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Authors: Shah, Rikhav
Advisor: Schott, Matthias
Title: A TES detector for ALPS II : characterising a cryogenic, low-background, low energy single photon detector
Online publication date: 26-Jan-2023
Year of first publication: 2023
Language: english
Abstract: Axions are Weakly Interacting sub-eV Particles (WISPs) predicted to explain phenomena like the lack of Charge-Parity (CP) violation in Quantum Chromodynamics (QCD). With axion-like-particles, they can also contribute to dark matter and explain other astrophysical phenomena. These particles can couple to photons, a process used in most experiments attempting to search for them. One such experiment is ALPS II, a light-shining-through-a-wall experiment. Photons stored in an optical cavity can convert to axions or axion-like-particles, aided by the presence of a magnetic field. These can traverse an opaque wall and, in another such optical cavity, reconvert to photons which can be detected. The rate of these low energy (1.165 eV) 1064nm photons comprising the signals for ALPS II is O(10^{-5}) cps. A Transition Edge Sensor (TES) can prove to be a suitable candidate to detect them. This sensor exploits the drastic dependence of the resistance of a superconducting microchip near its transition temperature, which can detect the incidence of a photon (as energy) on it from a macroscopic change in its resistance. The characterisation of a such a TES system to serve as a detection scheme for ALPS II is covered by this work. Firstly, the setup and design of this scheme is detailed with its defining features and readout with SQUIDs (Superconducting Quantum Interference Devices). It is housed in a dilution refrigerator capable of stably cooling down to temperatures <30 mK. The working, response and operation of this TES system and SQUID readout is detailed, readying it for the reception of signals and background alike with a data acquisition and processing scheme. Secondly, the analysis of these TES pulses is discussed. Here, the pulses can be fit with a variety of fitting schemes (as best suited to the TES) and studied with a PCA (Principal Component Analysis) as well. The application of these procedures yields an energy resolution 7-12% for 1064 nm photons. The fitting scheme which best assimilates the data in a TES pulse is adopted as the baseline for pulse characterisation and forms the basis for a pulse selection procedure. Thirdly, the discussion turns to background events inveigling the detection scheme. For use in ALPS II, a background rate of 8.1 x 10^{-6} cps over 20 days of data taking is the upper limit for the detector, assuming a detection efficiency of 50%. The backgrounds are split into extrinsic and intrinsic backgrounds i.e. those detected with an optical fiber coupled to the TES and those detected without. It is essential to substantiate the viability of the TES for use in the ALPS II experiment. In order to do this, a 20 day intrinsic background dataset is subjected to the pulse selection procedure(s), resulting in a rate of 6.9 x 10^{-6} cps, with a 1064 nm-photon selection 90%. Considering the intrinsic backgrounds, the TES is thus viable for use in the ALPS II experiment. A setup to measure the detection efficiency of the system has also been developed and is also described. This influences the extrinsic background events detected. The first measurements with this setup have resulted in an efficiency of at least 5% and will be optimised. The backgrounds can in general originate from a variety of sources including cosmic rays and radioactivity, but are suspected to be dominated by photons from blackbody radiation and their pile-ups. To suppress this, hardware options such as an in-cold filter bench and fiber curling are being investigated for use in the main detection line to the TES. Testing these suppression methods forms the next series of investigations for the TES system along with background studies, simulations, and the use of machine learning techniques for pulse analysis. These forthcoming steps form the efforts to fully characterise the TES detection system in preparation for ALPS II.
DDC: 530 Physik
530 Physics
Institution: Johannes Gutenberg-Universität Mainz
Department: FB 08 Physik, Mathematik u. Informatik
Place: Mainz
URN: urn:nbn:de:hebis:77-openscience-8fff8b19-ae05-45ed-9309-524b6f28ee8a2
Version: Original work
Publication type: Dissertation
License: CC BY-ND
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Extent: viii, 130 Seiten ; Illustrationen, Diagramme
Appears in collections:JGU-Publikationen

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