Time-based Selection of Kaonic Atom X-ray Events with Quasi-Hemispherical CZT Detectors at the DAFNE collider

TL;DR

This study demonstrates a novel time-based event selection method using CZT detectors at the DAFNE collider, enabling the first observation of kaonic atom X-ray transitions with high background suppression.

Contribution

Developed a timing correlation strategy with CZT detectors to isolate kaonic atom X-ray signals, achieving significant background reduction and first-time detection of specific transitions.

Findings

Observed two kaonic aluminum X-ray transitions at 50 keV and 106 keV.

Achieved approximately 95% background suppression with timing selection.

Demonstrated CZT detector's effective timing capabilities for X-ray spectroscopy.

Abstract

This work presents the results of a time-based event selection for searching X-ray signals from kaonic atom X-ray transition using a single quasi-hemispherical Cadmium-Zinc-Telluride (CZT) detector at the DA$\Phi$NE collider. To mitigate the high background level in the measured X-ray spectrum, a dedicated event selection strategy was developed, exploiting the precise timing correlation between e+e- collisions and detector signals. This approach enabled, for the first time, the observation of two characteristic X-ray transitions from kaonic aluminum atoms using a CZT detector: for the 5-4 transition at 50~keV, 362~$\pm$~41~(stat.)~$\pm$~20~(sys.) signal events over 1698~$\pm$~197~(stat.)~$\pm$~25~(sys.) background events in 5$\sigma$ were observed, with a resolution of 9.2\%~FWHM; for the 4-3 transition at 106~keV, 295~$\pm$~50~(stat.)~$\pm$~20~(sys.) signal events over 2939~$\pm$~500~(stat.)~$\pm$~16~(sys.) background events in 5$\sigma$ were measured, with a resolution of 6.6 ~FWHM. A strong background suppression of approximately 95\% of the triggered data was achieved through this time-based selection. The demonstrated timing capability of the CZT detector proved highly effective in isolating time-correlated events within an 80 ns window, setting an important benchmark for the application of these semiconductors in timing-based X-ray spectroscopy. These results highlight the potential of CZT-based detection systems for future precision measurements in high-radiation environments, paving the way for compact, room-temperature X-ray and $\gamma$-ray spectrometers in fundamental physics and beyond.