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World’s smallest neutrino detector finds big physics fingerprint

OAK RIDGE, Tenn — A team of physicists, including three from the Department of Energy’s Pacific Northwest National Laboratory, has found a big fingerprint of one of the smallest particles — the neutrino — that interacts only weakly with matter. The work will ultimately help scientists understand the universe better.

The universe is made up of a large amount of unseeable dark matter. Research to advance dark matter detectors has driven development of very sensitive technologies. The COHERENT measurement helps characterize radiation backgrounds that will affect future dark matter detectors.
Credit: NASA/ESA/JPL-Caltech/Yale/CNRS

The research, performed at the DOE’s Oak Ridge National Laboratory‘s Spallation Neutron Source and reported in the journal Science, provides compelling evidence for a neutrino interaction process predicted by Standard Model theorists 43 years ago, but never seen.

The scientists, a collaboration of 80 researchers from 19 institutions and 4 nations performing the COHERENT experiment, are the first to detect and characterize a phenomenon known as coherent elastic scattering of neutrinos off nuclei. In this behavior, a neutrino bumps into the entire the nucleus of an atom and imparts a tiny amount of energy to the nucleus.

The energy’s signal is as tough to spot as a bowling ball’s recoil after a ping-pong ball hits it. In nature, the phenomenon occurs during neutron star formation and supernovae explosions.

The team took advantage of the fact that the SNS generates a high amount of neutrinos as a byproduct of its normal operations in research. Placing the world’s smallest neutrino detector a mere 65 feet (20 meters) from the neutrino source at SNS vastly improved the chances of detecting interactions.

A four-pound prototype detector, a replica of the 32-pound (14.5 kilogram) one used at the SNS. The detectors contain copper electroformed using techniques developed by COHERENT collaborators at PNNL, resulting in the material with the lowest known radioactive content. The lead visible on top of the prototype was recovered from a Spanish galleon sunk in a Dutch harbor some 300 years ago, and was similarly selected for its very low radioactivity.
Credit: COHERENT Collaboration

Physicist Juan Collar of the University of Chicago led the design of the detector used at SNS. Three physicists from PNNL — John Orrell, Todd Hossbach and Cory Overman — helped build the detector. Among other contributions, the instrument relied especially on copper free from background radiation coming from cosmic rays pouring in from the universe. The PNNL researchers electroformed the ultrapure copper in PNNL’s underground laboratory, where cosmic rays can’t reach.

Source: PNNL

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