-parton scattering, using 20.2 fb⁻¹ of data recorded in the ATLAS detector at the LHC at centre-of-mass energy √s = 8 TeV. In the four-lepton invariant-mass range of 80<m_4ℓ<1000 GeV, an artificial neural network is used to enhance the separation between single- and double-parton scattering based on the kinematics of the four leptons in the final state. An upper limit on the fraction of events originating from double-parton scattering is determined at 95% confidence level to be f_DPS = 0.042, which results in an estimated lower limit on the effective cross section at 95% confidence level of 1.0 mb.