arXiv subjects

Alvaro E. Chavarria

Publications and source records attributed to Alvaro E. Chavarria.

7 recordsLinked to original sources

arXiv2024

Skipper-CCD Sensors for the Oscura Experiment: Requirements and Preliminary Tests

Oscura is a proposed multi-kg skipper-CCD experiment designed for a dark matter (DM) direct detection search that will reach unprecedented sensitivity to sub-GeV DM-electron interactions with its 10 kg detector array. Oscura is planning to operate at SNOLAB with 2070 m overburden, and aims to reach a background goal of less than one event in each electron bin in the 2-10 electron ionization-signal region for the full 30 kg-year exposure, with a radiation background rate of 0.01 dru. In order to achieve this goal, Oscura must address each potential source of background events, including instrumental backgrounds. In this work, we discuss the main instrumental background sources and the strategy to control them, establishing a set of constraints on the sensors' performance parameters. We present results from the tests of the first fabricated Oscura prototype sensors, evaluate their performance in the context of the established constraints and estimate the Oscura instrumental background based on these results.

physics.ins-det↗

arXiv2023

Searching for millicharged particles with 1 kg of Skipper-CCDs using the NuMI beam at Fermilab

Oscura is a planned light-dark matter search experiment using Skipper-CCDs with a total active mass of 10 kg. As part of the detector development, the collaboration plans to build the Oscura Integration Test (OIT), an engineering test with 10% of the total mass. Here we discuss the early science opportunities with the OIT to search for millicharged particles (mCPs) using the NuMI beam at Fermilab. mCPs would be produced at low energies through photon-mediated processes from decays of scalar, pseudoscalar, and vector mesons, or direct Drell-Yan productions. Estimates show that the OIT would be a world-leading probe for mCPs in the MeV mass range.

hep-ex↗

arXiv2022

Even Lighter Particle Dark Matter

We report on recent progress in the search for dark matter particles with masses from 1 MeV to 1 GeV. Several dark matter candidates in this mass range are expected to generate measurable electronic-recoil signals in direct-detection experiments. We focus on dark matter particles scattering with electrons in semiconductor detectors since they have fundamentally the highest sensitivity due to their low ionization threshold. Charge-coupled device (CCD) silicon detectors are the leading technology, with significant progress expected in the coming years. We present the status of the CCD program and briefly report on other efforts.

astro-ph.CO↗

arXiv2022

Background Rejection in Highly Pixelated Solid-State Detectors

Highly pixelated solid-state detectors offer outstanding capabilities in the identification and suppression of backgrounds from natural radioactivity. We present the background-identification strategies developed for the DAMIC experiment, which employs silicon charge-coupled devices to search for dark matter. DAMIC has demonstrated the capability to disentangle and measure the activities of every $β$ emitter from the $^{32}$Si, $^{238}$U and $^{232}$Th decay chains in the silicon target. Similar strategies will be adopted by the Selena Neutrino Experiment, which will employ hybrid amorphous $^{82}$Se/CMOS imagers to perform spectroscopy of $ββ$ decay and solar neutrinos. We present the proposed experimental strategy for Selena to achieve zero-background in a 100-ton-year exposure.

physics.ins-det↗

arXiv2022

The low-energy spectrum in DAMIC at SNOLAB

The DAMIC experiment employs large-area, thick charge-coupled devices (CCDs) to search for the interactions of low-mass dark matter particles in the galactic halo with silicon atoms in the CCD target. From 2017 to 2019, DAMIC collected data with a seven-CCD array (40-gram target) installed in the SNOLAB underground laboratory. We report dark-matter search results, including a conspicuous excess of events above the background model below 200 eV$_{\rm ee}$, whose origin remains unknown. We present details of the published spectral analysis, and update on the deployment of skipper CCDs to perform a more precise measurement by early 2023.

astro-ph.CO↗

arXiv2021

The Selena Neutrino Experiment

Imaging sensors made from an ionization target layer of amorphous selenium (aSe) coupled to a silicon complementary metal-oxide-semiconductor (CMOS) active pixel array for charge readout are a promising technology for neutrino physics. The high spatial resolution in a solid-state target provides unparalleled rejection of backgrounds from natural radioactivity in the search for neutrinoless $ββ$ decay and for solar neutrino spectroscopy with $^{82}$Se. We present results on the ionization response of aSe measured from the photoabsorption of 122 keV $γ$ rays in a single-pixel device. We report on the progress in the fabrication and testing of the first prototype imaging sensors based on the Topmetal-II$^{\rm -}$ pixelated CMOS charge readout chip. We explore the scientific reach of a large neutrino detector with the proposed technology based on our experimental understanding of the sensor performance.

physics.ins-det↗

arXiv2021

Measurement of the ionization response of amorphous selenium with 122keV $γ$ rays

We performed a measurement of the ionization response of 200 $μ$m-thick amorphous selenium (aSe) layers under drift electric fields of up to 50 V/$μ$m. The aSe target was exposed to ionizing radiation from a $^{57}$Co radioactive source and the ionization pulses were recorded with high resolution. Using the spectral line from the photoabsorption of 122 keV $γ$ rays, we measured the charge yield in aSe and the line width as a function of drift electric field. From a detailed microphysics simulation of charge generation and recombination in aSe, we conclude that the strong dependence of recombination on the ionization track density provides the dominant contribution to the energy resolution in aSe. These results provide valuable input to estimate the sensitivity of a proposed next-generation search for the neutrinoless $ββ$ decay of $^{82}$Se that aims to employ imaging sensors with an active layer of aSe. We estimate the RMS line width of the integrated ionization signal from neutrinoless $ββ$ decay events (of deposited energy 3 MeV) to be 2.0% for a drift field of 50 V/$μ$m. The energy resolution can be improved to 1% by correcting for the charge yield as a function of ionization density along the imaged electron tracks.

physics.ins-det↗