Centre for Dark Matter Particle Physics

The nature of dark matter is one of the great questions of modern physics.

We know dark matter ("DM") exists- but we do not yet know what it is. This is no small problem, since dark matter constitutes nearly five times as much of the universe's mass-energy as does the ordinary (or baryonic) matter that we see (us, our world, planets, stars, galaxies...).

The ARC Centre of Excellence for Dark Matter Particle Physics (CDMPP) is dedicated to this question. What is dark matter? What are its properties? What role does it play in the universe? Can we detect it? 

The Adelaide node of the CDMPP hosts researchers and students who are part of this endeavour. Our work ranges from theoretical research into the possible nature of dark matter particles, to helping to build the southern hemisphere's first underground dark matter direct-detection experiment. 

We collaborate not only with the other CDMPP nodes (and associated institutions such as ANSTO) across Australia, but also with researchers at overseas institutions such as CERN, INFN/LNGS, MIT and Caltech, amongst others.

The structural relationship between dark matter (red), gas (blue) and galaxies (yellow), in a simulation by Florent Renaud.

Science/engineering-based video channel Veritasium visited Australia recently, producing a video discussing the search for dark matter, and the roles of SABRE South and SUPL in this endeavour.


Research

  • Experimental

    Cross-section of SABRE South

    Cross-section of the SABRE South experimental hardware.

    The Adelaide node is involved in the construction of the SABRE South direct-detection experiment. This experiment will hunt for a candidate type of particle known as WIMPs (Weakly-Interacting Massive Particles), and will be located around 1,000 metres below ground in the Stawell Underground Physics Laboratory (SUPL) in western Victoria.

    We are contributing effort in a number of areas, including:

    • modelling and experimental characterisation of the background radiation in SUPL;
    • simulation of the overall behaviour of the experiment, using GEANT4
    • the optical calibration system for the liquid veto;
    • crystal purity measurements;
    • the fluid-handling system (high-purity nitrogen, liquid scintillator);
    • and to broader areas such as organisation and equipment specifications.
  • Theoretical

    We also undertake investigations into the theoretical side of dark matter physics, including the following:

    • using the SABRE experiment for the detection of axions (another class of candidate DM particles, of much lower mass than WIMPs);
    • the inelastic boosted dark matter (IBDM) model, which will be tested by the SABRE experiment;
    • a two-component dark matter model, taking into account the gravitational focusing effect, which will attempt to put constraints on the dark matter parameter space by analysing the experimental data of direct detections;
    • dark photon searches from the global QCD analysis (with JAM Collaboration at Jefferson Lab, USA).

Research notes

  • Sensitivity of Parity-violating Electron Scattering to a Dark Photon

    The ARC Centre of Excellence for Dark Matter Particle Physics (CDMPP) aims to discover what this mysterious stuff, dark matter, is made of. It is five times as plentiful as the baryonic matter we have explored so successfully, and of which we are composed. We do not know what kind of particle it is, but we (along with a very large number of people around the world) want to understand this. One key approach is the SABRE experiment that is being built in a new laboratory in a gold mine (1km underground) in Stawell, which will hopefully shed light on this question in a few years. 

    The present work, published in Physical Review Letters1, explores the possibility that dark matter is in the form of  a dark massive photon. In particular, we explore the discovery potential of the new tool enabled by the upgrade at Thomas Jefferson National Accelerator Facility (JLab) in the United States. 

    This new tool is parity-violating electron scattering. Parity violation is, simply put, the difference between what happens in the laboratory and what happens when you view the experiment in a mirror. The differences are very small, typically less than a part per million, but incredibly precise measurements enable us to observe this and use it as a signal of the existence of this new particle.

    We show that the effects of this new particle may reconcile a surprising discrepancy between the neutron density in a lead nucleus inferred from the PREX experiment at JLab, and that predicted by nuclear structure theory. We also show that there may be corrections as large as 10% in the valence quark distributions extracted from data taken at HERA in Germany. Finally, it is shown (see figure below) that a future experiment comparing electron and positron deep inelastic scattering on the deuteron could provide a vital test of the existence of such a particle.

     

    1 A. W. Thomas, X.-G. Wang and A. G. Williams, Physical Review Letters 129 (2022) 011807

    dark photon figure

    Figure: Relative size of the correction to the measured difference in the cross section for electron versus positron scattering from the deuteron.