The Majorana Demonstrator neutrinoless double-beta decay experiment comprises a 44 kg (30 kg enriched in ^{76}Ge) array of p-type, point-contact germanium detectors. With its unprecedented energy ...resolution and ultralow backgrounds, Majorana also searches for rare event signatures from beyond standard model physics in the low energy region below 100 keV. In this Letter, we test the continuous spontaneous localization (CSL) model, one of the mathematically well-motivated wave function collapse models aimed at solving the long-standing unresolved quantum mechanical measurement problem. While the CSL predicts the existence of a detectable radiation signature in the x-ray domain, we find no evidence of such radiation in the 19-100 keV range in a 37.5 kg-y enriched germanium exposure collected between December 31, 2015, and November 27, 2019, with the Demonstrator. We explored both the non-mass-proportional (n-m-p) and the mass-proportional (m-p) versions of the CSL with two different assumptions: that only the quasifree electrons can emit the x-ray radiation and that the nucleus can coherently emit an amplified radiation. In all cases, we set the most stringent upper limit to date for the white CSL model on the collapse rate, λ, providing a factor of 40-100 improvement in sensitivity over comparable searches. Our limit is the most stringent for large parts of the allowed parameter space. If the result is interpreted in terms of the Diòsi-Penrose gravitational wave function collapse model, the lower bound with a 95% confidence level is almost an order of magnitude improvement over the previous best limit.
With excellent energy resolution and ultralow-level radiogenic backgrounds, the high-purity germanium detectors in the Majorana Demonstrator enable searches for several classes of exotic dark matter ...(DM) models. In this work, we report new experimental limits on keV-scale sterile neutrino DM via the transition magnetic moment from conversion to active neutrinos ν_{s}→ν_{a}. We report new limits on fermionic dark matter absorption (χ+A→ν+A) and sub-GeV DM-nucleus 3→2 scattering (χ+χ+A→ϕ+A), and new exclusion limits for bosonic dark matter (axionlike particles and dark photons). These searches utilize the (1-100)-keV low-energy region of a 37.5-kg y exposure collected by the Demonstrator between May 2016 and November 2019 using a set of ^{76}Ge-enriched detectors whose surface exposure time was carefully controlled, resulting in extremely low levels of cosmogenic activation.
Abstract
The electron drift in germanium detectors is modeled making
many assumptions. Confronted with data, these assumptions have to be
revisited. The temperature dependence of the drift of ...electrons was
studied in detail for an n-type segmented point-contact germanium
detector. The detector was mounted in a temperature controlled,
electrically cooled cryostat. Surface events were induced with
collimated 81 keV photons from a
133
Ba source. A detailed
analysis of the rise time of pulses collected in surface scans,
performed at different temperatures, is presented. The longitudinal
anisotropy of the electron drift decreases with rising
temperature. A new approach, making use of designated rise-time
windows determined by simulations using
SolidStateDetectors.jl
, was used to isolate the longitudinal
drift of electrons along different axes to quantify this
observation. The measured temperature dependence of the longitudinal
drift velocities combined with the standard electron-drift model as
widely used in relevant simulation packages results in unphysical
predictions. A modification of the electron-drift model based on
assuming phonons to be the dominating scattering centers for
electrons is motivated and described. The results of a first
implementation of the modified model in
SolidStateDetectors.jl
are shown. They describe the
temperature dependence of the data reasonably well. A general review
of the model and the standard input values for mobilities is
suggested.
The MAJORANA DEMONSTRATOR is searching for neutrinoless double-beta decay($0\nu\beta\beta$) in 76Ge using arrays of point-contact germanium detectors operating at the Sanford Underground Research ...Facility. Background results in the $0\nu\beta\beta$ region of interest from data taken during construction, commissioning, and the start of full operations have been recently published. A pulse shape analysis cut applied to achieve this result, named AvsE, is described in this paper. This cut is developed to remove events whose waveforms are typical of multi-site energy deposits while retaining (90 ± 3.5)% of single-site events. This pulse shape discrimination is based on the relationship between the maximum current and energy, and tuned using 228Th calibration source data. In conclusion, the efficiency uncertainty accounts for variation across detectors, energy, and time, as well as for the position distribution difference between calibration and $0\nu\beta\beta$ events, established using simulations.
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 detector’s response to
α
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
ν
β
β
) in
76
Ge.
α
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
α
identification, reliably identifying
α
background events on the passivated surface of the detector. We demonstrate effective rejection of all surface
α
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
ν
β
β
region of interest window by an order of magnitude in the
Majorana
Demonstrator
and will be used in the upcoming LEGEND-200 experiment.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
P-type point contact (PPC) high-purity germanium detectors are an important technology in astroparticle and nuclear physics due to their superb energy resolution, low noise, and pulse shape ...discrimination capabilities. Analysis of data from the Majorana Demonstrator, a neutrinoless double-β decay experiment deploying PPC detectors enriched in 76Ge, has led to several novel improvements in the analysis of PPC signals. In this work we discuss charge trapping in PPC detectors and its effect on energy resolution. Small dislocations or impurities in the crystal lattice result in trapping of charge carriers from an ionization event of interest, attenuating the signal, and degrading the measured energy. We present a modified digital pole-zero correction to the signal energy estimation that counters the effects of charge trapping and improves the energy resolution of the Majorana Demonstrator by approximately 30 % to around 2.4 keV full width at half-maximum at 2039 keV, the 76Ge Q value. An alternative approach achieving similar resolution enhancement is also presented.
Abstract
The
Majorana Demonstrator
was a search for neutrinoless double-beta decay (0
νββ
) in the
76
Ge isotope. It was staged at the 4850-foot level of the Sanford Underground Research Facility ...(SURF) in Lead, SD. The experiment consisted of 58 germanium detectors housed in a low background shield and was calibrated once per week by deploying a
228
Th line source for 1 to 2 hours. The energy scale calibration determination for the detector array was automated using custom analysis tools. We describe the offline procedure for calibration of the
Demonstrator
germanium detectors, including the simultaneous fitting of multiple spectral peaks, estimation of energy scale uncertainties, and the automation of the calibration procedure.
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