## Publicly Accessible Penn Dissertations

2020

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

Physics & Astronomy

Ira J. Kroll

#### Abstract

This thesis presents two analyses that involve the identification of hadronic jets produced by the fragmentation of $b$-quarks or $b$-jets''.

The identification exploits the hard fragmentation of $b$-quarks and relatively long lifetime of $B$ hadrons.

The first analysis is the calibration of the efficiency of the $MV2c10$ $b$-jet identification algorithm using a sample of $b$-jets with muons from $B$ hadron decays and a kinematic property of these jets knows as \ptrel'', which is constructed from the muons.

This analysis was performed using 68 \ifb\ of data collected at $\sqrt{s} = 13$ \TeV\ with the ATLAS detector during Run 2 of the Large Hadron Collider.

Improvements in the methods of this calibration have led to a reduction by more than an order of magnitude in the uncertainty of earlier measurements of $b$-jet tagging efficiency using this approach.

This work included substantial contributions to the software and computing framework used to the study the identification of jets produced by heavy flavor decay; these contributions are described herein.

The second analysis is a search for electroweakly-produced supersymmetric partners of the gauge bosons or gauginos''.

This search uses 140 \ifb\ of data collected at $\sqrt{s} = 13$ \TeV\ with the ATLAS detector during Run 2 of the Large Hadron Collider.

My work focused on developing a new signal region that targeted final states specifically containing two $b$-jets and two light-quark jets.

As part of this optimization, I examined different supersymmetric scenarios and explored alternative techniques for estimating the Standard Model backgrounds.

Based on preliminary results, in the wino-bino scenario, this search is expected to provide sensivity to charginos with masses up to $\sim1$ \TeV.

For a scenario in the general-gauge-mediation model (where higgsino becomes the next-lightest SUSY particle), this search will provide sensitivity for higgsinos with masses up to 600 \GeV\ (discovery) or 800 \GeV\ (exclusion) for most of the possible $Z/h$ branching ratios.

Finally, the sensitivity to the scenarios where higgsino is next-lightest and bino is the lightest SUSY particle has been studied, on which no explicit exclusion has been reported yet by the searches in LHC.

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