Solar and atmospheric neutrinos: Background sources for the direct dark matter searches

Physik-Department E15, Technische Universität München, D-85748 Garching, Germany
Astroparticle Physics (Impact Factor: 4.78). 03/2010; DOI: 10.1016/j.astropartphys.2010.06.002
Source: arXiv

ABSTRACT In experiments for direct dark matter searches, neutrinos coherently scattering off nuclei can produce similar events as Weakly Interacting Massive Particles (WIMPs). The calculated count rate for solar neutrinos in such experiments is a few events per ton-year. This count rate strongly depends on the nuclear recoil energy threshold achieved in the experiments for the WIMP search. We show that solar neutrinos can be a serious background source for direct dark matter search experiments using Ge, Ar, Xe and CaWO4 as target materials. To reach sensitivities better than ∼10−10 pb for the elastic WIMP nucleon spin-independent cross section in the zero-background limit, energy thresholds for nuclear recoils should be ≳2.05 keV for CaWO4, ≳4.91 keV for Ge, ≳2.89 keV for Xe, and ≳8.62 keV for Ar as target material. Next-generation experiments should not only strive for a reduction of the present energy thresholds but mainly focus on an increase of the target mass. Atmospheric neutrinos limit the achievable sensitivity for the background-free direct dark matter search to ≳10−12 pb.

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    ABSTRACT: The direct detection of dark matter through its elastic scattering off nucleons is among the most promising methods for establishing the particle identity of dark matter. The current bound on the spin-independent scattering cross section is sigma^SI < 10 zb for dark matter masses m_chi ~ 100 GeV, with improved sensitivities expected soon. We examine the implications of this progress for neutralino dark matter. We work in a supersymmetric framework well-suited to dark matter studies that is simple and transparent, with models defined in terms of four weak-scale parameters. We first show that robust constraints on electric dipole moments motivate large sfermion masses mtilde > 1 TeV, effectively decoupling squarks and sleptons from neutralino dark matter phenomenology. In this case, we find characteristic cross sections in the narrow range 1 zb < sigma^SI < 40 zb for m_chi > 70 GeV. As sfermion masses are lowered to near their experimental limit mtilde ~ 400 GeV, the upper and lower limits of this range are extended, but only by factors of around two, and the lower limit is not significantly altered by relaxing many particle physics assumptions, varying the strange quark content of the nucleon, including the effects of galactic small-scale structure, or assuming other components of dark matter. Experiments are therefore rapidly entering the heart of dark matter-favored supersymmetry parameter space. If no signal is seen, supersymmetric models must contain some level of fine-tuning, and we identify and analyze several possibilities. Barring large cancellations, however, in a large and generic class of models, if thermal relic neutralinos are a significant component of dark matter, experiments will discover them as they probe down to the zeptobarn scale.
    Journal of Cosmology and Astroparticle Physics 09/2010; 5(05). · 6.04 Impact Factor

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