Experimental Search for Solar Axions and Chameleons
Final Report Abstract
Since it has started data-taking in 2003, CAST has successfully improved the limit on the axion-photon coupling constant for axion masses < 0.02 eV by a factor of almost 6 compared to previous axion helioscopes. Detector upgrades implemented allowed us to push this limit even further. In addition to axions, the results also limit the parameter space for axion-like particles (ALPS), which share part of its phenomenology. Axions, ALPS, and, more generally, Weakly Interacting Slim Particles (WISPs), are of interest for cosmology and astrophysics, since they have been proposed as candidates for dark matter and as an explanation for other astrophysical phenomena. Together with observational data, the limits on the coupling constant can serve as a consistency check of the various astrophysical and cosmological models. With our upgraded detectors, we expect to improve the signal sensitivity (for axion masses below 0.02 eV). The CAST physics program is, however, not limited to solar ALP searches but points to several directions with the potential to cover a large sector of WISP searches. In addition to studying axions and other ALPS, which are relevant as dark matter candidates, CAST did launch a program to extend its reach also in the Dark Energy sector by attempting the detection of solar chameleons. These particles have a rest mass that depends on the surrounding energy density, an effect mediated by a direct coupling to matter. For the interior of the sun, the theoretical model for chameleons predicts their creation via the Primakoff effect. Likewise, they are expected to back-convert into photons in a strong magnetic field (such as in the CAST magnet) via the inverse Primakoff effect. The energy balance of the sun puts a limit on the rate of chameleon production in the sun, and thus the chameleon-photon coupling constant. First tests to search for chameleons with CAST were carried out with a silicone drift detector (SDD) and the results were published. This makes CAST the first chameleon helioscope in the world. Moreover an ultra-sensitive opto-mechanical force sensor has been built and tested (collaboration with IFN Trieste). Its application to experiments in the Dark Energy sector, such as those for Chameleon-type WISPs, is particularly attractive, as it enables a search for their direct coupling to matter. The main characteristics of the KWISP (Kinetic WISP detection) sensor are based on a thin Si3N4 micro-membrane placed inside a Fabry-Perot optical cavity. By monitoring the cavity characteristic frequencies it is possible to detect the tiny membrane displacements caused by an applied force. Far from the mechanical resonant frequency of the membrane, the measured force sensitivity is 2.0.10(-13) N/root Hz, corresponding to a displacement sensitivity of 1.0.10(-14) m/root Hz, while near resonance the sensitivity is 6.0.10(-14) N/root Hz, reaching the estimated thermal limit, or, in terms of displacement, 3.0.10(-15) m/root Hz. These displacement sensitivities are comparable to those that can be achieved by large interferometric gravitational wave detectors.
Publications
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Detecting solar chameleons through radiation pressure. Physics Letters B Volume: 739 Pages: 167-173 Dec 12, 2014 5
Baum, S.; Cantatore, G.; Hoffmann, D. H. H.; et al.
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Flux Enhancement of Slow-Moving Particles by Sun or Jupiter: Can They Be Detecte On Earth? Astrophysical Journal Volume: 780 Issue: 2, Jan 10, 2014
Patla, Bijunath R.; Nemiroff, Robert J.; Hoffmann, Dieter H. H.; et al.
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The 11 years solar cycle as the manifestation of the dark Universe. Modern Physics Letters A Volume: 29 Issue: 37, Dec 7, 2014
Zioutas, K.; Tsagri, M.; Semertzidis, Y. K.; et al. with Hoffmann DHH
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New solar axion search using the CERN Axion Solar Telescope with He-4 filling. Physical Rev. D Volume: 92 Issue: 2, Jul 28, 2015
Arik, M.; Aune, S.; Barth, K.; et al. with Hoffmann DHH, Group Author(s): CAST Collaboration
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Search for chameleons with CAST. Physics Letters B Volume: 749 Pages: 172-180, Oct. 7, 2015
Anastassopoulos, V.; Arik, M.; Aune, S.; et al. with Hoffmann DHH, Group Author(s): CAST Collaboration
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KWISP: an ultra-sensitive force sensor for the Dark Energy sector. Phys. Dark Universe 12 (2016) 100
M. Karuza, G. Cantatore, A. Gardikiotis, D.H.H. Hoffmann, Y.K. Semertzidis, K. Zioutas
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(2017) New CAST limit on the axion–photon interaction. Nature Physics, 13 584-590
V. Anastassopoulos, S. Aune, K. Barth, A. Belov, et al., mit DHH Hoffmann (CAST Collaboration)
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aKWISP: investigating short-range interactions at sub-micron scales. CERN workshop, Physics Beyond Colliders, September 2016
G. Cantatore, H. Fischer, A. Gardikiotis, D.H.H. Hoffmann, M. Karuza, Y. Semertzidis, K. Zioutas
