Speaker
Description
The SuperNEMO Demonstrator is a double-beta-decay detector currently taking physics data at the LSM, France. It has a unique ability to measure the full topology of decay events, providing strong background rejection for $\beta\beta$ decay searches. However, extremely rare backgrounds from high-energy beta emitters can mimic $\beta\beta$-like signatures via secondary interactions. An important example is $^{208}$Tl ($Q_{\beta}$ $\simeq$ 5 MeV), which can contribute to the background in the $^{82}$Se region of interest ($Q_{\beta\beta}$ $\simeq$ 3 MeV). We constrain this by measuring the rate of the dominant $^{208}$Tl topology, 1e1$\gamma$ events, with a common vertex. This requires an accurate understanding of the calorimeter response to electrons and $\gamma$ rays in both energy and timing. Using $^{207}$Bi sources, which have well-known electron and $\gamma$ spectra, we calibrate the energy and timing response using selected 1e1$\gamma$ decays. This data-driven calibration supports the $\sim$ 200 ps timing target and improves the robustness of the $^{208}$Tl background estimate for SuperNEMO.