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Home page > PhD fellowships > Proposed PhD subjects 2016-2019 > STEREO : Sterile neutrino search at ILL

STEREO : Sterile neutrino search at ILL

by Luc Frappat - 17 December 2015

Topics:  Neutrino physics

Proponents: Jean-Sébastien Réal

Address:  LPSC Grenoble - 53, rue des Martyrs - 38026 GRENOBLE CEDEX

Phone:  + 33 (0)476 28 41 75

Contact Email: real@lpsc.in2p3.fr


Overview : Since their discovery in 1956, neutrinos have been extensively studied. Recently, neutrino oscillations have been measured and show that they are massive particles. The three known types (flavor) of neutrino interact only through the weak force. Due to their very small interaction probabilities, measurement of their characteristics needs very intense sources and/or large detectors. In this context, nuclear reactors are privileged sources of electron’s antineutrinos. All experiments done closer than 100 m from a reactor core show a lack of neutrinos compared to what was expected, this is the so called neutrino reactor anomaly ( about 7% less). A similar lack is observed when measuring neutrinos from intense nuclear sources. One explanation of these discrepancies could be the existence of a fourth neutrino (called sterile neutrino due to the fact that it is insensitive to the weak interaction).

Since it is sterile, it cannot be detected, but due to its oscillation with the other neutrino flavors, a deficit of known neutrinos depending on their energy and on the distance from the source will unambiguously sign its existence. In this context, several experiments in Europe and around the world will try to measure a new oscillation at few meters from a reactor core or from a radioactive source with almost all the same timing, beginning the data taking in 2015 or 2016. The Stereo experiment is a small international collaboration which includes 2 laboratories of the labex ENIGMASS (the LPSC and the LAPP). The detector is under construction and will be installed in April 2016 at Institut Laue Langevin (ILL) in Grenoble. The first data taking will take place in June 2016 for 2 years. The LPSC has in charge the design and the construction of the cosmic veto detector, the relative LED calibration system and the electronics of all the experiment.

The detection process used is the inverse beta decay, which gives a coincidence between a positron (from which we can measure the neutrino energy) and a neutron. The target volume consists in 6 cells, stacked along the direction of the core and filled with Gd-doped liquid. The segmentation of the detector will allow us to measure neutrino rates and energy spectra at 6 different locations from the reactor core, signing a possible oscillation.

The PhD student will contribute to the detector installation, to the 2 years of data taking and to the analysis of the experiment. The goal at the end of the 3 years PhD is to be able to confirm or not the existence of a new sterile neutrino. The student will focus on the subtraction of the cosmic background and on the estimate of the systematics induced by that background. He will also actively participate in keeping running the parts devolved to the LPSC (calibration LED system, Veto detector and data acquisition).