Abstract
A measurement of the cross-section for Z-boson production in the forward region of pp collisions at 8TeV centre-of-mass energy is presented. The measurement is based on a sample of $\rm Z\rightarrow e^+e^-$ decays reconstructed using the LHCb detector, corresponding to an integrated luminosity of 2.0fb$^{-1}$. The acceptance is defined by the requirements $2.0<\eta<4.5$ and $p_{\rm T}>20$GeV for the pseudorapidities and transverse momenta of the leptons. Their invariant mass is required to lie in the range 60--120GeV. The cross-section is determined to be $$ \sigma({\rm pp\to Z\to e^+e^-})=93.81\pm0.41({\rm stat})\pm1.48({\rm syst})\pm1.14({\rm lumi})\;{\rm pb}\,,$$ where the first uncertainty is statistical and the second reflects all systematic effects apart from that arising from the luminosity, which is given as the third uncertainty. Differential cross-sections are presented as functions of the Z-boson rapidity and of the angular variable $\phi^*$, which is related to the Z-boson transverse momentum.
Highlights
Differential cross-sections are presented as functions of the Z-boson rapidity and of the angular variable φ∗, which is related to the Z-boson transverse momentum
Where ∆η is the difference in pseudorapidity between the leptons, the acoplanarity angle φacop = π − |∆φ| depends on the difference between the azimuthal directions of the lepton momenta, ∆φ, and M and pT are the invariant mass and transverse momentum of the lepton pair
The results are given as Born-level cross-sections, which do not include the effects of final-state radiation
Summary
The LHCb detector [1, 6] is a single-arm forward spectrometer designed for the study of particles containing b or c quarks. The trigger consists of a hardware stage, based on information from the calorimeter and muon systems, followed by a software stage, which applies a full event reconstruction. Events are first required to pass the hardware trigger for electrons, which selects events having an electromagnetic cluster of high transverse energy geometrically associated with signals in the PRS and SPD detectors. This high-pT single-electron trigger is refined by the software trigger. Simulated event samples of Z → e+e− with M (e+e−) > 40 GeV are used in the analysis. The interaction of the generated particles with the detector and its response are implemented using the Geant toolkit [10, 11] as described in ref. [12]
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