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In situ determination of Earth matter density in a neutrino factory

Abstract:

We point out that an accurate in situ determination of the earth matter density ρ is possible in neutrino factory by placing a detector at the magic baseline, L=2π/GFNe where Ne denotes electron number density. The accuracy of matter density determination is excellent in a region of relatively large θ13 with fractional uncertainty δρ/ρ of about 0.43%, 1.3%, and 3% at 1σ CL at sin 22θ13=0.1, 10-2, and 3×10-3, respectively. At smaller θ13 the uncertainty depends upon the CP phase δ, but it remains small, 3%-7% in more than 3/4 of the entire region of δ at sin 22θ13=10-4. The results would allow us to solve the problem of obscured CP violation due to the uncertainty of earth matter density in a wide range of θ13 and δ. It may provide a test for the geophysical model of the earth, or it may serve as a method for a stringent test of the Mikheyev-Smirnov-Wolfenstein theory of neutrino propagation in matter once an accurate geophysical estimation of the matter density is available. © 2007 The American Physical Society.