Differentiation of bulk and surface events in p-type point-contact germanium detectors for light WIMP searches

Abstract

The p-type point-contact germanium detectors are novel techniques offering kg-scale radiation sensors with sub-keV sensitivities. They have been used for light Dark Matter WIMPs searches and may have potential applications in neutrino physics. There are, however, anomalous surface behaviour which needs to be characterized and understood. We describe the methods and results of a research program whose goals are to identify the bulk and surface events via software pulse shape analysis techniques, and to devise calibration schemes to evaluate the selection efficiency factors. Efficiencies-corrected background spectra from the low-background facility at Kuo-Sheng Neutrino Laboratory are derived.PACS numbers: 95.35.+d, 29.40.-n,

Bulk and surface event identification in p-type germanium detectors

“…The anomalous surface charge collection effect in pGe was noted in early 40 literature [6]. Recent interest of adopting the pGe techniques in dark matter experiments gives rise to thorough studies [14,15,16]. The n + surface electrodes of pGe are fabricated by lithium diffusion and have a typical thickness of ∼1 mm [15,18].…”

“…Anomalous excess events from the CoGeNT experiment with pGe [7,8,9] have be taken as signatures of light WIMPs. This interpretation is contra- 10 dicted by the CDEX-1 experiment at China Jinping Underground Laboratory [10,11,12] and the TEXONO experiment at the Kuo-Sheng Reactor Neutrino Laboratory [13,14], also using pGe as target.…”

“…The anomalous surface events were studied with the "spectral shape 20 method" in an early work [14]. However, there are several inadequacies with this approach.…”

“…The application to the published data and comparison of their results are discussed in Section 6. 30 We follow the notations of earlier work [11,12,14], where AC and CR denote the anti-Compton detector and the cosmic-ray veto systems, respectively, while the superscript −(+) corresponds to anti-coincidence (coincidence) with the pGe signals. Neutrino-and WIMP-induced candidate events would therefore manifest as AC − and CR − ⊗AC − in the CDEX-1 and TEX-ONO data, respectively.…”

CDEX Dark Matter Experiment: Status and Prospects

“…The results represent the most sensitive measurements made with the pPCGe detector. Background spectra of CDEX-1 experiment with an exposure of 335.6 kg· day (modified from [7]). Spectra after various cuts of candidate events: basic cuts (TT+Ped+PSD), anti-Compton cut (AC -), and bulk/surface cut (BS).…”