Studies of Dark Matter Signals at the LHC

Abstract: Standard matter, the matter that we can see, only make up about 6% of the universe. Astronomical observations have found that there exist other matter, which is non-luminous, called dark matter. This matter can interact gravitationally with standard matter, but it is unknown if it can interact weakly with the help of some other force as well. If such interactions were possible, events between dark matter and standard matter could be created in a particle accelerator. This thesis has studied simulations of dark matter events possible in the ATLAS detector at the Large Hadron Collider. Our theoretical models include a mediator, a particle carrying the force between interacting particles, that can interact with both the standard matter particles called quarks and dark matter. When two quarks collide, it is now possible for them to decay into the mediator particle. This mediator can decay back into two quarks, which will be detected as jets. The invariant mass of the two jets will be equal to the mass of the mediator. Such events, called di-jet, have been examined in this thesis. The simulated events were generated in MadGraph5. The simulations are divided into different levels. At parton level only the interaction between quarks is considered. At particle level the creation of jets is simulated and will introduce a smearing to the energy values. The last level includes how the particles interact with the detector, which will add further smearing. At the end the measured energies will have a certain resolution caused by the smearing. This thesis compares the resolution at particle level and detector level. Furthermore, the energies at particle level were smeared using a simple formula to approximate the effects of the detector. These smeared values were compared to the values at detector level and seem to suggest that it is a good approximation. The detector level is more involved than particle level and parameterization of the detector resolution will thus save time for future di-jet event simulations.