Abstract
Abstract Measurements of the differential and double-differential Drell-Yan cross sections are presented using an integrated luminosity of 4.5 (4.8) fb−1 in the dimuon (dielectron) channel of proton-proton collision data recorded with the CMS detector at the LHC at $ \sqrt{s} $ = 7 TeV. The measured inclusive cross section in the Z-peak region (60–120 GeV) is σ(ℓℓ) = 986.4 ± 0.6 (stat.) ± 5.9 (exp. syst.) ± 21.7 (th. syst.) ± 21.7 (lum.) pb for the combination of the dimuon and dielectron channels. Differential cross sections dσ/dm for the dimuon, dielectron, and combined channels are measured in the mass range 15 to 1500 GeV and corrected to the full phase space. Results are also presented for the measurement of the double-differential cross section d2σ/dm d|y| in the dimuon channel over the mass range 20 to 1500 GeV and absolute dimuon rapidity from 0 to 2.4. These measurements are compared to the predictions of perturbative QCD calculations at next-to-leading and next-to-next-to-leading orders using various sets of parton distribution functions.
Highlights
Background estimationThere are several physical and instrumental backgrounds that contribute to the sample of dilepton candidates
Nui Ai iρi Nunorm Anorm normρnorm where Nui is the number of events after background subtraction and the unfolding procedure for the detector resolution and final-state photon radiation (FSR) correction, Ai is the acceptance, i is the efficiency, and ρi is the correction estimated from data in a given invariant mass bin i as defined earlier
The muon and electron cross sections in the Z-peak region are in good agreement with next-to-next-to-leading order (NNLO) predictions for the full phase space and with the previous C√ompact Muon Solenoid (CMS) measurements [37, 47]
Summary
A right-handed coordinate system is used in CMS, with the origin at the nominal collision point, the x axis pointing to the center of the LHC ring, the y axis pointing up (perpendicular to the LHC plane), and the z axis along the counterclockwise-beam direction. Muons are detected in the pseudorapidity range |η| < 2.4 with four stations of muon chambers These muon stations are installed outside the solenoid and sandwiched between steel layers, which serve both as hadron absorbers and as a return yoke for the magnetic field flux. They are made using three technologies: drift tubes (DT), cathode strip chambers (CSC), and resistiveplate chambers. The muons associated with the tracks measured in the silicon tracker have a transverse momentum (pT) resolution of about 1–6% in the muon pT range relevant for the analysis presented in this paper. The high-level trigger (HLT) is software-based and further decreases the event collection rate by using the full event information, including that from the tracker [28]
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