MISSING TRANSVERSE ENERGY MEASUREMENT IN ATLAS DETECTOR:FIRST LHC DATA RESULTS AND IMPORTANCE FOR PHYSICS STUDY
Tesi di Dottorato
Data di Pubblicazione:
2010
Citazione:
MISSING TRANSVERSE ENERGY MEASUREMENT IN ATLAS DETECTOR:FIRST LHC DATA RESULTS AND IMPORTANCE FOR PHYSICS STUDY / C. Pizio ; tutor: Donatella Cavalli ; coordinatore: Marco Bersanelli. Università degli Studi di Milano, 2010 Dec 16. 23. ciclo, Anno Accademico 2010.
Abstract:
The Large Hadron Collider (LHC) at CERN started its operation at the
end of November 2009, first at a centre-of-mass energy of 900 GeV, then,
since March 2010, at 7 TeV. During this period the ATLAS experiment has
collected a large number of proton-proton collision events, resulting up to
now in an integrated luminosity of about 45 pb−1 .
miss
A very good measurement of the missing transverse energy, ET , is es-
sential for many physics studies in ATLAS both for Standard Model chan-
nels, as W, Z bosons decaying to τ leptons or top quark decays, and for
miss are expected to be the key
discovering channels. Events with large ET
signature for new physics such as supersymmetry and extra dimensions. A
miss measurement in terms of linearity and resolution is crucial for
good ET
the efficient and accurate reconstruction of the Higgs boson mass when the
Higgs boson decays to a pair of τ -leptons.
miss in ATLAS with real
This thesis describes the first measurement of ET
data.
miss reconstruction has been
The performance of the algorithm for ET
widely tested in minimum bias and di-jet events that are not expected to
miss
miss is calculated from the calorimeter
have a genuine ET . In ATLAS ET
cell energies, from reconstructed muons energy and from an estimation of
the energy lost in dead materials. Since it is reconstructed from everything
miss is a complex quantity: particles escaping because
seen in the detector, ET
of the limited coverage of the detector, presence of dead regions and different
miss . A lot of effort has been dedicated
sources of noise can produce fake ET
miss distribution and to apply selection
to understand well the tails in the ET
miss signals.
cuts to remove fake ET
As the ATLAS calorimeters are not compensating, that is the response
to hadronic and electromagnetic particles is different, the calibration of the
miss perfor-
calorimeter cell energies is crucial. With 900 GeV data the ET
mance has been studied and it has been found as expected from simulation
miss calibration has been validated.
at the EM scale.With 7 TeV data the ET
miss performance using different calibrations algorithms has been tested,
ET
confirming the good agreement between data and simulation found at the
EM scale.
The effect of pileup has also been studied in details.
miss commissioning the absolute scale determination
To complete the ET
is needed. This will be possible only when enough statistics of events with
miss will be available.
genuine ET
First, with the already available statistics, using the standard ATLAS
miss scale can be checked from the shape of the W
W → lν selection, the ET
miss and
transverse mass distribution that is calculated from the lepton and ET has only a few percent of background contamination. This method allows to
miss scale with a precision of 3% considering only statistical errors
set the ET
and using less than 50 pb−1 of data at 7 TeV.
Then Z → τ τ events will be used where a Z boson decays into a couple
of τ leptons, then a τ decays into a lepton and neutrinos and the other
one into hadrons and a neutrino. It is possible to reconstruct the invariant
mass of the two taus using the reconstructed lepton, the hadronic part of
miss in the so-called collinear approximation. From the
the τ (τ -jet) and ET
miss scale. A
invariant mass peak position it is possible to determine the ET
detailed study has been done on simulated data to collect a very pure signal
miss
sample with low backgorund contamination. With this method the ET
scale can be fixed with a precision of 6% with an integrated luminosity of
about 100 pb−1 at 10 TeV.
The first chapter of this thesis is dedicated to the physics at LHC: the
theoretical motivati
Tipologia IRIS:
Tesi di dottorato
Elenco autori:
C. Pizio
Link alla scheda completa: