Convergence of interference term at next-to-next-to-leading order in Higgs boson to b bbar decay

Abstract

Higgs boson decay to bottom, anti-bottom quarks is the major decay channel due to the fact that these quarks have a relatively high mass and the Higgs coupling to a particle is proportional to its mass. This process is difficult to detect experimentally because of the jets produced by the quarks. In computations of this decay at next-to-next-to-leading order (NNLO), there is a specific term which has been claimed to be finite on its own and negligible. This term corresponds to the interference between two specific processes, firstly, the Higgs coupling to a top-quark loop, from which two gluons are produced and one of them produces a pair of bottom quarks. The other diagram being Higgs boson decay to bottom anti-bottom quarks, and emission of a gluon from one of these particles.

The aim of this paper is twofold: firstly, to show that this term is finite on its own by means of theoretical arguments as well as by analysis of numerical results. Secondly, to check that this term is negligible as it has been claimed.

Analyses of numerical results indicates that the term is finite, but its contribution is bigger than the current theoretical uncertainty. Thus, it is not negligible.

Popular Abstract

Particle physics is concerned with the small particles that all things around us are composed of. So, in a sense, it aims to find out what are the Lego bricks building up the universe. This is not an easy task and, for decades, scientists have devoted a lot of time and work to it. For instance, in the 19th century it was believed that the fundamental piece, our Lego brick, if you wish, was the atom. However, later on, when people were shooting things at a thin golden sheet, they found out that that was actually not quite true. In fact, the atom is made up of a positively charged nucleus and negatively charged particles, electrons, going around. Later on, yet again, scientists found out that the nucleus is made up of more fundamental particles - up and down quarks - and up to this point, it has been experimentally shown that these are fundamental particles.

More generally, it has been found that there are a total of 12 fundamental particles which matter consists of also known as fermions, and 5 bosons or force carriers, which act like messengers between the other particles. Understanding how these bosons and fermions interact answers questions like, for example, why most matter around us is made up of only 3 fundamental particles. As it turns out, not all particles are equally long-lived and how long-lived they are can be understood from how they interact. For example, the analogue of the electron, but slightly heavier, is called the muon and it only lives a fraction of a second!
Afterwards, the muon decays into an electron and two very light particles known as neutrino.

To calculate how likely a way of decaying is, we normally make use of so-called Feynman diagrams. Feynman diagrams describe interactions through lines and points, where lines represent particles moving in space and points represent the interactions between particles. Counting the number of points in the Feynman diagram gives an idea of how likely the process is. Generally, the more complicated the diagram is the less likely it is that the process occurs.

But, when calculating the likelihood of some slightly more complicated interactions, the probability goes to infinity. This is not very good, but there are some known ways of solving this issue.

In my thesis, I focus on a particular decay of the Higgs boson - this heavy boson gives mass to other particles and decays quickly. More precisely, my thesis studies whether this particular decay is finite and how large it is, compared to the simplest diagram of the decay. In general, understanding these type of slightly-more-complicated diagram helps creating a better understanding of one of the Lego bricks. For my thesis, the Lego brick of interest is the Higgs boson.

• author: Martin Viveros Diaz Oliver, Cristina
• supervisor: Rikkert Frederix
• organization: Department of Physics; Particle and nuclear physics
• course: FYSK04 20241
• year: 2024
• type: M2 - Bachelor Degree
• subject: Physics and Astronomy
• keywords: Higgs decay, NNLO, madgraph
• language: English
• id: 9161515
• date added to LUP: 2024-06-13 14:43:04
• date last changed: 2024-06-13 14:43:04