Master student Projects

Projects for Master students in the Nikhef ATLAS group

date: June 2012

This is an overview with all available Master student projects in the Nikhef ATLAS group.

If you have your own research proposal, need more detailed information on the (availability) of individual proposals or would like to discuss about other available projects in the group you are always welcome to contact either the contact person for the project and/or the Nikhef ATLAS group leaders:

Stan Bentvelsen ___ [ E-mail: stanb_at_nikhef.nl, Tel 020-5925140, Nikhef room H250]

Paul de Jong ______ [ E-mail: h26_at_nikhef.nl, Tel 020-5922087, Nikhef room H253]

For an overview of the theses written in the Nikhef ATLAS group you can look at the Nikhef ATLAS group theses page

Master projects in the Nikhef ATLAS group

1) New Physics: scrutinizing top quarks in ATLAS for signs of new physics

Supervisors: Paul de Jong (staf) 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) New physics: decaying "dark matter" particles in ATLAS

Supervisors: Paul de Jong (staf), 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) New Physics: search for lepton flavor violating decays tau -> mu gamma

Supervisors: Olya Igonkina (staf), 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

5) Higgs: Higgs spin determination (mass reconstruction and decay angles)

Supervisors: Pamela Ferrari, Stan Bentvelsen (Ivo van Vulpen) (staf) and Koen Oussoren (Antonio Castelli) (PhD student).

Research description:

If a Higgs signal is discovered, the reconstruction of its mass and properties will be the final proof of its existence and will also provide information about the theoretical model which describes the Higgs interactions and therefore about the possible existence of physics beyond the Standard Model. By reconstructing the Higgs mass in the decay channels where it decays to ZZ or WW bosons, subsequently decaying into leptons ( or leptons and neutrinos), it is also possible to determine the spin of the Higgs. This can be done by reconstructing the decay angles of the final state leptons in the Higgs rest frame. The aim of this project is to establish how accurate the measurement of the above mentioned Higgs properties can be using the data collected by the ATLAS detector at the LHC.

This project should also determine the best decay channel among the above mentioned and the amount of data that are necessary to obtain an optimal measurement. Utimately, when enough data will be collected and if the Higgs boson will be observed, the determination of the Higgs spin can be performed.

5) Higgs: WW to WW boson scattering at the LHC

Supervisors: Pamela Ferrari, Stan Bentvelsen (staf), and Rosemarie Aben (PhD student)

Research description:

Understanding the scattering of two W-bosons (WW->WW) is essential in the Standard Model. Calculations show that, in the absence of a Higgs particle, this process grows with the cm energy of the W-bosons, and ultimately become larger than unity. This is unphysical and is one of the main motivations for including the Higgs particle in the model.

The measurement of this process at ATLAS is very complex and may need a few years of data taking. But its interesting to see if the current amount of data (including the whole of 2012) reaches sensitivity to this process.

This project aims at the observation of the scattering of two W-bosons - in the so-called 'vector boson fusion' process. One of the first goals is to isolate events where the two W-bosons produce one Z-boson (WW->Z), which subsequent decay is measured in the ATLAS detector. In addition the study includes the effect if a Higgs particle in the process. Ultimately we have to see what is needed to isolate the WW->WW process in data.