Ultralow energy calibration of LUX detector using Xe127 electron capture

Author(s): Akerib, DS; Alsum, S; Araujo, HM; Bai, X; Bailey, AJ; Balaithy, J; Beltrame, P; Bernard, EP; Bernstein, A; Biesiadzinski, TP; Boulton, EM; Bras, P; Byram, D; Cahn, SB; Carmona-Benitez, MC; Chan, C; Currie, A; Cutter, JE; Davison, TJR; Dobi, A; Druszkiewicz, E; Edwards, BN; Fallon, SR; Fan, A; Fiorucci, S; Gaitskell, RJ; Genovesi, J; Ghang, C; Gilchriese, MGD; Hall, CR; Hanhardt, M; Haselschwardt, SJ; Hertel, SA; Hogan, DP; Horn, M; Huang, DQ; Ignarra, CM; Jacobsen, RG; Ji, W; Kamdin, K; Kazkaz, K; Khaitan, D; Knoche, R; Larsen, NA; Lenardo, BG; Lesko, KT; Lindote, A; Lopes, MI; Manalaysay, A; Mannino, RL; Marzioni, MF; McKinsey, DN; Mei, D-M; Mock, J; Moongweluwan, M; Morad, JA; Murphy, ASJ; Nehrkom, C; Nelson, HN; Neves, F; Neves, F; O'Sullivan, K; Oliver-Mallory, KC; Palladino, KJ; Pease, EK; Rhyne, C; Shaw, S; Shutt, TA; Silva, C; Solmaz, M; Solovov, VN; Sorensen, P; Sumner, TJ; Szydagis, M; Taylor, DJ; Taylor, WC; Tennyson, BP; Terman, PA; Tiedt, DR; To, WH; Tripathi, M; Tvrznikova, L; Uvarov, S; Velan, V; Verbus, JR | Abstract: We report an absolute calibration of the ionization yields($\textit{Q$_y$})$ and fluctuations for electronic recoil events in liquid xenon at discrete energies between 186 eV and 33.2 keV. The average electric field applied across the liquid xenon target is 180 V/cm. The data are obtained using low energy $^{127}$Xe electron capture decay events from the 95.0-day first run from LUX (WS2013) in search of Weakly Interacting Massive Particles (WIMPs). The sequence of gamma-ray and X-ray cascades associated with $^{127}$I de-excitations produces clearly identified 2-vertex events in the LUX detector. We observe the K- (binding energy, 33.2 keV), L- (5.2 keV), M- (1.1 keV), and N- (186 eV) shell cascade events and verify that the relative ratio of observed events for each shell agrees with calculations. The N-shell cascade analysis includes single extracted electron (SE) events and represents the lowest-energy electronic recoil $\textit{in situ}$ measurements that have been explored in liquid xenon.