In order not to complicate the figure, we do not show very recent relative SBL measurements of Neutrino-4 (SM-3 HEU research reactor, Dimitrovgrad), STEREO (ILL HEU research reactor, Grenoble), PROSPECT (HFIR HEU research reactor, Oak Ridge), and DANSS (a 3.1 GW th LEU industrial reactor, Kalinin NPP), all of which, however, are critical for the present study and will be discussed in detail in Section 6. The newer high-precision measurements are absolute (in Figure 1 they are placed at the effective flux-weighted baselines). Note that the RENO and Daya Bay datasets from, respectively,, are relative measurements they are simply normalized to the curve to demonstrate that these measurements are in excellent agreement in shape with the standard 3 ν oscillation scenario. and then renormalized to the new world average value of the neutron mean life, as explained in Section 6.1. The original data (references are listed in the caption to the figure) are rescaled according to Mention et al. In Figure 1 and similar plots shown below, all the curves correspond to a reactor with pure 235U fuel in all subsequent calculations, we explicitly take into account the particular fuel composition in each experiment, although the corresponding effect is very small (see Section 6.5 for explanation). The inverse β decay (IBD) cross section is calculated by using the results of (see Section 6.3 for more details). here and below, we assume the normal neutrino mass ordering and no C P violation (irrelevant to the issue under consideration).
Here, and below, we use the best-fit values for the neutrino mass-squared splittings and mixing angles from the recent global analysis of the neutrino oscillation data by Esteban et al. This deficit known as the “reactor antineutrino anomaly” (RAA) still remains an unresolved problem of particle and nuclear physics.įigure 1 illustrates the current state-of-the-art of the RAA the early and more recent reactor data in this figure are compared with the prediction based on the ν ¯ e flux by Mueller et al. This implies that the measured event rates in the reactor experiments is about 6% less than previously thought. The flux normalization uncertainty in the calculation by Mueller et al.
Rather sophisticated (decade ago) calculations yielded a net 3–3.5% upward shift in the predicted spectrum-averaged event rate with respect to the previously expected flux used in the earlier short baseline (SBL) reactor experiments (ILL, SRP, Gösgen, Krasnoyarsk, Rovno, Bugey ), as well as in the medium and long baseline (MBL, LBL) experiments Palo Verde, CHOOZ, and KamLAND. Calculating this spectrum is not an easy and well-defined task. The ν ¯ e spectrum is composed of thousands of spectral components formed by the β decay of the fission products of four main isotopes, 235U, 238U, 239Pu, and 241Pu (see for comprehensive reviews). Nuclear reactors produce a clean and intense flux of electron antineutrinos and thus are very good sources for experiments in neutrino physics.
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