Ionization yield measurement in a germanium CDMSlite detector using photo-neutron sources

Abstract

Two photo-neutron sources, ${}^{88}$Y${}^9$Be and ${}^{124}$Sb${}^9$Be, have been used to investigate the ionization yield of nuclear recoils in the CDMSlite germanium detectors by the SuperCDMS collaboration. This work evaluates the yield for nuclear recoil energies between 1 keV and 7 keV at a temperature of $\sim$ 50 mK. We use a Geant4 simulation to model the neutron spectrum assuming a charge yield model that is a generalization of the standard Lindhard model and consists of two energy dependent parameters. We perform a likelihood analysis using the simulated neutron spectrum, modeled background, and experimental data to obtain the best fit values of the yield model. The ionization yield between recoil energies of 1 keV and 7 keV is shown to be significantly lower than predicted by the standard Lindhard model for germanium. There is a general lack of agreement among different experiments using a variety of techniques studying the low-energy range of the nuclear recoil yield, which is most critical for interpretation of direct dark matter searches. This suggests complexity in the physical process that many direct detection experiments use to model their primary signal detection mechanism and highlights the need for further studies to clarify underlying systematic effects that have not been well understood up to this point.

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• Reactor antineutrinos CE$\nu$NS on germanium: CONUS+ and TEXONO as a new gateway to SM and BSM physics
• On the impact of the Migdal effect in reactor CE$\nu$NS experiments
• First observation of isolated nuclear recoils following neutron capture for dark matter calibration
• Detection and Calibration of Low-Energy Nuclear Recoils for Dark Matter and Neutrino Scattering Experiments
• Modeling Athermal Phonons in Novel Materials using the G4CMP Simulation Toolkit
• Neutron capture-induced silicon nuclear recoils for dark matter and CE$\nu$NS
• Intrinsic Fano factor of nuclear recoils for dark matter searches
• Novel coincidence detection technique for precision measurement of neutron-capture-induced nuclear recoils
• Phenomenological implications of the high-precision COHERENT germanium CE$\nu$NS data