High-Energy Physics

The experimental program in HEP currently is focused on collider searches for BSM physics using the ATLAS detector in the Large Hadron Collider (LHC) at CERN.

Adelaide physicists were involved in the 2012 discovery of the Higgs boson by ATLAS.

Other experimental research activities include precision studies of flavour physics at Belle II, and the development of new detector systems and collider simulations. We also participate in experiments at Jefferson Lab which aim to explore the origin of the mass of hadrons as well as the spin of the proton, including mapping its structure in three dimensions.

Allied to these efforts is the development of associated computational tools. 

The theoretical program is broad and includes studies of:

• topics investigating BSM theories and associated phenomena including models ofsupersymmetry; composite Higgs and other BSM models; models of dark matter and its interaction with Standard Model particles, and
• precision tests of the Standard Model (SM) including SM processes at both low- and high-energy scales.

Allied to these efforts is the development of associated computational tools. 

Supersymmetry (SUSY) is an extension of the SM in which every SM fermion has a boson partner, and every SM boson has a fermion partner.

SUSY has a number of distinct advantages over the SM, including a better unification of the SM forces at the Grand Unified Theory (GUT) scale and an absence of the extremely large quantum corrections to the Higgs mass that occur in the SM.

Since SUSY is not observed at low energies, then SUSY must be broken, but in order to avoid so-called fine-tuning and naturalness problems with SUSY it is expected to be broken near the tera-electron volt (TeV) scale. If so, then SUSY should be within the reach of the LHC or possibly its successor.

Experimental searches for SUSY continue at the LHC with both the ATLAS and CMS detectors, and Adelaide contributes to this with our involvement in ATLAS. No SUSY particles have yet been observed, and the simplest SUSY models (for example the Minimal Supersymmetric Standard Model or MSSM) are beginning to experience some tension with experiment.

The theory group is actively involved in studying extensions of the MSSM and in studying fine-tuning of these extensions in order that they be consistent with current experimental constraints.

One of the most important unsolved problems in current physics is the nature of the dark matter that apparently fills much of the universe. We are co-leading an international effort to combine all relevant astrophysical and particle physics data in order to understand the particle physics of dark matter.

Current projects include the development of quantum field theories for explaining dark matter observations, and using measurements coming from direct search experiments, gamma ray astronomy and the LHC to understand which current models are viable.

CoEPP also is involved in the development of the Stawell Underground Physics Laboratory (SUPL), where various experiments will be located including the southern installation of the SABRE dark matter-detection experiments.

CoE for Dark Matter Particle Physics

There are alternative approaches to extend the Standard Model other than through SUSY, which include:

• Grand Unified Theories;
• extra-dimensional models such as Randall-Sundrum type models; and
• Composite Higgs models of various types, such as Technicolour (that is essentially ruled out already), Little Higgs models and models where the Higgs is a pseudo-Nambu-Goldstone boson.

The Standard Model is correct until it fails a test - any test. In addition to the direct tests at the LHC, there are a number of very subtle, high-precision processes that can be probed at lower energy, including a precise determination of the parton distribution functions of the proton.

We are particularly interested in the search for new physics in parity-violating electron scattering, and a number of anomalies surrounding the muon, its interactions and properties.

The collisions at the LHC provide a precise laboratory for testing our understanding of quantum chromodynamics (QCD), from subtle flavour dependence to nuclear effects in proton-lead and lead-lead collisions that promise new insights into the role of quarks and gluons in nuclear structure.

We lead searches for BSM physics using the presence of third-generation Standard Model particles as a probe.

Data collected with the ATLAS experiment are interrogated using kinematic techniques developed by our group to search for evidence of squarks and gluinos decaying to produce tau leptons, or direct production of the top and bottom squarks yielding final states enriched in b-jets, charged leptons and missing transverse momentum.

We perform analyses of the data collected with ATLAS, study the environment in which physics will occur during the phase-I (2019-) and phase-II (2023-) upgrades and develop tools useful to our collaborators.

The data are further used to search for evidence of long-lived particle signatures which yield slow-moving particles and displaced vertices in the detector.

As members of the Belle II experiment, we are involved in the next generation of flavour physics experiments. Following on from the pioneering work of the BaBar and Belle experiments, Belle II aims to probe the asymmetric electron-positron collisions of the SuperKEKB accelerator to produce peak luminosities around 50 times higher than those previously achieved.

The experiment aims to collect a dataset 100 times greater than those of its predecessors, opening a new window to precision flavour physics.

This environment will provide a unique window to make precise measurements of deviations from the Standard Model, and is a complementary approach to the experiments at the LHC where the 'energy frontier' is probed, compared to the 'precision frontier' at Belle II.

The generic high-bandwidth data acquisition (DAQ) development with reconfigurable cluster element (RCE) concept on Advanced Telecommunications Computing Architecture (ATCA) is a primary readout technology candidate for the ATLAS upgrade. The concept has been adopted by many other experiments (LCLS, LSST, LBNE, HPS...) for a broad user community.

In Adelaide we have a High-Energy Physics DAQ laboratory in which this technology is studied as a candidate for the readout of the Inner Tracker (ITK) of the ATLAS phase-II upgrade. The phase-II upgrade is priced at around $300 million and synergy among the readout approaches of the silicon strip and pixel detectors may be a key driver in helping reduce the cost.

Our RCE test stand, using next-generation equipment, is built to demonstrate the viability of this approach to providing a DAQ solution for silicon detectors of the future.

This work is in collaboration with SLAC, Stanford University and CERN. We are also working on the development of beam loss monitors for Future Linear Colliders in collaboration with CERN, the Australian Synchrotron and the University of Liverpool.

Working in close conjunction with the South Australian Health and Medical Research Institute (SAHMRI) and the Royal Adelaide Hospital, we are developing tools to simulate the beam delivery in the Molecular Imaging and Therapy Research Unit.

We are also working with staff at SAHMRI and Jefferson Lab to develop a better understanding of the Relative Biological Effectiveness of protons used in cancer therapy, with the aim of developing improved treatment protocols.

The high-energy physics group at the University of Adelaide is actively involved in the grid and cloud computing activities of CoEPP, through the LHC grid for ATLAS and also with other experiments such as Belle II at KEK.

Adelaide operates its own Tier 3 site in the LHC Grid. The storage is made available through eRSA resources funded through Research Data Services (RDS) and the processing capabilities are made available through the National eResearch Collaboration Tools and Resources (NeCTAR) Project.

Adelaide continues to play a leading role through the development of each of these activities.