Breaking Ground on a New Era of Particle Physics

UH Faculty Involved in International DUNE Collaboration

The origin of matter. Black hole formation. The mystery of whether protons live forever or eventually decay.

Andrew Renshaw and Lisa Whitehead KoernerTwo University of Houston physicists are involved in an international collaboration, called the Deep Underground Neutrino Experiment (DUNE), which is designed to answer these questions.

On July 21, at the Sanford Underground Research Facility in Lead, South Dakota, a group of scientists, engineers and dignitaries from around the world met for the groundbreaking ceremony marking the start of construction for the Long-Baseline Neutrino Facility (LBNF), which will provide the beam and infrastructure for DUNE.

DUNE: Largest Neutrino Experiment Built in U.S.

When complete, DUNE will be the largest experiment ever built in the United States to study the properties of mysterious particles known as neutrinos. Along the way, DUNE will require the hard work of almost 1,000 scientists and engineers from 30 countries.

FigureIn the Deep Underground Neutrino Experiment, a beam of neutrinos will be sent straight through the earth from Fermilab in Batavia, Illinois, to the Sanford Underground Research Facility in Lead, South Dakota. (Photo: Sandbox Studios)At the University of Houston, Andrew Renshaw, assistant professor of physics, and Lisa Whitehead Koerner, associate professor of physics, have stepped up to the challenge, offering their expertise for an experiment that will take years, and the efforts of hundreds, in order to turn into reality.

Their efforts will include developing data analysis software, installing electronics, building a detector to analyze argon purity, as well as working on the high-voltage subsystem that provides the electric field within the detectors.

Neutrinos Oscillate Between Different States

Neutrinos are tiny particles with a neutral charge and a mass that is at most one-millionth that of an electron. Interacting via only a very weak force, neutrinos pass through matter nearly unimpeded and undetected. There are three types of neutrinos, all of which have the ability to change into the other types.

“Neutrinos can change from one type to another type; this is called neutrino oscillations,” Koerner said. “One question we are hoping to answer about neutrinos is related to charge-parity violation, which is the difference between the way matter and antimatter behave.”

When the Big Bang happened, there should have been equal amounts of matter and antimatter created. However, the universe is predominantly made of matter, with only tiny amounts of antimatter. How this happened is one of physics’ big unanswered questions.

DUNE: The Future of Particle Physics

When finished, the LBNF will catch a beam of neutrinos shot from the U.S. Department of Energy’s Fermi National Accelerator Laboratory, which is 800 miles away, near Chicago. This beam of neutrinos, which will travel through the ground in under a second, will arrive at DUNE’s four-story, 70,000 ton detector sitting 5,000 feet below the earth.

As scientists observe the changes that happen to neutrinos after journeying hundreds of miles through the earth, they will better understand their properties.

In a departure from previous large neutrino experiments, these detectors will be made of pure liquid argon.

“Using liquid argon gives you much more information,” Renshaw said. “The detector we are using allows us to do 3D position reconstruction for each neutrino interaction.”

“Looking at the topology of the tracks tells you what kind of neutrino interaction it was, while measuring the energy and momentum of the particles gives information about the incoming neutrino energy,” Koerner said. “Getting this picture can tell us a lot about what happened.”

Seeking Evidence for Charge-Parity (CP) Violation

“Matter and antimatter particles have opposite charges,” Koerner said. “If the physical properties are different when you change the charge and look at the mirror image, then this is evidence of CP violation and could help explain the matter, antimatter difference we observe in the universe.”

In addition to looking for evidence of CP violation, DUNE will also watch for neutrinos that are produced after a star explodes, called a supernova event, and for evidence of proton decay.

Detector at Location of Historic Neutrino Experiment

The location of the LBNF is in an old gold mine of unique significance to the neutrino community. This mine was the location of a famous experiment, for which Ray Davis won the 2002 Nobel Prize in Physics, which offered the initial evidence for neutrinos that come from the sun.

During this experiment, which ran for years, Davis observed only a third of the expected neutrinos, a finding that contradicted the accepted model.

“For almost 40 years, there was this mystery of ‘Where have all the solar neutrinos gone?’” Renshaw said.

This mystery was solved in 2001, when further experiments demonstrated neutrinos have the ability to oscillate between three different states.

Ground-breaking Marks Start of Construction

But before this experiment can happen, the facility must be built, an effort that will take an estimated 10 years. Crews will excavate an estimated 870,000 tons of rock to create the underground caverns that will house the DUNE detector.

While this is happening, scientists and engineers from around the world will work on the many requirements needed to ensure DUNE’s success. This will include Koerner’s research group, which includes postdoctoral researcher Aaron Higuera and physics graduate student Casandra Morris, as well as Renshaw’s research group, which includes physics graduate student William Ellsworth.

This research is funded by the U.S. Department of Energy Office of Science in conjunction with CERN and international partners from 30 countries.

- Rachel Fairbank, College of Natural Sciences and Mathematics