Search for superlight dark matter particles heats up

This release was originally issued today by the U.S. Department of Energy. 

Earlier today, April 16, 2018, U.S. Secretary of Energy Rick Perry and India’s Atomic Energy Secretary Dr. Sekhar Basu signed an agreement in New Delhi to expand the two countries’ collaboration on world-leading science and technology projects. It opens the way for jointly advancing cutting-edge neutrino science projects underway in both countries: the Long-Baseline Neutrino Facility (LBNF) with the international Deep Underground Neutrino Experiment (DUNE) hosted at the U.S. Department of Energy’s Fermilab and the India-based Neutrino Observatory (INO).

LBNF/DUNE brings together scientists from around the world to discover the role that tiny particles known as neutrinos play in the universe. More than 1,000 scientists from over 170 institutions in 31 countries work on LBNF/DUNE and celebrated its groundbreaking in July 2017. The project will use Fermilab’s powerful particle accelerators to send the world’s most intense beam of high-energy neutrinos to massive neutrino detectors that will explore their interactions with matter.

INO scientists will observe neutrinos that are produced in Earth’s atmosphere to answer questions about the properties of these elusive particles. Scientists from more than 20 institutions are working on INO.

“The LBNF/DUNE project hosted by the Department of Energy’s Fermilab is an important priority for the DOE and America’s leadership in science, in collaboration with our international partners,” said Secretary of Energy Rick Perry. “We are pleased to expand our partnership with India in neutrino science and look forward to making discoveries in this promising area of research.”

Scientists from the United States and India have a long history of scientific collaboration, including the discovery of the top quark at Fermilab.

“India has a rich tradition of discoveries in basic science,” said Atomic Energy Secretary Basu. “We are pleased to expand our accelerator science collaboration with the U.S. to include the science for neutrinos. Science knows no borders, and we value our Indian scientists working hand-in-hand with our American colleagues. The pursuit of knowledge is a true human endeavor.”

This DOE-DAE agreement builds on the two countries’ existing collaboration on particle accelerator technologies. In 2013, DOE and DAE signed an agreement authorizing the joint development and construction of particle accelerator components in preparation for projects at Fermilab and in India. This collaborative work includes the training of Indian scientists in the United States and India’s development and prototyping of components for upgrades to Fermilab’s particle accelerator complex for LBNF/DUNE. The upgrades, known as the Proton Improvement Plan-II (PIP-II), include the construction of a 600-foot-long superconducting linear accelerator at Fermilab. It will be the first ever particle accelerator built in the United States with significant contributions from international partners, including also the UK and Italy. Scientists from four institutions in India – BARC in Mumbai, IUAC in New Delhi, RRCAT in Indore and VECC in Kolkata – are contributing to the design and construction of magnets and superconducting particle accelerator components for PIP-II at Fermilab and the next generation of particle accelerators in India.

Under the new agreement signed today, U.S. and Indian institutions will expand this productive collaboration to include neutrino research projects. The LBNF/DUNE project will use the upgraded Fermilab particle accelerator complex to send the world’s most powerful neutrino beam 800 miles (1,300 kilometers) through the earth to a massive neutrino detector located at Sanford Underground Research Facility in South Dakota. This detector will use almost 70,000 tons of liquid argon to detect neutrinos and will be located about a mile (1.5 kilometers) underground; an additional detector will measure the neutrino beam at Fermilab as it leaves the accelerator complex. Prototype neutrino detectors already are under construction at the European research center CERN, another partner in LBNF/DUNE.

“Fermilab’s international collaboration with India and other countries for LBNF/DUNE and PIP-II is a win-win situation for everybody involved,” said Fermilab Director Nigel Lockyer. “Our partners get to work with and learn from some of the best particle accelerator and particle detector experts in the world at Fermilab, and we benefit from their contributions to some of the most complex scientific machines in the world, including LBNF/DUNE and the PIP-II accelerator.”

INO will use a different technology — known as an iron calorimeter — to record information about neutrinos and antineutrinos generated by cosmic rays hitting Earth’s atmosphere. Its detector will feature what could be the world’s biggest magnet, allowing INO to be the first experiment able to distinguish signals produced by atmospheric neutrinos and antineutrinos. The DOE-DAE agreement enables U.S. and Indian scientists to collaborate on the development and construction of these different types of neutrino detectors. More than a dozen Indian institutions are involved in the collaboration on neutrino research.

Additional quotes:

Prof. Vivek Datar, INO spokesperson and project director, Taha Institute of Fundamental Research:

“This will facilitate U.S. participation in building some of the hardware for INO, while Indian scientists do the same for the DUNE experiment. It will also help in building expertise in India in cutting-edge detector technology, such as in liquid-argon detectors, where Fermilab will be at the forefront. At the same time we will also pursue some new ideas.”

Prof. Naba Mondal, former INO spokesperson, Saha Institute of Nuclear Physics:

“This agreement is a positive step towards making INO a global center for fundamental research. Students working at INO will get opportunities to interact with international experts.”

Prof. Ed Blucher, DUNE co-spokesperson, University of Chicago, United States:

“The international DUNE experiment could fundamentally change our understanding of the universe. Contributions from India and other partner countries will enable us to build the world’s most technologically advanced neutrino detectors as we aim to make groundbreaking discoveries regarding the origin of matter, the unification of forces, and the formation of neutron stars and black holes.”

Prof. Stefan Soldner-Rembold, DUNE co-spokesperson, University of Manchester, UK:

“DUNE will be the world’s most ambitious neutrino experiment, driven by the commitment and expertise of scientists in more than 30 countries. We are looking forward to the contributions that our colleagues in India will make to this extraordinary project.”

To learn more about LBNF/DUNE, visit www.fnal.gov/dunemedia. More information about PIP-II is available at pip2.fnal.gov.

Fermilab is America’s premier national laboratory for particle physics and accelerator research. A U.S. Department of Energy Office of Science laboratory, Fermilab is located near Chicago, Illinois, and operated under contract by the Fermi Research Alliance LLC, a joint partnership between the University of Chicago and the Universities Research Association, Inc. Visit Fermilab’s website at www.fnal.gov and follow us on Twitter at @Fermilab.

The DOE Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

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Fermilab’s largest operating neutrino experiment gains a new leader as it prepares to search for new physics that could reshape our understanding of the universe.

Tricia Vahle, Mansfield associate professor of physics at William & Mary and longtime leader and scientist on Fermilab’s NOvA neutrino experiment, was recently elected as its new co-spokesperson. She assumed her role on March 21.

Vahle joined NOvA in 2008, when it was still in its infancy — designed, but not yet built. She was instrumental in the experiment’s early years as one of the founders of a NOvA data analysis group. Later she became its analysis coordinator, overseeing teams focused on using the experiment’s data to investigate different physics phenomena.

Now, as NOvA co-spokesperson, she will lead the experiment alongside Fermilab scientist Peter Shanahan, who played a major role in completing NOvA’s construction on time and under budget and taking it into its data collection and analysis phase.

“Tricia has a huge amount of experience on NOvA, and with neutrino physics in general,” Shanahan said. “She’s been working on NOvA for many years and has a good sense of both organizational and scientific aspects of leading such an experiment.”

Vahle succeeds former co-spokesperson Mark Messier of Indiana University. Shanahan and Vahle say the collaboration is grateful to Messier for his 12 years of outstanding service to the experiment, from its design to its first scientific results, bringing the experiment to where it is today.

“Tricia is taking the helm at a really exciting time for the experiment. We’re just starting to push the experiment to answer the scientific questions it was meant to answer,” Messier said. “NOvA is moving forward into the next era of science.”

The NOvA experiment, which started up in 2014, aims to study the shape-shifting behavior of neutrinos, which are mysterious subatomic particles that could help us better understand how our universe evolved. They come in three types, and as they travel, they shift from one type into another according to so-called oscillation patterns.

To get a better handle on how they oscillate, scientists study how neutrinos change over long distances: Fermilab’s powerful particle accelerators send a beam of neutrinos 500 miles from the lab (just outside Chicago, Illinois) straight through Earth to a giant neutrino detector in Ash River, Minnesota. Scientists compare the measurements made at Fermilab to those in Minnesota.

After four years of taking data on neutrinos, NOvA recently shifted to recording data on their antimatter counterparts, antineutrinos. Differences in the oscillations of the two particles could solve the mystery of why there is an asymmetry between matter and antimatter in our universe. They could also reveal new physics.

“It’s a very exciting time because we’re on the verge of realizing NOvA’s full physics potential,” Vahle said. “We’re looking forward to using more sensitive data analyses to study both antineutrinos and neutrinos and compare them.”

NOvA, which is made up of almost 250 scientists from 48 institutions around the world, will continue to run until at least 2024, switching between antineutrino and neutrino measurements to obtain roughly equal amounts of data for each. NOvA will also focus on making ever more precise measurements of neutrinos’ basic properties, such as the relationship between the masses of the different types.

“My goal in the near future is to work together with Tricia, the collaboration and Fermilab to meet the challenge of furthering our understanding of neutrino physics,” Shanahan said. “Our work ahead will focus on getting the most possible data for NOvA and making the most of it through ongoing improvements to our analysis.”

Vahle says she’s happy to be at the forefront of potential neutrino discovery.

“In the long term, we aim to keep people excited about our experiment and the top-notch physics we are doing,” Vahle said.

 

For some, a target is part of a game of darts. For others, it’s a retail chain. In particle physics, it’s the site of an intense, complex environment that plays a crucial role in generating the universe’s smallest components for scientists to study.

The target is an unsung player in particle physics experiments, often taking a back seat to scene-stealing light-speed particle beams and giant particle detectors. Yet many experiments wouldn’t exist without a target. And, make no mistake, a target that holds its own is a valuable player.

Scientists and engineers at Fermilab are currently investigating targets for the study of neutrinos — mysterious particles that could hold the key to the universe’s evolution.

Intense interactions

The typical particle physics experiment is set up in one of two ways. In the first, two energetic particle beams collide into each other, generating a shower of other particles for scientists to study.

In the second, the particle beam strikes a stationary, solid material — the target. In this fixed-target setup, the powerful meeting produces the particle shower.

As the crash pad for intense beams, a target requires a hardy constitution. It has to withstand repeated onslaughts of high-power beams and hold up under hot temperatures.

You might think that, as stalwart players in the play of particle production, targets would look like a fortress wall (or maybe you imagined dartboard). But targets take different shapes — long and thin, bulky and wide. They’re also made of different materials, depending on the kind of particle one wants to make. They can be made of metal, water or even specially designed nanofibers.

In a fixed-target experiment, the beam — say, a proton beam — races toward the target, striking it. Protons in the beam interact with the target material’s nuclei, and the resulting particles shoot away from the target in all directions. Magnets then funnel and corral some of these newly born particles to a detector, where scientists measure their fundamental properties.

The particle birthplace

The particles that emerge from the beam-target interaction depend in large part on the target material. Consider Fermilab neutrino experiments.

In these experiments, after the protons strike the target, some of the particles in the subsequent particle shower decay — or transform — into neutrinos.

The target has to be made of just the right stuff.

“Targets are crucial for particle physics research,” said Fermilab scientist Bob Zwaska. “They allow us to create all of these new particles, such as neutrinos, that we want to study.”

Graphite is a goldilocks material for neutrino targets. If kept at the right temperature while in the proton beam, the graphite generates particles of just the right energy to be able to decay into neutrinos.

For neutron targets, such as that at the Spallation Neutron Source at Oak Ridge National Laboratory, heavier metals such as mercury are used instead.

Maximum interaction is the goal of a target’s design. The target for Fermilab’s NOvA neutrino experiment, for example, is a straight row — about the length of your leg — of graphite fins that resemble tall dominoes. The proton beam barrels down its axis, and every encounter with a fin produces an interaction. The thin shape of the target ensures that few of the particles shooting off after collision are reabsorbed back into the target.

Robust targets

“As long as the scientists have the particles they need to study, they’re happy. But down the line, sometimes the targets become damaged,” said Fermilab engineer Patrick Hurh. In such cases, engineers have to turn down — or occasionally turn off — the beam power. “If the beam isn’t at full capacity or is turned off, we’re not producing as many particles as we can for science.”

The more protons that are packed into the beam, the more interactions they have with the target, and the more particles that are produced for research. So targets need to be in tip-top shape as much as possible. This usually means replacing targets as they wear down, but engineers are always exploring ways of improving target resistance, whether it’s through design or material.

Consider what targets are up against. It isn’t only high-energy collisions — the kinds of interactions that produce particles for study — that targets endure.

Lower-energy interactions can have long-term, negative impacts on a target, building up heat energy inside it. As the target material rises in temperature, it becomes more vulnerable to cracking. Expanding warm areas hammer against cool areas, creating waves of energy that destabilize its structure.

Some of the collisions in a high-energy beam can also create lightweight elements such as hydrogen or helium. These gases build up over time, creating bubbles and making the target less resistant to damage.

A proton from the beam can even knock off an entire atom, disrupting the target’s crystal structure and causing it to lose durability.

Clearly, being a target is no picnic, so scientists and engineers are always improving targets to better roll with a punch.

For example, graphite, used in Fermilab’s neutrino experiments, is resistant to thermal strain. And, since it is porous, built-up gases that might normally wedge themselves between atoms and disrupt their arrangement may instead migrate to open areas in the atomic structure. The graphite is able to remain stable and withstand the waves of energy from the proton beam.

Engineers also find ways to maintain a constant target temperature. They design it so that it’s easy to keep cool, integrating additional cooling instruments into the target design. For example, external water tubes help cool the target for Fermilab’s NOvA neutrino experiment.

Targets for intense neutrino beams

At Fermilab, scientists and engineers are also testing new designs for what will be the lab’s most powerful proton beam — the beam for the laboratory’s flagship Long-Baseline Neutrino Facility and Deep Underground Neutrino Experiment, known as LBNF/DUNE.

LBNF/DUNE is scheduled to begin operation in the 2020s. The experiment requires an intense beam of high-energy neutrinos — the most intense in the world. Only the most powerful proton beam can give rise to the quantities of neutrinos LBNF/DUNE needs.

Scientists are currently in the early testing stages for LBNF/DUNE targets, investigating materials that can withstand the high-power protons. Currently in the running are beryllium and graphite, which they’re stretching to their limits. Once they conclusively determine which material comes out on top, they’ll move to the design prototyping phase. So far, most of their tests are pointing to graphite as the best choice.

Targets will continue to evolve and adapt. LBNF/DUNE provides just one example of next-generation targets.

“Our research isn’t just guiding the design for LBNF/DUNE,” Hurh said. “It’s for the science itself. There will always be different and more powerful particle beams, and targets will evolve to meet the challenge.”