CDMSlite: A Search for Low-Mass WIMPs using Voltage-Assisted Calorimetric Ionization Detection in the SuperCDMS Experiment

TL;DR

This Letter presents WIMP-search results using a calorimetric technique the authors call CDMSlite, which relies on voltage-assisted Luke-Neganov amplification of the ionization energy deposited by particle interactions to constrain new WIMp-nucleon spin-independent parameter space for W IMP masses below 6  GeV/c2.

Abstract

SuperCDMS is an experiment designed to directly detect Weakly Interacting Massive Particles (WIMPs), a favored candidate for dark matter ubiquitous in the Universe. In this paper, we present WIMP-search results using a calorimetric technique we call CDMSlite, which relies on voltage- assisted Luke-Neganov amplification of the ionization energy deposited by particle interactions. The data were collected with a single 0.6 kg germanium detector running for 10 live days at the Soudan Underground Laboratory. A low energy threshold of 170 eVee (electron equivalent) was obtained, which allows us to constrain new WIMP-nucleon spin-independent parameter space for WIMP masses below 6 GeV/c2.

Figures (4)

• Figure 1: Recoil energy spectrum of WIMP-search events, after application of event-selection cuts. Inset: Low-energy spectrum in terms of raw counts (blue); also shown is the analysis efficiency. Both are expressed in $\text{keV}_{\text{ee}}$. The analysis threshold of $170\; \text{eV}_{\text{ee}}$ is indicated by the vertical dot-dashed line. The resolution of the 1.3 keV line is 43 eV$_\text{ee}$ ($1\sigma$).
• Figure 2: The efficiency-corrected WIMP-search energy spectrum is shown in $\text{keV}_{\text{nr}}$, and compared with expected rates for WIMPs with the most likely masses and cross sections suggested by the analysis of CoGeNT PhysRevD.88.012002 and CDMS II Si Agnese:2013rvf data (dashed curves). Note that the $k=0.157$ Lindhard yield model was used to convert from an electron-equivalent to a nuclear-recoil-equivalent energy scale. The $170\; \text{eV}_{\text{ee}}$ ionization threshold translates to $841\; \text{eV}_{\text{nr}}$ (amber dot-dashed line). The $1.3~\text{keV}_{\text{ee}}$ activation line appears at $\sim5.3~\text{keV}_\text{nr}$.
• Figure 3: The 90% upper confidence limit from the data presented here are shown with exclusion limits from other experiments. These are grouped as Ge bolometers in blue: CDMS II Ge regular (dot-dash) CDMSScience:2010, CDMS II Ge low threshold (solid) PhysRevLett.106.131302, EDELWEISS II low threshold (dash) PhysRevD.86.051701; point-contact Ge detectors in purple: TEXONO (dash) PhysRevLett.110.261301, CDEX (dot-dash) Zhao:2013xsf; liquid Xenon in red: XENON100 (dot-dash) PhysRevLett.109.181301, XENON10 S2 only (dash) PhysRevLett.107.051301*PhysRevLett.110.249901, LUX (solid) Akerib:2013tjd; and other technologies in magenta: Low threshold reanalysis of CRESST II data (dot-dash) PhysRevD.85.021301, PICASSO (dash) Archambault2012153. The contours are from CDMS II Si (light and dark gray correspond to 68% and 90% CL regions respectively) Agnese:2013rvf, CRESST II (blue) Angloher:2012fk, DAMA (orange) Bernabei:2010uqSavage:2008er, CoGeNT (pink) PhysRevD.88.012002.
• Figure 4: The effect of the choice of the yield model on the 90% confidence level upper limit is shown. For the Lindhard model, the $0.170~\text{keV}_\text{ee}$ analysis threshold corresponds to 0.84 $\text{keV}_{\text{nr}}$ ($k=0.157$), 1.1 $\text{keV}_{\text{nr}}$ ($k=0.1$), 0.73 $\text{keV}_{\text{nr}}$ ($k=0.2$). For the power-law model used by CoGeNT, the analysis threshold corresponds to 0.75 $\text{keV}_{\text{nr}}$ .