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Dark Matter Searches in Space Xin Wu

Dark Matter Searches in Space Xin Wu. Evidence for Dark Matter. Mass determined by light emission ≠ mass determined by motion ⇒ Dark “Mass”!. Visible objects in the universe moves faster than expected Velocities of stars in the Milky Way (1932, Oort)

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Dark Matter Searches in Space Xin Wu

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  1. Dark Matter Searches in SpaceXin Wu

  2. Evidence for Dark Matter Mass determined by light emission ≠ mass determined by motion ⇒ Dark “Mass”! • Visible objects in the universe moves faster than expected • Velocities of stars in the Milky Way (1932, Oort) • Velocities of galaxies in clusters (1933, Zwicky) • Rotational speeds of galaxies (galactic rotation curves) (1970, Rubin) -> Dark Matter halo • Gravitational lensing • Mass-to-light ratios obtained from strong and weak lensing effect correspond to dynamical measurements • The bullet cluster No other evidence that the Newton dynamics is invalid at large scales

  3. Dark Matter Searches SM DM indirect • Dark matter searches rely on interactions between DM and SM particles • Has not yet been seen! SM DM direct collider • “Direct searches”: DM-SM scattering • Look for nuclear recoil from galactic DM scattering • Very weak signal → deep underground, cryogenic DPNC participations! • “Indirect searches”: DM-DM annihilating to SM particles • Look for edges/bumps in SM particle spectrums in cosmic rays with ground-based or space observatories • “Collider searches”: production of DM particles via SM interactions • signature: missing Et (MET) (Johanna’s analysis in ATLAS) • Astronomical observations (“gravitational probes”) continue to explore the nature of the DM

  4. Indirect searches • DM-DM annihilations in our galaxy might give detectable signature of SM particles • n, g, e+, antiproton, antinuclei • Sensitive to high masses and different couplings ⇒ complementary to direct searches • challenges: astrophysical background and propagation • Annihilation rate ∝ r2DM⇒ more flux from regions of dense DM: galaxy clusters, galactic center, Sun, earth • BUT only neutrino (and somewhat g) can easily escape from these regions • Indirect signature depend on DM mass, annihilation cross section, DM-SM couplings • Very model dependent! ⇒ lots of fun for signal/limit interpretation

  5. Indirect search experiments • Ground-based detectors • Large acceptance (with arrays) • Resolution Is good for very high energies • Space detectors • Can detect all signatures except n • small acceptance

  6. Indirect search with neutrinos • Ground-based neutrino telescope • MACRO, SuperK, ANTARES, AMANDA/IceCube, … • Detect upward going muons from muon neutrinos interacting in the Earth • Setting limits on muon flux or annihilation cross section as function of mass • Model dependent, typically use MSSM with WW, bb, tt, mm, nn channels • s(annihilation) ∝ s(scattering) in the Sun because of equilibrium • ⇒ Relate result to direct searches Setting upper limit to s(annihilation) using some models of SUSY and halo profile

  7. Indirect search with gamma-ray • Ground-based Imaging Atmospheric Cherenkov telescopes • MAGIC, HESS, VERITAS, CTA, … • sensitive to g’s from 50 GeV – 50 TeV (>100 TeV for CTA) • Gamma-ray space telescopes • EGRET, FERMI/LAT, GAMMA-400, … • sensitive to g’s 20 MeV - 300 GeV, excellent pointing, mapping capability • Signature: Mono-energetic g-line from direct annihilation or continuum through annihilation into intermediate states • search in galactic dark matter halo, dwarf galaxies, galaxy clusters, galactic dark matter satellites, …

  8. Some results from gamma-ray telescopes Fermi/LAT dwarf galaxy search excluded WIMP below 25 GeV annihilating to b-bbar or t+t-, assume the DarkSUSY models No “smoking gun” (yet) in Fermi/LAT photon line search ⇒ constrain the gg and Zg annihilation cross section HESS J1745-290 Ground-based telescope has sensitivity for high energy (multi-TeV)

  9. Indirect search with charged particles • Annihilation of DM can add extra (stable) antiparticles (e+, pbar, antinuclei) to the cosmic ray but their detection can be done best above the atmosphere • high altitude balloons: BESS, CAPRICE, HEAT, BEST, ATIC, CREAM • satellites: PAMELA, GAMMA-400, … • space station: AMS2, CALET, … • Not always possible to put a magnet into the space • Look for structures in total spectra: e++e-, p+pbar, etc • Challenge: understand the galactic (charged) cosmic ray background • e-/p produced in SN explosion and accelerated in the shocks of the remnants • diffused in the galactic magnetic fields (mG): directions randomized • secondary e+/pbar produced in the collisions of primary proton with matter in the galactic disk • primary cosmic ray has a (broken) power law energy spectrum • Charged DM flux is affected by diffusion and, for e±, energy loss from synchrotron radiation and inverse Compton scattering on CMB and star-light

  10. Antiproton flux and ratio • Sensitivity reached 100 GeV (PAMELA) • In good agreement with cosmic ray models ⇒ can be used to ruled out some MSSM dark matter models AMS2 hurry up!

  11. Positron fraction e+/(e++e-) • Growing excess above 10 GeV • first observed in 1970’s, confirmed by PAMELA, Fermi/LAT, waiting for AMS2 • Astrophysical sources? • Pulsars? Primary e+? • DM? • would require very large annihilation cross section (or boost factor) and leptophilic models in order to to reconcile with the antiproton data of PAMELA • In general not favored • Multiple origins? remains a great puzzle!

  12. e++e- spectrum • “bump” at ~300-600 GeV reported first by ATIC, also seen by PPB-BETS • Fermi/LAT sees more like a “hardening” at ~100GeV and “softening” at ~1TeV • More data and new space detectors with thicker calorimeter will help to understand the high energy region • AMS2, CALET, DAMPE, … another puzzle!

  13. DAMPE • DAMPE: DArk Matter Particle Explorer • Chinese satellite experiment to be launched in 2015, mission time > 3 years • financed by the Chinese Academy of Sciences • High energy (GeV – 10 TeV) e/g detector to search for DM, also for cosmic ray studies and high energy g-ray astronomy • Baseline Detector Design: • Si-PIN charge detector (2.5x2.5 cm2) matrix, measure Z up to 20, DZ/Z~ 10% • Plastic Scintillatior strip telescope, cross section 2x1 cm2, 2 double layers (X,Y) • Interleaved with Tungsten plates • BGO imaging calorimeter • 305 crystal of 2.5x2.5x60 (cm3) • 14 layers, 31 X0 (total 33 X0) • multi dynode PMT+VA32 chip • Neutron detector (Boron doped plastic scintillator) for additional e/p separation

  14. DAMPE • Detector performance requirement • Detection of e/g of 5 GeV-10 TeV, energy resolution <1.5%@800GeV, pointing resolution <0.5°@800GeV, e/p separation >105, of e/g separation >20 • Detection of high energy cosmic ray 100 GeV – 100 TeV, energy resolution <40%@800GeV, pointing resolution <1°@1 TeV • Geometrical factor: e: >0.3 cm2∙sr, g: >0.2 cm2∙sr, p: >0.2 cm2∙sr • Collaborating institutes • Purple Mountain Observatory (PMO), Nanjing • University of Sci. & Tech. of China (USTC), Hefei • Institute of High Energy Physics (IHEP), Beijing • Institute of Modern Physics (IMP), Lanzhou • DPNC, Université de Genève • Participation of DPNC (Xin) • Coordination of test beam activities at CERN • Oct-Nov 2012 on H4 beam, calibration unit ~1/4 of full detector • Calibration and data analysis • Stepping stone to a more ambitious project ➯

  15. HERD • HERD: High Energy cosmic Radiation Detection facility • On board of the Chinese Space Station (~2020) • Proposed by the same community of the DAMPE • Much bigger GF, better energy and pointing resolutions, sensitive to very high energy cosmic rays (“knee region” ~1 PeV) • Two main goals: DM search and origin of galactic cosmic rays P (<A>~ 1) He (<A>~ 4) L (<A>~ 8) M (<A>~ 14) H (<A>~ 25) VH (<A>~ 35) Fe (<A>~ 56) • 305 crystal of 2.5x2.5x60 (cm3) • 14 layers, 31 X0 (total 33 X0) • multi dynode PMT+VA32 chip • Except for L (<A> ~ 8), PeV spectra feasible with GF~2-3 in several years. • Neutron detector (Boron doped plastic scintillator) for additional e/p separation s_yqxu 1986born 10-event sensitivities 1 PeV

  16. HERD conceptual detector design • Shower Tracker • W: 10x3.5mm + 2x17.5mm + 2x35mm (4X0 = 1.6l) • Scin. Fibers: 14 X-Y double layers, 1x1mm2, 1m long • Charge detector: Si-PIN (1cm×1cm×500mm) • Top: 2x(1mx1m), 4 Sides: 2x(1mx40cm) • Nucleon Tracker with Scin. Fibers • ECAL: 16X0 = 0.7l • PWO bar: 2.5x2.5x70cm3 • 6 layers alternate in X-Y PWO W+ CsI(Na) + Fiber + ICCD • HCAL: 30 layers of W plates + CsI cells • W: 30x3.5mm, 3X0 = 1.2 l • CsI cell:2.5x2.5cm2x0.2cm • Neutron detector: B-doped plastic scintillator with delayed signals

  17. Comparison of missions • The mains goals of the HERD detector design • Better energy resolution (e/g), larger geometrical factor (cosmic ray) and high energy reach (e/g and cosmic ray)

  18. Current Status of HERD • Mission concept (science goals with requirements) selected by JESSA of CAS • General Establishment of Space Science and Application, agency in charge of the selection of scientific mission • Conceptual detector design reviewed in Feb 2012, further technical review • final selection decision expected later this year • Simulation and detector optimization are just started • international collaborations are welcome at all levels • DPNC (Martin, Xin) have expressed interest in participating in the project • detector optimization, in particular using Si strips instead of scintillating fibers for the shower tracker • ECAL and Trigger electronics also potential collaboration areas • Swiss Industrial participation • Intention well received by GESSA • Good contact already exist through POLAR and DAMPE • By associating early, we can hope to play a major role in the project once it is concretized

  19. Conclusions • The nature of the DM is on of the most fundamental questions in astronomy, astrophysics, astroparticle physics, cosmology and particle physics • There is a small industry of DM search • Underground, underwater, under-ice, on the ground, in the space, … • DPNC has already involved in many of these experiments and a transverse synergy is emerging • IceCube, AMS, ATLAS, CTA • Also DPT • Can further develop this synergy by participating in the new space based projects (DAMPE and HERD) • People interested are very welcome to join

  20. Extra slides

  21. How much dark matter in the Universe? • Can be estimated from observations of clusters of galaxies • radial velocities, hot gas distribution, gravitational lensing → relic density: WDM ~ 0.2-0.3 (WX ≡rX/rcrit, rcrit : density of a flat Universe) • Can be obtained by a global fit of cosmological parameters assuming the “standard model of big bang cosmology” (LCDM) • observations: anisotropy of CMB (WMAP), large-scale structure (galaxy surveys) , Type Ia supernovae survey • → WL ≈ 0.72, WDM ≈ 0.23, Wb ≈ 0.05

  22. Nature of Dark Matter • Dark matter unlikely to be baryonic (MACHOs: Massive Compact Halo Objects) • Neutron stars, brown dwarf, planets, primordial black holes • ruled out by anisotropy of CMB, large-scale structure and big-bang nucleosynthesis (BBN) • Not observed by direct searches with microlesing (MACHO, EROS, OGLE) • Dark Matter is unlikely to be “hot” • Thermally produced ultrarelativistic particles (m<keV) prevent early formation of small structure of the Universe • inconsistent with the observed age of galaxies • SM neutrino severely constrained by CMB + large-scale structure observation • Wnh2 ≤ 0.0062 @ 95%CL (WMAP+BAO+H0) • Favored candidates: “non-baryonic cold dark matter” (CDM) ⇒ BSM physics! • Massive (~10 GeV-TeV) : Weakly Interacting massive particles (WIMP) • Created thermally in the early universe: SUSY LSP, KK states, … • Light: axion, keV sterile neutrino, … • Created non-thermally through phase transition or mixing

  23. DM-SM interaction • The strength of DM-SM interaction is constrained by the observed present DM relic density • WIMP pair annihilation cross section into SM particles determines the time at which WIMPs dropped out of thermal equilibrium (annihilation rate < expansion rate) ⇒ ~1 pb annihilation cross section gives correct relic density Number density time

  24. Direct Searches • Assume stationary DM halo in the galactic frame • The earth traverses the DM halo at ~230±15 km/s • At this speed DM-SM scattering is mainly elastic • Typical nuclear recoil energy is ~1-100 keV for WIMP of 10 GeV – 10 TeV • Recoil energy spectrum is approximately exponential • Resulting from the convolution of the Maxwellian distribution of the DM velocity and the model dependent DM-nuclei cross section ⇒ low threshold detectors (eg. Ge) more sensitive to WIMP of low mass • Cross section depends on the nature of DM-SM coupling • Spin-independent (SI) and spin-dependent (SD) • SI cross section scales as A2⇒ use heavy target nuclei, eg. Xe • Event rate depends on WIMP flux (~rv/M) and scattering cross section • Typically < 1 event/day/kg ⇒ need large target and low background site • Detection of the recoil energy • Ionization and/or scintillation and/or heat

  25. (Many) Direct Search Experiments • Starting from a 0.8 kg Ge ionization detector at Homestake Mine in 1986 … • sensitivity is reaching ~1 event/100kg/year (for 60 GeV WIMP) From Gaitskell

  26. Examples of direct search experiments • Pure germanium detector for ionization detection • Homestake, Heidelberg-Moscow, IGEX, (GERDA, MAJORANA) • CoGeNT, CDEX/TEXONO: very low energy threshold (sub-keV) • CoGeNT observed excess at 7-11 GeV • Crystal (NaI) detector for scintillation detection • DAMA/LIBRA, NaIAD, DM-Ice ⇒ DAMA/LIBRA observed annual modulation • Cryogenic detector for heat (vibration) detection • Heat and ionization detection with semiconductor: CDMS, Edelweiss • Heat detection with CaWO4crystal: CRESST ⇒ observed some excess • Nobel liquid detector for ionization and scintillation detection • ZEPLIN, XENON, XMASS, PANDA-X, LUX, ArDM … • Best DM limit from XENON100 ⇒ ruled out all positive claims above! • TPC to measure the direction of the nuclear recoils • DRIFT, MIMAC, DMTPC, …

  27. Current results of direct searches • Expressed as contour or excluded region in the WIMP mass – cross section plane • For fixed density, WIMP flux scales with inverse mass • SI cross section, normalized to nucleon assuming sN = A2sSI

  28. Collider searches • DM can be produced at the colliders if √s is sufficient • coupling is unknown, but cross section constrained by DM relic density • signature is MET (or nothing if pair produced back-to-back!) • Two main strategies of searches • “model” search: if a BSM model contains a DM candidate, search for all signatures (typically involving MET) → constrain the model → constrain DM phenomenology → compatibility with the relic density • SUSY, ED, Little Higgs, … • “generic” search: look for events with large MET, balanced by one ISR jet/photon → constrain rate → constrain “effective coupling” (vector, axial-vector, scalar) → constrain DM-nucleon cross section (SI and SD) • effective theory is only valid for heavy mediators; light mediators needs to be included explicitly with assumption on their masses (typically better limits for masses ≥ 100 GeV)

  29. Results from collider searches • But experimentalist are catching up fast! • Many DM interpretations of collider searches are done by phenomenologists

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