Phonon-mediated Detectors Research Articles

Energy loss in low energy nuclear recoils in dark matter detector materials

Recent progress in phonon-mediated detectors with eV-scale nuclear recoil energy sensitivity requires an understanding of the effect of the crystalline defects on the energy spectrum expected from dark matter or neutrino coherent scattering. We have performed molecular dynamics simulations to determine the amount of energy stored in the lattice defects as a function of the recoil direction and energy. This energy can not be observed in the phonon measurement, thus affecting the observed energy spectrum compared to the underlying true recoil energy spectrum. We describe this effect for multiple commonly used detector materials and demonstrate how the predicted energy spectrum from dark matter scattering is modified.

Performance of a Phonon-Mediated Detector Using KIDs Optimized for Sub-GeV Dark Matter

We provide an update on a gram-scale phonon-mediated KID-based device that was designed for a sub-GeV dark matter search at the Northwestern Experimental Underground Site. Currently, the device is demonstrating 6 eV resolution on the energy absorbed by the resonator. With some important assumptions, this translates to 20 eV baseline resolution on energy deposited in the substrate. We show that TLS noise dominates this energy resolution estimate. After modifying the design to mitigate TLS noise, we project 5 eV baseline resolution on energy deposited in the substrate (1.5 eV on energy absorbed by the resonator) for an amplifier-white-noise-dominated device. Finally, we present a clear path forward to sub-eV resolutions, which includes installation of a quantum-limited superconducting parametric amplifier and adjustments to the material makeup of our resonators.

Identifying Drivers of Energy Resolution Variation in a Multi-KID Phonon-Mediated Detector

Phonon-mediated particle detectors employing Kinetic Inductance Detectors (KIDs) on Silicon substrates have demonstrated both O(10) eV energy resolution and mm position resolution, making them strong candidates for instrumenting next generation rare-event experiments such as in looking for dark matter or in neutrino measurements. Previous work has demonstrated the performance of an 80-KID array on a Si wafer, however current energy resolution measurements show a 25x difference between otherwise identical KIDs on the same wafer - between 5 to 125 eV on energy absorbed by the KID. Here, we use a first principles approach and attempt to identify the drivers behind the resolution variation. In particular, we analyze a subset of 8 KIDs using the unique approach of pulsing neighboring KIDs to generate signals in the target. We tentatively identify differences in quality factor terms as the likely culprit for the observed variation.

Measurements and Simulations of Athermal Phonon Transmission from Silicon Absorbers to Aluminum Sensors

Phonon reflection and transmission at the interfaces plays a fundamental role in cryogenic particle detectors, in which the optimization of the phonon signal at the sensor (in case of phonon-mediated detectors) or the minimization of the heat transmission (when the detection occurs in the sensor itself) is of primary importance to improve sensitivity. Nevertheless, the mechanisms governing the phonon physics at the interfaces are still not completely understood. The two more successful models, the acoustic mismatch model (AMM) and diffuse mismatch model (DMM) are not able to explain all the accumulated experimental data and the measurement of the transmission coefficients between the materials remains a challenge. Here, we use measurements of the athermal phonon flux in aluminium Kinetic Inductance Detectors (KID) deposited on silicon substrates following a particle interaction to validate a Monte Carlo (MC) phonon simulation. We apply the Mattis-Bardeen theory to derive the phonon pulse energy and timing from the KID signal and compare the results with the MC for both AMM and DMM models, finding a remarkable good agreement for AMM, while diffuse reflection is clearly disfavored. For an aluminum film of 60 nm and a silicon substrate of 380~$\mu$m, we obtain transmission coefficients Si-Al in the range [0.3-0.55] and Si-Teflon in the range [0.1-0.15].

Energy resolution and efficiency of phonon-mediated kinetic inductance detectors for light detection

The development of sensitive cryogenic light detectors is of primary interest for bolometric experiments searching for rare events like dark matter interactions or neutrino-less double beta decay. Thanks to their good energy resolution and the natural multiplexed read-out, Kinetic Inductance Detectors (KIDs) are particularly suitable for this purpose. To efficiently couple KIDs-based light detectors to the large crystals used by the most advanced bolometric detectors, active surfaces of several cm2 are needed. For this reason, we are developing phonon-mediated detectors. In this paper, we present the results obtained with a prototype consisting of four 40 nm thick aluminum resonators patterned on a 2 × 2 cm2 silicon chip, and calibrated with optical pulses and X-rays. The detector features a noise resolution σE = 154 ± 7 eV and an (18 ± 2)% efficiency.

Cryogenic Wide-Area Light Detectors for Neutrino and Dark Matter Searches

Large-mass arrays of bolometers proved to be good detectors for neutrinoless double beta decay (0 $$\nu $$ DBD) and dark matter searches. CUORE and LUCIFER are bolometric 0 $$\nu $$ DBD experiments that will start to take data in 2015 at Laboratori Nazionali del Gran Sasso in Italy. The sensitivity of CUORE could be increased by removing the background due to $$\alpha $$ particles, by detecting the small amount of Cerenkov light ( $$\sim $$ 100 eV) emitted by the $$\beta $$ s’ signal and not by $$\alpha $$ s. LUCIFER could be extended to detect also dark matter, provided that the background from $$\beta $$ / $$\gamma $$ particles ( $$\sim $$ 100 eV of scintillation light) is discriminated from nuclear recoils of about 10 keV energy (no light). We have recently started to develop light detectors for CUORE, LUCIFER and similar bolometric experiments. The aim is to obtain detectors with an active area of $$5\times 5~\mathrm{cm}^2$$ (the face of bolometric crystals), operating at 10 mK, and with an energy resolution at the baseline below 20 eV RMS. We have chosen to develop phonon-mediated detectors with KID sensors. We are currently testing the first prototypes.

A WIMP Dark Matter Detector Using MKIDs

We are pursuing the development of a phonon- and ionization-mediated WIMP dark matter detector employing microwave kinetic inductance detectors (MKIDs) in the phonon-sensing channel. Prospective advantages over existing detectors include: improved reconstruction of the phonon signal and event position; simplified readout wiring and cold electronics; and simplified and more reliable fabrication. We have modeled a simple design using available MKID sensitivity data and anticipate energy resolution as good as existing phonon-mediated detectors and improved position reconstruction. We are doing preparatory experimental work by fabricating strip absorber architectures. Measurements of diffusion length, trapping efficiency, and MKID sensitivity with these devices will enable us to design a 1 cm^2×2 mm prototype device to demonstrate phonon energy resolution and position reconstruction.

Kinetic Inductance Phonon Sensors for the Cryogenic Dark Matter Search Experiment

An important challenge faced by phonon-mediated detectors for the next generation of dark matter detectors (>100 kg) is to instrument large target mass at low cost, while maintaining the large background suppression offered by the combination of phonons and ionization (or scintillation) measurement. Kinetic inductance phonon sensors, operating far below the superconducting transition temperature, offer an interesting solution to this scaling problem. They do not critically depend on the uniformity of T c and their resonant-cavity readout is easy to multiplex. We are studying a microstrip (two parallel planes) transmission line architecture that may offer the additional advantage of a separation of functions: the main detector is just covered by an unpatterned aluminum film and the number of quasi-particles created in it by athermal phonons are sensed by a second film, which has been independently patterned and is mounted a few microns away from the detector. We present current results on the responsivity and noise of large area (∼33 mm2) microstrip kinetic inductance phonon sensors.

Physics of low-temperature microcalorimeters

This introductory tutorial includes a short description of the various types of thermal or phonon-mediated detectors and a discussion of optimal filtering, energy resolution calculations, and electrothermal feedback. We concentrate on the basic operation of simple equilibrium calorimeters with an ideal resistive thermometer . The thermometer technology could be doped semiconductor or superconducting transition edge. The calculations consider only Johnson noise in the thermometer and thermodynamic fluctuation noise between the calorimeter and the heat sink. For many practical devices, this is a good approximation and it provides a starting point for the discussion of other noise sources, various non-ideal effects, and non-linearity. Other types of thermometers may in practice have quite different limiting factors.

Exclusion limits on the WIMP-nucleon scattering cross-section from the Cryogenic Dark Matter Search

Abstract The Cryogenic Dark Matter Search (CDMS) employs massive ionization- and phonon-mediated detectors to search for WIMPs via their elastic scattering interactions with nuclei while discriminating against interactions by other background particles. Limits on the WIMP-nucleon scattering cross-section, based on 3.1 kg d of exposure, exclude new parameter space in the 10–30 GeV WIMP mass region and also a portion of the region allowed by the DAMA annual modulation search (Bernabei, Phys. Lett. 450 (1999) 448).

Propagation of non-thermal phonons induced by α-particle bombardment in BaF2

We have measured the time dependence of the flux of non-thermal phonons generated by α particles in a BaF2 single crystal of mass 1 g using a Series Array of Superconducting Tunnel Junctions. Taking advantage of the almost perfect elastic symmetry of BaF2, we approximate the equations of quasidiffusive propagation to give a simple diffusion equation characterized by an effective diffusion coefficient D=KL8/9, where K is a material constant and L the distance between the phonon source and the point of detection. We use this model to perform pulse-shape analysis on our data and show that agreement is excellent, and highly preferred over a ballistic pulse shape. The distributions of values of K determined for different lengths L are found to overlap strongly, in support of the law D=KL8/9. We suggest that pulse-shape analysis may provide an alternative to time-difference measurements to achieve position sensitivity in a phonon-mediated detector based on a BaF2 absorber.

Phonon-mediated detectors for dark matter searches and neutrino experiments

Abstract Our group at Stanford is developing a new class of elementary particles detectors capable of sensing weakly interacting particles such as neutrinos. Our detectors are based on the propagation of phonons in silicon crystals at low temperatures. We have developed superconducting transition edge devices to sense the arrival of phonons at the crystal surfaces. During the past two years, we have characterized titanium transition-edge devices operated around 0.3 K and are beginning tests with tungsten transition-edge devices operated below 100 mK. The titanium devices have been operated in coincidence on both sides of silicon crystals up to 2 mm thick and have been used in calibration experiments with x-rays, alpha particles and neutrons. An underground facility is near completion at Stanford which provides 20 meters water equivalent of cosmic-ray shielding. This facility will house a pilot dark matter search which we will undertake collaboratively through the Center for Particle Astrophysics and the facility also will be used for developing our reactor neutrino detector.