Muon detector from IP2I will kick-start cosmic-ray research at SU and UWC

​Cutting edge technology in the form of a muon detector on loan from the Institute of Physics of the Two Infinities (IP2I) in Lyon, France, will kick-start cosmic-ray research at Stellenbosch University (SU) and the University of the Western Cape (UWC).

The exchange forms part of a series of scientific studies to determine the merits of constructing a deep underground laboratory north to the Huguenot tunnel in the Du Toitskloof Mountain pass between Worcester and Paarl. South Africa's Department of Science and Innovation (DSI) recently allocated seed funding of R5 million for scientific and engineering studies to determine the feasibility of the proposed Paarl Africa Underground Laboratory (PAUL). If it goes ahead, it will be a first for Africa and only the second such laboratory in the southern hemisphere.

The muon detector was developed by Dr Jacques Marteau, a particle physicist at IP2I, a joint research unit of France's National Centre for Scientific Research (CNRS) and Claude Bernard University Lyon 1. Martineau will be working closely with Dr JJ van Zyl, an experimental physicist at SU's Department of Physics, and Prof. Robbie Lindsay from UWC's Department of Physics and Astronomy and their postgraduate students.

What are muons?

Muons are fast moving, heavy electron-like particles that are naturally produced in the atmosphere when energetic cosmic rays from interstellar space interact with atoms and molecules high up in the atmosphere.

"We are bombarded by about 10 000 muons per square metre per minute. Or, about one muon goes through your outstretched hand every second.," Van Zyl explains.

Muons are unstable and decay within 2 millionths of a second, but because they travel close to the speed of light, they are fast enough to pass through matter over long distances without being absorbed.

"Like electrons, muons are negatively charged. But they are also 200 times heavier than electrons. This means they lose energy when passing through matter like the atmosphere and mountains, but they lose only a small amount of energy for every centimetre of material, depending on its density. A cosmic muon reaching the top of the Du Toitskloof Mountain will lose about 5% of its energy for every meter it passes through. After about 20 metres of rock, they will be stopped. Only the very large energy muons will make it through the 800 metres thick bedrock that covers the Huguenot tunnel," he explains.

One of the first projects will be to measure the muon background and flux in the tunnel and image the geology of the bedrock above and around the Huguenot tunnel. This will help to determine the criteria for the construction of PAUL in a service tunnel to the north of the main tunnel and will be important for the design and set-up of detectors in the future Paarl Africa Underground Laboratory.

Worldwide, deep underground laboratories are used to observe and study so-called rare events, that is, when neutrinos and dark matter particles interact with ordinary matter. Neutrinos are extremely light sub-atomic particles that do not emit, absorb, or reflect light, and are therefore extremely difficult to observe. Dark matter, on the other hand, makes up nearly 85% of the mass of the universe, yet there is still no clear theory of what it is.

Van Zyl says there are currently a plethora of experimental techniques out there that are trying to gain sensitivity to the small signals left by the interaction between dark matter and ordinary matter particles: "Rather than build ever larger detectors, the challenge is to develop detectors with very low energy thresholds and excellent control over detector backgrounds. The last few years have seen significant efforts in the direct-detection community on building small-scale experiments that can probe low-mass dark matter."

He is excited about the prospect of having access to an underground research facility a stone's throw from the Stellenbosch campus: "I believe this initiative will foster valuable collaborations with other similar facilities and create opportunities where local students can be trained in advanced detector development."

On the photo above: Physicists from Stellenbosch University and the University of the Western Cape are eager to start experimenting with a plastic scintillator type of muon detector, on loan from the Institute of Physics of the Two Infinities (IP21) in Lyon, France. From the left are Dr J.J. van Zyl, MSc student Stephan Jonker and Prof. Richard Newman - all from Stellenbosch University. Next to them are Prof. Robbie Lindsay and Dr Lumkile Msebi from the University of the Western Cape, followed by Prof. Faïrouz Malek and Dr Jacques Marteau, both affiliated with the National Centre for Scientific Research (CNRS) in France. Photo: Ignus Dreyer

Media enquiries​​

Prof. Richard Newman

Stellenbosch University, Department of Physics

E-mail: [email protected]

Mobile: +27 83 447 8928​

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