Presentation on theme: "W + jets: MET correction and measurement of the W Transverse Mass Autori: L. Brussich, I. LazzizzeraPadova, 7 ottobre 2008."— Presentation transcript:
W + jets: MET correction and measurement of the W Transverse Mass Autori: L. Brussich, I. LazzizzeraPadova, 7 ottobre 2008
Autori: L. Brussich, I. Lazzizzera GOAL: Measurement of the Electroweak W Mass using the first CMS data in the channel W + jets METHOD: the W Boson Mass M W will be extracted by fitting the transverse mass distribution as a function of M W. FIRST-STEPS: - W transverse mass M t (W) formula; - Using of GenMETCollection and CaloMETCollection in our analysis how to correct these objects? …THE-NEXT-STEP: event selection (eg: kinematic range) in order to analyse high-purity W samples using suggestions from the MC-distribution.
Padova, 7 ottobre 2008Autori: L. Brussich, I. Lazzizzera W transverse mass M t (W) formula: The familiar form of the W transverse mass is: M t 2 = 2 p t (l) p t (υ) [ 1 – cos(φ(l) – φ(υ)) ] It is interesting to note that this is the extremum (w.r.t. the parallel momentum of the neutrino) for the squared invariant mass M 2 (W) as well. Hence, from the cinematic point of view, we expect that distribution of M t 2 has its maximum at the W invariant mass. But the dynamics may change the position of the upper bound: since this doesnt happen, then the M t 2 is a good discriminator for the invariant mass.
Padova, 7 ottobre 2008Autori: L. Brussich, I. Lazzizzera GenMET Collection: In CMSSW, MET is determined from the transverse vector sum over energy deposits in the calorimeters. Hence, it may also contain muons, since the muons deposit their energy above all in the Muon Chambers. The first raw correction we have done, was the vector subtraction of the transverse momenta of all muons from the MET.
Padova, 7 ottobre 2008Autori: L. Brussich, I. Lazzizzera CaloMET Collection: But the figures tell us that our correction gives a quite good agreement for GenMET (even if it could be improved!), while we cant say the same for CaloMET. As for the previous case, the same work was done for CaloMETCollection.
Padova, 7 ottobre 2008Autori: L. Brussich, I. Lazzizzera MC vs Reco Muons: The figure probes that CaloMET and GenMET Collection have different ingredients and hence they need different types of corrections (jets). To understand if the difference between the M t (W) distributions in the MC and Reco case is given by the use of HepgMuon vs RecoMuon, it is sufficient to observe the p t -muon distributions.
Padova, 7 ottobre 2008Autori: L. Brussich, I. Lazzizzera Future improvement for muons: To have high purity samples, same quality selections about muons will be done (cuts of p t over 100 GeV, isolation…)
Padova, 7 ottobre 2008Autori: L. Brussich, I. Lazzizzera AIMS: EW analysis in the channel W + jets with the first CMS data; Work with MET, key element in the study of new physics (e.g. Dark Matter).