4th Year Projects in 2013

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Here you will find a list of the 4th year projects offered in Semester 1, 2013. 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 ttbar, WW, Z → τ τ, and Wt cross sections with the ATLAS detector at the Large Hadron Collider

Supervisors: Dr Andrea Bangert, Dr Aldo Saavedra, A/Prof. Kevin Varvell
Contact: Dr Andrea Bangert
Room: 364
Email: a.bangert AT physics.usyd.edu.au
Phone: (02) 9351 2712

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 simultaneously measure the cross sections or rate of production of a pair of top quarks, a pair of W bosons, and a lone Z. By considering these different but related processes together, we perform a global test of the model. Your task will be to investigate the feasibility of measuring a fourth cross section, that for production of a top quark together with a W boson. Discrepancies between the various simultaneous measurements or unexpected yields may show us the weak link where the vaunted Standard Model fails to describe nature correctly.


Associated production of quarkonium-like states at ATLAS

Supervisors: Dr Bruce Yabsley
Contact: Dr Bruce Yabsley
Room: 366
Email: b.yabsley AT physics.usyd.edu.au
Phone: (02) 9351 5970

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.


Searching for new physics at the LHC

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

The discovery of a Higgs-like particle at the Large Hadron Collider (LHC) by ATLAS and CMS has been a great triumph for particle physics. With any luck it will be one of many discoveries that will take place at the LHC over the years as the centre of mass energy of the collider increases together with its luminosity. A number of proposed Beyond the Standard Model theories implied an upper limit on the mass of the Higgs, and thus a number are now disfavoured by the measured value (approximately 126 GeV) of the new particle if it is indeed a Higgs.

The aim of this project will be to search for new physics which is still favoured at a centre mass of energy of 8 TeV by defining a phase space which is overwhelmingly occupied by Standard Model processes and a signal region where we could expect new physics to appear. The phase space can be defined by particle properties such as charge and event wide properties such as the momentum distribution within the plane transverse to the beam. The project will require an understanding of how Standard Model processes can fake new physics events and will use a multi-variate technique to separate the two scenarios.


Testing New Physics Models

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

To test how well a particular particle physics model describes nature, a statistical analysis can be performed to compare its predictions with experimental precision measurements. In the case of the Standard Model of Physics packages such as GFitter (cern.ch/Gfitter) allow one to perform a global fit using predicted observables and electroweak precision measurements such as the mass of the Z boson. Such techniques led to a prediction for the top quark mass, and that the Higgs Boson was relatively light, before they were discovered, showing the power of the method.

In this project, a similar package will be employed to test the validity of popular Beyond the Standard Model theories using the latest results from the LHC and cosmological measurements such as the Cold Dark Matter density. The parameters of the models being studied will be scanned to obtain the most probable set and to also determine the reach of the present and future LHC results.


Semileptonic decays of D mesons in the Belle detector

Supervisors: Dr Alexei Sibidanov, A/Prof. Kevin Varvell
Contact: Dr Alexei Sibidanov
Room: 364
Email: a.sibidanov AT physics.usyd.edu.au
Phone: (02) 9351 2712

Measuring the rate of decay of B mesons to D mesons, a lepton and neutrino determines one of the fundamental parameters of the Standard Model of Particle Physics, known as |Vcb|. The Belle experiment performed this measurement ten years ago for the case of a neutral B meson and charged D, using its first 10 million pairs of B mesons. Since then Belle went on to collect the largest sample of pairs of B mesons in existence, over 750 million of them. In this project we will revisit the measurement using the full data set, better event reconstruction techniques, and the alternative transition of charged B meson to neutral D meson. This will allow us to study the dependence of the decay probability on the amount of energy transfered to the lepton and neutrino, which is important both in developing detailed models of how decays such as this occur, and in obtaining the best possible value for |Vcb|.


Slow pions from D* meson decay in the new Belle II experiment

Supervisors: Dr Alexei Sibidanov, A/Prof. Kevin Varvell
Contact: Dr Alexei Sibidanov
Room: 364
Email: a.sibidanov AT physics.usyd.edu.au
Phone: (02) 9351 2712

After a hugely successful decade-long run, the Belle experiment at KEK in Japan is now in a rebuilding phase, to be reborn as Belle II. With an upgraded accelerator and detector, Belle II will study many aspects of B meson decay with unprecedented precision. A number of very interesting decay modes of B mesons involve a charmed D*0 meson in the decay products, which itself decays to a D*0 meson and either a neutral pion (π0) or a photon. The neutral pion, which has rather low energy, is tricky to detect. It must be caught by the Belle II electromagnetic calorimeter, which is being upgraded with respect to Belle with a view to boosting its performance in the more demanding environment that the new experiment will experience. We are involved in assessing the potential performance of the upgraded calorimeter, and in this project we will tudy through simulation its ability to detect the slow π0 from D*0 decay and see how it will perform with respect to Belle. Ultimately this will be important in determining the sensitivity of Belle II when pursuing a number of its desired physics aims.


Scale invariance and the electroweak symmetry breaking

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

The recent observation of a Higgs-like resonance at the Large Hadron Collider (LHC) is a significant step forward in our understanding of the origin of mass of elementary particles.

In this project we explore a theoretical idea that all the masses of elementary particles emerge due to the quantum effects in a classically scale-invariant massless world. Models of particle physics will be studied where this idea is realised and corresponding theoretical predictions will be derived which can be verified in the experiments at the LHC.


Gauged baryon number and the matter-antimatter asymmetry in the Universe

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

While special relativity combined with quantum mechanics treats matter and antimatter on an equal footing, observations tell us that our Universe is predominantly composed of matter. It turns out that, in order to explain such matter-antimatter asymmetry, one must consider particle physics models beyond the celebrated Standard Model.

In this project we consider an extension of the Standard Model of particle physics by postulating an extra gauged anomalous baryon number invariance. Within this model a dynamical mechanism for the generation of an excess of matter over antimatter in the early Universe will be studied in detail.


Bringing hands-on particle detection to the general public

Supervisor: A/Prof. Kevin Varvell
Contact: A/Prof. Kevin Varvell
Room: 344
Email: k.varvell AT physics.usyd.edu.au
Phone: (02) 9351 2539

he world of experimental particle physics has the reputation of being located at large and expensive laboratories on the other side of the world. How can we bring the detection of particles closer to home and make it accessible to the general public and to schools?

A number of groups have explored the idea of portable particle detectors which can be taken to public talks and to schools, and used to conduct simple experiments as well to demonstrate basic detection principles. In this project we will join this exploration by examining the state-of-the-art in portable home-grown detectors and prototyping one of our own here in the School of Physics.