Léo RamosSince September 2013, when he assumed the position of director of Fermilab, the main U.S. particle physics lab, Nigel Lockyer, a Scottish-American physicist raised in Canada, has dedicated much of his time to attracting new international partners for the Deep Underground Neutrino Experiment (DUNE), a billion dollar megaproject that will try to discover new properties of neutrinos, a slippery almost-massless elementary particle that travels at very close to the speed of light. Although they are considered the second most abundant particle in the Universe, second only to photons, neutrinos are extremely difficult to detect because they barely interact with other particles.
The DUNE project provides for the construction of an underground source emitting a beam of neutrinos at Fermilab, outside Chicago. This particle beam will travel underground and be observed by two detectors: one at a depth of 600 meters, located at Fermilab, and a second, larger detector at a depth of 1.47 kilometers, at the Sanford Laboratory, in Lead, South Dakota, 1,300 kilometers from Chicago. The physicists hope that, on this long journey far from the atmosphere, the neutrinos will provide clues as to their most elementary characteristics and perhaps help us understand why the Universe has more matter than antimatter. “Fermilab is a large laboratory that needs a large project, involving the best scientists, that really broadens our knowledge,” says Lockyer, former director of TRIUMF, the Canadian particle physics laboratory. He recognizes that the United States became less relevant in particle physics after the European Organization for Nuclear Research (CERN) launched the Large Hadron Collider (LHC), the largest particle accelerator in the world, on the outskirts of Geneva in 2008.
In 2014, what is known as the P5 report, produced by a group of particle physics specialists, recommended that the United States concentrate its efforts in the area and develop a large neutrino experiment, in addition to collaborating closely with the LHC and supporting the construction of a linear particle collider in Japan. DUNE is the large neutrino project. This is the first time that the United States has proposed basing a huge international project on its home soil. In this interview, granted during a visit to FAPESP in August 2015, Lockyer talks about the plans to set up the experiment and possible Brazilian participation in the project.
What is the purpose of your visit to Brazil?
The main reason is to discuss the neutrino physics that will be studied through DUNE, which we see as the future of the particle physics research program in the United States. DUNE is just starting. From the beginning I have discussed with [Carlos Henrique de] Brito Cruz [FAPESP’s scientific director] the possibility of Brazil participating in this project, contributing to selecting the technologies that will be used. I wanted to meet with him in person. Until then we had only talked on the phone, the last time during the 2014 World Cup.
How is the international collaboration to implement DUNE coming along?
Twenty-six countries are already involved, most from Europe. In the Americas, Brazil is the country that has shown the most interest. Some researchers from São Paulo State are already working on experiments at Fermilab, both with neutrino beams and with electrically charged particle beams, which are a platform for development and evaluation of ideas for DUNE. The basic idea is to create a neutrino beam at Fermilab and, since the Earth is curved, point it downward and make it emerge in the right place. We are building an experiment in an old gold mine called Homestake in South Dakota, about 1 mile down. Since it is at a depth of 4,850 feet [1.47 km], we call this site level 4850. We will build a cryogenic detector containing liquid argon, with a total mass of 70,000 metric tons. It will be incredibly large.
Reidar Hahn / Fermilab The Cockcroft-Walton generator, one stage of the Fermilab particle acceleratorReidar Hahn / Fermilab
The project budget is $1.5 billion?
That is just the United States’ contribution. We don’t talk about the total so as to avoid scaring people. The project has not been defined yet. We are inviting everyone to participate in the project from the beginning and we ask all contributors what they would like to do. I’m putting all the possibilities on the table. We have closely followed the LHC governance structure because we have seen that it is a successful model. Relying on research funding agencies for each decision is important. But we need to have a board, like CERN does, to arbitrate when necessary. At the same time, the U.S. government wants a single person in command, who can be consulted when there is some problem.
Isn’t this international focus different from that usually adopted by the U.S., which tends to carry out its projects more independently?
Yes, very different. This is the first time that the United States has proposed basing a huge international project on its home soil. It is also the first time that CERN will invest in a project in another country. We promised to help them with the LHC and they promised to help us with neutrinos.
Is this new scenario the result of successful work at the LHC as well as the lack of financing for research, and not only in the U.S.?
I strongly believe in global planning for particle physics. The projects are very large. We have the European plan, the U.S. plan and the Asian plan. Little by little we need to reconcile the plans, because we will need an even larger structure in the future. We must learn to work together from the beginning. The director of the Office of Science and Technology Policy, John Holdren, has shown a good deal of interest in DUNE. He says that this is how we should do things in the future. Energy Secretary Ernest Moniz has a background in neutrino physics and really understands what we are trying to do.
What are the difficulties expected in carrying out this new neutrino experiment?
The hard part is convincing the U.S. government to start DUNE before knowing if other countries will participate in the project. But I often say that if we start, others will join us. Everyone is involved, but investment agreements take years. We are hoping for an agreement with CERN, which will give the government confidence that other countries will participate. CERN represents the funding agencies of 21 countries. The European organization will vote on the budget in September 2015. A year earlier, CERN approved funding to build a development platform that would allow it to work together with any country on a neutrino research program. Whether the country would be the United States or Japan was left open. This, however, allowed European physicists working at CERN to develop prototypes of neutrino detector components.
Is Japan also considering investing in a large neutrino experiment that would compete with DUNE?
Certainly. They can choose to build an extension for their current neutrino detector, the Super-K, which currently has a 50,000 metric ton tank of water. They have been talking about increasing it to 1 million metric tons of water, which is unbelievable. But this expansion will depend on the decision they make with respect to building the International Linear Collider. Of course we would like Japan to join us. We’ll have to wait and see what their position is. I don’t think that they can pursue projects, the collider and a neutrino experiment.
What kind of partnership in DUNE are you proposing for Brazil?
We are trying to motivate Brazilian physicists interested in our program to, first, become part of the Fermilab community through collaboration. They should say what they want to do, indicate what part of the detector they would want to be responsible for. All groups are working that way. Then would come the research funding part. I have not yet been in any other country in South America, but there are signs of interest from others. There are physicists here who have already participated in Fermilab experiments to carry out their research. We would like Brazil to think about the possibility of forming a group with 10 leading researchers, with a critical mass focused in one area. That is what we do in Canada: we focus on specific areas in order to have an impact in the field. Brazilian physicists were interested in the light collection area. When an electrically charged particle passes through liquid argon, it emits light at different frequencies. In this case, the most obvious thing would be to build detectors in the far ultraviolet range to record very fast information, since it is light. In DUNE, we’ll be looking at the properties of neutrinos coming from a particle beam created at Fermilab, neutrinos arising from the collision of cosmic rays in the upper atmosphere, which creates a shower of particles, and also neutrinos coming from the explosion of stars, like supernovas. The liquid-argon detector will allow us to identify and separate the different types of neutrinos. It will be possible to see the details of the formation of a neutron star. If we are lucky, this neutron star will form a black hole, whose signals we will be able to see.
Is it true that particle physicists in the United States, Europe and Japan will divide up the different lines of research in this field of knowledge, given that there is not enough funding for all them to focus on all lines?
It is the funding agencies that say that you cannot do everything everywhere. Physicists would never say this, because we like to do everything everywhere! But, in fact, you cannot work like that, it would require a lot of money. DUNE is a huge project. No one will build a similar project in a different location. It would make no sense. We need to bring together all of the world’s specialists to build the equipment for DUNE. And we have to make it work. Fermilab worked on high-energy particle collisions for more than 20 years [before the LHC, the largest particle accelerator was the Fermilab Tevatron that operated from 1987 to 2011]. The United States began to build a supercollider in Texas, which was to be larger and more powerful than the LHC, but the project was canceled in the early 1990s for financial reasons. The LHC wasn’t. The question then arose: who would like to build a linear collider, which is a machine to study particles more precisely? Europe already has the LHC. The United States could build a linear collider. But it is too expensive. When I arrived at Fermilab, I said that they should invest in a neutrino beam jointly with other countries. There is no reason to do it alone. Things don’t work that way nowadays. CERN will not have a neutrino beam. Their priority is to take advantage of the LHC and do neutrino research somewhere else. Thus, what we are doing is asking for help. We can do more if partners want to contribute to the project. In neutrino physics, it is the total mass that matters. Few neutrinos will interact with the detector each day, maybe even only one. Thus, if we can double the size of the detector, we would have two neutrinos interacting.
After the LHC, is it no longer worth it to build small machines to make discoveries in particle physics?
Some things will be small, but there will be mega-science projects, and these will be increasingly larger. The accelerator that will succeed the LHC has been called the Future Circular Collider (FCC). We say, jokingly, that FCC could stand for Future CERN Collider, Future Chicago Collider or Future China Collider. The meaning of the acronym will depend on where the accelerator will be housed. It could have a circumference of up to 100 kilometers. The world wants to build this machine, but, ironically, no country has enough resources. So the FCC will be a global machine. There is no doubt about this. No one knows, either, where neutrino physics will go. It is a new area to be explored, in some ways.
When do you expect that the DUNE neutrino detector will begin operating?
In 2021 or 2022 we intend to commission its first module. We talk about two numbers: total mass and fiducial [reference] mass. The total mass is 17,000 metric tons and the fiducial mass is 10,000 metric tons. Part of the mass is used as a shield, protecting the detector from rocks and cosmic rays. The mass that really matters is the 10,000 metric tons. This technology was already chosen through collaboration [with researchers in other countries], but other things have not yet been decided and we can choose to do them a little differently.
How many physicists and researchers will participate in DUNE?
Currently, 775 principal investigators have signed the proposal to participate. But the number is expected to double. It is a large group. There are also post-doctoral researchers, students and others.
Could you say that, with the LHC, leadership in the field of particle physics was lost to Europe?
Yes, it’s fair to say that. That’s my job, to fix this problem. The first thing we need to do is start digging a hole in South Dakota. This is the plan. It will be the strongest sign that the United States could give that we are moving forward with the project. We hope that this starts during the 2017 fiscal year, since it is in the budget that we are discussing now. Thus, funding would begin in October 2016, a year from now. The project team itself has until 2019 to decide what will actually be built. The definition of how best to build the first of the four neutrino detector modules, via CERN and Fermilab prototypes, will require two or three years of heavy development. We need to work quickly.
