Hunting chameleons with the KWISP detector at the CAST experiment at CERN

Abstract: Astrophysical and cosmological observations strongly indicate the existence of dark matter and dark energy. These phenomena demand physics beyond the standard model or the modification of the theoretical framework of general relativity. The so-called chameleon mechanism introduces a non-linear self-interacting scalar field, coupling to matter and photons, which can act as a dark energy quintessence field.
To evade detection by classical fifth-force searches, the chameleon field exhibits a screening mechanism leading to an effective mass of the scalar depending on the ambient density. Thus, the chameleon can be light on cosmological scales but have a short Compton wavelength in the solar system. Different experimental efforts based on indirect detection methods were performed in the last decade. This work presents a complementary novel direct detection method for the search of solar chameleons with the Kinetic Weakly Interacting Slim Particle (KWISP) detector, utilizing an
ultra-sensitive optomechanical force sensor.
The KWISP detector is part of the CAST experiment at CERN, and the working principle is based on the reflection of solar chameleons off a thin Si3N4 membrane placed in the middle of a Fabry-Perot cavity. Due to their coupling to photons,
chameleons are assumed to be produced in the tachocline, a region of the Sun with strong magnetic fields, where a real photon and a virtual photon, provided by the magnetic field, convert to a chameleon via a Primakoff-like process. The KWISP detector is mounted behind the CAST helioscope, which tracks the movement of the Sun, and the incoming solar chameleon flux is focused on the membrane by an X-ray
telescope. Because of their density-dependent effective mass, part of the chameleon spectrum is reflected off the membrane due to energy conservation. A chopper placed between the X-ray telescope and the detector modulates the chameleon flux at a known frequency, causing a periodic displacement of the membrane and consequently a detuning of the cavity, which is frequency-locked to an infrared laser by a feedback loop. Therefore, a potential chameleon signal could be observed in the FFT spectrum of the error signal generated by the feedback loop at the chopper frequency.
This work covers several characterization studies of the latest detector version, KWISP 3.5, examining the membrane response, chopper performance, background noise, and detector sensitivity. Furthermore, the tracking data acquired during ten solar tracking shifts performed in May 2021 is evaluated. The analysis yields a detector sensitivity of S = (849 ± 19) fN/sqrt(Hz) and a minimum detectable force of F_min = 282 fN at 95% CL, which is used to place a chameleon exclusion limit. In the sensitive region of the detector for the coupling to matter, 4 < log10 β_m < 8, the coupling to photons is locally bound to log10 β_ < 10, improving the previous limit set with KWISP 1.5 by a factor of ≈ 17

Angaben zum Objekt

• Standort: Deutsche Nationalbibliothek Frankfurt am Main
• Umfang: Online-Ressource
• Sprache: Englisch
• Anmerkungen: Universität Freiburg, Dissertation, 2022

Klassifikation und Themen

• Schlagwort: Dunkle Energie ; Optomechanik ; Fabry-Pérot-Interferometer

Beteiligte, Orts- und Zeitangaben

• Ereignis: Veröffentlichung
• (wo): Freiburg
• (wer): Universität
• (wann): 2023
• Urheber: Baier, Justin Sillvan
• Beteiligte Personen und Organisationen: Fischer, Horst ; Fischer, Horst ; Heinemann, Beate ; Albert-Ludwigs-Universität Freiburg. Physikalisches Institut ; Albert-Ludwigs-Universität Freiburg. Fakultät für Mathematik und Physik

Weitere Informationen

• DOI: 10.6094/UNIFR/235702
• URN: urn:nbn:de:bsz:25-freidok-2357028
• Rechteinformation: Open Access; Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Letzte Aktualisierung: 25.03.2025, 13:48 MEZ