HypeX: high yield polarimetry experiment in x-rays

Abstract

We present the development of a large-volume, increased field-of-view Time Projection Chamber (TPC) for X-ray polarimetry, utilizing a triple-GEM detector with optical readout. Initially optimized for directional Dark Matter searches, this system employs a scientific CMOS (sCMOS) camera and a PMT to detect secondary scintillation light produced during the TPC amplification stage. A prototype TPC with a cylindrical active volume of radius 3.7 cm and height 5 cm was tested at the INAF-IAPS calibration facility in Rome, Tor Vergata to establish the instrument's sensitivity to low-energy electron direction. Complete reconstruction of electrons in the 10-60 keV range with angular resolution down to 15°was measured, resulting in inferred modulation factors up to 0.9. We will present the initial results from our test campaign, which confirm effective photoelectron tracking in the tens of keV range with a strong modulation factor. This innovative approach could extend X-ray polarimetry sensitivity to higher energies and possibly enable the observation of rapid transient phenomena, such as Gamma Ray Bursts (GRBs) and solar flares, thus contributing significantly to X-ray astronomy.