arXiv subjects

Nader Mirabolfathi

Publications and source records attributed to Nader Mirabolfathi.

At least 19 recordsLinked to original sources

arXiv2024

Spontaneous damage annealing reactions as a possible source of low energy excess in semiconductor detectors

In semiconductor detectors designed for capturing dark matter particles or neutrinos, when the detection threshold is constantly improved to increasingly low energies, an "excess" signal of apparent energy release events below a few hundred eV is observed in several different kinds of detectors. This becomes a big obstacle to the observation of actual dark matter signals, hindering the detectors' sensitivity for rare events in this energy range. Using atomistic simulations with a classical thermostat and a quantum thermal bath, we show that this kind of signal is consistent with energy release from long-term annealing events of complex defects that can be formed by any kind of nuclear recoil radiation events. Such energy releases are shown to have a very similar exponential dependence on energy release magnitudes as that observed in experiments. By detailed analysis of the annealing events, we show that crossing very low energy barriers can trigger larger energy releases in an avalanche-like effect. This explains why large energy release events can occur even down to cryogenic temperatures, where the significant migration of point defects in silicon is hardly ever possible.

cond-mat.mtrl-sci↗

arXiv2024

Measurement of Low Energy Nuclear Recoil Events with the phonon-mediated Voltage-Assisted Hybrid Detector for Rare Event Searches

The phonon-mediated hybrid detector is made out of a monolithic silicon crystal characterized by two interconnected regions linked through a narrow neck. Operating solely on phonon signal measurements, the hybrid design facilitates the differentiation between electron recoil and nuclear recoil events, effectively discerning two types of interaction down to low energy levels. With a newly implemented software triggering technique (SWT), low-energy nuclear recoil events of approximately $500~eV_{ee}$ have been measured. In addition to this, an electron recoil background reduction of up to $95\%$ has been successfully demonstrated.

physics.ins-det↗

arXiv2023

Daily and annual modulation rate of low mass dark matter in silicon detectors

Low threshold detectors with single-electron excitation sensitivity to nuclear recoil events in solid-state detectors are also sensitive to the crystalline structure of the target and, therefore, to the recoil direction via the anisotropic energy threshold for defect creation in the detector material. We investigate this effect and the resulting daily and annual modulation of the observable event rate for dark matter mass range from 0.2 to 5 GeV/c$^{2}$ in a silicon detector. We show that the directional dependence of the threshold energy and the motion of the laboratory result in modulation of the event rate which can be utilized to enhance the sensitivity of the experiment. We demonstrate that the spin-independent interaction rate in silicon is significant for both high and low dark matter masses. For low-mass dark matter, we show that the average interaction rate in silicon is larger than germanium, making silicon an important target for identifying dark matter from backgrounds. We find 8 and 12 hours periodicity in the time series of event rates for silicon detector due to the 45-degree symmetry in the silicon crystal structure.

hep-ph↗

arXiv2022

Identification of the low energy excess in dark matter searches with crystal defects

An excess of events of unknown origin at low energies below 1 keV has been observed in multiple low-threshold dark matter detectors. Depending on the target material, nuclear recoil events at these energies may cause lattice defects, in which case a part of the true recoil energy is stored in the defect and not observed in the phonon detector. If the threshold for defect creation is sharp, this effect leads to a prominent feature in the observed recoil spectrum. Electronic recoils at low energies do not create defects and therefore the feature in the observed spectrum is not expected in that case. We propose to use the sharp defect creation threshold of diamond to test if the low energy events are due to nuclear recoils. Based on simulated data we expect the nuclear recoil bump in the observed spectrum to be visible in diamond with just ~0.1 gram days of exposure.

hep-ph↗

arXiv2022

Energy loss due to defect creation in solid state detectors

The threshold displacement energy in solid state detector materials varies from several eV to ~100 eV. If a stable or long lived defect is created as a result of a nuclear recoil event, some part of the recoil energy is stored in the deformed lattice and is therefore not observable in a phonon detector. Thus, an accurate model of this effect is necessary for precise calibration of the recoil energy measurement in low threshold phonon detectors. Furthermore, the sharpness of the defect creation threshold varies between materials. For a hard material such as diamond, the sharp threshold will cause a sudden onset of the energy loss effect, resulting in a prominent peak in the observed recoil spectrum just below the threshold displacement energy. We describe how this effect can be used to discriminate between nuclear and electron recoils using just the measured recoil spectrum.

physics.ins-det↗

arXiv2022

Anisotropic ionization threshold and directional sensitivity in solid state DM detectors

The threshold displacement energy for nuclear recoils depends strongly on the direction of the recoiling nucleus with respect to the crystal lattice. Assuming that similar dependence holds for the ionization threshold for low energy nuclear recoils, we explore the consequences of the resulting directional dependence of the observable event rate in ionization detectors. For low mass dark matter, this effect leads to a daily modulation in the event rate. We discuss how this effect can be utilized to separate the DM signal from the solar neutrino background and how the structure of the modulation signal can be used to identify the type of the DM-nucleon coupling.

hep-ph↗

arXiv2022

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.

hep-ph↗

arXiv2022

A Stress Induced Source of Phonon Bursts and Quasiparticle Poisoning

The performance of superconducting qubits is degraded by a poorly characterized set of energy sources breaking the Cooper pairs responsible for superconductivity, creating a condition often called ``quasiparticle poisoning". Both superconducting qubits and low threshold dark matter calorimeters have observed excess bursts of quasiparticles or phonons that decrease in rate with time. Here, we show that a silicon crystal glued to its holder exhibits a rate of low-energy phonon events that is more than two orders of magnitude larger than in a functionally identical crystal suspended from its holder in a low-stress state. The excess phonon event rate in the glued crystal decreases with time since cooldown, consistent with a source of phonon bursts which contributes to quasiparticle poisoning in quantum circuits and the low-energy events observed in cryogenic calorimeters. We argue that relaxation of thermally induced stress between the glue and crystal is the source of these events.

physics.ins-det↗

arXiv2022

A Search for Low-mass Dark Matter via Bremsstrahlung Radiation and the Migdal Effect in SuperCDMS

In this paper, we present a re-analysis of SuperCDMS data using a profile likelihood approach to search for sub-GeV dark matter particles (DM) through two inelastic scattering channels: bremsstrahlung radiation and the Migdal effect. By considering possible inelastic scattering channels, experimental sensitivity can be extended to DM masses that would otherwise be undetectable through the DM-nucleon elastic scattering channel, given the energy threshold of current experiments. We exclude DM masses down to $220~\textrm{MeV}/c^2$ at $2.7 \times 10^{-30}~\textrm{cm}^2$ via the bremsstrahlung channel. The Migdal channel search excludes DM masses down to $30~\textrm{MeV}/c^2$ at $5.0 \times 10^{-30}~\textrm{cm}^2$.

hep-ex↗

arXiv2021

Solar neutrinos and dark matter detection with diurnal modulation

We investigate the diurnal modulation of the event rate for dark matter scattering on solid targets arising from the directionally dependent defect creation threshold energy. In particular, we quantify how this effect would help in separating dark matter signal from the neutrino background. We perform a benchmark analysis for a germanium detector and compute how the reach of the experiment is affected by including the timing information of the scattering events. We observe that for light dark matter just above the detection threshold the magnitude of the annual modulation is enhanced. In this mass range using either the annual or diurnal modulation information provides a similar gain in the reach of the experiment, while the additional reach from using both effects remains modest. Furthermore, we demonstrate that if the background contains a feature exhibiting an annual modulation similar to the one observed by DAMA experiment, the diurnal modulation provides for an additional handle to separate dark matter signal from the background.

hep-ph↗

arXiv2020

Single Electron-Hole Pair Sensitive Silicon Detector with Surface Event Rejection

We demonstrate single electron-hole pair resolution in a single-sided, contact-free 1 cm$^2$ by 1 mm thick Si crystal operated at 48 mK, with a baseline energy resolution of 3 eV. This crystal can be operated at voltages in excess of $\pm50$ V, resulting in a measured charge resolution of 0.06 electron-hole pairs. The high aluminum coverage ($\sim$70%) of this device allows for the discrimination of surface events and separation of events occurring near the center of the detector from those near the edge. We use this discrimination ability to show that non-quantized dark events seen in previous detectors of a similar design are likely dominated by charge leakage along the side wall of the device.

physics.ins-det↗

arXiv2020

Crystal Defects: A Portal To Dark Matter Detection

We propose to use the defect creation energy loss in commonly used high energy physics solid state detectors as a tool to statistically identify dark matter signal from background. We simulate the energy loss in the process of defect creation using density functional theory and molecular dynamics methods and calculate the corresponding expected dark matter spectra. We show that in phonon-mediated solid state detectors, the energy loss due to defect creation convolved with the expected dark matter interaction signal results in a significant change in the expected spectra for common detector materials. With recent progress towards $\sim$10 eV threshold low-mass dark matter searches, this variation in expected dark matter spectrum can be used as a direct signature of dark matter interactions with atomic nuclei.

physics.ins-det↗

arXiv2019

Energy Loss Due to Defect Formation from $^{206}$Pb Recoils in SuperCDMS Germanium Detectors

The Super Cryogenic Dark Matter Search experiment (SuperCDMS) at the Soudan Underground Laboratory studied energy loss associated with Frenkel defect formation in germanium crystals at mK temperatures using in situ $^{210}$Pb sources. We examine the spectrum of $^{206}$Pb nuclear recoils near its expected 103 keV endpoint energy and determine an energy loss of $\left(6.08\pm0.18\right)$ %, which we attribute to defect formation. From this result and using TRIM simulations, we extract the first experimentally determined average displacement threshold energy of $\left(19.7^{+0.6}_{-0.5}\right)$ eV for germanium. This has implications for the analysis thresholds of future germanium-based dark matter searches.

physics.ins-det↗

arXiv2019

Velocity Dependent Dark Matter Interactions in Single-Electron Resolution Semiconductor Detectors with Directional Sensitivity

We investigate the velocity and recoil momentum dependence of dark matter interactions with ordinary matter. In particular we focus on the single-electron resolution semiconductor detectors, which allow experimental assessment of sub-GeV dark matter masses. We find that, within a specific mass range depending on the detector material, the dark matter interactions result in a signal characterized by daily modulation. Furthermore, we find that the detailed structure of this modulation is sensitive to the velocity and momentum dependence of dark matter interactions. We identify the optimal mass range for the prevalence of these effects.

hep-ph↗

arXiv2018

Directional Sensitivity In Light-Mass Dark Matter Searches With Single-Electron Resolution Ionization Detectors

We propose a method using solid state detectors with directional sensitivity to dark matter interactions to detect low-mass Weakly Interacting Massive Particles (WIMPs) originating from galactic sources. In spite of a large body of literature for high-mass WIMP detectors with directional sensitivity, no available technique exists to cover WIMPs in the mass range <1 GeV. We argue that single-electron resolution semiconductor detectors allow for directional sensitivity once properly calibrated. We examine commonly used semiconductor material response to these low-mass WIMP interactions.

physics.ins-det↗

arXiv2016

Sensitivity to oscillation with a sterile fourth generation neutrino from ultra-low threshold neutrino-nucleus coherent scattering

We discuss prospects for probing short-range sterile neutrino oscillation using neutrino-nucleus coherent scattering with ultra-low energy ($\sim 10$ eV - 100 eV) recoil threshold cryogenic Ge detectors. The analysis is performed in the context of a specific and contemporary reactor-based experimental proposal, developed in cooperation with the Nuclear Science Center at Texas A\&M University, and references developing technology based upon economical and scalable detector arrays. The baseline of the experiment is substantially shorter than existing measurements, as near as about 2 meters from the reactor core, and is moreover variable, extending continuously up to a range of about 10 meters. This proximity and variety combine to provide extraordinary sensitivity to a wide spectrum of oscillation scales, while facilitating the tidy cancellation of leading systematic uncertainties in the reactor source and environment. With 100~eV sensitivity, for exposures on the order of 200 kg$\cdot$y, we project an estimated sensitivity to first/fourth neutrino oscillation with a mass gap $Δm^2 \sim 1 \, {\rm eV}^2$ at an amplitude $\sin^2 2θ\sim 10^{-1}$, or $Δm^2 \sim 0.2 \, {\rm eV}^2$ at unit amplitude. Larger exposures, around 5,000 kg$\cdot$y, together with 10 eV sensitivity are capable of probing more than an additional order of magnitude in amplitude.

hep-ph↗

arXiv2015

Toward Single Electron Resolution Phonon Mediated Ionization Detectors

Experiments seeking to detect rare event interactions such as dark matter or coherent elastic neutrino nucleus scattering are striving for large mass detectors with very low detection threshold. Using Neganov-Luke phonon amplification effect, the Cryogenic Dark Matter Search (CDMS) experiment is reaching unprecedented RMS resolutions of ~ 14 eV$_{ee}$ . CDMSlite is currently the most sensitive experiment to WIMPs of mass $\sim$5 GeV/c$^{2}$ but is limited in achieving higher phonon gains due to an early onset of leakage current into Ge crystals. The contact interface geometry is particularly weak for blocking hole injection from the metal, and thus a new design is demonstrated that allows high voltage bias via vacuum separated electrode. With an increased bias voltage and a $\times$ 2 Luke phonon gain, world best RMS resolution of sigma $\sim$7 eV$_{ee}$ for 0.25 kg (d=75 mm, h=1 cm) Ge detectors was achieved. Since the leakage current is a function of the field and the phonon gain is a function of the applied voltage, appropriately robust interface blocking material combined with thicker substrate (25 mm) will reach a resolution of $\sim$2.8 eV$_{ee}$. In order to achieve better resolution of $\sim$ eV, we are investigating a layer of insulator between the phonon readout surface and the semiconductor crystals.

physics.ins-det↗

arXiv2013

Dark Matter Direct Detection With Low Temperature Detectors

Low Temperature Detectors (LTDs) offer the best signal-to-noise performance and thus, lowest energy threshold among other particle detection technologies available today. The excellent background rejection provided by these detectors is essential to search for very rare and very low energy recoils expected from dark matter interactions. Furthermore, due to their very good event-by-event background rejection capabilities, LTDs do not heavily rely on self-shielding in order to mitigate radioactive backgrounds (in contrast with the monolithic liquid Noble Gas detectors) thus they can be more easily prototyped and tested for basic detector performance. A review of the status and prospects of the major Dark Matter search experiments using LTD technologies is presented here.

astro-ph.IM↗