Limits on Neutrino Oscillations from the CHOOZ Experiment
M. Apollonio, A. Baldini, C. Bemporad, E. Caffau, F. Cei, Y. Declais, H. de Kerret, B. Dieterle, A. Etenko, L. Foresti, J. George, G. Giannini, M. Grassi, Y. Kozlov, W. Kropp, D. Kryn, M. Laiman, C. E. Lane, B. Lefievre, I. Machulin, A. Martemyanov, V. Martemyanov, L. Mikaelyan, D. Nicolo, M. Obolensky, R. Pazzi, G. Pieri, L. Price, S. Riley, R. Reeder, A. Sabelnikov, G. Santin, M. Skorokhvatov, H. Sobel, J. Steele, R. Steinberg, S. Sukhotin, S. Tomshaw, D. Veron, V. Vyrodov
TL;DR
CHOOZ addresses electron antineutrino disappearance due to neutrino oscillations and constrains the parameters $\Delta m^2$ and $\sin^2(2\theta)$. The analysis combines three strategies on the full dataset: a spectral fit using both reactor spectra with absolute normalization, a reactor-distance spectral comparison independent of absolute flux, and a normalization-free variant; confidence intervals are derived with the Feldman–Cousins method. No oscillation signal is observed at 90% CL; the results exclude regions of the $(\Delta m^2, \sin^2(2\theta))$ plane, e.g., $\Delta m^2 \gtrsim 7 \times 10^{-4} \mathrm{eV}^2$ for maximal mixing and $\sin^2(2\theta) = 0.10$ for large $\Delta m^2$. These robust limits constrain electron antineutrino disappearance at atmospheric-scale $\Delta m^2$ and have important implications for $\theta_{13}$-driven oscillations.
Abstract
We present new results based on the entire CHOOZ data sample. We find (at 90% confidence level) no evidence for neutrino oscillations in the anti_nue disappearance mode, for the parameter region given by approximately Delta m**2 > 7 x 10**-4 eV^2 for maximum mixing, and sin**2(2 theta) = 0.10 for large Delta m**2. Lower sensitivity results, based only on the comparison of the positron spectra from the two different-distance nuclear reactors, are also presented; these are independent of the absolute normalization of the anti_nue flux, the cross section, the number of target protons and the detector efficiencies.