W jets: MET correction and measurement of the W Transverse Mass

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W jets MET correction and measurement of the
W Transverse Mass
Autori L. Brussich, I. Lazzizzera
Padova, 7 ottobre 2008
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GOAL Measurement of the Electroweak W Mass using
the first CMS data in the channel W jets

• METHODthe W Boson Mass MW will be extracted by
  fitting the transverse mass distribution as a
  function of MW.
• FIRST-STEPS
• W transverse mass Mt(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.

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W transverse mass Mt(W) formula
The familiar form of the W transverse mass
is Mt2 2 pt(l) pt(?) 1 cos(f(l) f(?))
It is interesting to note that this is the
extremum (w.r.t. the parallel momentum of the
neutrino) for the squared invariant mass M2 (W)
as well. Hence, from the cinematic point of view,
we expect that distribution of Mt2 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 Mt2 is a good
discriminator for the invariant mass.
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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.
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CaloMET Collection
As for the previous case, the same work was done
for CaloMETCollection.
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.
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MC vs Reco Muons
To understand if the difference between the Mt(W)
distributions in the MC and Reco case is given by
the use of HepgMuon vs RecoMuon, it is sufficient
to observe the pt-muon distributions.
The figure probes that CaloMET and GenMET
Collection have different ingredients and hence
they need different types of corrections (jets).
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Future improvement for muons
To have high purity samples, same quality
selections about muons will be done (cuts of pt
over 100 GeV, isolation)
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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).