Two distinct components of the delayed single electron noise in liquid xenon emission detectors

Abstract

Single electron background signals with millisecond timescales are known to follow ionizing events in liquid/gas xenon emission detectors. Due to the long timescale, these signals can present a limiting background to the low-energy threshold of dark matter searches, and prevent discoveryclass searches for MeV scale hidden sector dark matter. A systematic study reveals a fast (τ1) and slow (τ2) component to the background. The fast component is compatible with electrons which were trapped at the liquid surface, and can be reduced by increasing the electric field. However, the slow component increases linearly with electric field. Hypotheses for the origin of the effect are discussed, and techniques for mitigation are suggested.

Light Dark Matter Search with Ionization Signals in XENON1T

“…This cut also suppresses gas events, whose S1's are broader than those of events in the liquid and therefore often misidentified as S2's. Third, as high-energy events cause a temporary and localized enhancement in single-electron emission [23], we utilize a combined p-value cut [24] against events close in time or reconstructed position to recent highenergy events, with 80% efficiency, as determined with S1-tagged cathode events and shown in purple in Fig. 2.…”

Photoluminescence response of acrylic (PMMA) and polytetrafluoroethylene (PTFE) to ultraviolet light

“…The PTFE is used to reflect photons impinging on the detector walls until they hit a PMT. If instead of being reflected, photons are absorbed and re-emitted at a later time, the time signature of an event can be distorted [31]. Fig.…”

First ground-level laboratory test of the two-phase xenon emission detector RED-100

“…Their properties and hypotheses of their origin are discussed in ( [18], page 24), [31], [39], [41], [43]. As pointed out in [43] and observed by us in this test with RED-100, there is a large excess of SE events after the energetic events, especially muons, with exponential decay of their intensity. In order to reduce the average rate of "spontaneous" SE, the readout electronics was blocked during 1 ms after the S1 scintillation signal from muons by applying the blocking pulse to the electron shutter.…”

“…As recently discussed in [43], there are two components in the delayed SE emission: the first one is caused by the spontaneous emission of the un-emitted electrons (namely this component is suppressed when the shutter is on), and second one which origin is probably explained by trapping and subsequent releasing the ionization electrons by the electronegative impurities. It was pointed out in [43] on possible relation of the intensity of the second component with the liquid xenon purity. Similar correlation of the rate of such delayed S2 events with purity was observed in the DarkSide50 experiment with liquid argon [53].…”

“…The SE signals that appear without straightforward causal link to the presence of light in the detector are usually referred to as "spontaneous" ones [31], [39], [40], [41]. Their properties and hypotheses of their origin are discussed in ( [18], page 24), [31], [39], [41], [43]. As pointed out in [43] and observed by us in this test with RED-100, there is a large excess of SE events after the energetic events, especially muons, with exponential decay of their intensity.…”