4th Year Projects in 2014

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Here you will find a list of the 4th year projects offered in Semester 1, 2014. These are representative of the sort of projects we can offer - we may alter some of these closer to the time or indeed add new possibilities.

Measurement of Standard Model production cross-sections with the ATLAS detector at the Large Hadron Collider using inclusive dilepton events

Supervisors: Dr Aldo Saavedra, A/Prof Kevin Varvell and Dr Kevin Finelli
Contact: Dr Aldo Saavedra
Room: 366
Email: a.saavedra AT physics.usyd.edu.au
Phone: (02) 9351 5970

The Standard Model of Particle Physics describes elementary particles such as electrons and quarks that form the building blocks of atoms, as well as particles called bosons that mediate fundamental forces. The top quark is the most massive known quark, while the W and Z bosons are massive particles that mediate the weak nuclear force. The Large Hadron Collider is designed to produce exotic particles such as top, W, and Z by slamming protons together and using gigantic detectors like ATLAS to examine the debris. By fitting data collected by ATLAS to predictions made by the Standard Model, we can simultaneously measure the cross sections or rate of production for final states involving these particles, and considering these different but related processes together, we perform a global test of the model, with the ultimate aim of revealing new physics through discrepancies of the data with the model.

There are several approaches that projects in this area could focus on. These include improving the WW cross section measurement, with the aim of increasing its sensitivity to new physics; using the same sign lepton events to put limits on new processes; extending the measurement to include other diboson processes such as WZ by looking at trilepton rather than dilepton events; and technical work improving the overall fitting procedure and systematic effects using a software package such as RooFit.


Associated production of quarkonium-like states at ATLAS

Supervisors: Dr Bruce Yabsley
Contact: Dr Bruce Yabsley
Room: 363
Email: b.yabsley AT physics.usyd.edu.au
Phone: (02) 9351 6808

Some of the most surprising and interesting particle physics results in the last decade have been measurements of the quarkonia: the positronium-like spectra of cbar c and bbar b bound states. Several of the recently-discovered charmonium-like states, in particular the X(3872), do not fit into the expected cbar c spectrum and are likely exotic in structure. Quarkonium states are copiously produced at the LHC, and their production is being studied in detail, via J/ψ and Υ → μ+ μ- decays; an analysis of X(3872) → π+ π-, J/ψ is close to completion, and the search for a hidden-beauty analogue state, decaying to π+ π-, Υ, is being carried out in Sydney.

In this project we will take the next step and study the conditions under which π+ π-, Υ states are formed: are they produced together with heavy-flavour jets? With other, simpler quarkonium states? Is there rapidity- or transverse-momentum dependence? And what can this tell us about the fundamental processes by which these states are produced? A rich set of observables is available for study of associated production, and this subject is suitable both for a standalone honours project, and for honours work leading into subsequent PhD research.


Re-interpreting LHC results

Supervisor: Dr Aldo Saavedra
Contact: Dr Aldo Saavedra
Room: 366
Email: a.saavedra AT physics.usyd.edu.au
Phone: (02) 9351 5970

A large number of analyses published by the ATLAS and CMS experiments have focussed on the search for new physics signatures in the collected data. For most cases the result derived has been an upper limit on the probability for such processes to take place in the proton-proton collisions of the LHC. These measured limits create a number of questions. For example, what is the compatibility between CMS and ATLAS results that were obtained for a similar model with different analysis methods? Can the existing measured limit be re-interpreted to determine whether a new model has already been ruled out or not?

In this project we will attempt to develop a strategy that will shed light on these questions by using the published Standard Model background measured by the detector, and a “fast simulator” that is able to replicate the response of the detector to the new physics processes.

To achieve this aim, we will use a framework called GAMBIT, developed by a small international collaboration of which the Sydney Particle Physics group is a part, that includes theorists, astrophysicists, and particle physicists. The first task will be to select a recently-proposed new physics model, and particle processes that can be measured by the LHC experiments.


Study of the Decay B to rho lepton neutrino at Belle

Supervisors: Dr Alexei Sibidanov and A/Prof Kevin Varvell
Contact: Dr Alexei Sibidanov
Room: 364
Email: alexei.sibidanov AT sydney.edu.au
Phone: (02) 9351 2712

The rate of the charmless semileptonic decay of a B meson, via the weak force, to a rho meson, lepton and neutrino allows us to determine a fundamental parameter of the Standard Model of Particle Physics known as |Vub|. The measurement is complicated by the presence of the strong force, which binds quarks together to form the B and rho mesons. Using around 1000 examples of this decay reconstructed with the Belle detector at KEK in Japan, we will test various theoretical models which describe the decay, to see which performs best in taking into account these strong interaction effects.


Exploring the Origin of Neutrino Mass at the LHC

Supervisors: Dr Kristian McDonald and Dr Archil Kobakhidze
Contact: Dr Kristian McDonald
Room: 364
Email: klmcd AT physics.usyd.edu.au
Phone: (02) 9351 2712

The Standard Model of particle physics is currently the best available scientific theory for describing the interactions and properties of the fundamental building blocks of the universe. Amongst other things, this theory provides an explanation for the origin of mass via the Higgs mechanism. In the Standard Model the particles known as neutrinos are expected to be strictly massless. However, an impressive body of experimental evidence has been acquired that demonstrates the existence of massive neutrinos. In this project we investigate mechanisms that can generate neutrino mass. These generically require new particles beyond the Standard Model and we study the likelihood that the predicted new particles can be probed by the Large Hadron Collider.


Supersymmetry and naturalness in light of LHC data

Supervisor: Dr Archil Kobakhidze
Contact: Dr Archil Kobakhidze
Room: 367
Email: archilk AT physics.usyd.edu.au
Phone: (02) 9351 5439

The naturalness of the weak scale is one of the main theoretical problems motivating new particle physics, and the weak-scale supersymmetry has been the dominant proposed solution for a long time. This paradigm is now being challenged by experimental data collected at the Large Hadron Collider (LHC). The simplest supersymmetric models have already been excluded or highly disfavoured. In this project we investigate a new class of natural supersymmetric models with vector-like quark supermultiplets (`top partners'). We also will discuss prospects of verification of these models in future LHC experiments.


Grand Unified Theories

Supervisor: Dr Archil Kobakhidze
Contact: Dr Archil Kobakhidze
Room: 367
Email: archilk AT physics.usyd.edu.au
Phone: (02) 9351 5439

Grand Unification is a theoretical paradigm, which further unifies strong and electroweak fundamental interactions at high energies. It has interesting predictions, such as nucleon instability and relations between masses of quarks and leptons. In this project we will study non-supersymmetric models of Grand Unification with additional matter and interactions at energies accessible in LHC experiments.