PhD Thesis Defense: Karthik Ramanathan

10:00–11:00 am Zoom

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PARTICLES TAKING SELFIES: INVESTIGATIONS INTO LIGHT DARK MATTER USING SILICON CHARGE COUPLED DEVICES

Recent null results in searches for expected dark matter candidates have spurred interest in looking for lighter mass particles. Experiments searching for these alternatives require low energy thresholds and increased sensitivity since energy deposits can be of O(eV). An experiment uniquely suited to this parameter space is DAMIC (Dark Matter in CCDs) which uses scientific grade silicon charge-coupled devices (CCDs). These pixelated devices have an excellent read noise (2e-) and a very low threshold of 50 eV. However, searching for DM in this regime requires a good understanding of: a) detector backgrounds b) a model of the ionization response at these energies and c) perhaps some way to extend the reach of the experiment below threshold.
This work represents a deep-dive into addressing those challenges. We accurately measured and characterized the background from the small-angle scattering of environmental γ-rays and reported the first measurement of “Compton Steps”. Next we synthesized from existing literature a simple probabilistic model for charge yield. We then exploited the impressively low leakage current of DAMIC CCDs (<10^-21 A/cm^2) to set constraints on unexplored parameter space for dark matter recoiling off electrons with masses between 0.6 and 100 MeV and hidden photon dark matter with masses between 1.2-9 eV. Finally, we introduce and report on R&D progress at UChicago in using “Skipper” instrumented CCDs - a novel readout technique that allows for counting of individual charge pairs, with a demonstrated resolution of 0.07 e-, which ushers in a new era of sensitivity to low-energy interactions.

Committee:
Paolo Privitera (Chair)
Juan Collar
William Irvine
Carlos Wagner

Karthik will be starting a postdoc at Caltech, jointly advised by Sunil Golwala and Rana Adhikari, with a focus on R&D for new ideas in axion and light dark matter detection.

Event Type

Thesis Defense

Sep 21