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Small Detector: Big Results


From left, Professor Yuri Efremenko of the University of Tennessee and Jason Newby of Oak Ridge National Laboratory are among 80 participants in COHERENT, a large, collaborative, particle physics experiment to record neutrinos at the Spallation Neutron Source. Photomultiplier tubes look like giant light bulbs and are used to detect light from neutrino interactions in detectors. COHERENT’s cesium iodide detector, the first to espy neutrinos at the SNS, employs a 5-inch (13-centimeter) wide photomultiplier tube. An 8-inch (20-centimeter) wide photomultiplier (shown here) is deployed in COHERENT’s nearby liquid-argon detector. Measurements from different types of detectors are necessary for comprehensive studies of neutrinos at SNS. The scientists are standing in front of the cesium-iodide-detector shielding. Image credit: Oak Ridge National Laboratory, U.S. Dept. of Energy; photographer Genevieve Martin.

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UT Physics plays a key role on the scientific team that found neutrinos—typically among the least social subatomic particles—interact on a broader scale than previously shown. The results are published in Science (“Observation of Coherent Elastic Neutrino-Nucleus Scattering”) and provide compelling evidence of a concept that has been predicted for more than four decades but never seen.

The work was done by the COHERENT collaboration at Oak Ridge National Laboratory’s Spallation Neutron Source (SNS). The SNS produces neutrons for research, creating neutrinos—sometimes referred to as “ghost” particles because they can pass through our bodies without notice— as a byproduct. The COHERENT experiment constructed the world’s smallest working neutrino detector and placed it in the SNS basement at the place now called “Neutrino Alley.” Their analysis found that neutrinos interact with the nucleus as a whole, rather than just protons and neutrons inside it. This broader interactive process is predicted in the Standard Model of particle physics but had not been experimentally demonstrated until now.

For Physics Professor Yuri Efremenko, the result is professionally and personally validating after years of hard work and leadership.

“This result is the culmination of my 15 years working toward this day,” he said. “It includes leadership in all aspects: from building the physics case, looking for the appropriate location, building the collaboration, looking for funding, long study of backgrounds and understanding necessary shielding, and finally doing independent data analysis.”

Efremenko was among the scientists who proposed placing a neutrino facility at SNS, which has clearly already paid dividends. He holds a joint faculty appointment with ORNL and has a long and deep involvement with neutrino physics research, having worked with the KamLAND, DoubleChooz and Majorana experiments. Other UT Physics connections to the COHERENT experiment include Jason Newby (PhD, 2003), who is the technical coordinator for the collaboration, which comprises 80 researchers from 19 institutions and four nations. Physics graduate student Brandon Becker is also involved with the research.

Learn more at ORNL’s website.

Photos and captions provided by ORNL.

From left, Jason Newby of ORNL and Yuri Efremenko of the University of Tennessee/ORNL check equipment for the COHERENT experiment at the SNS. In 2005 Efremenko and others proposed a neutrino facility at the SNS; that vision is realized in the current work. Image credit: Oak Ridge National Laboratory, U.S. Dept. of Energy; photographer Genevieve Martin.

From left, Jason Newby of ORNL and Brandon Becker of the University of Tennessee examine equipment that will collect data for COHERENT. Becker, a graduate student, will model, simulate and analyze interesting physics that result from interactions between neutrinos and lead shielding that cause emission of neutrons inside the neutrino detector. So-called “neutrino-induced neutrons” have been theorized, but to date there is no conclusive evidence for their presence. Image credit: Oak Ridge National Laboratory, U.S. Dept. of Energy; photographer Genevieve Martin.

Research to advance dark matter detectors has greatly contributed to making coherent neutrino detectors a reality. No one really knows what dark matter is. Among the most popular candidates for dark matter are particles similar to neutrinos but much heavier, called weakly interacting massive particles (WIMPs). Because interactions between WIMPs and nuclei would convey just a little bit of energy, detected as nuclear recoils, dark-matter detectors must be sensitive to these tiny signals. Thus, dark matter experiments have driven technologies sensitive to low-energy nuclear recoils. In return, the COHERENT measurement helps characterize backgrounds that will affect future dark matter detectors, in which neutrinos from the sun may swamp the WIMP signal. Credits: NASA/ESA/JPL-Caltech/Yale/CNRS.

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