Ariadne

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 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.”

The current focus however is on developing the detector, validating the technology and assessing its effectiveness with respect to detecting neutrinos. The project is currently in the construction phase, and the plan is to build the detector on a fairly rapid timescale, after which it will be taken to CERN for validation. “A primary aim in Ariadne is the characterisation of the technology for the neutrino sector. So we will do that at CERN on a charged particle beam,” outlines Dr Mavrokoridis. Beyond probing some of the most fundamental question in physics, the Ariadne detector could potentially also be applied in medical imaging to help diagnose disease. “Ariadne can be used to take photographs of gamma particles, and by taking photographs of these low-energy gammas, potentially you will be able to tell where they came from. This is something that could be used in medical imaging,” explains Dr Mavrokoridis. “The current positron emission tomography (PET) scanners use positrons to detect gamma rays in the body.”

A better level of resolution of where these gamma rays are coming from would enable medical professionals to identify smaller tumours, which could lead to earlier diagnosis. Dr Mavrokoridis says the project is looking to demonstrate the feasibility of this approach to medical imaging, but at this stage they are not looking to take it any further. “We’ll try to see if it is feasible. Ariadne will be able to tell you – ‘well actually, if you give me a source in that position, I can trace back to that position with that kind of accuracy,’” he outlines. While the development of the ARIADNE Operation Principle detector holds important implications in terms of medical imaging, Dr Mavrokoridis is keen to stress that this is not its sole application, and researchers will be keen to use it in investigating new physics. “Currently there’s a lot of momentum behind the development of liquid argon detectors amongst the neutrino research community, so the Ariadne detector is going to have a tremendous impact if it’s successful,” he enthuses.

Full Project Title

ARgon ImAging DetectioN chambEr (ARIADNE)

Project Objectives

The ERC Starting Grant ARIADNE project aims to develop optical-based LAr TPC readout technologies for direct imaging of secondary scintillation light produced by electron avalanches in THick Gas Electron Multiplier (THGEM) holes within two-phase Neutrino Detectors. This approach has the potential to revolutionize future giant LAr Neutrino experiment design, offering highresolution imaging and a lower energy threshold thus enhancing the potential for new Particle Physics discoveries.

Project Funding

European Research Council (ERC) Starting Grant for ARIADNE

Project Partners

• European Organization for Particle

Physics (CERN), Geneva, Switzerland

Contact Details

Project Coordinator, Dr Konstantinos Mavrokoridis Lecturer in Experimental Particle Physics Department of Physics Oliver Lodge Laboratory University of Liverpool L69 7ZE, UK T: +44 (0)1517943378 E: k.mavrokoridis@liverpool.ac.uk W: hep.ph.liv.ac.uk/ariadne

Dr Konstantinos Mavrokoridis

Segmented THGEM Prototype Assembly

Images of Muon tracks taken with the ARIADNE Demonstrator. Dr Konstantinos Mavrokoridis is a lecturer in experimental particle physics at the University of Liverpool. Having started his career in Dark Matter searches, he now focuses on detector development for Neutrino Physics. He has established and runs the Liverpool Neutrino Liquid Argon program, developing new detector technologies for future giant LAr Neutrino experiments.