SuperCDMS SNOLAB will be a next-generation experiment aimed at directly detecting low-mass particles (with masses ≤ 10 GeV=c 2 ) that may constitute dark matter by using cryogenic detectors of two types (HV and iZIP) and two target materials (germanium and silicon). The experiment is being designed with an initial sensitivity to nuclear recoil cross sections ∼1 × 10 −43 cm 2 for a dark matter particle mass of * Corresponding author. tsaab@ufl.edu PHYSICAL REVIEW D 95, 082002 (2017) 2470-0010=2017=95(8)=082002 (17) 082002-1 © 2017 American Physical Society 1 GeV=c 2 , and with capacity to continue exploration to both smaller masses and better sensitivities. The phonon sensitivity of the HV detectors will be sufficient to detect nuclear recoils from sub-GeV dark matter. A detailed calibration of the detector response to low-energy recoils will be needed to optimize running conditions of the HV detectors and to interpret their data for dark matter searches. Low-activity shielding, and the depth of SNOLAB, will reduce most backgrounds, but cosmogenically produced 3 H and naturally occurring 32 Si will be present in the detectors at some level. Even if these backgrounds are 10 times higher than expected, the science reach of the HV detectors would be over 3 orders of magnitude beyond current results for a dark matter mass of 1 GeV=c 2 . The iZIP detectors are relatively insensitive to variations in detector response and backgrounds, and will provide better sensitivity for dark matter particles with masses ≳5 GeV=c 2 . The mix of detector types (HV and iZIP), and targets (germanium and silicon), planned for the experiment, as well as flexibility in how the detectors are operated, will allow us to maximize the low-mass reach, and understand the backgrounds that the experiment will encounter. Upgrades to the experiment, perhaps with a variety of ultra-low-background cryogenic detectors, will extend dark matter sensitivity down to the "neutrino floor," where coherent scatters of solar neutrinos become a limiting background.
The SuperCDMS experiment is designed to directly detect weakly interacting massive particles (WIMPs) that may constitute the dark matter in our Galaxy. During its operation at the Soudan Underground Laboratory, germanium detectors were run in the CDMSlite mode to gather data sets with sensitivity specifically for WIMPs with masses <10 GeV=c 2 . In this mode, a higher detector-bias voltage is applied to amplify the phonon signals produced by drifting charges. This paper presents studies of the experimental noise and its effect on the achievable energy threshold, which is demonstrated to be as low as 56 eV ee (electron equivalent energy). The detector-biasing configuration is described in detail, with analysis corrections for voltage variations to the level of a few percent. Detailed studies of the electric-field geometry, and the resulting successful development of a fiducial parameter, eliminate poorly measured events, yielding an energy resolution ranging from ∼9 eV ee at 0 keV to 101 eV ee at ∼10 keV ee . New results are derived for astrophysical uncertainties relevant to the WIMP-search limits, specifically examining how they are affected by variations in the most probable WIMP velocity and the Galactic escape velocity. These variations become more important for WIMP masses below 10 GeV=c 2 . Finally, new limits on spin-dependent low-mass WIMP-nucleon interactions are derived, with new parameter space excluded for WIMP masses ≲3 GeV=c 2 .
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 Letter, 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 ten live days at the Soudan Underground Laboratory. A low energy threshold of 170 eV ee (electron equivalent) was obtained, which allows us to constrain new WIMP-nucleon spin-independent parameter space for WIMP masses below 6 GeV=c Independent astrophysical surveys and cosmological studies confirm that dark matter constitutes 27% of the energy density of the Universe (reviewed in [1]). Weakly interacting massive particles (WIMPs) are one of the favored particle candidates for dark matter. Theoretical predictions for WIMP masses, and for WIMP-interaction cross sections on normal matter, both span many orders of magnitude. However, WIMPs may elastically scatter off nuclei with enough energy, and at a sufficient rate, to be detected by laboratory detectors [2]. Measurements of the nuclear-recoil energy spectrum by these experiments can constrain the properties of WIMP dark matter [3][4][5].
In the framework of the constrained MSSM we re-examine the gravitino as the lightest superpartner and a candidate for cold dark matter in the Universe. Unlike in most other recent studies, we include both a thermal contribution to its relic population from scatterings in the plasma and a non-thermal one from neutralino or stau decays after freeze-out. Relative to a previous analysis (Roszkowski et al 2005 J. High. Energy Phys. JHEP08(2005)080) we update, extend and considerably improve our treatment of constraints from observed light element abundances on additional energy released during BBN in association with late gravitino production. Assuming the gravitino mass in the GeV to TeV range, and for natural ranges of other supersymmetric parameters, the neutralino region is excluded, except for rather exceptional cases, while for smaller values of it becomes allowed again. The gravitino relic abundance is consistent with observational constraints on cold dark matter from BBN and CMB in some well defined domains of the stau region but, in most cases, only due to a dominant contribution of the thermal population. This implies, depending on , a large enough reheating temperature. If then TR > 108 GeV, if allowed by BBN and other constraints but, for light gravitinos, if then TR > 3 × 103 GeV. On the other hand, constraints mostly from BBN imply an upper bound , which is marginally consistent with thermal leptogenesis. Finally, most of the preferred stau region corresponds to the physical vacuum being a false vacuum. The scenario can be partially probed at the LHC.
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