Summary:
The decay channel H > ZZ() > 4, where = e, μ, is one 820 of the
experimentally
cleanest signatures for the search of the Standard Model Higgs boson. The main
backgrounds
to the H > ZZ > 4 search at LHC is the irreducible ZZ/γ 822 > 4, while
the reducible backgrounds are mainly Z + QQ (Q=b or c), tt, and Z + light
jets with
one or more ”fake” leptons in the final state.
For the high mass region, MH > 180GeV , the two on-shell Z bosons from the
Higgs
decay allow for a selection which strongly suppresses the reducible
backgrounds leaving
only the irreducible ZZ > 4 component. At low Higgs masses, where one of the
decay
bosons is off-shell, contributions from Z + jets and tt can be significant
and tighter
cuts are therefore applied to reduce these backgrounds to a level safely below
the ZZ
continuum.
This analysis presents a search for Z + μ+μ events using the first 43pb1 of
pp
collisions at the LHC at s = 7TeV with the ATLAS detector. Events with a
dilepton
pair consistent with a Z decay, both Z > μ+μ and Z > e+e 833 decays, are
studied.
With this search, which is using the same selection criteria with H > 4
analysis, the
Z+ heavy quark background is measured in a control region and it is compared
with
the corresponding Monte Carlo expectation. Further more, because of the low
statistics
of these early data, the Z +μ final state is also studied, allowing for more
quantitative
comparison of the different muon components in data and MC.
Finally, the efficiency of the additional muon selection criteria is
investigated using
a tag and probe like method on muons originating from Z decays.
Keywords:
ATLAS, Experiment, Boson, Higgs, Cern