New light on dark matter Dark matter is the focus of a great deal of attention in research, yet mystery still surrounds its nature and structure. The DarkSPHERE project aims to shed new light on the topic through experiments with Spherical Proportional Counters, an innovative type of detector that will open up new possibilities in research, as Dr Ioannis Katsioulas explains. Evidence from astronomical
and astrophysical observations points to the existence of dark matter, which is thought to account for around 85% of the matter in the universe, yet its nature is still unknown. Based at the University of Birmingham, Dr Ioannis Katsioulas is leading the DarkSPHERE project, an initiative which aims to shed new light on dark matter, focusing on the 0.05-10 GeV (the proton has a mass of approximately 1 GeV) mass region. “Our aim is to tune our experiment to look in this region, specifically below 2 GeV,” he outlines. A novel type of detector called a Spherical Proportional Counter (SPC) will be used in this work. “It’s essentially a big sphere, with which we can read-out the signals induced inside the gaseous volume of the detector,” explains Dr Katsioulas. “There is an anode at the centre of the sphere. Whatever interactions take place in the volume of the detector, produce free electrons that drift towards the anode, to create a signal.”
Dr Katsioulas and members of the University of Birmingham installing an SPC in the Boulby underground laboratory for neutron background measurements.
DarkSPHERE Search for light Dark Matter with a Spherical Proportional Counter Funded under H2020-EU.1.3.2. Marie Skłodowska-Curie Fellow, Dr Ioannis Katsioulas School of Physics and Astronomy University of Birmingham Edgbaston Campus, B15 2TT Birmingham, United Kingdom T: +44 0 121 4144623 E: i.katsioulas@bham.ac.uk W: http://darksphere.eu/ Dr Ioannis Katsioulas is a Marie Skłodowska-Curie fellow at the University of Birmingham. He was awarded his undergraduate and doctoral degrees at the Aristotle University of Thessaloniki, Greece. He has spent three years at CEA Saclay, Paris developing novel detector technologies. He’s an experimental particle physicist with a particular interest in dark matter searches and neutrino physics and a founding member of the NEWS-G experiment.
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The NEWS-G 140 cm in diameter SPC during installation in SNOLAB, Canada.
Spherical Proportional Counter The spherical shape allows the construction of large volume low capacitance detectors which results in low electronic noise, together with the large amplification of the signal, allows for single-electron detection threshold making the SPC ideal for light dark matter searches. “In order to detect light dark matter, you need to be able to detect very faint electric
matter to generate a signal, and this is done through ionisation.” The detector itself is at SNOLAB in Canada, where the experiment will be conducted. SNOLAB is located deep underground, which helps to reduce background from cosmic radiation. “The basic goal with this type of experiment is to reduce the background as much as possible. We put the detectors under the surface of the earth to reduce any cosmic ray flux to a very minimal level,” explains Dr Katsioulas. The detector was assembled underground, from pure copper parts that were quickly moved there to reduce cosmogenic activation. On the inside surface of the copper hemispheres, a layer of ultra-pure copper was deposited using an innovative method called electroforming, to further reduce background. In the near future, a new detector will be put together entirely underground at the SNOLAB which Dr Katsioulas says will also help reduce the background further and improve sensitivity and discovery potential. “We will build an electroformed detector underground with ultra-pure copper, which contains miniscule amount of radioactive isotopes,” he continues. “We’re also considering future upgrades of the detector’s capabilities, and how it can deal with high gas pressure underground.” This is a highly ambitious project, with researchers looking to extend dark matter searches to an unexplored region, which would represent a major scientific breakthrough. Alongside this exploratory research, Dr Katsioulas and his colleagues also plan to utilise the detector for certain industrial applications. “We
In order to detect light dark matter, you need to be able to detect very faint electrical signals, at the level of a single electron. signals, at the level of a single electron to a few electrons,” says Dr Katsioulas. The nature of dark matter means it cannot be observed directly, but researchers can find evidence of these particles through their wider effects. “We cannot really see the dark matter passing through the detector. If it passes without interacting with the normal matter then we won’t see anything.” explains Dr Katsioulas. “But the SPC is an ionisation detector. We can convert part of the kinetic energy of the dark
are investigating how to use this technology for neutron spectroscopy for example, and to help understand the neutron background in rare event searches,” he says. Another potential application of the detector is in medicine, where the use of radiation treatments can lead to the production of neutrons. “The production of neutrons in a medical environment could be dangerous for the people working there, as well as patients. It would be fantastic if we could use the detector to measure these effects,” concludes Dr Katsioulas.
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