Solar and atmospheric neutrinos as background for direct dark matter searches Achim Gütlein TU-München Joined seminar on neutrinos and dark matter.0.0
utline Direct Dark Matter Search eutrinos as background for direct dark matter searches Coherent eutrino ucleus Scattering (CS) Solar neutrinos Solar neutrino count rates for different materials Atmospheric neutrinos as background source Limits for direct dark matter searches Conclusions Achim Gütlein (TU-München) eutrino background.0.0 / 0
Direct Dark Matter Search Hints for dark matter Dynamics in galaxies and galaxy clusters Colliding galaxy clusters WMAP data Achim Gu tlein (TU-Mu nchen) eutrino background.0.0 / 0
Direct Dark Matter Search Direct dark matter search Dark matter candidate: WIMP (Weakly Interacting Massive Particle) Assumption: WIMP scatters coherently off target nucleus Most direct dark matter search detectors can discriminate between electron (background) and nuclear recoils (signal) Achim Gütlein (TU-München) eutrino background.0.0 / 0
WIMP model Direct Dark Matter Search Spin independent interaction Elastic scattering WIMP scatters coherently off all nucleons Isothermal WIMP halo Recoil spectrum of WIMPs: dr(e rec ) de rec = c A ρ D πµ σ W (E rec ) A v 0 e cerec E 0 r E 0 c, c : constants describing the annular modulation of the WIMP flux, A : Avogadro s number, ρ D : local WIMP density, µ : reduced mass for A=, σ W : WIMP-nucleon cross section, v 0 : velocity of the earth relativ to the galaxy, A: mass number, E 0 : kinetic energy of the WIMPs, E rec : recoil energy, r = M DM T (M D +M T ) : kinematic factor, M D : WIMP mass, M T : mass of target nucleus Achim Gütlein (TU-München) eutrino background.0.0 / 0
WIMP recoil spectrum Direct Dark Matter Search Helm form factor: ( ) (q) j (qr) = e q s qr q: transferred momentum, j : spherical essel function, R: effectiv nuclear radius, s: nuclear skin thickness (E rec ) Argon Germanium Xenon Tungsten Iodine y ] ton count rate [kev Germanium Xenon Argon Sodium iodide Calcium tungstate Tungsten in CaW 0 0 0 0 00 0 00 recoil energy [kev] Recoil spectra for different materials: 0 0 0 0 0 60 0 0 90 0 recoil energy [kev] WIMP-nucleon cross section: cm ˆ= pb WIMP-mass: 60 GeV Achim Gütlein (TU-München) eutrino background.0.0 6 / 0
eutrinos as background for direct dark matter searches Coherent eutrino ucleus Scattering (CS) CS - A neutral current process ν x A 0 Z ν x A eutral current process CS independent of ν-flavor or low transferred momenta: Z 0 wave length comparable to radius of nuclei ν scatters coherently off all nucleons Achim Gütlein (TU-München) eutrino background.0.0 / 0
eutrinos as background for direct dark matter searches CS - Cross Section Coherent eutrino ucleus Scattering (CS) dσ(e ν, E rec ) de rec = G π [ ( Z sin θ W ) + ] M ( E ) recm Eν σ tot = G [ ( Z sin θ W ) + ] E π ν with neutrino energy E ν, recoil energy E rec, ermi constant G, Weinberg angle θ W, mass of traget nucleus M, proton number Z and neutron number. sin θ W = 0. σ tot G π E ν ut recoil energy E rec +Z. Higher neutron number higher cross section σ tot but also lower recoil energy E rec Achim Gütlein (TU-München) eutrino background.0.0 / 0
] eutrinos as background for direct dark matter searches Solar neutrinos Solar neutrinos s kev neutrino flux [cm 9 6 pp e neutrino energy [kev] eutrinos scattering coherently off a nucleus mimic a WIMP scattering event Strongest natural neutrino source: solar neutrinos Expected count rate for solar neutrinos is about per ton-year Solar neutrinos can be a background source for direct dark matter searches Achim Gütlein (TU-München) eutrino background.0.0 9 / 0
eutrinos as background for direct dark matter searches Count rates for argon Solar neutrino count rates for different materials Argon year ] ton count rate [kev 6 pp e total recoil energy [kev] Argon year ] [ton count rate R th pp e total recoil energy threshold [kev] E th [kev] 0.66. count rate per ton-year. 0. 0.0 Achim Gütlein (TU-München) eutrino background.0.0 / 0
eutrinos as background for direct dark matter searches Count rates for germanium Solar neutrino count rates for different materials year ] ton count rate [kev 6 Germanium pp e total recoil energy [kev] year ] [ton count rate R th Germanium pp e total recoil energy threshold [kev] E th [kev] 0.9. count rate per ton-year.6 0. 0.0 Achim Gütlein (TU-München) eutrino background.0.0 / 0
eutrinos as background for direct dark matter searches Count rates for xenon Solar neutrino count rates for different materials Xenon year ] ton count rate [kev 6 pp e total recoil energy [kev] year ] [ton count rate R th Xenon pp e total recoil energy threshold [kev] E th [kev] 0.9. count rate per ton-year.0 0. 0.0 Achim Gütlein (TU-München) eutrino background.0.0 / 0
eutrinos as background for direct dark matter searches Count rates for sodium iodide Solar neutrino count rates for different materials year ] ton count rate [kev 6 Sodium iodide pp e total recoil energy [kev] year ] [ton count rate R th Sodium iodide pp e total recoil energy threshold [kev] E th [kev] 0..6 count rate per ton-year. 0. 0.0 Achim Gütlein (TU-München) eutrino background.0.0 / 0
eutrinos as background for direct dark matter searches Count rates for calcium tungstate Solar neutrino count rates for different materials year ] ton count rate [kev 6 Calcium tungstate pp e total recoil energy [kev] year ] [ton count rate R th Calcium tungstate pp e total recoil energy threshold [kev] E th [kev] 0 6.9.0. count rate per ton-year. 0.. 0.0 Achim Gütlein (TU-München) eutrino background.0.0 / 0
eutrinos as background for direct dark matter searches Tungsten in calcium tungstate Solar neutrino count rates for different materials year ] ton count rate [kev 6 Calcium tungstate Calcium Tungsten xygen recoil energy [kev] Counts for larger recoil energies (> kev) mainly due to scatterings off oxygen It is possible to discriminate between W recoils and Ca or recoils Solar neutrino events with recoil energies > kev can be rejected Count rates for W in CaW E th [kev] 0.0. count rate per ton-year. 0. 0.0 Achim Gütlein (TU-München) eutrino background.0.0 / 0
eutrinos as background for direct dark matter searches Solar neutrino count rates for different materials Energy thresholds for different target materials Material 0. counts 0 counts Ar.66 kev. kev Ge.9 kev. kev Xe.9 kev. kev aj. kev.6 kev CaW 6.9 kev. kev W in CaW.0 kev. kev Energy threshold for CaW is given without discrimination between W, Ca and recoils Energy threshold for W in CaW is given with discrimination between W, Ca and recoils applied Achim Gütlein (TU-München) eutrino background.0.0 6 / 0
eutrinos as background for direct dark matter searches Recoil spectra of atmospheric neutrinos Atmospheric neutrinos as background source Count rates for solar neutrino thresholds are per ton-year. Atmospheric neutrinos limit the achievable sensitivity to cm. Achim Gütlein (TU-München) eutrino background.0.0 / 0
Limits for direct dark matter searches WIMP recoil spectrum y ] ton count rate [kev Germanium Xenon Argon Sodium iodide Calcium tungstate Tungsten in CaW 0 0 0 0 0 60 0 0 90 0 recoil energy [kev] Recoil spectra for different materials: WIMP-nucleon cross section: cm ˆ= pb WIMP-mass: 60 GeV Achim Gütlein (TU-München) eutrino background.0.0 / 0
Limits for direct dark matter searches Exclusion plots for optimal WIMP search regions ] wimp nucleon cross section [cm Germanium 6 Xenon Argon Sodium iodide Calcium tungstate Tungsten in CaW wimp mass [GeV] Exposure ton-year Achim Gütlein (TU-München) eutrino background.0.0 9 / 0
Conclusions Conclusions Solar neutrinos can be a background source for sensitivities below 6 cm ˆ= pb for the WIMP-nucleon cross section However, solar neutrino background can be rejected by a proper choice of the WIMP search region W and Xe are the best target materials for the direct dark matter search, if WIMP masses are GeV The discrimination between W, Ca and recoils is very important for the use of CaW as target material Atmospheric neutrinos become a background source for the direct dark matter search for sensitivities below cm ˆ= pb Achim Gütlein (TU-München) eutrino background.0.0 0 / 0