Measurement of the Production Cross Section of Four Top Quarks in Proton-Proton Collisions at 13 TeV
Thesis Defense
9:00 am –
10:30 am
Jorgensen Hall Room: 207
Contact:
Physics Department, (402) 472-2770, paoffice@unl.edu
Caleb Fangmeier
Advisor: Frank Golf
ABSTRACT:
The field of particle physics involves not only searches for new particles and measurements of their interactions, but also the design and construction of advanced particle detectors. This thesis presents the measurement of the production cross section of four top quarks in proton-proton collisions at a center-of-mass energy of 13 TeV using data recorded by the CMS experiment over 2016, 2017, and 2018. Four top quark production is a rare Standard Model process with a cross section predicted to be $12.0^{+2.2}_{-2.5}$ fb using next-to-leading order calculations. Its measurement can be used to constrain the top Yukawa coupling as well as various theories beyond the standard model.
This analysis specifically examines the final state with a same-sign pair of leptons, notable for being a final state with relatively few standard model background events. A boosted decision tree is utilized to discriminate four top quark events from background events. The four top quark production cross section is measured to be $12.6^{+5.8}_{-5.2}$ fb, consistent with the standard model prediction.
This thesis also describes efforts made in the construction and testing of silicon pixel detector modules used in the Phase I upgrade of the CMS pixel detector. Specifically, the role of software automation of a robotic gantry used in the assembly will be discussed, as well as efforts towards the construction of a high precision silicon strip detector based telescope.
Advisor: Frank Golf
ABSTRACT:
The field of particle physics involves not only searches for new particles and measurements of their interactions, but also the design and construction of advanced particle detectors. This thesis presents the measurement of the production cross section of four top quarks in proton-proton collisions at a center-of-mass energy of 13 TeV using data recorded by the CMS experiment over 2016, 2017, and 2018. Four top quark production is a rare Standard Model process with a cross section predicted to be $12.0^{+2.2}_{-2.5}$ fb using next-to-leading order calculations. Its measurement can be used to constrain the top Yukawa coupling as well as various theories beyond the standard model.
This analysis specifically examines the final state with a same-sign pair of leptons, notable for being a final state with relatively few standard model background events. A boosted decision tree is utilized to discriminate four top quark events from background events. The four top quark production cross section is measured to be $12.6^{+5.8}_{-5.2}$ fb, consistent with the standard model prediction.
This thesis also describes efforts made in the construction and testing of silicon pixel detector modules used in the Phase I upgrade of the CMS pixel detector. Specifically, the role of software automation of a robotic gantry used in the assembly will be discussed, as well as efforts towards the construction of a high precision silicon strip detector based telescope.