TY  - GEN
TI  - Feasibility Study for the Measurement of pp -> Z(e^+e^-) + b b-bar in Proton-Proton Collisions at 
\sqrt{s} = 8 TeV using a Soft Electron Tagger with the ATLAS Experiment at LHC
Y1  - 2014///
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/17681/
ID  - heidok17681
N2  - In this thesis, data from proton-proton collisions at a center of mass energy of ps = 7 TeV and sqrt{s} = 8 TeV delivered by the Large Hadron Collider and recorded
by the ATLAS experiment in the year 2011 and 2012 are used to develop a timing
monitoring framework for the ATLAS Level-1 Calorimeter trigger system, to develop
a soft electron tagger and carry out a feasibility study for the measurement of
pp ->Z(e^+e^-) + b b-bar process respectively.

The Level-1 Calorimeter trigger is a hardware based trigger with a decision latency
of up to 2.5 ?s. It performs bunch-crossing identification and coarse energy measurement
to make a trigger decision. These operations depend on precise timing
adjustments which are done to achieve a correct sampling of the signal peaks. For
an energy measurement of better than 2% in the trigger, the peak has to be sampled
within +/- 5 ns. Software has been written to monitor the signal peak sampling offsets
for all 7168 channels. This was done by measuring the signal peak location to the
nanosecond level and monitoring this value as a function of time to verify the signal
stability.

Conventional jet based b-tagging methods introduce jet energy scale uncertainties
in measurements. Alternatively electrons from semileptonic decays of b-quarks can
be used for b-tagging, avoiding these uncertainties. The new soft electron tagger
developed in this work extensively uses the precision capabilities of the ATLAS Inner
Detector and electromagnetic calorimeter system. Signal and background sources
identified with Monte Carlo samples were trained with a multivariate boosted decision
tree classifier, through supervised learning. The electron identification responses
of signal samples were verified by statistically extracting signal distributions from
J/psi->e^+e^- and Z -> e^+e^- enriched data samples. Efficiency and systematics of
the new soft electron tagger were also estimated using J/psi ->e^+e^- enriched data
samples.

A feasibility study for the measurement of pp->Z(e^+e^-)+b b-bar process using the soft
electron tagger also has been carried out. Along with the newly developed soft electron
tagger, charge combinations as well as kinematic distributions of soft-electron
pairs have been used to create regions which are enhanced in the signal with a
relatively large signal to background ratio.
A1  - Narayan, Rohin Thampilali
AV  - public
ER  -