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Reactor neutrino experiments have seen major improvements in precision in recent years. With the experimental uncertainties becoming lower than those from theory, carefully considering all sources of ν ¯ e is important when making theoretical predictions. One source of ν ¯ e that is often neglected arises from the irradiation of the nonfuel materials in reactors. The ν ¯ e rates and energies from these sources vary widely based on the reactor type, configuration, and sampling stage during the reactor cycle and have to be carefully considered for each experiment independently. In this article, we present a formalism for selecting the possible ν ¯ e sources arising from the neutron captures on reactor and target materials. We apply this formalism to the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory, the ν ¯ e source for the the Precision Reactor Oscillation and Spectrum Measurement (PROSPECT) experiment. Overall, we observe that the nonfuel ν ¯ e contributions from HFIR to PROSPECT amount to 1% above the inverse beta decay threshold with a maximum contribution of 9% in the 1.8-2.0 MeV range. Nonfuel contributions can be particularly high for research reactors like HFIR because of the choice of structural and reflector material in addition to the intentional irradiation of target material for isotope production. We show that typical commercial pressurized water reactors fueled with low-enriched uranium will have significantly smaller nonfuel ν ¯ e contribution.

There is a well-known $2\ensuremath{\sigma}$ tension in the measurements of the solar $\mathrm{\ensuremath{\Delta}}{m}^{2}$ between KamLAND and SNO/Super-KamioKANDE. Precise determination of the solar $\mathrm{\ensuremath{\Delta}}{m}^{2}$ is especially important in connection with current and future long baseline $CP$ violation measurements. Seo and Parke [Phys. Rev. D 99, 033012 (2019)] points out that currently running short baseline reactor neutrino experiments, Daya Bay and RENO, can also constrain solar $\mathrm{\ensuremath{\Delta}}{m}^{2}$ value as demonstrated by a GLoBES simulation with a limited systematic uncertainty consideration. In this work, the publicly available data, from Daya Bay (1958 days) and RENO (2200 days) are used to constrain the solar $\mathrm{\ensuremath{\Delta}}{m}^{2}$. Verification of our method through $\mathrm{\ensuremath{\Delta}}{m}_{ee}^{2}$ and ${\mathrm{sin}}^{2}{\ensuremath{\theta}}_{13}$ measurements is discussed in Appendix A. Using this verified method, reasonable constraints on the solar $\mathrm{\ensuremath{\Delta}}{m}^{2}$ are obtained using above Daya Bay and RENO data, both individually and combined. We find that the combined data of Daya Bay and RENO set an upper limit on the solar $\mathrm{\ensuremath{\Delta}}{m}^{2}$ of $18\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }{\mathrm{eV}}^{2}$ at the 95% C.L., including both systematic and statistical uncertainties. This constraint is slightly more than twice the KamLAND value. As this combined result is still statistics limited, even though driven by Daya Bay data, the constraint will improve with the additional running of this experiment.

Assuming that neutrinos are Majorana particles, we explore what information can be inferred from future strong limits (i.e. nonobservation) for neutrinoless double beta decay. Specifically we consider the case where the mass hierarchy is normal and the different contributions to the effective mass ⟨m⟩ee partly cancel. We discuss how this fixes the two Majorana CP phases simultaneously from the Majorana triangle and how it limits the lightest neutrino mass m1 within a narrow window. The two Majorana CP phases are in this case even better determined than in the usual case for larger ⟨m⟩ee. We show that the uncertainty in these predictions can be significantly reduced by the complementary measurement of reactor neutrino experiments, especially the medium baseline version JUNO/RENO-50. We also estimate the necessary precision on ⟨m⟩ee to infer nontrivial Majorana CP phases and the upper limit ⟨m⟩ee≲1 meV sets a target for the design of future neutrinoless double beta decay experiments.

Recent data of reactor neutrino experiments set more stringent constraint on leptonic mixing patterns. We examine all possible patterns on the basis of combinations of elementary correlations of elements of leptonic mixing matrix. we obtain 62 viable mixing patters at 3$\sigma$ level of mixing parameters. Most of these patterns can be paired via the {\mu}- interchange which changes the octant of $\theta_{23}$ and the sign of $\cos{\delta}$. All viable patterns can be classified into two groups: the perturbative patterns and non-perturbative patterns. The former can be obtained from perturbing TBM. The latter cannot be obtained from perturbing any mixing pattern whose $\theta_{13}$ is zero. Different predictions of Dirac CP phase $\delta$ of these two types of mixing patterns are discussed. Evolutions of mass matrices of neutrinos with small mixing parameters are discussed via special mixing patterns on the basis of flavor groups. In general cases, a small variation of $\sin\theta_{13}$ may bring about large modifications to alignment of vacuum expectation values in a mixing model. Therefore, small but nonzero $\sin\theta_{13}$ brings a severer challenge to leptonic mixing models on the basis of flavor groups than usual views., Comment: 29pages, 5 figures

A search for vacuum neutrino oscillations in the range $\ensuremath{\Delta}{m}^{2}g0.01$ e${\mathrm{V}}^{2}$ with ${sin}^{2}2\ensuremath{\theta}g0.05$ was performed with a detector placed at two different distances (18 and 24 m) from a production reactor at the Savannah River Site. The results observed are inconsistent with oscillations in this region and consistent with other reactor experiments.

The neutrino mixing angle �13 is at the focus of current neutrino research. From a global analysis of the available oscillation data in a 3� framework, we previously reported [Phys. Rev. Lett. 101, 141801 (2008)] hints in favor of �13 > 0 at the 90% C.L. Such hints are consistent with the recent indications of �µ ! �e appearance in the T2K and MINOS long-baseline accelerator experiments. Our global analysis of all the available data currently provides > 3� evidence for nonzero �13, with 1� ranges sin 2 �13 = 0.021 ± 0.007 or 0.025 ± 0.007, depending on reactor neutrino flux systematics. Updated ranges are also reported for the other 3� oscillation parameters (�m 2 , sin 2 �12) and (�m 2 , sin 2 �23).

We study the impact of very light sterile neutrinos ($\ensuremath{\Delta}{m}_{\mathrm{new}}^{2}\ensuremath{\in}[1,10]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\text{ }\text{ }{\mathrm{eV}}^{2}$, ${sin }^{2}2{\ensuremath{\theta}}_{\mathrm{new}}l{10}^{\ensuremath{-}1}$) on analyses of upcoming ${\ensuremath{\theta}}_{13}$-driven reactor antineutrino experiments like Double CHOOZ and Daya Bay. Oscillations driven by these values of $\ensuremath{\Delta}{m}_{\mathrm{new}}^{2}$ affect data in the near and far detectors differently and hence potentially modify the capability of these experimental setups to constrain and measure ${sin }^{2}2{\ensuremath{\theta}}_{13}$. We find that the hypothesis ${\ensuremath{\theta}}_{\mathrm{new}}\ensuremath{\ne}0$ negatively impacts one's ability to place an upper bound on ${sin }^{2}2{\ensuremath{\theta}}_{13}$ in the advent of a no-oscillation signal or to measure ${sin }^{2}2{\ensuremath{\theta}}_{13}$ if a ${\ensuremath{\theta}}_{13}$-driven signal is observed. The impact of sterile neutrino effects, however, depends dramatically on one's ability to measure the recoil positron energy spectrum. If ${sin }^{2}2{\ensuremath{\theta}}_{\mathrm{new}}\ensuremath{\gtrsim}{10}^{\ensuremath{-}2}$, upcoming ${\ensuremath{\theta}}_{13}$-driven reactor antineutrino experiments should be able to measure ${sin }^{2}2{\ensuremath{\theta}}_{\mathrm{new}}$ and $\ensuremath{\Delta}{m}_{\mathrm{new}}^{2}$, along with ${sin }^{2}2{\ensuremath{\theta}}_{13}$, as long as one is sensitive to distortions in the recoil positron energy spectrum in the near (and far) detectors.

Nailing down the unknown neutrino mixing angle theta{13} is one of the most important goals in current lepton physics. In this context, we perform a global analysis of neutrino oscillation data, focusing on theta{13}, and including recent results [ (unpublished)]. We discuss two converging hints of theta{13}>0, each at the level of approximately 1sigma: an older one coming from atmospheric neutrino data, and a newer one coming from the combination of solar and long-baseline reactor neutrino data. Their combination provides the global estimate sin{2}theta{13}=0.016+/-0.010(1sigma), implying a preference for theta{13}>0 with non-negligible statistical significance ( approximately 90% C.L.). We discuss possible refinements of the experimental data analyses, which might sharpen such intriguing indications.

A search of neutrino magnetic moments was carried out at the Kuo-Sheng Nuclear Power Station at a distance of 28 m from the 2.9 GW reactor core. With a high purity germanium detector of mass 1.06 kg surrounded by scintillating NaI(Tl) and CsI(Tl) crystals as anti-Compton detectors, a detection threshold of 5 keV and a background level of 1 $\cpd$ near threshold were achieved. Details of the reactor neutrino source, experimental hardware, background understanding and analysis methods are presented. Based on 570.7 and 127.8 days of Reactor ON and OFF data, respectively, at an average Reactor ON electron anti-neutrino flux of $\rm{6.4 \times 10^{12} cm^{-2} s^{-1}}$, the limit on the neutrino magnetic moments of $\rm{\munuebar < 7.4 \times 10^{-11} \mub}$ at 90% confidence level was derived. Indirect bounds on the $\nuebar$ radiative decay lifetimes were inferred., 16 pages, 15 figures, 9 tables

We discuss the possibilities of high precision measurement of the solar neutrino mixing angle ${\ensuremath{\theta}}_{\ensuremath{\bigodot}}\ensuremath{\equiv}{\ensuremath{\theta}}_{12}$ in solar and reactor neutrino experiments. The improvements in the determination of ${sin }^{2}{\ensuremath{\theta}}_{12}$, which can be achieved with the expected increase of statistics and reduction of systematic errors in the currently operating solar and KamLAND experiments, are summarized. The potential of LowNu $\ensuremath{\nu}\ensuremath{-}e$ elastic scattering experiment, designed to measure the $pp$ solar neutrino flux, for high precision determination of ${sin }^{2}{\ensuremath{\theta}}_{12}$, is investigated in detail. The accuracy in the measurement of ${sin }^{2}{\ensuremath{\theta}}_{12}$, which can be achieved in a reactor experiment with a baseline $L\ensuremath{\sim}(50\char21{}70)\text{ }\text{ }\mathrm{km}$, corresponding to a survival probability minimum (SPMIN), is thoroughly studied. We include the effect of the uncertainty in the value of ${sin }^{2}{\ensuremath{\theta}}_{13}$ in the analyses. A LowNu measurement of the $pp$ neutrino flux with a 1% error would allow to determine ${sin }^{2}{\ensuremath{\theta}}_{12}$ with an error of 14% (17%) at $3\ensuremath{\sigma}$ from a two-generation (three-generation) analysis. The same parameter ${sin }^{2}{\ensuremath{\theta}}_{12}$ can be measured with an uncertainty of 2% (6%) at $1\ensuremath{\sigma}$ ($3\ensuremath{\sigma}$) in a reactor experiment with $L\ensuremath{\sim}60\text{ }\text{ }\mathrm{km}$, statistics of $\ensuremath{\sim}60$ GWkTy and systematic error of 2%. For the same statistics, the increase of the systematic error from 2% to 5% leads to an increase in the uncertainty in ${sin }^{2}{\ensuremath{\theta}}_{12}$ from 6% to 9% at $3\ensuremath{\sigma}$. The inclusion of the ${sin }^{2}{\ensuremath{\theta}}_{13}$ uncertainty in the analysis changes the error on ${sin }^{2}{\ensuremath{\theta}}_{12}$ to 3% (9%). The effect of ${sin }^{2}{\ensuremath{\theta}}_{13}$ uncertainty on the ${sin }^{2}{\ensuremath{\theta}}_{12}$ measurement in both types of experiments is considerably smaller than naively expected.

The interpretation of reactor-antineutrino-induced experiments in the investigation of neutrino oscillations is, in a decisive way, dependent on reliable calculations of the initial antineutrino spectra. Present calculations ignore the effects of low-lying structures in the beta strength function. These will have, however, a drastic influence on the $\ensuremath{\beta}$-decay properties of the fission products and thus on the shape of the antineutrino spectra.