Precision Standard Model Phenomenology for High Energy Processes

Abstract

The present status of particle physics is that the Standard Model has been completed with the discovery of the
Higgs boson in 2012, but there is a multitude of phenomena in nature which is not accounted for by this model.
Researchers are investigating possibilities for detecting new physics at the current particle physics facilities, with
the Large Hadron Collider (LHC) at the frontier. As no significant sign of new physics has been observed as of
today, precision phenomenology becomes increasingly important. This thesis and the four papers included in it
contribute to this field of precision predictions for various important processes at the LHC.

In paper I and paper IV, the Drell­-Yan process is investigated, and specifically, the decay coefficients which
parameterize the spherical distribution of the outgoing leptons in the process. In the first work, we investigate
the next­-to­-leading­-order (NLO) electroweak corrections to the coefficients of the neutral­-current process. In the
second work, a similar study, but including also next­-to­-next­-to­-leading­-order quantum chromodynamic (QCD)
corrections, is performed for the decay coefficients of the charged-­current Drell­-Yan process. The latter process
and the corresponding coefficients are of great importance for measuring the W ­boson mass at the LHC.

In paper II, the top quark pair production and the spin correlations for the process are investigated. The spin
correlation information of the top quarks may reveal underlying new physics when probed at high precision.
Therefore, this work computes approximate complete­-NLO corrections, including electroweak corrections to the
spin correlation coefficients and related leptonic distributions, contributing to the state-­of­-the­-art high precision
Standard Model predictions for these observables.

Finally, paper III is the theoretical base of a crucial improvement to matrix-­element generators. We propose
in this paper to utilize a next­-to­-leading­-colour truncation of the colour matrix in the large­-Nc limit, in order to
reduce the complexity of the cross section computation when a large number of QCD patrons are involved in the
process. The results suggest that such a truncation of the colour expansion will facilitate for efficient computation
of multi-­jet events, which are a dominant background for many important processes and new physics searches at
hadron colliders, such as the LHC.

Abstract (Swedish)

The present status of particle physics is that the Standard Model has been completed with the discovery of the
Higgs boson in 2012, but there is a multitude of phenomena in nature which is not accounted for by this model.
Researchers are investigating possibilities for detecting new physics at the current particle physics facilities, with
the Large Hadron Collider (LHC) at the frontier. As no significant sign of new physics has been observed as of
today, precision phenomenology becomes increasingly important. This thesis and the four papers included in it
contribute to this field of precision predictions for various important processes at the LHC.
In paper I and paper IV, the Drell­Yan process is investigated, and specifically, the decay coefficients which
parameterize the spherical distribution of the outgoing leptons in the process. In the first work, we investigate
the next­to­leading­order (NLO) electroweak corrections to the coefficients of the neutral­current process. In the
second work, a similar study, but including also next­to­next­to­leading­order quantum chromodynamic (QCD)
corrections, is performed for the decay coefficients of the charged­current Drell­Yan process. The latter process
and the corresponding coefficients are of great importance for measuring the W ­boson mass at the LHC.
In paper II, the top quark pair production and the spin correlations for the process are investigated. The spin
correlation information of the top quarks may reveal underlying new physics when probed at high precision.
Therefore, this work computes approximate complete­NLO corrections, including electroweak corrections to the
spin correlation coefficients and related leptonic distributions, contributing to the state­of­the­art high precision
Standard Model predictions for these observables.
Finally, paper III is the theoretical base of a crucial improvement to matrix­element generators. We propose
in this paper to utilize a next­to­leading­colour truncation of the colour matrix in the large­N C limit, in order to
reduce the complexity of the cross section computation when a large number of QCD patrons are involved in the
process. The results suggest that such a truncation of the colour expansion will facilitate for efficient computation
of multi­jet events, which are a dominant background for many important processes and new physics searches at
hadron colliders, such as the LHC.

• author: Vitos, Timea
• supervisor: Rikkert Frederix; Johan Bijnens
• opponent: Professor Vicini, Alessandro, Università degli Studi di Milano Statale, Italy.
• organization: Particle and nuclear physics
• publishing date: 2023-05-22
• type: Thesis
• publication status: published
• subject: Subatomic Physics
• keywords: precision phenomenology, Standard Model, NLO electroweak, decay coefficients, Drell-Yan process, top quark spin correlations, colour expansion, large-Nc limit, precision phenomenology, Standard Model, NLO electroweak, decay coefficients, Drell-Yan, top quark spin correlations, colour expansion, large-Nc truncation, Fysicumarkivet A:2023:Vitos
• pages: 228 pages
• defense location: Lundmarksalen, Astronomihuset, Sölvegatan 27, Lund.
• defense date: 2023-06-16 10:00:00
• ISBN: 978-91-8039-667-7
• ISBN: 978-91-8039-668-4
• language: English
• LU publication?: yes
• id: f947ff48-2a19-4cec-b6b8-c65c299c688e
• date added to LUP: 2023-05-16 09:09:01
• date last changed: 2023-05-30 14:39:24