Master student Projects

Research projects for students in the Nikhef/UU ALICE group (Jan 2016)

This is an overview of the student projects currently available in the ALICE group at Nikhef and Utrecht University. The research in ALICE focuses on the strong interactions. In particular, we use high-energy collisions of lead nuclei to study many-body systems in which the strong interaction is the main force. In these collisions, we expect to form a hot and dense system in which quarks and gluons are effectively deconfined: the Quark Gluon Plasma (QGP). The goal of the research is to understand the properties of the QGP, including transport properties such as viscosity and parton energy loss.

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 ALICE group leader, Raimond Snellings.

Particle Polarisation in Strong Magnetic Fields

When two atomic nuclei, moving in opposite directions, collide off- center then the Quark Gluon Plasma (QGP) created in the overlap zone is expected to rotate. The nucleons not participating in the collision represent electric currents generating an intense magnetic field. The magnetic field could be as large as 10^{18} gauss, orders of magnitude larger than the strongest magnetic fields found in astronomical objects. Proving the existence of the rotation and/or the magnetic field could be done by checking if particles with spin are aligned with the rotation axis or if charged particles have different production rates relative to the direction of the magnetic field. In particular, the longitudinal and transverse polarisation of the Lambda^0 baryon will be studied. This project requires some affinity with computer programming.

Supervisors: Panos Christakoglou

Forward Particle Production from the Color Glass Condensate

It has been proposed that a new state of matter (the color-glass condensate, or CGC) may provide a universal description of hadronic collisions (e.g. proton-proton collisions) at very high energy. The CGC may be seen as the classical field limit of Quantum Chromodynamics, and a framework for calculating observables from this state has been developed. Several measurements are consistent with the assumption of a CGC, but no experimental proof exists so far. In this project we intend to perform a systematic study of the sensitivity to the CGC of different possible measurements at the LHC. The work will be performed in close collaboration with an external world expert in this field. It is advantageous to have a good background in theoretical physics.

Supervisors: Thomas Peitzmann, Marco van Leeuwen

Blast-Wave Model in Heavy-Ion collisions

The goal of heavy-ion physics is to study the Quark Gluon Plasma (QGP), a hot and dense medium where quarks and gluons move freely over large distances, larger than the typical size of a hadron. Hydrodynamic simulations expect that the QGP will expand under its own pressure, and cool while expanding. These simulations are particularly successful in describing some of the key observables measured experimentally, such as particle spectra and elliptic flow. A reasonable reproduction of the same observables is also achieved with models that use parameterisations that resemble the hydrodynamical evolution of the system assuming a given freeze-out scenario, usually referred to as blast-wave models. The goal of this project is to work on different blast wave parametrisations, test their dependence on the input parameters and extend their applicability by including more observables studied in heavy-ion collisions in the global fit.

Supervisors: Panos Christakoglou

Energy Loss of Energetic Quarks and Gluons in the Quark-Gluon Plasma

One of the ways to study the quark-gluon plasma that is formed in high-energy nuclear collisions, is using high-energy partons (quarks or gluons) that are produced early in the collision and interact with the quark-gluon plasma as they propagate through it. There are several current open questions related to this topic, which can be explored in a Master's project. For example, we would like to use a new Monte Carlo generator model (JEWEL) of the collision to see whether we can measure the shape of the collision region using measurements of hadron pairs. In the project you will collaborate with one the PhD students in our group to use the model to generate predictions of measurements and compare those to data analysis results. Depending on your interests, the project can focus more on the modeling aspects or on the analysis of experimental data from the ALICE detector at the LHC.

Supervisors: Marco van Leeuwen

Chiral Magnetic Effect and the Strong CP Problem

Within the Standard Model, symmetries, such as the combination of charge conjugation (C) and parity (P), known as CP-symmetry, are considered to be key principles of particle physics. The violation of the CP-invariance can be accommodated within the Standard Model in the weak and the strong interactions, however it has only been confirmed experimentally in the former. Theory predicts that in heavy-ion collisions gluonic fields create domains where the parity symmetry is locally violated. This manifests itself in a charge-dependent asymmetry in the production of particles relative to the reaction plane, which is called Chiral Magnetic Effect (CME). The first experimental results from STAR (RHIC) and ALICE (LHC) are consistent with the expectations from the CME, but background effects have not yet been properly disentangled. In this project you will develop and test new observables of the CME, trying to understand and discriminate the background sources that affects such a measurement.

Supervisors: Panos Christakoglou

Quantum Coherence in Particle Production with Intensity Interferometry

Intensity interferometry – also known as HBT-effect or Bose-Einstein-correlations – is a method to study the space-time structure of the particle-emitting source in high-energy physics. The main interest so far has been on the width of correlation functions in momentum space, which reflects the space-time information. The strength of the correlation also carries information, but this has been ignored by many people. The correlation strength is in particular influenced by the degree of coherence of particle production. Recently new studies have been performed to extract this degree of coherence, however, many other effects might distort such a measurement, in particular the production of pions via resonance decay. In this project we will study the role of resonance decays for a measurement of coherence in intensity interferometry and try to establish possible correction methods for any distortions they may cause. We will perform theoretical model calculations with Monte-Carlo simulation methods.

Supervisors: Thomas Peitzmann

Higher Harmonic Flow

When two ions collide, if the impact parameter is not zero, the overlap region is not isotropic. This spatial anisotropy of the overlap region is transformed into an anisotropy in momentum space through interactions between partons and at a later stage between the produced particles. It was recently realized that the overlap region of the colliding nuclei exhibits an irregular shape. These irregularities originate from the initial density profile of nucleons participating in the collision which is not smooth and is different from one event to the other. The resulting higher order flow harmonics (e.g. v3, v4, and v5, usually referred to as triangular, quadrangular, and pentangular flow, respectively) and in particular their transverse momentum dependence are argued to be more sensitive probes than elliptic flow not only of the initial geometry and its fluctuations but also of shear viscosity over entropy density (η/s). The goal of this project is to study v3, v4, and v5 for identified particles in collisions of heavy-ions at the LHC.

Supervisors: Panos Christakoglou

A New Detector for Very High-Energy Photons: FoCal

High-energy photons are important messenger particles in particle physics. In particular direct photons (i.e. directly produced from elementary scattering processes) are interesting, but it is a difficult task to discriminate them from the photons originating from particle decays. Existing detector have limited capabilities for such a discrimination, in particular at the highest energies. Our institute has pioneered a detector based on a new concept, a digital pixel calorimeter with Si-sensors of unprecedented granularity. First proof-of-principle measurements have already been performed. In this project we will study the performance of a particular detector design for measurements of direct photons at the LHC and optimize the design parameters for such a measurement. Performance studies for other measurements – e.g. jets, J/ψ, or ϒ particles – may be carried out in addition.

Supervisors: Thomas Peitzmann, Marco van Leeuwen

Thermal Photon Emission: Quark-Gluon Plasma or Hadron Gas?

Recently, measurements of thermal photon emission in high-energy nuclear collisions have been performed at RHIC and at LHC. It is generally believed that a quark-gluon plasma equation of state is the natural description of the hot initial phase of these collisions, and so far only theoretical model calculations including such a phase have been compared to those measurements. In this project we will revisit hadron gas models and try to reproduce the thermal photon yield together with other observables. In this work we will use and possibly modify Monte Carlo implementations of relativistic hydrodynamics, tune it to existing data of hadron production and then estimate the photon production from the same model. The model implementation will be based on previous work of external theoretical colleagues and will be carried out in collaboration with them.

Supervisors: Thomas Peitzmann

A New Detector for Proton Therapy and Proton Computed Tomography

Conventional imaging of humans in medical treatment relies mostly on electromagnetic radiation (CT, MRT) or positrons (PET). A recently proposed new imaging strategy, in particular in the context of proton therapy for cancer treatment, is to use proton beams. Current detectors for the scattered protons have severe limitations, in particular for their precision and measurement times. New development of intelligent Si-sensors in particle physics offer possibilities to develop much more efficient detectors for such proton CT measurements. We will perform R&D on the use of new silicon pixel detectors developed in the context of the ALICE experiment at CERN for such medical applications. Studies will include Monte-Carlo simulations of a possible detector setup and measurements with the first samples of the appropriate silicon sensors, which will become available in early 2016. The project will be carried out in the context of a scientific collaboration with Bergen University, Norway.

Supervisors: Thomas Peitzmann