Search for signatures of sterile neutrinos with Double Chooz

We present a search for signatures of neutrino mixing of electron anti-neutrinos with additional hypothetical sterile neutrino flavors using the Double Chooz experiment. The search is based on data from 5 years of operation of Double Chooz, including 2 years in the two-detector configuration. The analysis is based on a profile likelihood, i.e. comparing the data to the model prediction of disappearance in a data-to-data comparison of the two respective detectors. The analysis is optimized for a model of three active and one sterile neutrino. It is sensitive in the typical mass range $${5 \times 10^{-3}}\,\mathrm{eV}^2 \lesssim \varDelta m^2_{41} \lesssim {3 \times 10^{-1}}\,\mathrm{eV}^2 $$ 5 × 10 - 3 eV 2 ≲ Δ m 41 2 ≲ 3 × 10 - 1 eV 2 for mixing angles down to $$\sin ^2 2\theta _{14} \gtrsim {0.02} $$ sin 2 2 θ 14 ≳ 0.02 . No significant disappearance additionally to the conventional disappearance related to $$\theta _{13} $$ θ 13 is observed and correspondingly exclusion bounds on the sterile mixing parameter $$\theta _{14} $$ θ 14 as a function of $$ \varDelta m^2_{41} $$ Δ m 41 2 are obtained.

Non-standard interactions in SMEFT confronted with terrestrial neutrino experiments

The Standard Model Effective Field Theory (SMEFT) provides a systematic and model-independent framework to study neutrino non-standard interactions (NSIs). We study the constraining power of the on-going neutrino oscillation experiments T2K, NOνA, Daya Bay, Double Chooz and RENO in the SMEFT framework. A full consideration of matching is provided between different effective field theories and the renormalization group running at different scales, filling the gap between the low-energy neutrino oscillation experiments and SMEFT at the UV scale. We first illustrate our method with a top- down approach in a simplified scalar leptoquark model, showing more stringent constraints from the neutrino oscillation experiments compared to collider studies. We then provide a bottom-up study on individual dimension-6 SMEFT operators and find NSIs in neutrino experiments already sensitive to new physics at ∼20 TeV when the Wilson coefficients are fixed at unity. We also investigate the correlation among multiple operators at the UV scale and find it could change the constraints on SMEFT operators by several orders of magnitude compared with when only one operator is considered. Furthermore, we find that accelerator and reactor neutrino experiments are sensitive to different SMEFT operators, which highlights the complementarity of the two experiment types.

Reactor rate modulation oscillation analysis with two detectors in Double Chooz

A θ13 oscillation analysis based on the observed antineutrino rates at the Double Chooz far and near detectors for different reactor power conditions is presented. This approach provides a so far unique simultaneous determination of θ13 and the total background rates without relying on any assumptions on the specific background contributions. The analysis comprises 865 days of data collected in both detectors with at least one reactor in operation. The oscillation results are enhanced by the use of 24.06 days (12.74 days) of reactor-off data in the far (near) detector. The analysis considers the $$ {\overline{\nu}}_e $$ ν ¯ e interactions up to a visible energy of 8.5 MeV, using the events at higher energies to build a cosmogenic background model considering fast-neutrons interactions and 9Li decays. The background-model-independent determination of the mixing angle yields sin2(2θ13) = 0.094 ± 0.017, being the best-fit total background rates fully consistent with the cosmogenic background model. A second oscillation analysis is also performed constraining the total background rates to the cosmogenic background estimates. While the central value is not significantly modified due to the consistency between the reactor-off data and the background estimates, the addition of the background model reduces the uncertainty on θ13 to 0.015. Along with the oscillation results, the normalization of the anti-neutrino rate is measured with a precision of 0.86%, reducing the 1.43% uncertainty associated to the expectation.

Addendum to: Updated constraints on non-standard interactions from global analysis of oscillation data

In this addendum we re-assess the constraints on Non-Standard Interactions (NSI) from the global analysis of neutrino oscillation data after including the new results released since the publication of ref. [1], in particular those presented at the Neutrino2020 conference. The new data considered here includes the total energy spectrum and the day-night asymmetry of the 2970-day SK4 solar neutrino sample [2], as well as the latest results from long-baseline (LBL) experiments T2K [3, 4] and NOvA [5, 6]. In addition, we have updated the reactor experiments Double-Chooz [7, 8] to 1276/587 days of far/near detector data and RENO [9, 10] to 2908 days of exposure.

Analysis of the reactor antineutrino spectrum anomaly with fuel burnup

Recently, three successful antineutrino experiments (Daya Bay, Double Chooz, and RENO) measured the neutrino mixing angle θ13; however, significant discrepancies were found, both in the absolute flux and spectral shape. Much effort has been expended investigating the possible reasons for the discrepancies. In this paper, the change of neutrino energy spectrum with burnup is analyzed from the point of view of the change of neutrino energy spectrum with burnup. An accurate method for calculating neutrino energy spectrum is proposed. The non-equilibrium correction is studied by using this method. It is found that the non-equilibrium correction contributes not only to the energy region less than 4.0 MeV, but also to the energy region greater than 4.0 MeV, with a maximum correction of about 3%.

Recent results from reactor antineutrino experiments

The smallest neutrino mixing angle \theta_{13}θ13 has been successfully measured by the disappearance of reactor antineutrinos at RENO, Daya Bay, and Double Chooz. The oscillation frequency is also measured based on energy and baseline dependent disappearance probability of reactor antineutrinos. Recent results find a variation in the observed reactor antineutrino flux as a function of the reactor fuel evolution. We report more precisely measured values of \theta_{13}θ13 and \Delta m_{ee}^2Δmee2 and results on the evolution of observed reactor antineutrino yield and spectrum.