Measurement of forward-backward asymmetry A FB and of the weak mixing angle in processes of dilepton production in proto
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EMENTARY PARTICLES AND FIELDS Experiment
Measurement of Forward–Backward Asymmetry AF B and of the Weak Mixing Angle in Processes of Dilepton Production in Proton–Proton √ Collisions at s = 7 TeV in the CMS Experiment at the LHC I. N. Gorbunov* and S. V. Shmatov** (On Behalf of the CMS Collaboration) Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia Received March 11, 2013
Abstract—The results obtained by measuring √ the forward–backward asymmetry (AF B ) of Drell–Yan lepton pairs in proton–proton collisions at s = 7 TeV at the LHC are presented. This asymmetry is measured as a function of the dilepton mass and rapidity in the dielectron and dimuon channels. The values of AF B were found for invariant masses of dileptons in the range of 40 Mll 600 GeV. The results for the effective weak mixing angle that were deduced from data on dimuon production in Drell–Yan processes are also presented. The respective data sample was collected by using the Compact Muon Solenoid (CMS) detector over the period spanning the years 2010 and 2011. The measured asymmetry and the effective weak mixing are consistent with the respective Standard Model predictions. DOI: 10.1134/S1063778813090081
INTRODUCTION Investigation of dilepton production in Drell– Yan processes [1], qq → Z/γ ∗ → l+ l− (Fig. 1), is of paramount importance: these processes permit testing predictions of the Standard Model of particle interaction (SM) in a new energy region and seeking new physics beyond the Standard Model [2]. The amplitude for Drell–Yan processes involves both the vector and the axial-vector couplings of electroweak bosons to fermions. This leads to a forward– backward asymmetry of lepton emission with respect to the reference frame comoving with the product dilepton (AF B ). This asymmetry is sensitive to the details of the theoretical models used (coupling constants). It is defined in the form AF B = where
F −B , F +B
hemisphere in which cos θ ∗ 0 (
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