The reactor antineutrino anomaly might be explained by the oscillation of reactor antineutrinos toward a sterile neutrino of eV mass. In order to explore this hypothesis, the STEREO experiment ...measures the antineutrino energy spectrum in six different detector cells covering baselines between 9 and 11 m from the compact core of the ILL research reactor. In this Letter, results from 66 days of reactor turned on and 138 days of reactor turned off are reported. A novel method to extract the antineutrino rates has been developed based on the distribution of the pulse shape discrimination parameter. The test of a new oscillation toward a sterile neutrino is performed by comparing ratios of cells, independent of absolute normalization and of the prediction of the reactor spectrum. The results are found to be compatible with the null oscillation hypothesis and the best fit of the reactor antineutrino anomaly is excluded at 97.5% C.L.
Anomalies in past neutrino measurements have led to the discovery that these particles have non-zero mass and oscillate between their three flavours when they propagate. In the 2010s, similar ...anomalies observed in the antineutrino spectra emitted by nuclear reactors have triggered the hypothesis of the existence of a supplementary neutrino state that would be sterile, that is, not interacting by means of the weak interaction1. The STEREO experiment2-6 was designed to investigate this conjecture, which would potentially extend the standard model of particle physics. Here we present an analysis of the full set of data generated by STEREO, confirming observed anomalies while rejecting the hypothesis of a light sterile neutrino. Installed at the Institut Laue-Langevin (ILL) research reactor, STEREO accurately measures the antineutrino energy spectrum associated to the fission of 235U. The segmentation of the detector and its very short distance to the compact core are crucial properties of STEREO for our analysis. The measured antineutrino energy spectrum suggests that anomalies originate from biases in the nuclear experimental data used for the predictions7,8. Our result supports the neutrino content of the standard model and establishes a new reference for the 235U antineutrino energy spectrum. We anticipate that this result will allow progress towards finer tests of the fundamental properties of neutrinos but also to benchmark models and nuclear data of interest for reactor physics9,10 and for observations of astrophysical or geoneutrinos11,12.
A
bstract
The OPERA neutrino experiment at the underground Gran Sasso Laboratory has measured the velocity of neutrinos from the CERN CNGS beam over a baseline of about 730 km. The measurement is ...based on data taken by OPERA in the years 2009, 2010 and 2011. Dedicated upgrades of the CNGS timing system and of the OPERA detector, as well as a high precision geodesy campaign for the measurement of the neutrino baseline, allowed reaching comparable systematic and statistical accuracies.
An arrival time of CNGS muon neutrinos with respect to the one computed assuming the speed of light in vacuum of
was measured corresponding to a relative difference of the muon neutrino velocity with respect to the speed of light
. The above result, obtained by comparing the time distributions of neutrino interactions and of protons hitting the CNGS target in 10.5
μ
s long extractions, was confirmed by a test performed at the end of 2011 using a short bunch beam allowing to measure the neutrino time of flight at the single interaction level.
The STEREO experiment is a very short baseline reactor antineutrino experiment. It is designed to test the hypothesis of light sterile neutrinos being the cause of a deficit of the observed ...antineutrino interaction rate at short baselines with respect to the predicted rate, known as the reactor antineutrino anomaly. The STEREO experiment measures the antineutrino energy spectrum in six identical detector cells covering baselines between 9 and 11 m from the compact core of the ILL research reactor. In this article, results from 179 days of reactor turned on and 235 days of reactor turned off are reported at a high degree of detail. The current results include improvements in the modelling of detector optical properties and the γ-cascade after neutron captures by gadolinium, the treatment of backgrounds, and the statistical method of the oscillation analysis. Using a direct comparison between antineutrino spectra of all cells, largely independent of any flux prediction, we find the data compatible with the null oscillation hypothesis. The best-fit point of the reactor antineutrino anomaly is rejected at more than 99.9% C.L.
Different extensions of the standard model of particle physics, such as braneworld or mirror matter models, predict the existence of a neutron sterile state, possibly as a dark matter candidate. This ...Letter reports a new experimental constraint on the probability p for neutron conversion into a hidden neutron, set by the STEREO experiment at the high flux reactor of the Institut Laue-Langevin. The limit is p<3.1×10^{-11} at 95% C.L. improving the previous limit by a factor of 13. This result demonstrates that short-baseline neutrino experiments can be used as competitive passing-through-walls neutron experiments to search for hidden neutrons.
.
The STEREO experiment measures the electron antineutrino spectrum emitted in a research reactor using the inverse beta decay reaction on H nuclei in a gadolinium loaded liquid scintillator. The ...detection is based on a signal coincidence of a prompt positron and a delayed neutron capture event. The simulated response of the neutron capture on gadolinium is crucial for the comparison with data, in particular in the case of the detection efficiency. Among all stable isotopes,
155
Gd and
157
Gd have the highest cross sections for thermal neutron capture. The excited nuclei after the neutron capture emit gamma rays with a total energy of about 8MeV. The complex level schemes of
156
Gd and
158
Gd are a challenge for the modeling and prediction of the deexcitation spectrum, especially for compact detectors where gamma rays can escape the active volume. With a new description of the Gd (n,
γ
) cascades obtained using the FIFRELIN code, the agreement between simulation and measurements with a neutron calibration source was significantly improved in the STEREO experiment. A database of ten millions of deexcitation cascades for each isotope has been generated and is now available for the user.
•PCV13 effectiveness since its inclusion in the Community of Madrid in 2010.•PCV13 implementation led to the almost total disappearance of serotype 19A.•Near-elimination of serotype 19A caused ...disappearance of all related meningitis cases.•Near-elimination of serotype 19A caused a decrease in antibiotic resistance.•PCV13 did not cause replacement by other serotypes not covered by the vaccine.
Streptococcus pneumoniae is a major cause of morbidity and mortality worldwide. Using the data from the HERACLES clinical surveillance study (2007–2016), we describe the population impact of the 13-valent pneumococcal conjugate vaccine (PVC13) on invasive pneumococcal disease (IPD) in children <15 years of age in the Community of Madrid, Spain. After six years of the inclusion of PCV13 in the vaccination calendar (2010–2016), and despite changes in the Regional Immunization Programme that limited its availability, the net benefit incidence rate (IR) of IPD fell by 70.1% (IRR 0.3 95% CI: 0.22–0.4; p ≤ 0.001), mainly due to a significant reduction (91%) in the PCV13 serotypes (IRR 0.09 95% CI: 0.05–0.16, p ≤ 0.001). Furthermore, no significant changes were detected in the IR of IPD caused by non-PCV13 serotypes. The IRs of the aggressive, resistant and most prevalent serotype in the analysed population, the 19A serotype, dramatically decreased from the beginning to the end of the study (98%) IRR 0.03 (95% CI: 0.00–0.19), p ≤ 0.001, to its almost total disappearance. Remarkably, this reduction led to a pronounced decline in the percentage of cefotaxime-resistant isolates and the incidence of meningitis cases. Assessment of the clinical impact revealed a reduction in the number of all clinical presentations of IPD, confirming the effectiveness of the PCV13. Finally, PCV13 detected by PCR is predicted to have a stronger impact than the one based on culture methods, which can overlook more than 20% of cases of IPD, mainly pleural empyemas.
The PROSPECT and STEREO collaborations present a combined measurement of the pure 235U antineutrino spectrum, without site specific corrections or detector-dependent effects. The spectral ...measurements of the two highest precision experiments at research reactors are found to be compatible with χ2/ndf = 24.1/21, allowing a joint unfolding of the prompt energy measurements into antineutrino energy. This $\bar{ν}_e$ energy spectrum is provided to the community, and an excess of events relative to the Huber model is found in the 5-6 MeV region. When a Gaussian bump is fitted to the excess, the data-model χ2 value is improved, corresponding to a 2.4σ significance.
Abstract
This paper describes a new νe identification method specifically designed to improve the low-energy ($\lt {30}\, {\rm GeV}$) νe identification efficiency attained by enlarging the emulsion ...film scanning volume with the next-generation emulsion readout system. A relative increase of 25–70% in the νe low-energy region is expected, leading to improvements in the OPERA sensitivity to neutrino oscillations in the framework of the 3 + 1 model. The method is applied to a subset of data where the detection efficiency increase is expected to be more relevant, and one additional νe candidate is found. The analysis combined with the ντ appearance results improves the upper limit on sin 22θμe to 0.016 at 90% C.L. in the MiniBooNE allowed region $\Delta m^2_{41} \sim {0.3}\, {\rm eV}^{2}$.
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