Abstract
This paper presents a measurement of the triple-differential cross section for the Drell-Yan process Z/γ* → ℓ+ℓ− where ℓ is an electron or a muon. The measurement is performed for invariant masses of the lepton pairs, mℓℓ, between 46 and 200 GeV using a sample of 20.2 fb−1 of pp collisions data at a centre-of-mass energy of sqrt{s}=8 TeV collected by the ATLAS detector at the LHC in 2012. The data are presented in bins of invariant mass, absolute dilepton rapidity, |yℓℓ|, and the angular variable cos θ* between the outgoing lepton and the incoming quark in the Collins-Soper frame. The measurements are performed in the range |yℓℓ| < 2.4 in the muon channel, and extended to |yℓℓ| < 3.6 in the electron channel. The cross sections are used to determine the Z boson forward-backward asymmetry as a function of |yℓℓ| and mℓℓ. The measurements achieve high-precision, below the percent level in the pole region, excluding the uncertainty in the integrated luminosity, and are in agreement with predictions. These precision data are sensitive to the parton distribution functions and the effective weak mixing angle.
Highlights
In the Drell-Yan process [1, 2] qq → Z/γ∗ → + −, parity violation in the neutral weak coupling of the mediator to fermions induces a forward-backward asymmetry, AFB, in the decay angle distribution of the outgoing lepton ( −) relative to the incoming quark direction as measured in the dilepton rest frame
The remaining two correlated components are propagated with the offset method, which when summed in quadrature amount to a measurement uncertainty of less than 0.1% of the cross section, except at low mee and large | cos θ∗| where it grows to almost 1% in the central electron channel
The measurements are extended to high rapidity in the electron channel up to |yee| = 3.6 in the mass range 66 < m < 150 GeV
Summary
In the Drell-Yan process [1, 2] qq → Z/γ∗ → + −, parity violation in the neutral weak coupling of the mediator to fermions induces a forward-backward asymmetry, AFB, in the decay angle distribution of the outgoing lepton ( −) relative to the incoming quark direction as measured in the dilepton rest frame. A complete description of the Drell-Yan cross section to all orders in quantum chromodynamics (QCD) depends on five kinematic variables of the Born-level leptons, namely m , the invariant mass of the lepton pair; y , the rapidity of the dilepton system; θ and φ, the lepton decay angles in the rest frame of the two incident quarks; and pT,Z, the transverse momentum of the vector boson.
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