No Arabic abstract
Searches for new physics push experiments to look for increasingly rare interactions. As a result, detectors require increasing sensitivity and specificity, and materials must be screened for naturally occurring, background-producing radioactivity. Furthermore the detectors used for screening must approach the sensitivities of the physics-search detectors themselves, thus motivating iterative development of detectors capable of both physics searches and background screening. We report on the design, installation, and performance of a novel, low-background, fourteen-element high-purity germanium detector named the CAGe (CUP Array of Germanium), installed at the Yangyang underground laboratory in Korea.
A new package to simulate the formation of electrical pulses in segmented true-coaxial high purity germanium detectors is presented. The computation of the electric field and weighting potentials inside the detector as well as of the trajectories of the charge carriers is described. In addition, the treatment of bandwidth limitations and noise are discussed. Comparison of simulated to measured pulses, obtained from an 18-fold segmented detector operated inside a cryogenic test facility, are presented.
P-type point contact (PPC) HPGe detectors are a leading technology for rare event searches due to their excellent energy resolution, low thresholds, and multi-site event rejection capabilities. We have characterized a PPC detectors response to $alpha$ particles incident on the sensitive passivated and p+ surfaces, a previously poorly-understood source of background. The detector studied is identical to those in the MAJORANA DEMONSTRATOR experiment, a search for neutrinoless double-beta decay ($0 ubetabeta$) in $^{76}$Ge. $alpha$ decays on most of the passivated surface exhibit significant energy loss due to charge trapping, with waveforms exhibiting a delayed charge recovery (DCR) signature caused by the slow collection of a fraction of the trapped charge. The DCR is found to be complementary to existing methods of $alpha$ identification, reliably identifying $alpha$ background events on the passivated surface of the detector. We demonstrate effective rejection of all surface $alpha$ events (to within statistical uncertainty) with a loss of only 0.2% of bulk events by combining the DCR discriminator with previously-used methods. The DCR discriminator has been used to reduce the background rate in the $0 ubetabeta$ region of interest window by an order of magnitude in the MAJORANA DEMONSTRATOR, and will be used in the upcoming LEGEND-200 experiment.
We present a study of magnetic fields effects on the position resolution and energy response of hyper-pure germanium detectors. Our results provide realistic estimates of the potential impact on the resolving power of tracking-arrays from (fringe) magnetic fields present when operating together with large spectrometers. By solving the equations of motion for the electron and holes in the presence of both electric and magnetic fields, we analyzed the drift trajectories of the charge carriers to determine the deviations in the positions at the end point of the trajectories, as well as changes in drift lengths affecting the energy resolution and peak shift due to trapping. Our results show that the major effect is in the deviation of the transverse (to the electric field direction) position and suggest that, if no corrective action is taken in the pulse-shape and tracking data analysis procedures, a field strength $gtrsim$ 0.1 T will start to impact the intrinsic position resolution of 2 mm (RMS). At fields above $sim$1 T, the degradation of the energy response becomes observable.
PROSPECT, the Precision Reactor Oscillation and Spectrum Experiment, will use two segmented detectors positioned 7-20 m from the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory to measure the U-235 antineutrino spectrum and perform a search for short-baseline oscillations as a signature of eV-scale sterile neutrinos. PROSPECT has developed Li-6 loaded liquid scintillator detectors for efficient identification of reactor antineutrinos and has measured reactor and cosmogenic backgrounds in the HFIR reactor building. Multiple test detectors have been built, operated, and characterized at HFIR and elsewhere to understand the optical performance of the scintillator and pulse-shape discrimination capabilities for enhanced background rejection. The results from this R&D effort are discussed, in the context of the design and physics potential of PROSPECT.
A Set of new MPGD-based Photon Detectors is being built for the upgrade of COMPASS RICH-1. The detectors cover a total active area of 1.4 m$^2$ and are based on a hybrid architecture consisting of two THGEM layers and a Micromegas. A CsI film on one THGEM acts as a reflective photocathode. The characteristics of the detector, the production of the components and their validation tests are described in detail.