科研之友
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摘要
Proposed medium-baseline reactor neutrino experiments offer unprecedented opportunities to probe, at the same time, the mass-mixing parameters which govern nu(e) oscillations both at long wavelength (delta m(2) and theta(12)) and at short wavelength (Delta m(2) and theta(13)), as well as their tiny interference effects related to the mass hierarchy (i.e., the relative sign of Delta m(2) and delta m(2)). In order to take full advantage of these opportunities, precision calculations and refined statistical analyses of event spectra are required. In such a context, we revisit several input ingredients, including nucleon recoil in inverse beta decay and its impact on energy reconstruction and resolution, hierarchy and matter effects in the oscillation probability, spread of reactor distances, irreducible backgrounds from geoneutrinos and from far reactors, and degeneracies between energy scale and spectrum shape uncertainties. We also introduce a continuous parameter alpha, which interpolates smoothly between normal hierarchy (alpha + 1) and inverted hierarchy (alpha = -1). The determination of the hierarchy is then transformed from a test of hypothesis to a parameter estimation, with a sensitivity given by the distance of the true case (either alpha + 1 or alpha = -1) from the "undecidable" case (alpha = 0). Numerical experiments are performed for the specific setup envisaged for the JUNO project, assuming a realistic sample of O(10(5)) reactor events. We find a typical sensitivity of similar to 2 sigma to the hierarchy in JUNO, which, however, can be challenged by energy scale and spectrum shape systematics, whose possible conspiracy effects are investigated. The prospective accuracy reachable for the other mass-mixing parameters is also discussed.
- 出版日期2014-1-9
