A milestone for the DUNE experiment: scientists measured the first neutrinos with a prototype detector on 10 July. This prototype was built in an existing neutrino beam at the Fermilab accelerator in the US. Measuring the neutrinos is an important step towards validating the design. Nikhef PhD student Marjolein van Nuland-Troost was involved in the installation, software and analysis.
The 2×2 prototype consists of four modules containing liquid argon. When neutrinos pass through this argon, they can interact with argon particles, and this can be measured. In the final design of the DUNE near detector, there will be 35 such liquid argon modules, all larger than the prototype.
The fact that this 2×2 prototype works is an important step for the experiment. ‘With this prototype, we mainly want to show that the modular design works.’ explains Van Nuland-Troost. ‘That the individual components work well has already been extensively tested. But that gives no guarantees for the whole system together. With this experiment, we can see exactly what the impact is of dividing the detector into modules.’
Compared to the final near detector, the prototype is only small. But Van Nuland-Troost stresses that it is nevertheless impressive ‘There is so much to take into account, an enormous number of systems that all have to work together. And that to the millimetre and nanosecond, in liquid argon, at a temperature of -186 degrees Celsius, in a strong electric field. It’s great to see how everything comes together. And that this allows us to make images of neutrino interactions!’
Next steps
Now that this step has been taken and the data has been collected, it’s time for further analysis. ‘What exactly did we measure? What does it mean? Are improvements of the detector needed? ‘ Van Nuland Troost continues. ‘In addition, we are already working on a prototype of the final size. Because even a small scale change can have unexpected consequences and needs to be tested beforehand.’
About the DUNE experiment
The future DUNE experiment should be operational by 2028. The idea is that an accelerator at Fermilab produces neutrino particles that fly straight through the earth. Near this accelerator in Illinois is then the underground near detector that characterises the neutrino beams at the beginning of the journey. 1,300 kilometres away, at the Sanford Underground Research Facility in South Dakota, is the far detector, also underground. By studying the neutrino particles before and after the journey, scientists aim to learn more about particle change, possible new particles and other subatomic phenomena.
Measuring enigmatic neutrinos with DUNE
Neutrinos are almost massless elementary particles that hardly interact with other matter. They fly virtually unhindered by matter and are therefore very difficult to measure. Neutrinos exist in three variants and constantly change identities: electron, muon and tau neutrinos. Fermilab will produce anti-muon neutrinos and muon neutrinos for the experiment.
In the DUNE experiment, a neutrino occasionally collides with an argon particle. This interaction produces other particles, some of which are charged. And when those charged particles in turn fly through the argon, they leave behind a trail of electrons. These electrons can be collected with the help of an electric field, and with this an image can be made of the (charged) reaction products. This allows scientists to learn more about neutrinos and their interaction.
The properties of neutrinos are still puzzling, for instance their masses and mass ratios are not well known. However, they do form an essential part of the Standard Model of particle physics. So knowing more about neutrinos is an important link to better understand matter and forces in the universe.
The role of Nikhef
The DUNE project now involves 200 institutions in 36 countries, including researchers from Nikhef. Nikhef has long been closely involved in ProtoDUNE, a preparatory project at CERN in Geneva, says project leader Paul de Jong.
For DUNE, Nikhef sees opportunities mainly in the construction of the so-called near detector at Fermilab. The work at Nikhef mainly involves researchers from the Neutrino Physics section, which also builds and operates, for example, the KM3NeT neutrino detector in the Mediterranean Sea. KM3NeT studies neutrinos from the cosmos.