Baryon number violating neutron decays to dark matter via the emission of a π 0 meson, η meson or photon
(2024) FYSK04 20241Department of Physics
Particle and nuclear physics
- Abstract
- The existence of a baryon number violating process is one of Shakarov's conditions to explain the observed baryon asymmetry in the universe. The Standard Model is nearly symmetric with respect to the baryon number, and hence we are motivated to look for physics beyond the Standard Model. In this thesis, we consider an effective field theory operator that couples the neutron to a proposed dark fermion $X$, leading to decay channels containing mesons and photons. The unpolarized width for these decays is computed analytically. The model is subsequently implemented in \verb|CalcHEP| via the definition of a new effective vertex. This allows for a Monte Carlo simulation of the three-body decay n → X + γγ, where the off-shell meson decays into a... (More)
- The existence of a baryon number violating process is one of Shakarov's conditions to explain the observed baryon asymmetry in the universe. The Standard Model is nearly symmetric with respect to the baryon number, and hence we are motivated to look for physics beyond the Standard Model. In this thesis, we consider an effective field theory operator that couples the neutron to a proposed dark fermion $X$, leading to decay channels containing mesons and photons. The unpolarized width for these decays is computed analytically. The model is subsequently implemented in \verb|CalcHEP| via the definition of a new effective vertex. This allows for a Monte Carlo simulation of the three-body decay n → X + γγ, where the off-shell meson decays into a pair of photons. The narrow width of the mesons is seen in the invariant mass reconstruction of the photons in this channel. The case of a small mass gap between the neutron and the decay products is considered, where these channels are kinematically forbidden for bound neutrons in stable nuclei. We conclude that the analyzed decays are less experimentally constrainted for free neutrons, and argue that searches for exotic neutron decays with a small mass gap could take place at the upcoming HIBEAM and NNBAR experiments at the European Spallation Source. (Less)
- Popular Abstract
- Everything around us is made of matter, consisting of three fundamental building blocks: the positively charged proton, the negatively charged electron and the neutron without any charge. All types of matter have twins with opposite electric charge, called antimatter. The three fundamental building blocks of antimatter are the negatively charged antiproton, the positively charged positron and the neutral antineutron. When a matter and antimatter particle come together, they annihilate each other in a big burst of energy.
The current leading theory of particle physics, called the Standard Model, is nearly symmetric with respect to matter and antimatter. This means that every interaction allowed within the Standard Model creates nearly... (More) - Everything around us is made of matter, consisting of three fundamental building blocks: the positively charged proton, the negatively charged electron and the neutron without any charge. All types of matter have twins with opposite electric charge, called antimatter. The three fundamental building blocks of antimatter are the negatively charged antiproton, the positively charged positron and the neutral antineutron. When a matter and antimatter particle come together, they annihilate each other in a big burst of energy.
The current leading theory of particle physics, called the Standard Model, is nearly symmetric with respect to matter and antimatter. This means that every interaction allowed within the Standard Model creates nearly equal amounts of matter and antimatter. However, in everyday life we only encounter matter. After all, if there would be any antimatter around us, it would collide with the ordinary matter and annihilate into pure energy.
One of the current questions in physics is why there is so much matter, and so little antimatter in the universe. This observation has led physicists to speculate that there might be interactions beyond the Standard Model. These interactions would violate the matter-antimatter symmetry, allowing for a process that creates an excess of matter.
In this thesis, we consider such a process and analyze its consequences. Namely, we consider a model where the neutron decays to a new stable particle and an unstable particle, which can in turn decay to rays of energy. The new particle would not interact with particles in any other way, and hence it would create a different type of matter called dark matter.
This process would destroy a neutron, leading to matter disappearing instead of appearing. However, in the dense conditions of the early universe, the inverse of this process could occur frequently, leading to the creation of matter. In contrast, the process would be rare in the conditions of a laboratory. Many experiments have searched for such exotic neutron decays, putting very strict experimental limits on this model.
However, most of these experiments deal with \textit{bound} neutrons, neutrons tied to other matter. If the difference between the mass of the neutron and the mass of the particles that it decays into is small, this decay cannot happen for bound neutrons. In contrast, the decay is possible for free neutrons.
The upcoming HIBEAM/NNBAR experiments at the European Spallation Source (ESS) analyze large amounts of free neutrons, and hence could observe this decay. In this thesis, we consider this case of a small mass difference and compute how rare the processes allowed by the model would be under this condition. Additionally, we run numerical simulations which allows us to see what it would be like to observe these interactions in experiments. We conclude that this model is a candidate for observation at HIBEAM/NNBAR and that the possibility of observing such exotic neutron decays should be further investigated. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9163796
- author
- Nieuwenhuis, Rutger LU
- supervisor
- organization
- course
- FYSK04 20241
- year
- 2024
- type
- M2 - Bachelor Degree
- subject
- keywords
- baryon number violation, exotic neutron decays, dark matter, European Spallation Source, HIBEAM, NNBAR
- language
- English
- id
- 9163796
- date added to LUP
- 2024-06-14 14:50:00
- date last changed
- 2024-06-14 14:50:00
@misc{9163796,
abstract = {{The existence of a baryon number violating process is one of Shakarov's conditions to explain the observed baryon asymmetry in the universe. The Standard Model is nearly symmetric with respect to the baryon number, and hence we are motivated to look for physics beyond the Standard Model. In this thesis, we consider an effective field theory operator that couples the neutron to a proposed dark fermion $X$, leading to decay channels containing mesons and photons. The unpolarized width for these decays is computed analytically. The model is subsequently implemented in \verb|CalcHEP| via the definition of a new effective vertex. This allows for a Monte Carlo simulation of the three-body decay n → X + γγ, where the off-shell meson decays into a pair of photons. The narrow width of the mesons is seen in the invariant mass reconstruction of the photons in this channel. The case of a small mass gap between the neutron and the decay products is considered, where these channels are kinematically forbidden for bound neutrons in stable nuclei. We conclude that the analyzed decays are less experimentally constrainted for free neutrons, and argue that searches for exotic neutron decays with a small mass gap could take place at the upcoming HIBEAM and NNBAR experiments at the European Spallation Source.}},
author = {{Nieuwenhuis, Rutger}},
language = {{eng}},
note = {{Student Paper}},
title = {{Baryon number violating neutron decays to dark matter via the emission of a π 0 meson, η meson or photon}},
year = {{2024}},
}