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Understanding Rt using two-particle correlations by simulating proton-proton collisions in a Monte-Carlo model

Leygonie, Johan LU (2021) FYSK02 20202
Particle Physics
Department of Physics
Abstract
The observable Rt is investigated in the Monte Carlo Model Pythia in order to better understand
results from experimental data obtained in the ALICE detector at CERN. The purpose is to reproduce
the experiment in a simulation and use the features proposed by Pythia to dig into the unexpected
outcomes. The analysis is conducted using (∆φ, ∆η) two particle correlations. Three different
methods are used for the investigation of Rt, a general two-particle correlation, a correlation with
respect to the leading track and a correlation between tracks contained in each region separately. The
comparison made between the events generated by Pythia and the experimental data are mostly in
agreement although some unexpected features emerge in... (More)
The observable Rt is investigated in the Monte Carlo Model Pythia in order to better understand
results from experimental data obtained in the ALICE detector at CERN. The purpose is to reproduce
the experiment in a simulation and use the features proposed by Pythia to dig into the unexpected
outcomes. The analysis is conducted using (∆φ, ∆η) two particle correlations. Three different
methods are used for the investigation of Rt, a general two-particle correlation, a correlation with
respect to the leading track and a correlation between tracks contained in each region separately. The
comparison made between the events generated by Pythia and the experimental data are mostly in
agreement although some unexpected features emerge in the simulation. The influence of the initial
state radiation on the general distribution of the tracks around the collision is also investigated. (Less)
Popular Abstract
A fraction of second after the big bang, the density and the temperature were so high that no neutrons
of protons could be formed. The universe could, at this moment, be described as a soup made of their
basic component, known as quarks and gluons. It was as big as our solar system. This hot soup is called
Quark-Gluon Plasma (or QGP). It lasted only for a fraction of seconds before it cooled down sufficiently
to condense in neutrons and protons, which in their turn formed atoms. The Quark-Gluon Plasma is
described as a soup because it behaves like a fluid. It is, in fact, a perfect liquid as it has close to no
viscosity, i.e., internal friction. It was actually first thought to be a gas.
Now the question is, how do we recreate this... (More)
A fraction of second after the big bang, the density and the temperature were so high that no neutrons
of protons could be formed. The universe could, at this moment, be described as a soup made of their
basic component, known as quarks and gluons. It was as big as our solar system. This hot soup is called
Quark-Gluon Plasma (or QGP). It lasted only for a fraction of seconds before it cooled down sufficiently
to condense in neutrons and protons, which in their turn formed atoms. The Quark-Gluon Plasma is
described as a soup because it behaves like a fluid. It is, in fact, a perfect liquid as it has close to no
viscosity, i.e., internal friction. It was actually first thought to be a gas.
Now the question is, how do we recreate this insanely hot and dense fluid, in a laboratory, without
colliding two neutron stars? Well, it was done two decades ago in the Super Proton Synchrotron (SPS)
at CERN in Geneva. The point is that, instead of directly applying extreme temperature and pressure
on a stationary object until the bonds between the quarks snaps, which is extremely far beyond our
reach, we accelerate particles to relativistic speed (close to the speed of light) and make them collide
with each other. As a result, at a very tiny scale, for the blink of an eye, the conditions needed for the
creation of QGP are fulfilled, which then allows scientists to study what the universe was made of at
the very beginning.
We have been able to recreate this QGP in laboratories, by colliding heavy nuclei. For a long time, the
scientific community agreed to say that the creation of QGP in particle accelerator could only be done
with heavy nuclei. Until recently, when during a proton-proton collision (much smaller elements),
signals indicating the formation of QGP were detected. The reason why it was a surprise is the
following: heavy nuclei, such as lead, contain many neutrons and protons, which significantly increases
the energy released during the collision, as they are much heavier.
The discovery presented above could lead to two outcomes. Either the creation of this plasma does,
in fact, occur when colliding smaller particles or it is the way we detect the formation of QGP is wrong.
My study focuses on the latter. To detect the formation of QGP, we look at the pattern of the collision,
i.e., the configuration in which the particles come out of the collision. High-multiplicity isotropic events
(when a large number of particles coming out in every direction) are the most propitious for QGP
formation. On the other hand, if they are concentrated in one direction (also called jet), then it is a
regular collision. The point of this paper is to get a better understanding of the tools used to classify
those events. (Less)
Please use this url to cite or link to this publication:
author
Leygonie, Johan LU
supervisor
organization
course
FYSK02 20202
year
type
M2 - Bachelor Degree
subject
keywords
QGP, Quark-Gluon-Plasma, Rt, Particle Physics, Proton-proton Collisions, Pythia, Monte-Carlo Model, Bachelor's Thesis, Heavy-ion Collisions, ALICE, CERN, Relative Transverse Activity, Jets, Two-Particles Correlations, Quantum Physics
language
English
id
9040372
date added to LUP
2021-02-17 10:51:41
date last changed
2021-02-17 10:51:41
@misc{9040372,
  abstract     = {{The observable Rt is investigated in the Monte Carlo Model Pythia in order to better understand
results from experimental data obtained in the ALICE detector at CERN. The purpose is to reproduce
the experiment in a simulation and use the features proposed by Pythia to dig into the unexpected
outcomes. The analysis is conducted using (∆φ, ∆η) two particle correlations. Three different
methods are used for the investigation of Rt, a general two-particle correlation, a correlation with
respect to the leading track and a correlation between tracks contained in each region separately. The
comparison made between the events generated by Pythia and the experimental data are mostly in
agreement although some unexpected features emerge in the simulation. The influence of the initial
state radiation on the general distribution of the tracks around the collision is also investigated.}},
  author       = {{Leygonie, Johan}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Understanding Rt using two-particle correlations by simulating proton-proton collisions in a Monte-Carlo model}},
  year         = {{2021}},
}