Latest results from Double Chooz
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atest Results from Double Chooz1, 2 A. Minotti on behalf of Double Chooz collaboration Université de Strasbourg, IPHC, France e-mail: [email protected] Abstract⎯Double Chooz is a short-baseline neutrino disappearance experiment. It detects ν e produced in the power plant of Chooz, France, where is located. The main goal of the experiment is the measurement of θ13 mixing angle and in 2011 for the first time the experiment observed an indication for a non zero value of such an oscillation parameter. The mixing angle was successively measured using only the far detector finding the best fit value of sin2(2θ13) = 0 . 090 +−00.. 032 029 . The near detector is under construction and will start data taking by the middle of 2014 allowing the reduction of the systematic errors. In this paper I make a review of the Double Chooz experiment, focusing in particular on the latest results of the measurement of the mixing angle θ13 relying on the neutron absorption on Gadolinium. I also present results proving the capability of Double Chooz to identify the ortho-positronium. This has been done in an event-by-event basis for the first time in a large liquid scintillator experiments, and can be an additional handle for the electron/positron discrimination in future detectors based on such technology. DOI: 10.1134/S1063779616060162
1. INTRODUCTION The standard three-families neutrino oscillation can be described by three mixing angles, two independent mass square differences, and a CP-violation phase. Among the three mixing angle, θ13 is the smallest and was the last to be measured. Double Chooz was the first experiment to show a hint of a non-zero value of θ13 [1] and currently plays an important role in the race to improve the precision on this parameter, along with two other reactor neutrino experiments, DayaBay [2], RENO [3], and the accelerator neutrino experiment T2K [4]. This discovery of a non-zero θ13 paved the way for designing of future experiment aiming to measure the CP-violation in the leptonic sector. Double Chooz detects reactor ν e via inverse beta decay (IBD), with the signature given by a delayed coincidence between the positron signal and the neutron capture. Basing on which nucleus captures the neutron, we distinguish between hydrogen (n-H) and gadolinium (n-Gd) analysis, with the former being exploited by Double Chooz for the first time [5]. The n-Gd analysis has seen a major improvement in the last publication [6], with respect to the previous results of [7]. This article is focused on these latest results.
2. EXPERIMENTAL CONCEPT As a reactor neutrino oscillation experiments, Double Chooz aims to measure θ13 by looking at the disappearance of ν e produced in nuclear fissions happening inside a power reactor. The survival probability of ν e can be expressed by 2 2 2 ⎛ Δm L ⎞ P (ν e → ν e) 1 − sin (2θ13 ) sin ⎜ 23 ⎟ ⎝ 4E ⎠ ⎛ Δm2 L ⎞ − cos 4 (θ13 ) sin 2(2θ12 ) sin 2 ⎜ 12 ⎟ , ⎝ 4E ⎠
(1)
where L (km) is the distance between the neutrino source and the detector, or baseline, E (MeV) the neu2 2 tri
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