Confirmation of the spectral excess in DAMIC at SNOLAB with skipper CCDs
A. A. Aguilar-Arevalo, I. J. Arnquist, N. Ávalos, L. Barak, D. Baxter, X. Bertou, Itay M. Bloch, Ana Martina Botti, Mariano Cababié, Gustavo Cancelo, N. Castelló-Mor, Brenda A. Cervantes-Vergara, Á. Chavarría, J. Cortabitarte-Gutiérrez, M. B. Crisler, J. Cuevas-Zepeda, A. Dastgheibi-Fard, C. De Dominicis, Olivier Deligny, A. Drlica-Wagner, J. Duarte-Campderros, Juan Carlos D’Olivo, Rouven Essig, E. Estrada, J. Estrada, E. Etzion, F. Favela-Pérez, N. Gadola, R. Gaïor, S. Holland, T. W. Hossbach, L. Iddir, B. Kilminster, Yaron Korn, A. Lantero-Barreda, I. Lawson, S. Lee, A. Letessier‐Selvon, P. Loaiza, A. Lopez-Virto, S. Luoma, E. Marrufo-Villalpando, Kellie McGuire, G. F. Moroni, Sravan Munagavalasa, D. Norcini, Aviv Orly, G. Papadopoulos, S. Paul, Santiago Pérez, A. Piers, P. Privitera, P. Robmann, Darío Rodrigues, Nate Saffold, S. Scorza, M. Settimo, Aman Singal, R. Smida, M. Sofo-Haro, Leandro Stefanazzi, K. Stifter, Javier Tiffenberg, M. Traina, Sho Uemura, I. Vila, R. Vilar, Tomer Volansky, G. Warot, R. Yajur, T-T. Yu, J. P. Zopounidis
Abstract
We present results from a $3.25\text{ }\text{ }\mathrm{kg}\text{\ensuremath{-}}\mathrm{day}$ target exposure of two silicon charge-coupled devices (CCDs), each with 24 megapixels and skipper readout, deployed in the DAMIC setup at SNOLAB. With a reduction in pixel readout noise of a factor of 10 relative to the previous detector, we investigate the excess population of low-energy events in the CCD bulk previously observed above expected backgrounds. We address the dominant systematic uncertainty of the previous analysis through a depth fiducialization designed to reject surface backgrounds on the CCDs. The measured bulk ionization spectrum confirms the presence of an excess population of low-energy events in the CCD target with characteristic rate of $\ensuremath{\sim}7$ events per kg-day and electron-equivalent energies of $\ensuremath{\sim}80\text{ }\text{ }\mathrm{eV}$, whose origin remains unknown.