Solar and Atmospheric Neutrinos: Background Sources for the Direct Dark Matter Searches

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 CaWO_4 as target materials. To reach sensitivities better than approximatly 10^-10 pb for the elastic WIMP nucleon spin-independent cross section in the zero-background limit, energy thresholds for nuclear recoils should be approximatly >2.05 keV for CaWO_4, >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 approximatly >10^-12 pb.Comment: accepted by Astroparticle Physic

Optical Scattering Lengths in Large Liquid-Scintillator Neutrino Detectors

For liquid-scintillator neutrino detectors of kiloton scale, the transparency of the organic solvent is of central importance. The present paper reports on laboratory measurements of the optical scattering lengths of the organic solvents PXE, LAB, and Dodecane which are under discussion for next-generation experiments like SNO+, Hanohano, or LENA. Results comprise the wavelength range from 415 to 440nm. The contributions from Rayleigh and Mie scattering as well as from absorption/re-emission processes are discussed. Based on the present results, LAB seems to be the preferred solvent for a large-volume detector.Comment: 9 pages, 3 figures, accepted for publication by Rev. Scient. Instr

GNO Solar Neutrino Observations: Results for GNOI

We report the first GNO solar neutrino results for the measuring period GNOI, solar exposure time May 20, 1998 till January 12, 2000. In the present analysis, counting results for solar runs SR1 - SR19 were used till April 4, 2000. With counting completed for all but the last 3 runs (SR17 - SR19), the GNO I result is [65.8 +10.2 -9.6 (stat.) +3.4 -3.6 (syst.)]SNU (1sigma) or [65.8 + 10.7 -10.2 (incl. syst.)]SNU (1sigma) with errors combined. This may be compared to the result for Gallex(I-IV), which is [77.5 +7.6 -7.8 (incl. syst.)] SNU (1sigma). A combined result from both GNOI and Gallex(I-IV) together is [74.1 + 6.7 -6.8 (incl. syst.)] SNU (1sigma).Comment: submitted to Physics Letters B, June 2000. PACS: 26.65. +t ; 14.60 Pq. Corresponding author: [email protected] ; [email protected]

Complete results for five years of GNO solar neutrino observations

We report the complete GNO solar neutrino results for the measuring periods GNO III, GNO II, and GNO I. The result for GNO III (last 15 solar runs) is [54.3 + 9.9 - 9.3 (stat.)+- 2.3 (syst.)] SNU (1 sigma) or [54.3 + 10.2 - 9.6 (incl. syst.)] SNU (1 sigma) with errors combined. The GNO experiment is now terminated after altogether 58 solar exposure runs that were performed between May 20, 1998 and April 9, 2003. The combined result for GNO (I+II+III) is [62.9 + 5.5 - 5.3 (stat.) +- 2.5 (syst.)] SNU (1 sigma) or [62.9 + 6.0 - 5.9] SNU (1 sigma) with errors combined in quadrature. Overall, gallium based solar observations at LNGS (first in GALLEX, later in GNO) lasted from May 14, 1991 through April 9, 2003. The joint result from 123 runs in GNO and GALLEX is [69.3 +- 5.5 (incl. syst.)] SNU (1 sigma). The distribution of the individual run results is consistent with the hypothesis of a neutrino flux that is constant in time. Implications from the data in particle- and astrophysics are reiterated.Comment: 22 pages incl. 9 Figures and 8 Tables. to appear in: Physics Letters B (accepted April 13, 2005) PACS: 26.65.+t ; 14.60.P

The LAGUNA design study- towards giant liquid based underground detectors for neutrino physics and astrophysics and proton decay searches

The feasibility of a next generation neutrino observatory in Europe is being considered within the LAGUNA design study. To accommodate giant neutrino detectors and shield them from cosmic rays, a new very large underground infrastructure is required. Seven potential candidate sites in different parts of Europe and at several distances from CERN are being studied: Boulby (UK), Canfranc (Spain), Fr\'ejus (France/Italy), Pyh\"asalmi (Finland), Polkowice-Sieroszowice (Poland), Slanic (Romania) and Umbria (Italy). The design study aims at the comprehensive and coordinated technical assessment of each site, at a coherent cost estimation, and at a prioritization of the sites within the summer 2010.Comment: 5 pages, contribution to the Workshop "European Strategy for Future Neutrino Physics", CERN, Oct. 200

Low-Temperature Light Detectors: Neganov-Luke Amplification and Calibration

The simultaneous measurement of phonons and scintillation light induced by incident particles in a scintillating crystal such as CaWO4 is a powerful technique for the active rejection of background induced by gamma's and beta's and even neutrons in direct Dark Matter searches. However, less than ~1% of the energy deposited in a CaWO4 crystal is detected as light. Thus, very sensitive light detectors are needed for an efficient event-by-event background discrimination. Due to the Neganov-Luke effect, the threshold of low-temperature light detectors based on semiconducting substrates can be improved significantly by drifting the photon-induced electron-hole pairs in an applied electric field. We present measurements with low-temperature light detectors based on this amplification mechanism. The Neganov-Luke effect makes it possible to improve the signal-to-noise ratio of our light detectors by a factor of ~9 corresponding to an energy threshold of ~21 eV. We also describe a method for an absolute energy calibration using a light-emitting diode.Comment: additional figure, other figures improve