Dark Matter Lecture 1: Evidence and candidates March 27, 2012 Dark matter lectures University of Sao Paulo Laura Baudis, Universität Zürich 1 Content: first lecture • Overview: cosmological parameters in the standard model of cosmology • Dark matter in galaxies and in the Milky Way structure of the Milky Way galactic rotation curve and what can we learn from it dark matter distribution simulations of the Milky Way’s dark halo - spatial distribution of dark matter - velocity distribution of dark matter - the dark matter disk • Candidates for dark matter, overview neutrinos WIMPs and freeze-out candidates from supersymmetry - allowed parameter space in a constrained SUSY model 2 Content: second lecture • Direct detection of WIMPs: principles expected rates in a terrestrial detector kinematics of elastic WIMP-nucleus scattering differential rates corrections I: movement of the Earth corrections II: form factors cross sections for scattering on nucleons - spin independent - spin dependent • Expected WIMP signal and backgrounds time and directional signal dependance quenching factors and background discrimination background sources in direct detection experiments detector strategies: overview 3 Content: third lecture • Overview of experimental techniques example: theoretical predictions and experimental limits vanilla exclusion plot WIMP mass and cross section determination complementarity between different targets and astrophysical uncertainties • Cryogenic experiments at mK temperatures Principles of phonon mediated detectors Detection of fast and thermalized phonons Temperature measurements: thermistors, SC transition sensors (SPT, TES) • Phonon and light detectors Example: CRESST • Phonon and charge detectors Examples: CDMS, EDELWEISS • Future detectors Challenges; examples: SuperCDMS, EURECA, GEODM 4 Content: fourth lecture • Liquid Noble Element Experiments Principles and properties of noble liquids Charge and light in noble liquids Calibration issues (electronic and nuclear recoils) • Single Phase Experiments Principles Examples: XMASS, DEAP/CLEAN • Double Phase Experiments Principles Examples: XENON, ZEPLIN, ArDM, WARP, LUX • Future detectors Challenges Examples: DARWIN, MAX, LZS • Overall summary and conclusions 5 Literature 1. “Particle Dark Matter”, editor Gianfranco Bertone; Cambridge University Press, December 2009 2. Cold thermal relics: “The Early Universe”, by Edward W. Kolb, Michael S. Turner, Addison Wesley, 1990 3. Introduction to supersymmetry: “Weak Scale Supersymmetry”, by Howard Baer, Xerxes Tata, Cambridge University Press, 2006 4. Direct and indirect detection: “Supersymmetric Dark Matter”, by G. Jungmann, M. Kamionkowski and K. Griest, Physics Reports 267 (1996) 5. Principles of direct dark matter detection: “Review of mathematics, numerical factor and corrections for dark matter experiments based on elastic nuclear recoils”, by J.D. Lewin and P.F. Smith, Astroparticle Physics 6 (1996) 6. Reviews of direct detection experiments: “Direct Detection of Dark Matter” by R.J. Gaitskell, Ann. Rev. Nucl. Part. Sci. 54 (2004), L. Baudis, “Direct Detection of Cold Dark Matter” SUSY07 Proceedings 7. Low background techniques: “Low-radioactivity background techniques” by G. Heusser, Ann. Rev. Part. Sci. 45 (1995) 8. Particle Astrophysics: “Particle and Astroparticle Physics” by U. Sarkar. Taylor & Francis 2008; “Particle Astrophysics” by D. Perkins, Oxford University Press 2003 9. mK Cryogenic Detectors: “Low-Temperature Particle Detectors”, by N.E. Booth, B. Cabrera, E. Fiorini, Annu. Rev. Nucl. Part. Sci. 46, 1996 10.Liquid xenon detectors: “Liquid xenon detectors for particle physics and astrophysics”, by E. Aprile and T. Doke, Reviews of Modern Physics, Volume 82, 2010 11. 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This matter, different from atoms, does not emit or absorb light. It has only been detected indirectly by its gravity. • 72% of the universe, is composed of "dark energy", that acts as a sort of an anti-gravity. This energy, distinct from dark matter, is responsible for the present-day acceleration of the universal expansion. Credit: NASA / WMAP Science Team 8 The Standard Model of Cosmology • Cosmological Parameters (WMAP7) ➡ Total matter and energy density: Ωtot = 1.02 ± 0.02 ➡ Total matter density: Ωm = 0.266 ± 0.029 ➡ Density of baryons: Ωb = 0.0449 ± 0.0028 ➡ Energy density of the vacuum: ΩΛ = 0.743 ± 0.029 ➡ Hubble constant: H0 = (71.0 ± 2.5) km/s/Mpc ➡ Age of the Universe: τU = (13.75 ± 0.13) Gy http://lambda.gsfc.nasa.gov/product/map/current/parameters.cfm 2 expansion rate 3H0 −27 −3 ρ ρc ≡ = 9.47 × 10 kg m a& Ω ≡ x 8πG H(t) ≡ x a ρc 3 ⇢ 6H atoms m− c ' − a(t) = scale factor, describes the expansion of the Universe density parameter critical density 9 Dark Matter in the Milky Way and in galaxies 10 The MilkyASTRO II, S SWay06 as9.1 Inater sgalaxytellarer Staub 93 Die Milchstraße im optischen Spektralbereich • Complex system made of stars, dust, gas and dark matter Sternlicht, starke Absorption durch Dunkelwolken (Staub) 11 93 The Milky Way as a galaxy, initial remarks • Its study has proven to be quite challenging, as we live at the edge of a disk of stars, dust and gas that severely impacts our ability to “see” beyond our stellar neighborhood when we look along the plane of the disk, and the problem is most severe when we look towards the Galactic Center (GC) • Much of what is known today about the formation and evolution of our galaxy is encoded in the motion of its constituents • Measuring this motion is complicated, because it occurs from an “observing platform” that is itself undergoing a complex motion that involves the motion of the Earth around the Sun and the Sun’s path around the Galaxy • As we shall see, the detailed study of these motions lead to the conclusion that the luminous, baryonic matter in the Galaxy is only a small fraction of what the Milky Way is composed of COBE near IR view 12 Structure of the Milky Way • The Milky Way consists of: galactic thin disk (scale height* zthin ≈ 350 pc), composed of relatively young stars and region of current star formation galactic thick disk (zthick ≈ 1000 pc), composed of an older population of stars; the stars per unit volume is only about 8.5% of the one in the think disk galactic bulge visible (stellar) halo dark halo dark disk (new!) • The diameter of the disk (including dust, • The distance Sun - Galactic Center (GC) stars and gas) is: D ≈ 50 kpc R0 = 8.5 kpc (official value, IAU 1985) new value R0 = 8.0±0.5 kpc * one scale height (z) = the distance over which the number density decreases by e-1 13 Mass-to-light ratio • Based on data from star counts and orbital motions, the estimated stellar mass of the thin disk is roughly: 6 1010M ⇠ ⇥ • To this, we must add the contribution from dust and gas: 0.5 1010M ⇠ ⇥ • The luminosity of stars in the think disk in the blue-wavelength band is: 10 LB 1.8 10 L ' ⇥ • From this, we obtain a mass-to-light ratio of: M M 3 LB L ' • For the thick disk, the blue-band luminosity is ~ 1% of the one of the thin disk, with the mass around 3% of the thin-disk mass (it has been much more difficult to detect; diagnostic importance for the dynamics of the disk); the bulge is very similar to the thin disk.