Using an InGrid Detector to Search for Solar Chameleons with CAST

TL;DR

This paper describes the development and deployment of an InGrid detector at CERN's CAST experiment to search for solar chameleons, including background measurements and potential sensitivity improvements.

Contribution

It introduces a novel InGrid detector with CMOS readout for solar chameleon searches and reports on its operation and background performance at CAST.

Findings

Background rate of 1-5×10^{-5} keV^{-1}cm^{-2}s^{-1} above 2 keV

Estimated limit on chameleon photon coupling: β_γ ≲ 5×10^{10}

Smooth detector operation achieved during data taking

Abstract

We report on the construction, operation experience, and preliminary background measurements of an InGrid detector, i.e. a MicroMegas detector with CMOS pixel readout. The detector was mounted in the focal plane of the Abrixas X-Ray telescope at the CAST experiment at CERN. The detector is sensitive to soft X-Rays in a broad energy range (0.3--10 keV) and thus enables the search for solar chameleons. Smooth detector operation during CAST data taking in autumn 2014 has been achieved. Preliminary analysis of background data indicates a background rate of $1-5\times 10^{-5}\,\mathrm{keV}^{-1}\mathrm{cm}^{-2}\mathrm{s}^{-1}$ above 2 keV and $\sim 3\times 10^{-4}\,\mathrm{keV}^{-1}\mathrm{cm}^{-2}\mathrm{s}^{-1}$ around 1 keV. An expected limit of $\beta_\gamma \lesssim 5\times 10^{10}$ on the chameleon photon coupling is estimated in case of absence of an excess in solar tracking data. We also discuss the prospects for future operation of the detector.