CoGeNT: A search for low-mass dark matter usingp-type point contact germanium detectors

Abstract

CoGeNT employs p-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 (mχ ∼ 10 GeV/c 2 ). 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 on 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.PACS numbers: 85.30.-z, 95.35.+d

Complementarity of dark matter direct detection: the role of bolometric targets

“…Also, the CoGeNT collaboration (using a germanium target) observed an irreducible excess in their data [5] that, if interpreted in terms of WIMPs, would correspond to a very light particle, with mass in the range 7 − 12 GeV, and a large elastic scattering cross section, of order 10 −4 pb. Furthermore, hints of an annual modulation in the CoGeNT experiment were also claimed [6] but with a limited statistical significance of 2.8 σ in the first year data. Moreover, data presented by the CRESST collaboration (which uses CaWO 4 as target and beta/gamma background rejection) also displayed an excess that could be compatible with light WIMPs [7].…”

Dark matter effective field theory scattering in direct detection experiments

“…Numerous experiments are engaged in efforts to detect rare collisions between WIMPs and target nuclei in terrestrial detectors. Results from DAMA [3], CoGeNT [4], CRESST-II [5], and CDMS II Si [6] can be interpreted in terms of interactions of WIMPs with masses of 6-30 GeV/c 2 . A similar range of masses could also account for a possible excess in the gamma-ray flux near the galactic center in Fermi-LAT data [7,8].…”

Direct dark matter searches review

“…In another proposed model, the WIMP masses would be less than 10 GeV·c −2 (lower than the LEP bounds for neutralinos), combined with the possibility -discarded by now [22] -that recoiling ions in NaI have a high probability for channeling. Another hint of a low-mass WIMP had been the report by the CoGeNT collaboration [23] of an excess rate below 2 keV in a ionization-only detector (corresponding to ∼9 keV if the reduced ionization yield for nuclear recoils is taken into account), a claim inconsistent with a majority of observations by other experiments.…”