Session B9: Detectors for Neutrino Oscillation Experiments

Low Background Counting at the 4850L of the Stanford Underground Research Facility (SURF)

Future generation of rare-event experiments require the use of material with unprecedented radio-purity. A low-background counting (LBC) facility has been established at the 4850L (Davis Campus) of SURF to perform initial radio-assay for material and detector parts with respect to the activity of 238U and 232Th decay chains, 40K and cosmic-ray induced isotopes. This facility currently consists of a single commercial low-background high purity germanium (HPGe) detector with the best cosmic-ray shield in the USA. This talk describes the facility, detector systems, calibration, analysis techniques and selected assay results. This research is supported by PHYS-0758120 and PHYS-0919278 and The South Dakota governor's research center - CUBED.   

Design and Operation of Cryogenic Distillation Research Column for Ultra-Low Background Experiments

Motivated by isotopically enriched germanium (76Ge and 73Ge) for monocrystalline crystal growth for neutrinoless double-beta decay and dark matter experiments, a cryogenic distillation research column was developed. Without market availability of distillation columns in the temperature range of interest with capabilities necessary for our purposes, we designed, fabricated, tested, refined and operated a two-meter research column for purifying and separating gases in the temperature range from 100-200K. Due to interest in defining stratification, purity and throughput optimization, capillary lines were integrated at four equidistant points along the length of the column such that real-time residual gas analysis could guide the investigation. Interior gas column temperatures were monitored and controlled within 0.1oK accuracy at the top and bottom. Pressures were monitored at the top of the column to four significant figures. Subsequent impurities were measured at partial pressures below 2E-8torr. We report the performance of the column in this paper.   

Neutron Imaging with the Double Chooz Time Projection Chamber

Detecting and understanding neutron background is important in many fields, including dark matter and neutrino physics research. DCTPC or the Double Chooz Time Projection Chamber will be used to detect fast neutron events and increase neutrino measurement precision in the Double Chooz experiment. The neutrons are detected by amplifying the ionized particles that are produced when a neutron collides with one of the atoms in the chamber. The amplified ionization can be seen as a ``track'' which is then captured by a CCD camera and sensing electrode. This technique allows us to not only detect the neutron events but also to measure their direction and energy. I will discuss current progress on the running of the DCTPC prototype, the construction of the primary DCTPC detector, and the most recent results.   

Double Chooz Laser Calibration

The Double Chooz experiment focuses on measuring the neutrino mixing angle without the ambiguity of matter effects and CP violation. A multi-detector setup can extend the reach in sensitivity for theta-13 with reduced systematic error. Two identical detectors, the far and the near, are constructed at 1050 m and 400 m respectively, from the Chooz nuclear cores. The far detector is taking data while the near detector is being constructed. The university of alabama group is responsible for the laser calibration system development in both the hardware design and the analysis software including extracting calibration constants of the inner detector PMT gains, charge likelihoods, PMT time offsets and effective speed of light. Two types of lasers are used for the PMT charge and time related calibrations respectively. A UV laser with a wavelength of 380 nm is mainly responsible for the PMT gains and charge likelihoods calibrations. A blue laser of 470 nm wavelength is used in calibrating the PMT time offsets and measuring the speed of light in the medium. In this presentation I will talk about the laser system hardware design and laser calibration data analysis.   

Energy Calibration of Double Chooz Detector

Reactor anti-neutrino oscillation experiment Double Chooz was designed to measure the mixing angle theta-13 with unprecedented sensitivity. The Double Chooz detector system consists of a main detector, an outer veto system and several calibration systems. The main detector has a cylindrical structure. It consists of the target vessel, a liquid scintillator loaded with Gd, surrounded by the gamma-catcher, a non-loaded liquid scintillator. A buffer region of non-scintillating liquid surrounds the gamma-catcher and serves to host 390 photomultiplier tubes and to decrease the level of accidental background. The Inner Veto region is outside the buffer, and the Outer Veto system covers all detector components. Far detector is operational and the near detector is under construction. The detector is calibrated with light sources, radioactive point sources, cosmics and natural radioactivity. In this presentation we will describe use of radioactive calibration sources and cross-checks performed with cosmics and natural radioactivity.   

The Double Chooz Outer Veto

Double Chooz is unique among reactor neutrino experiments for its Outer Veto -- a multi-layered plastic scintillator strip muon detector. The far detector Outer Veto covers 95\,m$^2$ on top of the main detector volumes and is composed of 44 modules, each made up of 64 scintillator strips outfitted with wavelength-shifting fibers coupled to a multi-anode PMT. The Outer Veto serves two purposes: first, as a veto, it reduces muon-induced backgrounds to the neutrino signal, in particular the fast neutron and stopping muon backgrounds; second, the high-quality muon tracking it provides allows for detailed studies of these backgrounds, as well as long-lived backgrounds, which cannot be vetoed, such as $^{9}$Li and ${^8}$He. I will describe the design of the Outer Veto, its performance, and some background studies.   

Techniques in Extracting Spectral Signals of Neutrino Oscillation at Daya Bay

The Daya Bay Reactor Neutrino Experiment recently produced the leading measurement of neutrino mixing parameter $\theta_{13}$ from the observation of electron antineutrino disappearance. The experiment operates functionally identical detectors at sites near to and far from the Daya Bay nuclear reactor complex, which provides a powerful measurement of antineutrino oscillation over a distance of about 2km. The next phase in the analysis is to exploit spectral distortions caused by the energy dependence of neutrino oscillations. This talk will discuss techniques for fitting Daya Bay's spectral data against a flux prediction incorporating systematic uncertainties to measure $\sin^2 2\theta_{13}$ and $\Delta m^2_{ee}$.   

Low-Energy Neutrinos in Liquid Argon Detectors

This talk will describe a study of the sensitivity of large liquid argon time-projection chamber detectors to neutrinos in the few-tens-of-MeV range.