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Search for Higgs-like bosons through optimization of top-quark modelling

Lopez, Rafael Antonio LU (2021) FYSM60 20202
Particle Physics
Department of Physics
Abstract
Accurate estimations of background processes associated with top-quarks are vital to studies concerned with finding new physics at the Large Hadron Collider (LHC)at CERN. Search for Higgs-like bosons in the ATLAS experiment at LHC was performed by optimising the use of b-jet tagging algorithms and improving on tt backgroundmodelling. Improved modelling was achieved using two different methods, tt modelling correction and data-driven tt estimation. The correction method showed slight improvements in all regions of analysis. Furthermore, the data-driven method showed promising results reconstructing well-behaved kinematic variables, although the uncertainty was considerable.
Popular Abstract
People often talk about the importance of colliders when creating new and exciting particles. True enough, without them, modern particle physics as we know it would not exist, and the Higgs boson would never have been verified. However, there is one crucial aspect which is often overlooked in popular media, and that is computer simulations.

It all boils down to the question: how do we know what we see is truly what we believe it to be? We know now from observations and established theories that many particles share similar signatures. It would be easy to mistake one particle for another.

The solution is found in the form of extensive Monte-Carlo simulations. By generating the expected outcome on a computer using state-of-the-art... (More)
People often talk about the importance of colliders when creating new and exciting particles. True enough, without them, modern particle physics as we know it would not exist, and the Higgs boson would never have been verified. However, there is one crucial aspect which is often overlooked in popular media, and that is computer simulations.

It all boils down to the question: how do we know what we see is truly what we believe it to be? We know now from observations and established theories that many particles share similar signatures. It would be easy to mistake one particle for another.

The solution is found in the form of extensive Monte-Carlo simulations. By generating the expected outcome on a computer using state-of-the-art physics simulators, we can make an educated guess to what we would find in a particular region of phase-space (a region of space with a fixed set of parameters). By comparing our expectations (in the form of simulations) to what we observe, we can learn a lot from our surroundings, by either actively looking for a theorised particle or by stumbling upon an anomaly. The former is, for instance, how the Higgs particle was finally verified.

Alas, it is not always as straight forward as that. Some interactions may be too difficult to compute, and other times they are not well understood. Such problems may result in
unintended discrepancies between data and simulations which can be wildly misleading. This would be similar to reading ancient Greek using a faulty translator - nothing would make sense!

When in doubt, we go back to the basics. When we notice obvious discrepancies, the algorithm is sent back to the workshop where we analyse the issue and make attempts to adjust it. This is done by testing our algorithms in regions of phase-space, which we understand particularly well. After that, we are ready to try again!

In this study, the search for Higgs-like particles was attempted by improving the modelling of certain top-quark processes. While the methods implemented showed some improvements to the modelling, there is certainly room for improvement. In the future, we hope to develop these methods in more detail using various approaches and perhaps in different conditions. (Less)
Please use this url to cite or link to this publication:
author
Lopez, Rafael Antonio LU
supervisor
organization
course
FYSM60 20202
year
type
H1 - Master's Degree (One Year)
subject
keywords
ttbar, top quark modelling, BSM, 2HDM+S, Higgs-like bosons, ATLAS, HWW, XSh, top estimation, top remodelling
language
English
id
9039396
date added to LUP
2021-02-04 11:47:52
date last changed
2021-06-07 09:53:09
@misc{9039396,
  abstract     = {{Accurate estimations of background processes associated with top-quarks are vital to studies concerned with finding new physics at the Large Hadron Collider (LHC)at CERN. Search for Higgs-like bosons in the ATLAS experiment at LHC was performed by optimising the use of b-jet tagging algorithms and improving on tt backgroundmodelling. Improved modelling was achieved using two different methods, tt modelling correction and data-driven tt estimation. The correction method showed slight improvements in all regions of analysis. Furthermore, the data-driven method showed promising results reconstructing well-behaved kinematic variables, although the uncertainty was considerable.}},
  author       = {{Lopez, Rafael Antonio}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Search for Higgs-like bosons through optimization of top-quark modelling}},
  year         = {{2021}},
}