Preparing for the sterile neutrino search: Fermilab breaks ground on Short-Baseline Near Detector building

On April 27, Fermilab broke ground on the building that will house the future Short-Baseline Near Detector.

The particle detector, SBND, is one of three that, together, scientists will use to search for the sterile neutrino, a hypothesized particle whose existence, if confirmed, could not only help us better understand the types of neutrino we already know about, but also provide clues about how the universe formed.

Members of the Fermilab Neutrino and Particle Physics divisions, working together with international collaborators, are currently refining the design of the detector itself. It will take about eight months to complete the SBND building.

The three detectors make up the laboratory’s Short-Baseline Neutrino Program, which will use a powerful neutrino beam generated by the Fermilab accelerator complex. The beam will pass first through SBND and then through the MicroBooNE detector, which is already installed and taking data, having observed its first neutrino interactions in October. Finally, the beam will travel through ICARUS, the largest of the three detectors. ICARUS, which was used in a previous experiment at the Italian Gran Sasso laboratory, is currently at the CERN laboratory in Switzerland receiving upgrades before its big move to Fermilab in 2017.

“The entire Short-Baseline Neutrino Program is looking for oscillations, or the transformations, of muon neutrinos into electron neutrinos,” said Peter Wilson, SBN program coordinator. “Sterile neutrinos might have a role in this oscillation process.”

The beam coming out of the accelerator comprises primarily muon neutrinos; the detectors will measure their transformation into electron neutrinos.

All three detectors have specific functions in detecting the transformation. As the detector closest to the beam source, SBND will take an initial measurement of the beam’s composition – how much the beam contains each of the different neutrino types.

“The intermediary and far detectors are used to search for sterile neutrinos in two different ways,” said Ornella Palamara, co-spokesperson for the SBND experiment. “Either there’s an appearance of an excess of electron neutrinos or there’s a disappearance of the number of muon neutrinos compared to the number we start with.”

If there are more electron neutrinos than predicted, then muon neutrinos may have oscillated first into sterile neutrinos and then to electron neutrinos. If the data show a smaller number of muon neutrinos than predicted, the muon neutrinos may have transformed only into sterile neutrinos, which cannot be seen in the far detectors.

Scientists first picked up on experimental hints of a sterile neutrino at Los Alamos National Laboratory’s LSND experiment in 1995. When the Fermilab experiment MiniBooNE followed up, scientists could not confirm the sterile neutrino’s existence, but neither could they rule it out.

“That’s the power of this program,” Palamara said. “We’re building off previous measurements, but we have more sensitive tools to measure the neutrinos.”

Part of the sensitivity of SBND lies in its liquid-argon time projection chamber, the active part of the detector, which will contain 112 tons of liquid argon. Neutrinos will interact with the nuclei of the argon atoms, and scientists on SBND will study the resulting particles to better understand the neutrinos that caused the interaction. Their findings will likely have application in future accelerator-based neutrino programs, such as the international Deep Underground Neutrino Experiment hosted by Fermilab.

The Short-Baseline Neutrino Program will begin taking data in 2018.

“The SBND groundbreaking is a noteworthy milestone, but it’s part of a much larger program,” Wilson said. “Many people are working on it, and everyone is excited to get the chance to understand new physics.”

Late April is always a special time of year at Fermilab. Spring is in the air, the leaves are green, the birds are singing, and adorable baby bison are born.

Fermilab welcomed the first baby bison of 2016 on Tuesday, April 26, increasing the herd size to 18. As many as 14 more calves are expected before early June.

All are welcome to visit the laboratory to see and photograph the new baby bison. (They’re always a hit with young children.) The site is open every day from 8 a.m. to 8 p.m., and admission is free. You’ll need a valid photo ID to enter the site.

Fermilab’s first director, Robert Wilson, established the bison herd in 1969 as a symbol of the history of the Midwestern prairie and the laboratory’s pioneering research at the frontiers of particle physics. The herd remains a major attraction for families and wildlife enthusiasts.

And just recently, thanks to the science of genetic testing, Fermilab’s ecologist Ryan Campbell confirmed that the laboratory’s herd is 100 percent bison, with no cattle genes. Farmers during the early settlement era would breed bison with other bovine species to keep them from extinction, but Fermilab’s bison are purebred.

A herd of pure bison is a natural fit for a prairie ecosystem, like the kind that exists on the Fermilab site. Fermilab hosts 1,100 acres of reconstructed tall-grass prairie, and the U.S. Department of Energy designated the 6,800-acre site a National Environmental Research Park in 1989.

While you’re at the Fermilab site visiting the bison, you can learn more about our ecological efforts by hiking the Interpretive Prairie Trail, a half-mile-long trail located near the Pine Street entrance in Batavia. The Lederman Science Center also offers exhibits on the prairie and hands-on physics displays. The Lederman Center hours are Monday-Friday from 8:30 a.m. to 4:30 p.m. and Saturdays from 9 a.m. to 3 p.m.

For up-to-date information for visitors, please visit www.fnal.gov or call 630-840-3351. To learn more about Fermilab’s bison herd, please visit the wildlife area of our website.

Fermilab is America’s premier national laboratory for particle physics 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. Visit Fermilab’s website at http://www.fnal.gov and follow us on Twitter @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 http://science.energy.gov. 

If you’ve passed by the old SciBooNE hall at Fermilab in the last couple of months, you might have heard a bit of commotion. A little experiment with big ambitions just finished moving in this week after a year’s worth of planning and research. The Accelerator Neutrino-Neutron Interaction Experiment, called ANNIE, recently settled down and began taking phase one data on April 15.

“We want to better understand the nature of neutrino interactions by looking at their effects on an atom’s nucleus,” said Matthew Wetstein, a co-spokesperson for the ANNIE project and a Fermilab visiting scientist from Iowa State University. ANNIE will be the first realization of a new kind of detector in a large neutrino experiment. The technology will help look for particle interactions that are hard to distinguish in other detectors, he said.

The ANNIE team aims to study phenomena and techniques relevant to neutrino energy and proton decay measurements through the use of a water Cherenkov detector loaded with a chemical element called gadolinium and surrounded by never before used photosensors called large-area picosecond photodetectors (LAPPDs).

Light travels slower in a medium such as glass, water or other transparent materials than in air or in a vacuum. Sometimes, light travels slow enough in these materials that particles can overtake it. That’s why Cherenkov detectors are common in neutrino experiments. When neutrinos hit atoms in such media, the resulting free-flying electrically charged particles emit their own light, known as Cherenkov radiation, and these detectors record this light, allowing scientists to identify the type of particle and calculate its energy. In ANNIE’s case, neutrinos streaming down the Fermilab Booster Neutrino Beam will strike water molecules in the detector and knock off neutrons. Neutrons are electrically neutral and do not emit Cherenkov radiation, so they need to be detected some other way. After the initial neutrino-nucleus collisions, the gadolinium salts in the water effectively capture the neutrons and subsequently emit photons, which can be detected by photosensors.

“Neutrons have always been a challenging particle to detect,” Wetstein said. “We hope ANNIE can determine how many neutrons are produced when neutrinos interact.”

Observing this neutron release is useful because neutrons carry some energy with them that was transferred from the neutrino collision. Physicists believe higher-energy neutrino-nucleus interactions produce a larger number of knocked-off neutrons. To test this, ANNIE physicists will use accelerator-born neutrinos that have an energy level similar to atmospheric neutrinos, which have some of the highest-energy yields. The ANNIE team aims to understand how tagging free-flying neutrons can help them differentiate between a possible proton-decay signal and background noise from the neutrinos.

One of the best ways for the team to determine the effects of neutron tagging is to use the LAPPDs, a photosensor technology that researchers had been developing for nearly five years prior to the 2015 proposal for ANNIE. These sensors are currently in the commercialization phase.

LAPPDs are based on a technology called microchannel plates, which are tiny arrays with densely packed, tinier tubes that detect light. Conventional photodetectors, for physics research and commercial use, have single-pixel resolutions. In large neutrino experiments, these single-pixel phototubes can detect, for example, only one “blob” of charge coming from three separate photons in a neutrino-nucleus collision. Now with LAPPDs, scientists can read each individual photon, retrace where the photon came from and determine the time the light was emitted roughly 10 times better than previous photodetectors.

Think of it as tracing photons’ movements at the scale of 50 to 60 trillionths of a second.

High-precision timing with LAPPDs and accurate neutron tagging with the gadolinium-loaded water detector takes neutrino and proton-decay research to another level.

Thirty collaborators, including postdoctoral researchers and students, were very active in building and installing the electronics, water systems and photodetection tubes.

“We’ve done an excellent job of working together and making it happen as quickly as possible,” said Mayly Sanchez, a co-spokesperson for the ANNIE project and an Intensity Frontier fellow at Fermilab.

Now that the ANNIE detector is in its home in the Fermilab SciBooNE building and taking data, the collaboration is preparing to analyze their results.

“For phase one, we will be doing some neutrino background measurements for the ultimate physics measurements that we want to do,” Sanchez said. “The physics measurement in phase two will have an impact both in our knowledge of neutrino interactions and as the first application of a new photodetector technology in high-energy physics.”

Phase one, supported by Fermilab, will continue until the Fermilab accelerator shutdown begins in July. The main physics experimentation and R&D studies will take place during phase two, which awaits funding. ANNIE researchers, supported by the U.S. Department of Energy Office of Science and the National Science Foundation, will later compare results from both phases to see what the experiment yields.

“We learned what it takes to get an experiment like ANNIE off the ground at Fermilab,” Wetstein said. “I’m really proud that we got the whole thing from basically a big proposal to a fully designed experiment to turning all of our systems on within a year.”

ANNIE’s collaborating institutions are Argonne National Laboratory, Fermilab, Iowa State University, Ohio State University, Queen Mary University of London, University of California, Berkeley, University of California, Davis, University of California, Irvine, University of Chicago and University of Sheffield.