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Resolving Quasi-Degenerate Higgs Bosons

Lindberg, Gustav LU (2021) FYTK02 20211
Theoretical Particle Physics
Abstract
Many models beyond the Standard Model that predict the existence of multiple Higgs bosons. In general, some of these additional Higgs bosons could be quasi-degenerate in mass either to each other or to the observed 125 GeV Higgs boson. The goal of this thesis is to study under which circumstances we can resolve such Higgs bosons. We first make the simplifying assumption that the observed and predicted invariant mass distributions are exact Gaussians, and use a $\chi^2$ test to determine how closely a combination of several particles resembles a single particle. We find that quasi-degenerate Higgs bosons with similar couplings are unlikely to be resolved by the experiments if their mass separation is less than twice the experimental... (More)
Many models beyond the Standard Model that predict the existence of multiple Higgs bosons. In general, some of these additional Higgs bosons could be quasi-degenerate in mass either to each other or to the observed 125 GeV Higgs boson. The goal of this thesis is to study under which circumstances we can resolve such Higgs bosons. We first make the simplifying assumption that the observed and predicted invariant mass distributions are exact Gaussians, and use a $\chi^2$ test to determine how closely a combination of several particles resembles a single particle. We find that quasi-degenerate Higgs bosons with similar couplings are unlikely to be resolved by the experiments if their mass separation is less than twice the experimental resolution. We validate our findings by running Monte Carlo simulations of several important Higgs processes, and we find that the Gaussian approximation provides a decent description of when quasi-degenerate particles are resolvable. We finally consider interference effects in order to study cases where Higgs bosons have a much larger decay width than the Standard Model Higgs boson. We find that interference can make it significantly easier or significantly harder to resolve the two Higgs bosons, depending on the parameters of the model. (Less)
Popular Abstract
Currently, scientists have managed to explain most things that happen in nature with only a limited number of fundamental particles. However, some things remain unexplained, such as dark matter. Dark matter is matter that has not been observed but is still known to exist and have mass because of the gravitational force it exerts on stars and galaxies. Dark matter is one of the greatest mysteries in physics since we know almost nothing about it. This, together with other unexplained phenomena, seems to be an indication that there are more particles than those discovered so far.

The latest fundamental particle that has been discovered is the so-called Higgs boson, which explains why other particles have mass. Imagine that particles are... (More)
Currently, scientists have managed to explain most things that happen in nature with only a limited number of fundamental particles. However, some things remain unexplained, such as dark matter. Dark matter is matter that has not been observed but is still known to exist and have mass because of the gravitational force it exerts on stars and galaxies. Dark matter is one of the greatest mysteries in physics since we know almost nothing about it. This, together with other unexplained phenomena, seems to be an indication that there are more particles than those discovered so far.

The latest fundamental particle that has been discovered is the so-called Higgs boson, which explains why other particles have mass. Imagine that particles are like balloons. If you leave them alone, they will fly away because they are so light. Now imagine Higgs bosons are like stones that you attach to some of these balloons. The balloons that you attached stones to will become heavier and not fly away. This corresponds to particles such as protons and electrons having mass. However, balloons that do not have any stones attached to them still fly away. An example of this is light, which does not interact with the Higgs boson and therefore has no mass.

However, so far, experiments have only detected one Higgs boson. If other Higgs bosons exist, there must be a reason why experiments have not detected them. One reason could be that the new Higgs bosons have masses very similar to the one already detected, meaning that even though they in fact are different, they might still look identical to the experiments. The goal of this thesis is to determine exactly how similar these new Higgs bosons can be to the one already found, while still not being detected as a separate particle. Setting limits on the properties of the new Higgs bosons can be important for scientists who want to search for them, and searching for these new Higgs bosons could be a way to indirectly search for a way to explain dark matter.

Therefore, this thesis can be useful to the search for additional Higgs bosons, which might be useful for solving one of the greatest mysteries in physics, namely dark matter. (Less)
Please use this url to cite or link to this publication:
author
Lindberg, Gustav LU
supervisor
organization
course
FYTK02 20211
year
type
M2 - Bachelor Degree
subject
keywords
Particle physics, Higgs boson, Beyond the Standard Model
language
English
id
9053521
date added to LUP
2021-06-14 18:45:11
date last changed
2021-06-14 18:52:41
@misc{9053521,
  abstract     = {{Many models beyond the Standard Model that predict the existence of multiple Higgs bosons. In general, some of these additional Higgs bosons could be quasi-degenerate in mass either to each other or to the observed 125 GeV Higgs boson. The goal of this thesis is to study under which circumstances we can resolve such Higgs bosons. We first make the simplifying assumption that the observed and predicted invariant mass distributions are exact Gaussians, and use a $\chi^2$ test to determine how closely a combination of several particles resembles a single particle. We find that quasi-degenerate Higgs bosons with similar couplings are unlikely to be resolved by the experiments if their mass separation is less than twice the experimental resolution. We validate our findings by running Monte Carlo simulations of several important Higgs processes, and we find that the Gaussian approximation provides a decent description of when quasi-degenerate particles are resolvable. We finally consider interference effects in order to study cases where Higgs bosons have a much larger decay width than the Standard Model Higgs boson. We find that interference can make it significantly easier or significantly harder to resolve the two Higgs bosons, depending on the parameters of the model.}},
  author       = {{Lindberg, Gustav}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Resolving Quasi-Degenerate Higgs Bosons}},
  year         = {{2021}},
}