W and Z candidates decaying into leptons can be observed in the very early phase of the LHC run. The results for the W/Z production presented are obtained for 10TeV simulated data and are fully valid for 7TeV center-of-mass energy (via a scale factor of the W and Z signals around 0.7)

De Gruttola, M.

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DOI 10.1393/ncc/i2011-10802-5Colloquia: IFAE 2010IL NUOVO CIMENTO Vol. 33 C, N. 6 Novembre-Dicembre 2010Inclusive W and Z production at LHC startupwith the CMS experimentM. De GruttolaUniversita` “Federico II” and INFN, Sezione di Napoli - Napoli, Italy(ricevuto l’ 8 Ottobre 2010; pubblicato online il 15 Febbraio 2011)Summary. — W and Z candidates decaying into leptons can be observed in thevery early phase of the LHC run. The results for the W/Z production presentedare obtained for 10TeV simulated data and are fully valid for 7TeV center-of-massenergy (via a scale factor of the W and Z signals around 0.7).PACS 13.38.Be – Decays of W bosons.PACS 13.38.Dg – Decays of Z bosons.1. – IntroductionW and Z bosons decay into isolated high transverse momentum leptons with a cleanexperimental signature. The W/Z cross section into muons and electron is given byσ(W/Z) =Nsig −NbkgdAW/Z × W/Z ×∫Ldt,(1)where Nsig,bkg are the number of signal and background in each channel; W/Z are theefficiency to detect and trigger the leptons and the neutrino; AW/Z is the geometricacceptance of the signal from Monte Carlo.2. – W and ZHigh momentum electrons in CMS are reconstructed by matching a cluster in theelectromagnetic calorimiter (ECAL) and track in the silicon Tracker. The selection ofthe W → eν [1] decay starts from a cluster with high transverse energy. The neutrinoinstead results in events with unbalanced energy in the transverse plane (EmissT ). Toidentify the Z → e+e− [1] decay one looks for two isolated and opposite sign clusterswith high ET and very high Electron ID footprint.High-pT muons are reconstructed in CMS matching a track in the muon chambersoutside the magnet plus a track in the tracker. The W → μν [2] selection starts requiringc© Societa` Italiana di Fisica 251252 M. DE GRUTTOLAFig. 1. – EmissT distribution for W → eν and background after selection.Fig. 2. – Mee distribution for Z → e+e− and background.Fig. 3. – MmissT distribution for W → μν and background after selection.Fig. 4. – Mμμ distribution for Z → μ+μ− and background.a global track with high transverse momentum pT . The transverse mass of the W, MT ,is computed by combining the measured muon and the missing transverse energy in theevent. The Z → μ+μ− [2] selection requires two opposite signs tracks with high pT .Estimation of the background from W signal using data is done with the “templatemethod”: the signal missing energy shape is built from the observed missing energy inINCLUSIVE W AND Z PRODUCTION AT LHC STARTUP WITH THE CMS EXPERIMENT 253Z events, while the QCD shape is obtained applying the full set of selection cuts butreverting the isolation one. The Z signal is instead almost background free.A common way to measure the efficiencies on data is to use the “Tag & Probe” methodon Z events.Figures 1-4 show the preliminary plots obtained by the CMS experiment using 10 TeVsignal and background simulated data for events passing the W decaying into electronand neutrino, Z decaying into electrons, W into muon and neutrino and Z decaying intomuons, respectively.3. – ConclusionLHC aims to deliver 100 pb−1 of integrated luminosity of pp collision data by the endof 2010. We expect to see about 3000W/pb−1 in each leptonic channel for the LHCoperation at 7TeV and about 300Z/pb−1 in each leptonic channel. The high-purity andwell-known properties of the W/Z signals make them one of the most promising channelsfor the commissioning of CMS physics and lepton identification and selection.REFERENCES[1] The CMS Collaboration, CMS PAS-EWK-09/004.[2] The CMS Collaboration, CMS PAS-EWK-09/001.

Inclusive W and Z production at LHC startup with the CMS experiment

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Inclusive W and Z production at LHC startup with the CMS experiment

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