The Deep Underground Neutrino Experiment (DUNE) is a neutrino experiment in the mid-western United States. The experiment is currently being developed by an international team of 1000 scientists from 30 countries. Construction will start in 2019 and DUNE plans to start taking data in 2026.
There are three known types of neutrino: electron, muon and tau. Neutrinos have the unusual property that they change from one type to another as they travel a few hundred km; this is known as "neutrino oscillation". DUNE will make a beam of muon neutrinos or muon antineutrinos at Fermilab in Chicago; the properties of this beam will be first be measured by a detector only 600 metres from where the neutrinos are made, which is too short a distance for changes of type to occur. The beam will then travel 1300 km through the earth to a huge underground far detector at the Sanford Underground Research Facility (SURF) in South Dakota, which will measure it again to look for changes of neutrino type.
DUNE scientists will look for differences between neutrinos and antineutrinos in the way they change type. This could provide an answer to one of the most fundamental questions in physics: why do we see only matter in the Universe when equal quantities of matter and antimatter were created in the Big Bang ? It is possible that neutrinos hold the key to this mystery, and DUNE will enable scientists to find out.
The difference in neutrino oscillation between muon neutrinos and muon antineutrinos is quantified by a parameter called δCP, which can take any value from 0 to 360 degrees. If δCP is 0 or 180 degrees, there is no difference in neutrino oscillation between neutrinos and antineutrinos. The further away from 0 or 180 degrees the value of δCP, the larger the difference in oscillation between neutrinos and antineutrinos.
DUNE will make measurements of the value of δCP by looking at differences between oscillation from muon neutrinos to electron neutrinos and muon antineutrinos to electron antineutrinos. For this reason, the neutrino beam will be of muon neutrinos 50% of the time and muon antineutrinos the other 50%.
In order to make these measurements, it is essential to have a very large far detector. The DUNE far detector will consist of four large liquid argon time projection chambers (LArTPCs).
The LArTPCs will be located 1500 metres underground at SURF, which is in a disused gold mine in South Dakota. Each of the four detectors will contain 10000 metric tons of liquid argon cooled to -190oC. LArTPCs give excellent tracking of charged particles as they pass through the detector, and their energies and positions in the detector can be measured very accurately.
Other aims of DUNE are:
- Neutrino mass hierarchy: oscillations between one neutrino type and another take place according to the mathematics of quantum mechanics. This mathematics tells us that oscillations can only occur if neutrinos have different masses. To be precise, oscillations depend on the difference between the squares of the masses of two of the neutrinos. These squared masses are usually written as m12, m22 and m32. We know from observations of neutrinos from the Sun that m22 > m12, but it is not currently known whether m32 is > m12 and m22 or < m12 and m22. This ordering of the squared masses is known as the "neutrino mass hierarchy"; DUNE will make measurements that aim to determine which ordering is correct.
- Search for physics beyond the Standard Model including proton decay, heavy neutral leptons and non-standard neutrino interactions.
- The far detector will be ready to detect low-energy neutrinos from a core-collapse supernova if one occurs.
Physicists at the University of Warwick are making several important contributions to DUNE; please look here for more details of them.