Weak-interaction and nuclear-structure aspects of nuclear double beta decay

Particle acceleration and loss in the million electron Volt (MeV) energy range (and above) is the least understood aspect of radiation belt science. In order to measure cleanly and separately both the energetic electron and energetic proton components, there is a need for a carefully designed detector system. The Relativistic Electron-Proton Telescope (REPT) on board the Radiation Belt Storm Probe (RBSP) pair of spacecraft consists of a stack of high-performance silicon solid-state detectors in a telescope configuration, a collimation aperture, and a thick case surrounding the detector stack to shield the sensors from penetrating radiation and bremsstrahlung. The instrument points perpendicular to the spin axis of the spacecraft and measures high-energy electrons (up to ∼20 MeV) with excellent sensitivity and also measures magnetospheric and solar protons to energies well above E=100 MeV. The instrument has a large geometric factor (g=0.2 cm2 sr) to get reasonable count rates (above background) at the higher energies and yet will not saturate at the lower energy ranges. There must be fast enough electronics to avert undue dead-time limitations and chance coincidence effects. The key goal for the REPT design is to measure the directional electron intensities (in the range 10−2–106 particles/cm2 s sr MeV) and energy spectra (ΔE/E∼25 %) throughout the slot and outer radiation belt region. Present simulations and detailed laboratory calibrations show that an excellent design has been attained for the RBSP needs. We describe the engineering design, operational approaches, science objectives, and planned data products for REPT.

The Relativistic Electron-Proton Telescope (REPT) Instrument on Board the Radiation Belt Storm Probes (RBSP) Spacecraft: Characterization of Earth’s Radiation Belt High-Energy Particle Populations

In recent decades, several detector technologies have been developed with the quest to directly detect dark matter interactions and to test one of the most important unsolved questions in modern physics. The sensitivity of these experiments has improved with a tremendous speed due to a constant development of the detectors and analysis methods, proving uniquely suited devices to solve the dark matter puzzle, as all other discovery strategies can only indirectly infer its existence. Despite the overwhelming evidence for dark matter from cosmological indications at small and large scales, clear evidence for a particle explaining these observations remains absent. This review summarises the status of direct dark matter searches, focusing on the detector technologies used to directly detect a dark matter particle producing recoil energies in the keV energy scale. The phenomenological signal expectations, main background sources, statistical treatment of data and calibration strategies are discussed.

https://iopscience.iop.org/article/10.1088/0954-3899/43/1/013001/pdf

Dark matter direct-detection experiments

Dark matter in the sub-GeV mass range is a theoretically motivated but largely unexplored paradigm. Such light masses are out of reach for conventional nuclear recoil direct detection experiments, but may be detected through the small ionization signals caused by dark matter-electron scattering. Semiconductors are well-studied and are particularly promising target materials because their $$ \mathcal{O} $$
 (1 eV) band gaps allow for ionization signals from dark matter particles as light as a few hundred keV. Current direct detection technologies are being adapted for dark matter-electron scattering. In this paper, we provide the theoretical calculations for dark matter-electron scattering rate in semiconductors, overcoming several complications that stem from the many-body nature of the problem. We use density functional theory to numerically calculate the rates for dark matter-electron scattering in silicon and germanium, and estimate the sensitivity for upcoming experiments such as DAMIC and SuperCDMS. We find that the reach for these upcoming experiments has the potential to be orders of magnitude beyond current direct detection constraints and that sub-GeV dark matter has a sizable modulation signal. We also give the first direct detection limits on sub-GeV dark matter from its scattering off electrons in a semiconductor target (silicon) based on published results from DAMIC. We make available publicly our code, QEdark
 , with which we calculate our results. Our results can be used by experimental collaborations to calculate their own sensitivities based on their specific setup. The searches we propose will probe vast new regions of unexplored dark matter model and parameter space.

/pdf/direct-detection-of-sub-gev-dark-matter-with-semiconductor-1rhj9fy7sy.pdf

Direct detection of sub-GeV dark matter with semiconductor targets

The existence of dark matter as evidenced by numerous indirect observations is one of the most important indications that there must be physics beyond the Standard Model of particle physics. This article reviews the concepts of direct detection of dark matter in the form of Weakly Interacting Massive Particles (WIMPs) in ultra-sensitive detectors located in underground laboratories, discusses the expected signatures, detector concepts, and how the stringent low-background requirements are achieved. Finally, it summarizes the current status of the field and provides an outlook on the years to come.

https://iopscience.iop.org/article/10.1088/1361-6471/ab2ea5/pdf

Direct detection of WIMP dark matter: concepts and status

A large-volume (150 cm/sup 3/) germanium detector with a full-depletion capacitance of only approximately=1 pf has been fabricated. The effect of impurity space charge was utilized to obtain an appropriate electric field distribution in the detector so that carriers are collected on a small-area electrode. Detectors based on this principle are capable of very-low-noise operation and have immediate applications in experiments for the direct detection of dark matter. Detector pulse shapes and carrier-trapping effects were also examined for possible applications involving higher energy radiations. >

/pdf/low-capacitance-large-volume-shaped-field-germanium-detector-16v0cne8yg.pdf

Low capacitance large volume shaped-field germanium detector

We have measured the ionization produced in a Si(Li) detector by silicon nuclei of kinetic energies in the range 3.2--21 keV. The results are in rather good agreement with the calculations of Lindhard, Scharff, and Schiott and demonstrate the interest of Si(Li) detectors for dark-matter searches. We have also measured the intrinsic fluctuations in the ionization energy due to nucleon recoils.

Measurement of the ionization of slow silicon nuclei in silicon for the calibration of a silicon dark-matter detector.

At high energies the energy resolution of gamma -ray spectrometers using large-diameter coaxial germanium detectors can be dominated by ballistic-deficit effects, particularly when short processing times are used to permit high-rate operation. This results because that rise-time variations in the detector signal are reflected in amplitude fluctuations after the signals pass through pulse shapes. A method is described for compensating for these effects on a pulse-by-pulse basis, using the observation that the loss of amplitude for slowly rising signals is accompanied by a delay in the peak time of the shaped output signal. The simple analog corrector circuit uses a relationship whereby the amplitude deficit is roughly proportional to the square of the time delay in the peak. Results show considerable improvements in the energy resolution of germanium gamma -ray spectrometers at high energies. >

/pdf/ballistic-deficit-correction-in-semiconductor-detector-36sii46b5v.pdf

Ballistic deficit correction in semiconductor detector spectrometers

Methods of applying pulsed-charge feedback to the charge-sensitive preamplifiers used with semiconductor detectors are discussed. All have in commn the accumulation of radiation-induced charge pulses on a feedback capacitor to produce a voltage ramp at the output of the feedback stage, which is reset at an appropriate point by pulsing a charge feedback path. Advantages of pulsed feedback over the conventional dc feedback techniques are discussed, together with the precautions required to reduce the effect of the large reset pulse on the later electronics. The application of pulsed-light feedback to low energy X-ray spectrometers is discussed and results are presented. We also discuss sane aspects of this system that tend to limit its high-rate performance. A brief account of the use of a transistor current-switch feedback system to reduce overload problems in high-energy ?-ray spectrometers is also given.

Pulsed Feedback Tecniques for Semicondctor Detector Radiation Spectrometers

The authors consider the problem of ballistic deficit, which is the loss of output signal amplitude due to the interplay between the finite charge-collection times in a detector and the characteristic time constants of the amplifier. Quantitative estimates of ballistic deficits have been developed by using numerical integration techniques on a microcomputer and by exact calculations using Laplace transforms. A practical procedure is developed in which an actual amplifier with even an unspecified complex-pole network can be accurately related to an equivalent semi-Gaussian shaping network the exact solution of which is known. Simple formulas for estimating ballistic deficits and resulting degradation in spectral energy resolutions are given. >

/pdf/ballistic-deficits-in-pulse-shaping-amplifiers-49avafaayx.pdf

F.S. Goulding

Papers

Low capacitance large volume shaped-field germanium detector

Measurement of the ionization of slow silicon nuclei in silicon for the calibration of a silicon dark-matter detector.

Ballistic deficit correction in semiconductor detector spectrometers

Pulsed Feedback Tecniques for Semicondctor Detector Radiation Spectrometers

Ballistic deficits in pulse shaping amplifiers