[en] In the last recent years, two unsolved anomalies have appeared during the study of the reactor neutrinos: one related to the neutrino spectral shape, and another to the absolute neutrino flux. The last one, known as the Reactor Antineutrino Anomaly (RAA), presents a deficit in the observed flux compared to the expected one. This anomaly could point to the existence of a light sterile neutrino participating in the oscillation phenomena. The study of the nuclear reactor flux at very short baselines is a key to prove these hypothesis. The STEREO experiment observes neutrinos emitted from the compact, highly ${}^{235}$U enriched fuel element of the research reactor of the Institut Laue Langevin (Grenoble, France). The detector target is placed at only 10 meters of the reactor core, and in order to have an independent measurement of the neutrino spectrum, it is segmented in six independent cells providing a multiple baseline analysis. The recorded data during 113 (138) days of reactor turned on (off) analyzed and presented last year, are compatible with the null oscillation hypothesis and reject the original best-fit of the RAA at 98 % C.L. These results, and the most recent improvements of the second phase of data taking will be presented in this talk, providing a crucial input in the search of sterile neutrinos.

[en] Liquid scintillators have become a well established detection medium in the context of neutrino experiments. They offer good transparency and light yield while allowing for geometrical flexibility of the fiducial volume at low costs. By loading the scintillators with metal compounds, effectiveness of neutron detection can be highly increased making them suitable for applications e.g. in reactor neutrino physics. Depending on the respective usage-case, additional scintillator properties such as particle identification and vertex resolution become beneficial. We report the development of scintillator in the context of the STEREO experiment which allows for good particle identification by exploiting light pulse shape discrimination. In addition we present the current status of a LAB-based scintillator aiming for improved spatial resolution.

[en] Nuclear reactors are an intense and pure source of low energy electron antineutrinos. In combination with other sources, they have been used to discover and understand neutrino oscillations. However, two unsolved anomalies have appeared during the study of the reactor neutrinos: one related to the neutrino spectral shape, and another to the absolute neutrino flux. The latter, known as the Reactor Antineutrino Anomaly, presents a deficit in the observed flux compared to the expected at very short baselines (distance $<$ 100 meters). This anomaly could point to the existence of a light sterile neutrino participating in the oscillation phenomena, and a way to prove it is the study of the reactor neutrino flux at very short baselines. The Stereo experiment, taking data since November 2016, is trying to resolve this anomaly. It is placed at 10 meters from the compact, highly enriched ${}^{235}$U fuel element of the research reactor of the Institut Laue Langevin (Grenoble, France). The detector target is segmented in six cells providing a multiple baselines analysis. Oscillations to a sterile neutrino in the eV mass scale can be identified by characteristic distortions in the neutrino energy spectrum of the different cells. The most recent results of this experiment are going to be presented in this talk.

No abstract available

[en] In the recent past major milestones in neutrino physics were accomplished at nuclear reactors: the smallest neutrino mixing angle θ₁₃ was determined with high precision and the emitted antineutrino spectrum was measured with unprecedented resolution. However, two anomalies - related to the absolute flux and the spectral shape - have yet to be solved. The flux anomaly is known as reactor antineutrino anomaly and could be caused by the existence of a light sterile neutrino participating in the neutrino oscillation phenomenon. Introducing a sterile eigenstate implies the presence of a fourth mass eigenstate and global fits favor sin²2θ=0.09 and Δm²=1.8 eV² as oscillation parameters. The Stereo experiment was built to finally solve this puzzle. It is one of the first running experiments built to search for eV sterile neutrinos and takes data since end of 2016 at ILL Grenoble (France). At a short baseline of 10 meters it measures the antineutrino flux and spectrum emitted by a compact research reactor. The segmentation of the detector in six target cells allows for independent measurements of the neutrino spectrum at multiple baselines. An active-sterile flavor oscillation could be unambiguously detected, as it distorts the spectral shape of each cell's measurement differently. This talk gives an overview of the Stereo experiment, including details on the detector design, detection principle and the current status.

[en] The Double Chooz experiment is a reactor neutrino disappearance experiment, which aims for the measurement of the still uncertain neutrino mixing angle θ₁₃. It consists of two identical detectors filled with liquid scintillator which are located at different distances to the reactor cores. The far detector is currently being commissioned. Physics data taking is aimed to start in spring 2011. The signature of a neutrino interaction in the detector is the delayed coincidence of a neutron and a positron signal which are created by inverse beta decay. In this contribution we present simulation studies on the development of an initial algorithm for the selection of neutrino candidates from the data stream. Of particular interest is the utilization of the event classification provided by the trigger system and the evaluation of its efficiency. The simulations are done with a full simulation of the detector response and include various backgrounds. The aim is to use this algorithm during the early phase of the physics commissioning of Double Chooz for the verification of the detector performance.

No abstract available

[en] The Stereo experiment, running since November 2016 at the ILL Grenoble, aims to test the hypothesis of sterile neutrinos as a possible the cause of the reactor antineutrino anomaly at short baselines. The detector is divided in two main volumes each filled with liquid scintillator. The central volume is segmented in six independent cells corresponding to the neutrino target (NT). Its scintillator is doped with gadolinium to enhance the detection of the correlated neutrino signal produced by the inverse beta decay. Surrounding the NT there is the outer crown (OC) volume, optimized to capture escaping gammas originating from interactions in the NT. The energy deposited in the detector is measured as scintillation light that is collected by a set of photomultiplier tubes. The readout charge signals are linked to visible energy by a non-linear energy scale. To determine such energy scale and to monitor the detector stability, several gamma and neutron sources are deployed by means of three different calibration systems: an internal set of tubes located within the NT cells, a single tube underneath the detector to introduce sources below the NT and OC, and a rail system optimized for OC calibration. The calibration runs performed provided Stereo with a better understanding of the detector response and an energy scale reconstruction that will be presented in this talk.

[en] The Stereo experiment, running since November 2016 at the ILL Grenoble, aims to test the hypothesis of sterile neutrinos being the cause of the reactor antineutrino anomaly observed at short baselines. The detector is divided in two main volumes each filled with liquid scintillator. The inner volume is segmented in six independent cells corresponding to the neutrino target (TG). It is doped with gadolinium to enhance the detection of the correlated signal produced by the inverse beta decay. Surrounding the TG there is the gamma catcher (GC) volume, optimized to capture escaping gammas originating from interactions in the TG. The energy deposited in the detector is measured as scintillation light that is collected by a set of photomultiplier tubes. The readout charge signals are converted to visible energy by a dedicated non-linear energy scale. To determine the energy scale, detection efficiency and to observe the detector stability, several gamma and neutron sources have been deployed by means of three different calibration systems: an internal set of tubes located within the TG cells, a central rail underneath the detector crossing the TG and GC volume, and an outer pantograph-rail system for 2d calibration around the GC. The calibration runs performed during the phases I and II of Stereo and their use on the energy scale and detection efficiency determination are discussed in this talk.

[en] The STEREO experiment is an antineutrino disappearance experiment located at the ILL research reactor in Grenoble, France. Its goal is to test the sterile neutrino hypothesis via oscillations. The detector has a segmented design, to measure the relative effect of neutrino oscillations at six different baselines between 9 and 11 metres. Neutrinos are detected in six Gd-loaded liquid scintillator volumes by the inverse beta decay reaction (IBD). In this reaction, an antineutrino capture by a proton yields a positron, giving a prompt energy deposition and annihilation signal, and a neutron, giving a delayed capture signal after thermalisation. Due to its proximity to the reactor a significant flux of neutrons reaches the detector. In addition, atmospheric muons produce neutrons via spallation. Neutrons can mimic IBDs as they generate prompt proton recoils followed by their delayed capture. However, the scintillator deexcitation time differs for a proton recoil and a positron or gamma event. Thus, it is possible to distinguish both types of particle signals by analysing the time shape of their scintillation pulses. This contribution presents in-situ and laboratory measurements of pulse shapes for gamma and neutron events. A strategy for background rejection using scintillation pulse shape is described and its performance reviewed.