We present a study of jets production in association with W bosons in proton-proton collisions at a centre-of-mass energy of 7TeV using the full 2010 dataset collected by CMS corresponding to an integrated luminosity of (35.9±1.4) pb−1

Gonzi, Sandro

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DOI 10.1393/ncc/i2013-11459-8Colloquia: IFAE 2012IL NUOVO CIMENTO Vol. 36 C, N. 1 Gennaio-Febbraio 2013Study of W and jets associated production with CMSS. Gonzi(∗) on behalf of the CMS CollaborationUniversita` di Firenze and INFN, Sezione di Firenze - Firenze, Italyricevuto il 31 Agosto 2012Summary. — We present a study of jets production in association with W bosons inproton-proton collisions at a centre-of-mass energy of 7TeV using the full 2010 data-set collected by CMS corresponding to an integrated luminosity of (35.9±1.4) pb−1.PACS 13.38.Be – Decays of W bosons.PACS 29.85.Fj – Data analysis.The study of the production of vector bosons W in association with hadronic jetsprovides a stringent test of perturbative QCD calculations. Moreover, this process is asignificant source of background in searches for new physics and for studies of the topquark; a precise measurement of its cross section is then essential. This paper presentsa study of W + jets production performed by the CMS detector [1] in proton-protoncollisions at√s = 7TeV with 35.9 pb−1 of integrated luminosity collected in 2010 [2].Monte Carlo (MC) simulation samples with a W or a Z boson in association withjets are generated with the MadGraph [3] parton-level event generator on the basis ofa matrix element calculation. MadGraph is interfaced to the PYTHIA [4] software fora parton shower simulation. Top background processes are generated with MadGraphwhile QCD multi-jet and γ + jets processes are generated with PYTHIA alone. When-ever available, a NNLO or NLO normalization is performed. Minimum-bias events aresuperimposed to the hard interaction to simulate the event pile-up observed in data.Signal selection begins with the identification of a so-called “leading lepton”. Forelectron candidates we require a transverse-momentum selection pT > 20GeV and afiducial region of the ECAL supercluster |η| < 2.5, with 1.44 < |η| < 1.57 excluded. Theselected electron must match the object that triggered the event readout and pass sometight quality requirements (including identification, isolation, and conversion rejection).If a second electron of pT > 10GeV, detected within the ECAL fiducial region, passes alooser set of quality cuts and its invariant mass with the leading electron is in the range[60–120]GeV, then the event is rejected. Events with a muon with pT > 15GeV and|η| < 2.4 are rejected to reduce tt¯ contamination.(∗) E-mail: sandro.gonzi@fi.infn.itc© CERN on behalf of the CMS Collaboration under CC BY-NC 3.0 277278 S. GONZI on behalf of the CMS COLLABORATION(W)σ n-jets)≥(W + σ-310-210-110 data energy scale unfolding       MadGraph Z2 MadGraph D6T Pythia Z2CMS = 7 TeVs  at  -136 pbν e→W  > 30 GeVjetTEinclusive jet multiplicity, n (n-1)-jets)≥(W + σ n-jets)≥(W + σ 00.10.21 2 3 4(W)σ n-jets)≥(W + σ-310-210-110 data energy scale unfolding       MadGraph Z2 MadGraph D6T Pythia Z2CMS = 7 TeVs  at  -136 pbνμ →W  > 30 GeVjetTEinclusive jet multiplicity, n (n-1)-jets)≥(W + σ n-jets)≥(W + σ 00.10.21 2 3 4Fig. 1. – The ratio σ(W+ ≥ n jets)/σ(W) and σ(W+ ≥ n jets)/σ(W+ ≥ (n − 1) jets) in theelectron channel (left) and the muon channel (right) compared to predictions from MadGraphand PYTHIA with different tunes (Z2 and D6T tunes).For muon candidates we require the presence of an isolated high-quality muon withpT > 20GeV in the region |η| < 2.1. If a second muon of pT > 10GeV is detectedin the region |η| < 2.5, and its invariant mass with the leading muon is in the range[60–120]GeV, the event is rejected. Finally, we require a transverse mass MT > 20GeV.Jets are reconstructed with the anti-kT clustering algorithm [5] in a R = 0.5 cone.Jets are selected in the tracker acceptance |η| < 2.4, with ET > 30GeV to reduce thepile-up effects.In order to provide model-independent results, we quote them within the lepton andjet acceptance, and only correct for efficiency of the selection. The lepton efficiencies areobtained by means of a tag-and-probe method with fits on the invariant-mass distribu-tions in Z/γ* + jets data samples.In order to estimate the scaling rule of jets at the particle level, we apply an unfoldingprocedure that removes the effects of jet energy resolution and reconstruction efficiency.The main sources of systematic uncertainties are the determination of the jet energyand jet energy resolution. We apply the jet energy scale (JES) corrections, to account forthe detector response and inhomogeneities, and a pile-up energy correction. All statisticaland systematic uncertainties are propagated in the unfolding procedure.From the unfolded exclusive jet multiplicity distributions we derive the inclusive onesand we calculate two sets of ratios: σ(W+ ≥ n jets)/σ(W) and σ(W+ ≥ n jets)/σ(W+ ≥(n−1) jets), where σ(W ) is the inclusive cross section. The results are reported in fig. 1,where the systematic uncertainties associated with the JES and the unfolding are shownas error bands. For a large number of jets, the PYTHIA simulation alone fails to describethe data, while the MadGraph + PYTHIA simulation agrees well, as expected.REFERENCES[1] CMS Collaboration, JINST, 3 (2008) S08004, doi:10.1088/1748-0221/3/08/S08004.[2] CMS Collaboration, JHEP, 01 (2012) 010, doi:10.1007/JHEP01(2012)010.[3] Maltoni F. et al., JHEP, 02 (2003) 027, doi:10.1088/1126-6708/2003/02/027.[4] Sjo¨strand T. et al., JHEP, 05 (2006) 026, doi:10.1088/1126-6708/2006/05/026.[5] Cacciari M. et al., JHEP, 04 (2008) 063, doi:10.1088/1126-6708/2008/04/063.

Study of W and jets associated production with CMS

We present a study on the associated production of hadronic jets and W bosons in proton-proton collisions at the center of mass energy of 7 TeV using the data collected by the CMS experiment at the LHC. The associated production of vector bosons and jets provides a stringent and important test of perturbative QCD calculations and it is an important background in searches for new physics and in studies about the top quark. We show results on multiplicity and transverse momentum distributions of jets and we report on the measurements of the cross section ratios  $\sigma(W + \ge n  jets)/ \sigma(W)$ and $\sigma(W + \ge (n + 1) jets)/ \sigma(W +  \ge n jets)$, where n is the number of jets reconstructed with a threshold of 30 GeV. We finally report on the results for the W charge asymmetry as a function of the number of jets

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Study of W and jets associated production with CMS

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