Estimation of the fake background for the doubly charged Higgs boson production in the ATLAS experiment
(2025) FYSM64 20251Particle and nuclear physics
Department of Physics
- Abstract
- The existence of doubly charged Higgs bosons (H±±) is predicted by several theories beyond the Standard Model that aim to explain the origin of neutrino masses. These particles are expected to decay into same-sign lepton pairs H±± → ℓ±ℓ±. At the LHC, they are produced predominantly via the Drell–Yan process, resulting in four-lepton final states. Due to the rarity of events involving doubly charged Higgs bosons, an accurate estimation of background contributions is crucial. This thesis focuses on estimating the fake-lepton background using the fake factor method. The analysis is based on 13 TeV ATLAS Open Data events with exactly one lepton, corresponding to an integrated luminosity of 10.06 ± 0.37 fb−1. Separate sets of fake factors were... (More)
- The existence of doubly charged Higgs bosons (H±±) is predicted by several theories beyond the Standard Model that aim to explain the origin of neutrino masses. These particles are expected to decay into same-sign lepton pairs H±± → ℓ±ℓ±. At the LHC, they are produced predominantly via the Drell–Yan process, resulting in four-lepton final states. Due to the rarity of events involving doubly charged Higgs bosons, an accurate estimation of background contributions is crucial. This thesis focuses on estimating the fake-lepton background using the fake factor method. The analysis is based on 13 TeV ATLAS Open Data events with exactly one lepton, corresponding to an integrated luminosity of 10.06 ± 0.37 fb−1. Separate sets of fake factors were measured for electrons and muons in bins of transverse momentum and pseudorapidity to account for their kinematic dependence. The method was validated by closure tests performed separately for each lepton flavor in regions orthogonal to those used for measurement, but with the same lepton multiplicity. The predicted fake background shows agreement with the observed data at low pT, while discrepancies appear at high pT, likely due to unquantified systematic uncertainties. (Less)
- Popular Abstract
- For thousands of years, humans have tried to understand the way our world is structured. The idea that everything is made up of a set of fundamental particles was first introduced by Leucippus and his student Democritus, according to whom our world consists of atoms. Nowadays, we know that an atom is not a fundamental particle, but it consist of a nucleus and a number of electrons that are bound to it. The nucleus itself has an inner structure, since it is made of protons and neutrons, which are also made up of particles, called quarks.
Our current understanding of the world’s structure is based on a number of theories that altogether constitute the Standard Model of particle physics. With the discovery of the Higgs boson at the LHC... (More) - For thousands of years, humans have tried to understand the way our world is structured. The idea that everything is made up of a set of fundamental particles was first introduced by Leucippus and his student Democritus, according to whom our world consists of atoms. Nowadays, we know that an atom is not a fundamental particle, but it consist of a nucleus and a number of electrons that are bound to it. The nucleus itself has an inner structure, since it is made of protons and neutrons, which are also made up of particles, called quarks.
Our current understanding of the world’s structure is based on a number of theories that altogether constitute the Standard Model of particle physics. With the discovery of the Higgs boson at the LHC (Large Hadron Collider) in 2012, the Standard Model was able to provide a successful description of most of the experimental data. However, with the experimental observation of neutrino oscillations, it became obvious that there are phenomena that cannot be explained by the Standard Model. Neutrinos are particles that, according to the Standard Model, are expected to be mass-less, but neutrino oscillations require the neutrinos to have mass, prompting particle physicists to explore alternative explanations for the origin of neutrinos’ mass.
Various theories beyond the Standard Model try to describe the origin of the neutrino mass assuming the existence of doubly charged Higgs bosons, noted as H±±, decaying into same-sign leptons. Doubly charged Higgs bosons can be produced in proton-proton collisions, like the ones occurring at the LHC. The proton consists of three quarks, called valence quarks, as well as virtual pairs of quarks and anti-quarks, called sea quarks. Hence, during proton collisions, the constituent quarks of the protons interact, and through those interactions new particles are produced. The interaction between a quark and its corresponding anti-quark is used for the doubly charged Higgs bosons pair production.
The doubly charged Higgs bosons are expected to be extremely unstable particles, thus they will not be observed directly. Instead, they will be observed through their decays, particularly through their decays into same-sign lepton pairs. The Standard Model consists of various processes that lead to the same final state. The detected measurements which do not correspond to the events that we are searching for are called background. To ensure that we have found a new particle, we should exclude the background measurements from the signal. The main
focus of this research project is the estimation of the background component originating from particles that are misidentified as charged leptons. This estimation will be carried out with a data-driven approach, known as the fake factor method. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9201294
- author
- Floros, Georgios LU
- supervisor
-
- Else Lytken LU
- Lara Calic LU
- organization
- course
- FYSM64 20251
- year
- 2025
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- doubly charged Higgs boson, ATLAS, LHC, fake factor method
- language
- English
- id
- 9201294
- date added to LUP
- 2025-06-18 09:20:23
- date last changed
- 2025-06-18 09:20:23
@misc{9201294,
abstract = {{The existence of doubly charged Higgs bosons (H±±) is predicted by several theories beyond the Standard Model that aim to explain the origin of neutrino masses. These particles are expected to decay into same-sign lepton pairs H±± → ℓ±ℓ±. At the LHC, they are produced predominantly via the Drell–Yan process, resulting in four-lepton final states. Due to the rarity of events involving doubly charged Higgs bosons, an accurate estimation of background contributions is crucial. This thesis focuses on estimating the fake-lepton background using the fake factor method. The analysis is based on 13 TeV ATLAS Open Data events with exactly one lepton, corresponding to an integrated luminosity of 10.06 ± 0.37 fb−1. Separate sets of fake factors were measured for electrons and muons in bins of transverse momentum and pseudorapidity to account for their kinematic dependence. The method was validated by closure tests performed separately for each lepton flavor in regions orthogonal to those used for measurement, but with the same lepton multiplicity. The predicted fake background shows agreement with the observed data at low pT, while discrepancies appear at high pT, likely due to unquantified systematic uncertainties.}},
author = {{Floros, Georgios}},
language = {{eng}},
note = {{Student Paper}},
title = {{Estimation of the fake background for the doubly charged Higgs boson production in the ATLAS experiment}},
year = {{2025}},
}