Fourth Flavor of Neutrino? Physics Experiment Suggests Existence of New Elementary Particle
ScienceDaily (Nov. 3, 2010) — The results of a high-profile Fermilab physics experiment appear to confirm strange 20-year-old findings that poke holes in the standard model, suggesting the existence of a new elementary particle: a fourth flavor of neutrino.
The MiniBooNE experiment records a neutrino event, in this 2002 image from Fermilab. The ring of light, registered by some of more than one thousand light sensors inside the detector, indicates the collision of a muon neutrino with an atomic nuclei. (Credit: Fermilab)
The new results go further to describe a violation of a fundamental symmetry of the universe asserting that particles of antimatter behave in the same way as their matter counterparts.
Neutrinos are neutral elementary particles born in the radioactive decay of other particles. The known "flavors" of neutrinos are the neutral counterparts of electrons and their heavier cousins, muons and taus. Regardless of a neutrino's original flavor, the particles constantly flip from one type to another in a phenomenon called "neutrino flavor oscillation."
An electron neutrino might become a muon neutrino, and then later an electron neutrino again. Scientists previously believed three flavors of neutrino exist. In this Mini Booster Neutrino Experiment, dubbed MiniBooNE, researchers detected more oscillations than would be possible if there were only three flavors.
"These results imply that there are either new particles or forces we had not previously imagined," said Byron Roe, professor emeritus in the University of Michigan's Department of Physics, and an author of a paper on the results newly published online in Physical Review Letters.
"The simplest explanation involves adding new neutrino-like particles, or sterile neutrinos, which do not have the normal weak interactions."
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Phys. Rev. Lett. 105, 181801 (2010) [5 pages]
Event Excess in the MiniBooNE Search for ν̅ μ→ν̅ e Oscillations
A. A. Aguilar-Arevalo et al. (MiniBooNE Collaboration)
The MiniBooNE experiment at Fermilab reports results from a search for ν̅ μ→ν̅ e oscillations, using a data sample corresponding to 5.66×1020 protons on target. An excess of20.9±14.0 events is observed in the energy range 475<EνQE<1250 MeV, which, when constrained by the observed ν̅ μ events, has a probability for consistency with the background-only hypothesis of 0.5%. On the other hand, fitting for ν̅ μ→ν̅ e oscillations, the best-fit point has a χ2 probability of 8.7%. The data are consistent with ν̅ μ→ν̅ e oscillations in the 0.1 to1.0 eV2 Δm2 range and with the evidence for antineutrino oscillations from the Liquid Scintillator Neutrino Detector at Los Alamos National Laboratory.
© 2010 The American Physical Society
URL:
http://link.aps.org/doi/10.1103/PhysRevLett.105.181801
DOI:
10.1103/PhysRevLett.105.181801
PACS:
14.60.St, 11.30.Er, 14.60.Lm, 14.60.Pq
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