Performances of a prototype point-contact germanium detector immersed in liquid nitrogen for light dark matter search

Abstract

The CDEX-10 experiment searches for light weakly-interacting massive particles, a form of dark matter, at the China JinPing underground laboratory, where approximately 10 kg of germanium detectors are arranged in an array and immersed in liquid nitrogen. Herein, we report on the experimental apparatus, detector characterization, and spectrum analysis of one prototype detector. Owing to the higher rise-time resolution of the CDEX-10 prototype detector as compared with CDEX-1B, we identified the origin of an observed category of extremely fast events. For data analysis of the CDEX-10 prototype, we introduced and applied an improved bulk/surface event discrimination method. The results of the new method were compared to those of the CDEX-1B spectrum. Both sets of results showed good consistency in the 0-12 keVee energy range, except for the 8.0 keV K-shell X-ray peak from the external copper.Established in 2009, the China Dark Matter Experiment (CDEX) Collaboration [6] searched for light WIMPS using p-type point-contact germanium (pPCGe) detectors at the China JinPing underground laboratory (CJPL) [7]. The CJPL is the worlds deepest underground laboratory, with a cosmic ray muon flux of 61.7 yr −1 m −2 [8]. Owing to the low physics analysis threshold (160 eVee, where"eVee" represents electron equivalent energy), the excellent energy resolution and low background characteristics of the pPCGe detectors, the CDEX collaboration has achieved a series of competitive results on light WIMP searches [9][10][11][12]. The CDEX-1 experiment, which uses 1 kg-scale single-element pPCGe detectors, has proceeded in two stages: CDEX-1A and CDEX-1B.In CDEX-1A and CDEX-1B, the germanium detector was cooled by a cold finger connected to a 30-L dewar filled with liquid nitrogen (LN 2 ). However, upscaling the mass of the germanium detector system, to further im-arXiv:1810.08808v1 [physics.ins-det]

Identification of the anomalous fast bulk events in a p-type point contact germanium detector

“…2 rays from the progeny of 238 U and 238 Th, are predominantly FBEs. The CDEX-10 experiment also gives the same behavior [22]. The alpha, beta and low-energy photon produced by the vicinity electronics and structural materials will be more likely to enter the detector through the O(100 nm) thin passivated layer contribute to the background at low energy.…”

Model independent analysis of MeV scale dark matter. II. Implications from e−e+ colliders and direct detection

“…And since standard methods do not work, the exception being those emanating from anomalous decays of certain mesons [23], new methods need to be devised for exploring these. Indeed, quite a few diverse ideas have already been proposed, such as the absorption signal in the 21-cm spectrum [24,25], the scattering of DM off atomic clocks [26], the use of optical cavities [27], the use of leptonic beam-dumps [28], the use of a cryogenic point-contact germanium detector [29] or more canonical setups such as the LDMX [27].…”

Direct Detection Constraints on Dark Photons with the CDEX-10 Experiment at the China Jinping Underground Laboratory

“…The detector array, consisting of three triple-element PPCGe detector strings (named C10-A, B, C, respectively), surrounded by the 20 cm thick high-purity oxygen-free copper as a passive shield against ambient radioactivity, is directly immersed in liquid nitrogen (LN 2 ) for cooling. The LN 2 cryostat, with an outer diameter of 1.5 m and a height of 1.9 m, together with the electronics readout and the data acquisition (DAQ) systems, is placed inside a shielding with 1 m thick polyethylene walls at CJPL-I [26,27]. The DAQ system consists of five readout channels with specific shaping and gain parameters for each PPCGe detector to record signal information.…”

“…The DAQ system consists of five readout channels with specific shaping and gain parameters for each PPCGe detector to record signal information. The configuration of the detector system was described in detail previously [26,27]. In this Letter, a raw dataset with exposure time of 363.9 day from two of the CDEX-10 detectors, named, C10-B1 and C10-C1, are used for γ Ã analysis.…”

“…Energy calibrations were done by the zero energy (defined by the random trigger events) and the internal cosmogenic K-shell x-ray peaks: 8.98 keVee of 65 Zn and 10.37 keVee of 68;71 Ge. The data preprocessing procedures for a single detector were described in previous papers [26,27], including energy calibrations, pedestal cut, physics event selection, and bulk or surface event discrimination [28]. The live times were reduced by 1.1% for C10-B1 and 0.6% for C10-C1 after pedestal cuts, which were energy independent and measured by the survival of the random trigger events.…”