Master student Projects

Projects for Master students in the Nikhef ATLAS group

date: June 2013 (Work in Progress)

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 quark production at the LHC

Supervisors: Paul de Jong (staf) and XXX (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. The goal of this master project is to study top quark production in detail. Measured data will be compared to simulations of top quarks in ATLAS, in order to check the performance of the simulation, and detect differences between data and simulations that cannot be explained by known Standard Model sources. We will start with typical top quark production kinematics, and during the project go to ever more extreme kinematic regions.

2) New physics: decaying "dark matter" particles in ATLAS

Supervisors: Paul de Jong (staf), XXX (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), Pier-Olivier DeViveiros (post-doc) and Joern Mahlstedt (PhD student)

Research description:

The Standard Model of particle physics (SM), though extremely successful, provides no insight on the mass structure of the quark and lepton families. Compositeness models - models in which leptons and quarks are non-fundamental particles made of 'preons' - can be used to explain these features. In such models, the 3 SM lepton families are the lowest energy bound-states of these 'preons'. Interestingly, such models imply the presence of higher energy excited states, which can be searched for at the LHC.

The goal of this project is to devise a search for these at ATLAS, in events where an excited lepton is produced along with a SM lepton. The excited lepton decay can have up to 3 SM lepton, giving a rise to 4 lepton topology. Such a signature could significantly improve the current limits on excited lepton production. The main focus of the project will be to determine which event observables are most sensitive to these signals by studying the various signals and the SM backgrounds. With this project, the student would gain close familiarity with Monte Carlo generators, the standard HEP analysis tools (ROOT, C++, etc.) and with modern experimental techniques (statistical analysis, SM background estimates, etc.).

4) New Physics: search for lepton flavor violating decays tau -> mu gamma

Supervisors: Olya Igonkina (staf), Saminder Dhaliwal (post-doc) and Ivan Angelozzi (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. The Standard model W->mu nu gamma decays are major background to the search and have to be studied with data, e.g. using the similarity to Z->mu mu gamma data.

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.

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

Supervisors: Stan Bentvelsen, Pamela Ferrari (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. Now the Higgs particle has been found, it remains to be seen if the particle is responsible for restoring unitarity.

The measurement of this process at ATLAS may need a few more 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.

7) Astroparticle physics at the LHC – from the caverns of CERN to the top of the atmosphere

Supervisors: David Berge (staff)

Research description:

Understanding particle acceleration up to very high energies in the Universe requires Earth-bound experimental techniques that exploit the Earth’s atmosphere as detection medium. Only the shear size of the atmosphere provides a sufficiently large sensitive area to measure the very rare highest energy particles from the cosmos as they impinge on the Earth. The idea of the atmospheric measurement is simple: a cosmic particle hitting the atmosphere is being absorbed by developing into an air shower, a spray of secondary particles that originates in the collision of the primary cosmic particle with air molecules, and successive interactions of those secondary particles in the atmosphere. Such air showers can be traced and therefore measured on Earth, providing information about the energy, type, and direction of the primary cosmic particle, by different means. Important examples of such atmospheric detection techniques include the measurement of muons with particle counters at the Earth’s surface and the measurement of Cherenkov or Fluorescence light emitted during the air shower development. The connection between measured quantities like particle numbers or light intensity and original quantities like particle energy or type is in all cases inferred using simulations of particle collisions and cascades in the atmosphere.

The goal of this master project is to exploit data of proton collisions measured with ATLAS, an experiment at the Large Hadron Collider (LHC), the highest energy human particle collider currently operating at CERN in Geneva (Switzerland), to test and improve simulations of particle collisions in the atmosphere up to the highest known energies (a few times 1020 eV). The student will work on ATLAS data analysis and Monte Carlo simulations of particle collisions, both for simulating proton colliding in ATLAS and cosmic-ray protons colliding with air molecules in the atmosphere. The ultimate goal is to improve Monte Carlo model predictions used for experiments like the upcoming CTA and Auger.

8) Astroparticle physics at the LHC – going after the Dark in ATLAS

Supervisors: David Berge (staff)

Research description:

It is currently believed that most of the matter in the Universe is a new species of so-called dark matter. This new form of matter dominates over all the known forms of matter. If the dark matter of the universe is a new particle that can be produced in proton-proton collisions at CERN's Large Hadron Collider (LHC), this new particle could couple to the recently discovered Higgs boson and could be searched for at the LHC in Higgs decays. Since a dark matter particle must be very weakly interacting it is expected that such a particle would leave the LHC detectors unseen. Looking for such invisible Higgs decays to undetectable particles is an important search for both new physics beyond the Standard Model of particle physics and dark matter. The master student will work on a search for new physics at the ATLAS experiment looking for signatures of invisibly decaying Higgs bosons, in particular in the context of dark matter. She or he will learn how to analyse high-energy particle-physics data and will focus on analysis optimisations and inter-disciplinary comparisons of the ATLAS dark matter search to direct and indirect dark matter searches on Earth and in space.