Determination of mass hierarchy with medium baseline reactor neutrino experiments

الأصل · EN

We study the sensitivity of future medium baseline reactor antineutrino experiments on the neutrino mass hierarchy. By using the standard chi² analysis, we find that the sensitivity depends strongly on the baseline length L and the energy resolution (delta E/E)² = (a/sqrtE/MeV)² + b², where a and b parameterize the statistical and systematic uncertainties, respectively. The optimal length is found to be L 40-55 km, where a slightly shorter L in the range is preferred for poorer energy resolution. The running time needed to determine the mass hierarchy also depends strongly on the energy resolution; for a 5 kton detector (with 12% weight fraction of free proton) placed at L 50 km away from a 20 GWth reactor, three-sigma determination needs 14 years of running with a = 3% and b = 0.5%, which can be reduced to 5 years if a = 2% and b = 0.5%. On the other hand, the experiment can measure the mixing parameters accurately, achieving delta sin²(2theta₁₂) 4*10⁻³, delta (m₂²-m₁²) 0.03*10⁻⁵ eV², and delta |m₃² -m₁²| 0.007*10⁻³ eV², in 5 years, almost independently of the energy resolution for a < 3% and b < 1%. In order to compare our simple (Delta chi²)min results with those obtained by simulating many experiments, we develop an efficient method to estimate the uncertainty of (Delta chi²)min, and the probability for determining the right mass hierarchy by an experiment is presented as a function of the mean (Delta chi²)min.