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martyb writes:

They are there and they are gone: ICARUS chases a fourth neutrino:

It is well-established that the three known neutrino types – electron, muon and tau – oscillate, or change, into one another. To study these oscillations and how they happen, scientists need neutrinos to interact with something. For ICARUS, that substance is liquid argon.

In the ICARUS experiment, a muon-type neutrino beam will interact with liquid argon and should, in theory, produce mostly charged particles called muons. (An electron-type neutrino beam should produce mostly electrons.) But given results from the Liquid Scintillator Neutrino Detector and MiniBooNE, this is only part of the story, and ICARUS intends to fill the gaps.

"What if the neutrinos are oscillating into a neutrino that does not interact at all, not even a little bit like other neutrinos do?" [Robert] Wilson [deputy spokesperson of ICARUS and professor of physics at Colorado State University] said. "This is not a natural extension of neutrino theory, but it could explain the LSND[*] and MiniBooNE results."

Such a fourth type of neutrino, unlike the others, would not change into a complementary charged particle upon interaction in a detector. In fact, it wouldn't interact at all. By quantum mechanics, however, this so-called sterile neutrino could still oscillate between neutrino types and alter the oscillation pattern that ICARUS will observe.

Discovery of a sterile neutrino would upend the Standard Model of subatomic particles and affect our understanding of how the universe has evolved.

[...] It will take approximately eight weeks to fill ICARUS with liquid argon. Once the detector is filled, scientists will check its stability and the argon's purity. Then, they will turn on power for the first time since ICARUS made its way to Fermilab across the Atlantic Ocean. They expect to see first particle tracks later this year.

[*] LSND: Liquid Scintillator Neutrino Detector.

Original Submission