Next generation detector to probe new physics A type of elementary particle, neutrinos hold enormous scientific interest, as they enable researchers to probe physics beyond the standard model. Dr Kostas Mavrokoridis tells us how the Ariadne project’s work in developing a next generation neutrino detector could open up new avenues of investigation in particle physics A type of elementary particle that lacks an electric charge, neutrinos are an area of enormous scientific interest, now researchers are aiming to develop effective detectors to analyse them further. As neutrinos don’t have an electric charge they don’t present any information to a detector on their own, yet Dr Kostas Mavrokoridis says it is possible to detect them through their interactions with other particles. “We can measure the products of neutrinos,” he explains. Based at the University of Liverpool in the UK, Dr Mavrokoridis is the Principal Investigator of the Ariadne project, an ERC-backed initiative aiming to develop a next-generation liquid argon neutrino detector. “Once a neutrino interacts with the liquid argon detector, it’s going to give you other particles. These other particles have a charge – and as they are charged particles, we can record them,” he continues. “We want to precisely record these particles. In their path, these particles leave tracks, and from these tracks, you can then do energy calibrations, look at complex vertices and do new physics.” This kind of research could lead to new insights into physics beyond the current standard model. While it was predicted in the standard model that neutrinos don’t have mass, research has since shown that this is not in fact the case. “We know now that neutrinos do have mass – that was part of the Nobel Prize in 2015,” says Dr Mavrokoridis. The standard model in general is very robust, but not when it comes to neutrinos, now researchers aim to gain further detail about their properties; major topics of interest include dark energy, dark matter and the a-symmetry between matter and antimatter. “Why are we living in a matterdominated universe and not in an antimatter dominated universe? What caused that?” asks Dr Mavrokoridis. “We have found that other types of particles and their anti-particles don’t behave in the same way. Now we need to find if that’s 70
the case for neutrinos – if they don’t then there’s a charge parity violation there. There are theoretical models to describe the behaviour of neutrinos, yet there is scope to improve the precision of the parameters.”
ARIADNE scale model
Once the neutrino interacts with the liquid argon detector, it’s going to give you other particles. These other particles have a charge – and as they are
charged particles, we can record them
Ariadne detector The Ariadne detector could have a significant impact in these terms, revolutionising the design of future experiments and opening up new research opportunities. Ariadne is designed as a
two-phase detector, meaning that there is a liquid, and on top of the liquid there is also the gas phase of the argon. “When a particle passes through the detector it ionises the argon – so it frees the electrons. So we get all these free electrons, then we apply an electric field, and the electrons drift to the surface of the liquid, then you apply a higher electric field, and extract them to the gas phase,” says Dr Mavrokoridis. There is a device on top of the gas phase called a Thick Gas Electron Multiplier (THGEM), which amplifies the electrons still further. “The THGEM has very small holes – around 500 microns – and within these holes, we then accelerate these electrons that we’ve just taken out to the gas phase of the detector,” outlines Dr Mavrokoridis. “If you accelerate electrons very fast in gas then you create even more electrons. So you have a multiplication, a cascade of electrons.” This type of experiment can generate large quantities of data. The unique point about Ariadne is that instead of dealing with potentially millions of strips, as would be the case with a conventional detector, electrons are processed in the holes on the THGEM to also generate light. “On top of generating electrons – or charge – we also generate light in the 128 nanometre wavelength, so it’s a vacuum ultraviolet light. Then we have a camera on top of that detector – and this camera is sensitive enough to take a picture of this light. Essentially now we are able to photograph the tracks of the particles,” explains Dr Mavrokoridis. This is potentially an easier and more efficient way to track particles, while Dr Mavrokoridis says this could also open up new avenues of scientific investigation. “As you are generating more light than charge in the THGEM holes, this could mean the detector will be more sensitive to lower energy levels. That potentially allows you to also go to lower energy physics – such as dark matter,” he says. “This type of detector is a very similar technology to a dark matter detector, although the read-out is different.”
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