INTURN 24-9

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Lepton Number Violation and the Baryon Asymmetry of the Universe

Mentor

Sebastián Urrutia Quiroga (email: suq90@uw.edu)

Prerequisites

The project will require getting involved with different software. While coding skills are not required (but certainly desired and highly appreciated), students must be comfortable working with a computer, especially for programming tasks.

What Students Will Do

Students are expected to get familiar with the big picture of the project to rapidly move forward to utilizing some standard computer tools in particle physics [4], such as Madgraph or Delphes, for event simulation and analysis. These tools are open-source, and there is a large, dedicated community to help solve installation and compatibility problems.

Expected Project Length

One year

Figure for INTURN 24-2b

Image Description and Credits: We live in a matter-dominated Universe. It is a mystery why this asymmetry exists. Leptogenesis is a promising model that could explain this imbalance providing that lepton-number conservation can be violated in nature. Credit: Symmetry Magazine / Sandbox Studio, Chicago

Project Description

Exploring lepton number violation (LNV) at colliders is crucial for a deeper understanding of particle physics. This search is not merely a quest for a rare phenomenon; it holds the key to understanding the intrinsic nature of neutrinos—their masses and fundamental properties. Observing LNV could provide conclusive evidence that neutrinos are Majorana particles, a type of particle that is its own antiparticle, offering a plausible explanation for their tiny masses through the seesaw mechanism [1]. This would not only revolutionize our understanding of the neutrino’s identity—whether it is a Dirac or Majorana particle—but also shed light on the asymmetry between matter and antimatter in the universe [2]. The potential discovery of LNV processes is a critical step that guides us toward a more complete theory of fundamental particles and interactions, underpinning the very structure of matter and the evolution of the cosmos itself.

Long-lived particles (LLPs) are new, beyond the SM (BSM) states that travel a substantial distance between creation and decay in collider systems, presenting distinct experimental signatures. The experimental signatures of LLPs are particularly interesting. In contrast to promptly decaying particles, LLPs can decay after flying some distance from the primary interaction point. This produces a displaced vertex, with decay products including charged and neutral SM particles (e.g., charged leptons, light neutrinos, and pions). This kind of displaced signature is most commonly associated with LLPs and is very different from the usual SM processes studied at colliders; if observed, constitutes a striking “smoking gun” of new physics.

Literature focusing on the interplay between LNV and mechanisms responsible for the matter/anti-matter asymmetry of the universe has shown the potential reach of LLP searches to regions that are compatible with current experimental limits for the baryon asymmetry of the universe [3]. The primary objective of this project is to perform a collider study to determine how realistic these statements are and how much the parameter space can be restricted by them.

References

[1]    Lepton Number Violation: Seesaw Models and Their Collider Tests, Y. Cai et al [1711.02180]
[2]    Falsifying High-Scale Leptogenesis at the LHC, F. Deppisch, J. Harz, M. Hirsch [1312.4447]
[3]    TeV-scale Lepton Number Violation: Connecting Leptogenesis, 0νββ Decay, and Colliders, J. Harz et al. [2106.10838]
[4]    Computer Tools in Particle Physics, A. Vicente [1507.06349]


In collaboration with Vincenzo Cirigliano (cirigv@uw.edu)