Todd W. Hossbach

Results from a Search for Light-Mass Dark Matter with a p -Type Point Contact Germanium Detector

We report on several features in the energy spectrum from an ultralow-noise germanium detector operated deep underground. By implementing a new technique able to reject surface events, a number of cosmogenic peaks can be observed for the first time. We discuss an irreducible excess of bulklike events below 3 keV in ionization energy. These could be caused by unknown backgrounds, but also dark matter interactions consistent with DAMA/LIBRA. It is not yet possible to determine their origin. Improved constraints are placed on a cosmological origin for the DAMA/LIBRA effect.

CoGeNT: A Search for Low-Mass Dark Matter using p-type Point Contact Germanium Detectors

CoGeNT employs

Experimental constraints on a dark matter origin for the DAMA annual modulation effect

p

A shallow underground laboratory for low-background radiation measurements and materials development.

-type point-contact (PPC) germanium detectors to search for weakly interacting massive particles (WIMPs). By virtue of its low-energy threshold and ability to reject surface backgrounds, this type of device allows an emphasis on low-mass dark matter candidates (

The C-4 dark matter experiment

{m}_{\ensuremath{\chi}}\ensuremath{\sim}10\text{ }\text{ }\mathrm{GeV}/{c}^{2}

Development of portable multicoincidence radionuclide analysis systems

). We report on the characteristics of the PPC detector presently taking data at the Soudan Underground Laboratory, elaborating on aspects of shielding, data acquisition, instrumental stability, data analysis, and background estimation. A detailed background model is used to investigate the low-energy excess of events previously reported and to assess the possibility of temporal modulations in the low-energy event rate. Extensive simulations of all presently known backgrounds do not provide a viable background explanation for the excess of low-energy events in the CoGeNT data or the previously observed temporal variation in the event rate. Also reported for the first time is a determination of the surface (slow pulse rise time) event contamination in the data as a function of energy. We conclude that the CoGeNT detector technology is well suited to search for the annual modulation signature expected from dark matter particle interactions in the region of WIMP mass and coupling favored by the DAMA/LIBRA results.

A High-Efficiency Fieldable Germanium Detector Array

A claim for evidence of dark matter interactions in the DAMA experiment has been recently reinforced. We employ a new type of germanium detector to conclusively rule out a standard isothermal galactic halo of weakly interacting massive particles as the explanation for the annual modulation effect leading to the claim. Bounds are similarly imposed on a suggestion that dark pseudoscalars might lead to the effect. We describe the sensitivity to light dark matter particles achievable with our device, in particular, to next-to-minimal supersymmetric model candidates.

Alternative treaty monitoring approaches using ultra-low background measurement technology

Pacific Northwest National Laboratory recently commissioned a new shallow underground laboratory, located at a depth of approximately 30 meters-water-equivalent. This new addition to the small class of radiation measurement laboratories located at modest underground depths houses the latest generation of custom-made, high-efficiency, low-background gamma-ray spectrometers and gas proportional counters. This paper describes the unique capabilities present in the shallow underground laboratory; these include large-scale ultra-pure materials production and a suite of radiation detection systems. Reported data characterize the degree of background reduction achieved through a combination of underground location, graded shielding, and rejection of cosmic-ray events. We conclude by presenting measurement targets and future opportunities.

Real-Time Digital Signal-Processor Implementation of Self-Calibrating Pulse-Shape Discriminator for High-Purity Germanium

We describe the experimental design of C-4, an expansion of the CoGeNT dark matter search to four identical detectors each approximately three times the mass of the p-type point contact germanium diode presently taking data at the Soudan Underground Laboratory. Expected reductions of radioactive backgrounds and energy threshold are discussed, including an estimate of the additional sensitivity to low- mass dark matter candidates to be obtained with this search.

Operation of a high-purity germanium crystal in liquid argon as a Compton-suppressed radiation spectrometer

Abstract Multicoincidence radionuclide analysis systems consisting of light-charged-particle detectors operating in coincidence with photon spectrometers are being developed to improve the sensitivity of radionuclide analysis in field applications. Requiring charged-particle/photon coincidence provides active shielding from environmental photon sources, and mapping photon–photon events into a coincidence plane can remove photon spectroscopy interferences. List-mode data acquisition and flexible hardware design ensures that the most sensitive coincidence schemes involving β, atomic electron, γ and X-ray emissions can be used for radionuclide quantification. System hardware design and preliminary measurement data are discussed. A centerpiece component of this project, the development of analysis tools and data libraries required to perform automated multicoincidence analysis, is also described.