Summarising Constraints On Dark Matter At The Large Hadron Collider

Abstract

Dark matter is estimated to make up around 25% of the Universe, but it is not known
what dark matter is. In particle physics, mediators of dark matter are used to model
interactions of dark matter particles with known particles (Standard Model particles).
These mediator particles can be produced from two quarks or gluons in high-energetic
proton-proton collisions, and decay immediately back into Standard Model particles - or
into dark matter particles.
We simulated different scenarios to study the signal shape of this mediator particle.
The event generation was done by using MadGraph 5. We used samples with the mediator
only decaying into quarks to compare them to samples in which the mediator can
additionally decay into dark matter, as well as various other changes to investigate the
different shapes of the mediator signal.

Popular Abstract

There is darkness around us - a kind of
darkness that escapes any light. About
85% of the matter in the entire Universe is
made up of a mysterious dark matter that
we cannot see and - so far - not detect. We
only know that it is there, and that the ordi-
nary matter that we can see only makes up a
small part of the Universe. This dark mat-
ter first came to people's attention in the
1930s when looking at the rotation curves of
galaxy clusters and galaxies. There seemed
to be more matter than was visible in stars
- and so, the hunt for dark matter began.
One theory to explain the missing mat-
ter assumes that dark matter is a new type
of particles. We have not been able to ob-
serve them yet because they do not absorb,
send out, or interact with light like ordinary
particles do.
Many experiments search for the small-
est hints of dark matter particles. In parti-
cle accelerators like the LHC (Large Hadron
Collider) at CERN, two particles are shot
onto each other at very high energies, with
the chance of producing dark matter parti-
cles. These would not give any signal in the
detector, but by measuring the other decay
products of the collisions, it is possible to
infer the properties of the dark matter par-
ticles.
Little is, however, known about these
potential dark matter particles. Therefore,
a wide range of masses and combinations of
properties has to be tried out. Since the ca-
pacities of particle accelerators are limited,
a good way is to simulate events to exclude
the model for masses that dark matter par-
ticles cannot have, according to the models.
These mass ranges could then be omitted
when carrying out the actual experiment.
We generated different samples of events
to compare them, and found that in some
cases it is not necessary to fully simulate
and analyse the generated data. Instead,
it is possible to rescale from one sample to
another with a simple scaling factor.
This result is helpful because the needed
time and computing power to make the sim-
ulations can be reduced if not all data sam-
ples have to be fully analysed.
The overall aim is to discover dark mat-
ter. Simulations like these can give direc-
tions on where to perform searches. With
so little known about dark matter, it can
already be a very crucial step to figure out
what is not. Eventually, we may be able
to find a way to shed light on this invisible
darkness to help us understand our Universe
and explain yet another of its many myster-
ies.

• author: John, Isabelle
• supervisor: Caterina Doglioni
• organization: Department of Physics; Particle and nuclear physics
• course: FYSK02 20162
• year: 2017
• type: M2 - Bachelor Degree
• subject: Physics and Astronomy
• language: English
• id: 8903100
• date added to LUP: 2017-02-14 09:02:53
• date last changed: 2017-02-14 09:02:53