Master student Projects

master student projects in the Nikhef ATLAS group

date: June 2012

General information

The Official SCT DQ shift twiki

The Nikhef ATLAS group leaders are Stan Bentvelsen and Paul de Jong.

1) Scrutinizing top quarks in ATLAS for signs of new physics

Supervisors: prof. dr. Paul de Jong and Priscilla Pani (PhD student)

Research description:

The LHC is a "top quark factory": more than 1 million top quark pairs are produced every year. Such large data sets give the opportunity to study top quark production and decay in great detail. New physics, such as 4th generation top-like quarks, or supersymmetric partners of the top quark, may lead to final states in the detector that look like top quark pairs, but are subtly different. A number of variables are suited to probe possible differences between Standard Model top quark production, and new physics. These include variables related to the missing energy in the event, but also other kinematic variables have been proposed. The goal of this master project is to study these variables in detail: what do they measure exactly and why are they sensitive? This will be done on simulated events, both representing SM top quark production and new physics production. Then, the knowledge gained will be applied to the ATLAS data of 2011 and 2012. If a deviation of SM-like behaviour is found, further studies will need to be done to estimate whether this is due to ununderstood detector behaviour, incomplete simulation of SM top quark pair production, or new physics.

Relevant papers:

Relavant publications: axXiv:1205.5805 axXiv:1205.4470 axXiv:1203.4813

2) Decaying "dark matter" particles in ATLAS

Supervisors: prof. dr. Paul de Jong, Ingrid (post-doc) and Pierfrancesco Butti (PhD student)

Research description:

One of the goals of ATLAS is to search for new phenomena beyond the Standard Model at the LHC. In supersymmetry, the lightest supersymmetric particle is often the lightest neutralino. It is assumed to be stable if a symmetry called R-parity is conserved. However, R-parity may well be a non-conserved symmetry, in which case the neutralino will decay into Standard Model particles. One promising way to look for this is to look for high-energy electrons or muons very close to hadronic jets. In this master project we will study these final states. First, with simulated events, we will try to see what the signal (supersymmetry) looks like. Then we will consider the possible SM backgrounds, and try and understand what kind of SM physics could lead to high momentum leptons close to hadronic jets. Based on simulated events, we will try to optimally separate signal and background. Then we will look at the ATLAS data of 2011 and 2012, and try and look for signs of decaying neutralinos.

3) Search for lepton flavor violating decays tau -> mu gamma

Supervisors: dr. Olya Igonkina, Saminder Dhaliwal (post-doc) and Hartger Weits (PhD student)

Research description:

The lepton flavor violation is a mechanism which is forbidden by Standard Model and is not observed so far in experiment. However, it could explain a large amount of matter (and lack of antimatter) found in the Universe. Such mechanism could manifest itself in decays of tau lepton into a muon and a photon. There are a lot of taus produced in ATLAS, but momenta are rather small, which make the search a challenging and interesting task.

All steps of this measurement (analysis of ATLAS data, tuning cuts on MC, understanding the background and trigger performance) are part of the master project. The programing of the code, the data analysis with ROOT and ATLAS software, work with grid tools will be everyday tasks.

Relevant papers:

Review of various lepton flavor violating processes: arXiv:1201.5093

Plans of competing experiments Belle-2 and Super-B : arXiv:1109.2377

Relation between leptogenesis and lepton flavor violation : arXiv:0904.1182