3rd Year Special Projects in 2016

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Particle Theory/Cosmology: Cosmological phase transition in scale-invariant Standard Model

Supervisor: Dr Archil Kobakhidze
Contact: Dr Archil Kobakhidze
Email: archil.kobakhidze AT sydney.edu.au
Phone: (02) 9351 5349

The Higgs boson field is known to be responsible for the masses of all known elementary particles and the cosmological phase transition in the early universe. However, the origin of the Higgs mass itself is still a mystery. In this project we investigate a scale-invariant extension of the Standard Model of particle physics, where mass emerges as a result of quantum fluctuations in a classically massless theory. We also study the cosmological phase transition within this model that supposedly happened a millionth of millionth of a second after the Big Bang.

Particle Theory/Cosmology: Dark Matter: from Interactions to its Abundance

Supervisors: Dr Michael Schmidt and Dr Archil Kobakhidze
Contact: Dr Michael Schmidt
Email: michael.schmidt AT sydney.edu.au
Phone: (02) 9351 3810

Several different astrophysical and cosmological observations at vastly different length scales indicate the existence of a new form of matter, dark matter (DM). It does not interact with light and its existence has only been inferred from its gravitational interactions. The origin and the nature of DM is unknown, but it is commonly believed to be explained by one or more new particles. A well-motivated candidate are weakly interaction massive particles (WIMPs). In this project, you will study how you can constrain the cosmological abundance of WIMPs by constraining its interactions with ordinary matter.

ATLAS Experiment: Searching for exotic mesons at Run 2 of the LHC

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

Many so-called exotic mesons have been seen since 2003: particles that do not have the quark-antiquark structure of the established mesons such as the pions, kaons, D-mesons, etc. The first, and still one of the most interesting states, is the X(3872). One model of its structure is that it is _two_ mesons, a D0 and a D*0bar, weakly bound by pion exchange (like a proton and a neutron forming a deuteron). Many have speculated that there should be a related state, an "Xb", made of B0 and B*0bar mesons.

The search for an Xb in LHC Run 1 data (from the ATLAS experiment) was performed here in Sydney. Data from Run 2 is now becoming available, but we still need to work out the best way of performing a new search. In this project, you will study the effect of the experimental trigger, and the kinematics of some Xb decays, to inform some key decisions about the Xb search at Run 2. There may be potential for this work to lead to a future honours or postgraduate project.

ATLAS Experiment: Charged Particle Tracking at the Large Hadron Collider

Supervisors: Dr Anthony Morley and Dr Aldo Saavedra
Contact: Dr Aldo Saavedra
Room: 542, School of Information Technologies Building (J12)
Email: aldo.saavedra AT sydney.edu.au
Phone: (02) 9036 9807

Improvements with the beams of the Large Hadron Collider have enabled the collider to achieve a luminosity close to its design value (1034 cm-2 s-1). The luminosity of the beams directly impacts the number of proton-proton collisions experiments, such as ATLAS and CMS, will record. The high luminosity value will result in datasets with enough collisions to study rare interactions and have the potential to discover new physics. The downside is the ability to determine the parameters associated with charged particles propagating through the detector becomes challenging in a busy environment.

The aim of the project is to explore whether using a statistical method called particle filter can be used to perform the task. Traditionally, a Kalman filter has been applied but it is limited to cases where there is no considerable scattering of the particles and the noise is Gaussian. The inner tracking of the LHC experiments is far from this ideal case. This project will be conducted in conjunction with the Centre for Translational Data Science.

ATLAS Experiment: Reconstructing the Wt system with the ATLAS detector at the LHC

Supervisors: Dr Kevin Finelli
Contact: Dr Kevin Finelli
Room: 366
Email: kevin.finelli AT sydney.edu.au
Phone: (02) 9351 5970

The LHC has resumed proton collisions at 13 TeV, and will continue collecting data throughout 2016 to create the largest collision dataset seen to date. The increased collision energy and number of collisions available for analysis enable a variety of new measurements that were previously not possible to perform. This project will focus on detailed studies of the production of a single top quark, the most massive elementary particle, in association with a W boson, the charged mediator of the weak nuclear interaction. Students will develop an algorithm to reconstruct the composite particles in a W+top quark event from final-state information collected by the ATLAS detector. In addition to studying the physics behind LHC collisions, students will gain proficiency in the statistical techniques used to analyze large datasets in particle physics.

Belle Experiment: Semileptonic decays of B mesons to light mesons in the Belle experiment

Supervisors: Prof. Kevin Varvell
Contact: Prof. Kevin Varvell
Room: 344
Email: kevin.varvell AT sydney.edu.au
Phone: (02) 9351 2539

B mesons can decay via the weak force to lighter mesons, a charged lepton and neutrino via a process known as semileptonic decay. Such decays allow us to determine fundamental parameters of the Standard Model of Particle Physics (SM). In this project, using data obtained with the Belle detector at KEK in Japan, we will test various theoretical models which describe these decays, with the aim of getting information on a SM parameter known as |Vub|.

Belle II Experiment: The Y(4260) particle at Belle II

Supervisors: Prof. Kevin Varvell
Contact: Prof. Kevin Varvell
Room: 344
Email: kevin.varvell AT sydney.edu.au
Phone: (02) 9351 2539

The Y(4260) is an exotic particle discovered about 10 years ago which does not fit into our current picture of how quarks and antiquarks bind together to form mesons. Some speculate that it may in fact be a bound state of quark, antiquark and gluon, which is in fact allowed by the Standard Model of Particle Physics. The Belle II experiment at KEK in Japan, which will commence running next year, will be able to study the Y(4260) in detail through a process known as “Initial State Radiation” (ISR). In this project we will investigate the prospects for doing this at Belle II.