The OPERA experiment

The aim of the OPERA experiment is to provide an unambiguous evidence for the νμ ↔ ντ oscillation by looking at the appearance of ντ in a pure νμ beam. This oscillation will be sought in the region of the oscillation parameters indicated by the atmospheric neutrino results. The experiment is part of the CNGS (Cern Neutrino beam to Gran Sasso) project. The νμ beam produced at CERN will be sent towards the Gran Sasso underground laboratory, where the OPERA detector is under construction. The detector, the physics potential and performance for neutrino oscillation studies including the subleading νμ ↔ νe search are presented

Double Chooz and recent results

Double Chooz is a reactor ¯νe disappearance experiment located in France near the power plant of Chooz. The main goal of the experiment is the measurement of the 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) = 0.109 ± 0.035. The near detector is under construction and will start data taking by the middle of 2014 allowing to reduce the systematic errors. In this paper I make a review of the experimental results, focusing in particular on independent analyses such as the measurement of the mixing angle θ13 relying on the neutron absorption on gadolinium and hydrogen, and on the reactor rate modulation. I also present for the first time the capability of Double Chooz to identify the ortho-positronium state on event-by-event basis, which could be an additional handle for the electron/positron discrimination in future liquid-scintillator–based detectors

A new anti-neutrino detection technique based on positronium tagging with plastic scintillators

The main signature for anti-neutrino detection in reactor and geo-neutrino experiments based on scintillators is provided by the space-time coincidence of positron and neutron produced in the Inverse Beta Decay reaction. Such a signature strongly suppresses backgrounds and allows for measurements performed underground with a relatively high signal-to-background ratio. In an aboveground environment, however, the twofold coincidence technique is not sufficient to efficiently reject the high background rate induced by cosmogenic events. Enhancing the positron-neutron twofold coincidence efficiency has the potential to pave the way future aboveground detectors for reactor monitoring. We propose a new detection scheme based on a threefold coincidence, between the positron ionization, the ortho-positronium (o-Ps) decay, and the neutron capture, in a sandwich detector with alternated layers of plastic scintillator and aerogel powder. We present the results of a set of dedicated measurements on the achievable light yield and on the o-Ps formation and lifetime. The efficiencies for signal detection and background rejection of a preliminary detector design are also discussed.Comment: 18 pages, 10 figure

The JUNO experiment

The Jiangmen Underground Neutrino Observatory (JUNO) is a large liquid scintillator detector aiming at the measurement of anti-neutrinos issued from nuclear reactors at a 53km distance, having as primary goal the determination of the neutrino mass hierarhcy. The detector will be located 1800m.w.e. underground and consists of a 20 kiloton liquid scintillator contained in a 35.4m diameter acrylic sphere, instrumented by more than 17000 20 inch PMTs ensuring a 77% photocatode coverage. The required energy resolution to discriminate between the hierarchies at the 3–4 σ C.L. in about 6 years of data taking is 3% at 1MeV. To achieve such a precision, severe constraints on the detector components quality are set: the PMTs need a quantum efficiency of more than 27% and the attenuation length of the liquid has to be better than 20m (at 430nm). The precise measurement of the antineutrino spectrum will allow to reduce the uncertainty below 1% on solar oscillation parameters. The international collaboration of JUNO was established in 2014, the civil construction started in 2015 and the R&D of the detectors is ongoing. The expected start of data taking is set for 2020

Measurement of ortho-Positronium Properties in Liquid Scintillators

Pulse shape discrimination in liquid scintillator detectors is a well-established technique for the discrimination of heavy particles from light particles. Nonetheless, it is not efficient in the separation of electrons and positrons, as they give rise to indistinguishable scintillator responses. This inefficiency can be overtaken through the exploitation of the formation of ortho-Positronium (o-Ps), which alters the time profile of light pulses induced by positrons. We characterized the o-Ps properties in the most commonly used liquid scintillators, i.e. PC, PXE, LAB, OIL and PC + PPO. In addition, we studied the effects of scintillator doping on the o-Ps properties for dopants currently used in neutrino experiments, Gd and Nd. Further measurements for Li-loaded and Tl-loaded liquid scintillators are foreseen. We found that the o-Ps properties are suitable for enhancing the electron-positron discrimination.Comment: 4 pages, 1 figure. Contribution to proceedings of the Low Radioactivity Techniques 2013 Workshop at LNGS, Assergi (AQ), Italy, April 10-12 201

Influence of Ion Implantation and Gas Exposure on the Charge in Silicon Oxide Created by Electronic Excitation

Low energy electron bombardment of amorphous SiO2 induces point defects such as oxygen vacancy by electronic excitation. The defects build a macroscopic negative charge by trapping of electrons on the localized levels in the band gap; this phenomenon was previously described as the mirror effect. In the present paper, we investigate, by mirror effect, the behavior of the charge after an argon, nitrogen and oxygen implantation at 1 and 4 keV, and after exposure to the same gases at various low pressures. We observe a difference of behavior between Ar (or N2) and O2, The results reinforce the outstanding role of oxygen in the defect production in SiO2 by electronic excitation

Visualisation of diesel injector with neutron imaging

The injection process of diesel engines influences the pollutant emissions. The spray formation is significantly influenced by the internal flow of the injector. One of the key parameters here is the generation of cavitation caused by the geometry and the needle lift.In modern diesel engines the injection pressure is established up to 3000 bar. The details of the flow and phase change processes inside the injector are of increasing importance for such injectors. With these experimental measurements the validation of multiphase and cavitation models is possible for the high pressure range. Here, for instance, cavitation effects can occur. Cavitation effects in the injection port area destabilize the emergent fuel jet and improve the jet break-up.The design of the injection system in direct-injection diesel engines is an important challenge, as the jet breakup, the atomization and the mixture formation in the combustion chamber are closely linked. These factors have a direct impact on emissions, fuel consumption and performance of an engine. The shape of the spray at the outlet is determined by the internal flow of the nozzle. Here, geometrical parameters, the injection pressure, the injection duration and the cavitation phenomena play a major role.In this work, the flow dependency in the nozzles are analysed with the Neutron-Imaging. The great advantage of this method is the penetrability of the steel structure while a high contrast to the fuel is given due to the interaction of the neutrons with the hydrogen amount. Compared to other methods (optical with glass structures) we can apply real components under highest pressure conditions. During the steady state phase of the injection various cavitation phenomena are visible in the injector, being influenced by the nozzle geometry and the fuel pressure. Different characteristics of cavitation in the sac and spray hole can be detected, and the spray formation in the primary breakup zone is influenced

A compact light readout system for longitudinally segmented shashlik calorimeters

The longitudinal segmentation of shashlik calorimeters is challenged by dead zones and non-uniformities introduced by the light collection and readout system. This limitation can be overcome by direct fiber-photosensor coupling, avoiding routing and bundling of the wavelength shifter fibers and embedding ultra-compact photosensors (SiPMs) in the bulk of the calorimeter. We present the first experimental test of this readout scheme performed at the CERN PS-T9 beamline in 2015 with negative particles in the 1-5~GeV energy range. In this paper, we demonstrate that the scheme does not compromise the energy resolution and linearity compared with standard light collection and readout systems. In addition, we study the performance of the calorimeter for partially contained charged hadrons to assess the $e/\pi$ separation capability and the response of the photosensors to direct ionization.Comment: To appear in Nuclear Instruments and Methods in Physics Research,

Solar neutrino detection in a large volume double-phase liquid argon experiment

Precision measurements of solar neutrinos emitted by specific nuclear reaction chains in the Sun are of great interest for developing an improved understanding of star formation and evolution. Given the expected neutrino fluxes and known detection reactions, such measurements require detectors capable of collecting neutrino-electron scattering data in exposures on the order of 1 ktonne yr, with good energy resolution and extremely low background. Two-phase liquid argon time projection chambers (LAr TPCs) are under development for direct Dark Matter WIMP searches, which possess very large sensitive mass, high scintillation light yield, good energy resolution, and good spatial resolution in all three cartesian directions. While enabling Dark Matter searches with sensitivity extending to the "neutrino floor" (given by the rate of nuclear recoil events from solar neutrino coherent scattering), such detectors could also enable precision measurements of solar neutrino fluxes using the neutrino-electron elastic scattering events. Modeling results are presented for the cosmogenic and radiogenic backgrounds affecting solar neutrino detection in a 300 tonne (100 tonne fiducial) LAr TPC operating at LNGS depth (3,800 meters of water equivalent). The results show that such a detector could measure the CNO neutrino rate with ~15% precision, and significantly improve the precision of the 7Be and pep neutrino rates compared to the currently available results from the Borexino organic liquid scintillator detector.Comment: 21 pages, 7 figures, 6 table