Search for the Migdal effect in liquid xenon with keV-level nuclear recoils

Search for the Migdal effect in liquid xenon with keV-level nuclear recoils

11 March 2024 | J. Xu, D. Adams, B. G. Lenardo, T. Pershing, R. L. Mannino, E. Bernard, J. Kingston, E. Mizrahi, J. Lin, R. Essig, V. Mozin, P. Kerr, A. Bernstein, and M. Tripati
This study reports the first direct search for the Migdal effect in liquid xenon (LXe) using nuclear recoils of 7.0 ± 1.6 keV produced by tagged neutron scatters. The experiment used a dual-phase xenon time projection chamber (TPC) to detect both scintillation (S1) and ionization (S2) signals from particle interactions. The S1 and S2 signals are proportional to the deposited energy and their ratio helps distinguish between electron recoils (ERs) and nuclear recoils (NRs). The study focused on detecting Migdal events where nuclear recoils are accompanied by atomic ionization, which can produce additional energy depositions. The Migdal effect is predicted to enhance the sensitivity of dark matter detection experiments to sub-GeV dark matter masses. The experiment searched for Migdal events in the M- and L-shell electrons of xenon, with the expected ER energy in the keV range. The observed background rate was lower than expected, but no signal consistent with predictions was found. Possible explanations include inaccurate predictions for the Migdal rate or the signal response in liquid xenon. The experiment used a neutron source and a xenon TPC to measure the Migdal effect. The neutron source was a deuterium-tritium (DT) generator, and the neutrons were collimated and directed at the TPC. The TPC was used to detect the S1 and S2 signals from the interactions. The experiment also used a circular array of liquid scintillator detectors to tag neutrons scattered at 15.0°. The analysis focused on the M-shell signals, with events having 4 PHE < S1 < 40 PHE and 25 e- < S2 < 200 e-. The results showed no significant signal, with the best-fit Migdal signal rate being 16.3 ± 21.7 counts. The results suggest that the Migdal effect may not be as significant as predicted, possibly due to inaccuracies in the theoretical models or other factors such as enhanced electron-ion recombination in liquid xenon. The study highlights the importance of understanding the Migdal effect in dark matter detection experiments and provides a foundation for future research in this area. The experiment demonstrated the capability to achieve low backgrounds in liquid xenon, which is crucial for studying the Migdal effect. The results suggest that further experiments are needed to better understand the Migdal effect and its implications for dark matter detection.This study reports the first direct search for the Migdal effect in liquid xenon (LXe) using nuclear recoils of 7.0 ± 1.6 keV produced by tagged neutron scatters. The experiment used a dual-phase xenon time projection chamber (TPC) to detect both scintillation (S1) and ionization (S2) signals from particle interactions. The S1 and S2 signals are proportional to the deposited energy and their ratio helps distinguish between electron recoils (ERs) and nuclear recoils (NRs). The study focused on detecting Migdal events where nuclear recoils are accompanied by atomic ionization, which can produce additional energy depositions. The Migdal effect is predicted to enhance the sensitivity of dark matter detection experiments to sub-GeV dark matter masses. The experiment searched for Migdal events in the M- and L-shell electrons of xenon, with the expected ER energy in the keV range. The observed background rate was lower than expected, but no signal consistent with predictions was found. Possible explanations include inaccurate predictions for the Migdal rate or the signal response in liquid xenon. The experiment used a neutron source and a xenon TPC to measure the Migdal effect. The neutron source was a deuterium-tritium (DT) generator, and the neutrons were collimated and directed at the TPC. The TPC was used to detect the S1 and S2 signals from the interactions. The experiment also used a circular array of liquid scintillator detectors to tag neutrons scattered at 15.0°. The analysis focused on the M-shell signals, with events having 4 PHE < S1 < 40 PHE and 25 e- < S2 < 200 e-. The results showed no significant signal, with the best-fit Migdal signal rate being 16.3 ± 21.7 counts. The results suggest that the Migdal effect may not be as significant as predicted, possibly due to inaccuracies in the theoretical models or other factors such as enhanced electron-ion recombination in liquid xenon. The study highlights the importance of understanding the Migdal effect in dark matter detection experiments and provides a foundation for future research in this area. The experiment demonstrated the capability to achieve low backgrounds in liquid xenon, which is crucial for studying the Migdal effect. The results suggest that further experiments are needed to better understand the Migdal effect and its implications for dark matter detection.
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