Measurement of the Low-Mass Drell-Yan Differential Cross Section at √s=7 TeV Using the ATLAS Detector

The differential cross section for the process Z/γ^∗ → ℓℓ (ℓ = e, μ) as a function of dilepton invariant mass is measured in pp collisions at s√ = 7 TeV at the LHC using the ATLAS detector. The measurement is performed in the e and μ channels for invariant masses between 26 GeV and 66 GeV using an integrated luminosity of 1.6 fb⁻¹ collected in 2011 and these measurements are combined. The analysis is extended to invariant masses as low as 12 GeV in the muon channel using 35 pb⁻¹ of data collected in 2010. The cross sections are determined within fiducial acceptance regions and corrections to extrapolate the measurements to the full kinematic range are provided. Next-to-next-to-leading-order QCD predictions provide a significantly better description of the results than next-to-leading-order QCD calculations, unless the latter are matched to a parton shower calculation.