Project Details
Description
Abstract
In the past, development of the PYTHIA event generator has mainly concentrated on the physics of proton–proton collisions at high energies, as this is the most important case to modern high energy physics experiments. However, there are situations where more generic beam configurations are relevant. This thesis presents implementations and applications of such processes in PYTHIA. The two applications discussed in this thesis are hadronic rescattering, and hadronic cascades in media. These are developed in Papers I and Iv, while Papers II and III present physics studies of rescattering.
In the past, development of the PYTHIA event generator has mainly concentrated on the physics of proton–proton collisions at high energies, as this is the most important case to modern high energy physics experiments. However, there are situations where more generic beam configurations are relevant. This thesis presents implementations and applications of such processes in PYTHIA. The two applications discussed in this thesis are hadronic rescattering, and hadronic cascades in media. These are developed in Papers I and Iv, while Papers II and III present physics studies of rescattering.
Popular science description
Physics research is about understanding how the universe works on a fundamental level. It tries to address questions such as how do things move, how does electricity work, and why do stars burn.
One deep physics question is what the fundamental building blocks of matter are. If you take a rock and smash it into pieces, then grind the pieces down to specks of dust, and continue breaking the grains of dust into smaller and smaller pieces, will you eventually reach a point where it is no longer possible to break it into smaller bits? Or, given the right tools and technology, will it always possible to break it into smaller pieces? If there are some smallest possible pieces, do they behave similarly to the large things we observe in our everyday lives, or are they very different? The philosophical idea that perhaps the laws of our universe are such that there is some smallest fundamental pieces of matter is called atomism. Over the course of the last couple centuries, humans have discovered that the answer seems to be that atomism is correct, and that there are at least 17 types of fundamental building blocks in our universe. These are called elementary particles, and everything we experience in our everyday lives – rocks, water, air, light, plants, animals, stars – is made from combinations of elementary particles. Particle physics is about studying the properties and behaviours of these elementary particles.
The best description of particle physics that we have today is a theory called the Standard Model. One of the most important questions in science is how do we know what we know? Our theories must predict something about reality, and it must be possible to perform experiments to test whether reality really behaves the way the theory predicts. Otherwise, it is not science, but science fiction. In particle physics, we make predictions by using computer simulations of our theoretical models. These predictions can then be compared to actual data, like the data from experiments at the Large Hadron Collider (LHC) at CERN. One example of such a simulation program is PYTHIA, whose development began in Lund about 40 years ago, and which this thesis revolves around.
There are many unanswered questions in particle physics. One question that a lot of particle physicists are working on these days is what happens when certain particles are put under extreme pressure and heated up to temperatures a 100,000 times warmer than the core of the sun. With what we know today, the most likely answer seems to be that these particles would “melt” into a new state of matter called a quark-gluon plasma (QGP), but we still don’t really understand how this happens, what the properties of this state of matter are, or if it can be used for anything interesting. The desire to learn the answers to questions like these is profound for many people – so much that some are willing to dedicate lifetimes of work and invest billions of euros on developing technology like the LHC that can help us find the answers.
Now, the QGP is so extreme that it evaporates within a fraction of a billionth of a nanosecond, which makes it impossible to detect it directly. Instead, many scientists believe in the QGP hypothesis because it makes certain predictions that turn out to fit really well with data. However, one of the ongoing research programmes in Lund is challenging this hypothesis, and asks whether there are other models that are unrelated to the QGP, but that still can make the same predictions. Building such a model requires a lot of additions to the PYTHIA simulation. The work I have done in Lund has been to make such improvements to PYTHIA, both as a contribution to this bigger project to challenge the QGP paradigm, and as part of other projects. This thesis is the culmination of that work.
One deep physics question is what the fundamental building blocks of matter are. If you take a rock and smash it into pieces, then grind the pieces down to specks of dust, and continue breaking the grains of dust into smaller and smaller pieces, will you eventually reach a point where it is no longer possible to break it into smaller bits? Or, given the right tools and technology, will it always possible to break it into smaller pieces? If there are some smallest possible pieces, do they behave similarly to the large things we observe in our everyday lives, or are they very different? The philosophical idea that perhaps the laws of our universe are such that there is some smallest fundamental pieces of matter is called atomism. Over the course of the last couple centuries, humans have discovered that the answer seems to be that atomism is correct, and that there are at least 17 types of fundamental building blocks in our universe. These are called elementary particles, and everything we experience in our everyday lives – rocks, water, air, light, plants, animals, stars – is made from combinations of elementary particles. Particle physics is about studying the properties and behaviours of these elementary particles.
The best description of particle physics that we have today is a theory called the Standard Model. One of the most important questions in science is how do we know what we know? Our theories must predict something about reality, and it must be possible to perform experiments to test whether reality really behaves the way the theory predicts. Otherwise, it is not science, but science fiction. In particle physics, we make predictions by using computer simulations of our theoretical models. These predictions can then be compared to actual data, like the data from experiments at the Large Hadron Collider (LHC) at CERN. One example of such a simulation program is PYTHIA, whose development began in Lund about 40 years ago, and which this thesis revolves around.
There are many unanswered questions in particle physics. One question that a lot of particle physicists are working on these days is what happens when certain particles are put under extreme pressure and heated up to temperatures a 100,000 times warmer than the core of the sun. With what we know today, the most likely answer seems to be that these particles would “melt” into a new state of matter called a quark-gluon plasma (QGP), but we still don’t really understand how this happens, what the properties of this state of matter are, or if it can be used for anything interesting. The desire to learn the answers to questions like these is profound for many people – so much that some are willing to dedicate lifetimes of work and invest billions of euros on developing technology like the LHC that can help us find the answers.
Now, the QGP is so extreme that it evaporates within a fraction of a billionth of a nanosecond, which makes it impossible to detect it directly. Instead, many scientists believe in the QGP hypothesis because it makes certain predictions that turn out to fit really well with data. However, one of the ongoing research programmes in Lund is challenging this hypothesis, and asks whether there are other models that are unrelated to the QGP, but that still can make the same predictions. Building such a model requires a lot of additions to the PYTHIA simulation. The work I have done in Lund has been to make such improvements to PYTHIA, both as a contribution to this bigger project to challenge the QGP paradigm, and as part of other projects. This thesis is the culmination of that work.
| Status | Not started |
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