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 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 has 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

4) 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.

6) Detector Development for ATLAS Upgrade

Supervisors: Nigel Hessey (Staff)

Research description:

The ATLAS Inner Detector will be completely renewed around 2022 in order to cope with the very high track densities to be delivered by the High Luminosity LHC Upgrade. A large team of physicists around the world is designing and prototyping ideas for the new tracker. Nikhef expects to build one of the silicon strip end-caps, and works on several projects for this. These include boiling liquid CO2 cooling, carbon-fibre structural support elements, and novel cooling materials such as carbon foams. We have built two prototype "petals" to support silicon strip detectors. We now need to equip these with heaters to simulate the detector electronics, and measure their cooling performance. We will also build up models to simulate the cooling, and compare the model predictions to the measurements to check our understanding of petal cooling performance. Several related projects are also possible, depending on the interest of the student, including novel ideas for helium gas cooling as well as testing sensor performance when new sensors are delivered early in 2013. This can include participation in radiation tests of the sensors.

This project is very much a hands-on hardware effort, suitable to experimental physicists.

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.