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The Missing Mass Problem. Introduction to Dark Matter. Christof Sailer - Universität Tübingen EUROGRAD WORKSHOP 2008 - BLAUBEUREN. Outline. The history of Dark Matter Evidence for the existence of Dark Matter Theories to explain „Missing Mass“ Experimental Detection Methods

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    1. The Missing Mass Problem Introductionto Dark Matter Christof Sailer - Universität Tübingen EUROGRAD WORKSHOP 2008 - BLAUBEUREN

    2. Outline • The history of Dark Matter • Evidence for the existence of Dark Matter • Theories to explain „Missing Mass“ • Experimental Detection Methods • Current Experiments and status • Where we would like to get…

    3. Fritz Zwicky “If this [overdensity] is confirmed we would arrive at the astonishing conclusion that dark matter is present [in the Coma Cluster] with a much greater density than luminous matter.” … • 1933 Radial velocitiesof 8 galaxies in theComa Cluster (Abell 1656) measured • velocitydispersiontoohigh • densityobtained 400 timeshigherthanpreviouslypublishedresults “It is, of course, possible that luminous plus dark (cold) matter together yield a significantly higher density…”

    4. ApplyingtheVirial Theorem on theComa Cluster • 1937Zwicky used the Virial Theorem for the first time on a Galaxy Cluster to estimate the Mass • Reminder: Virial TheoremCentral, conservative potential depends on Cluster Mass

    5. Zwicky‘sresults… • Comparing measurments of the Mass-to-Light Ratio with his obtained value for the mass, he derived a ratio… with e.g. formainsequencestars

    6. … andhiscomment Calculatingthemeanluminosityof a ComanebulaandusinghisnewlyobtainedvaluefortheComa Cluster mass, he commentsthatthisis… He consideredthefollowingexplanations: Stars in theComa Cluster areof a different type The CC is not in equilibrium The lawsofphysics in CC are different Thereis a greatamountof Dark Matter in the CC He did not consider, thatHubble‘sconstantcouldbewrong! But evenusingtoday‘svalueleadsto a …

    7. MeasuringthemassofAstrophysical Systems • Mass-to-light ratio • Strong lensing (rare events) • Weak lensing effect • Rotation curves • System dynamics (Virial theorem) • Stability of X-ray emitting gas clouds

    8. „Missingmass“ onlycertain in Systems? Someevidence… System Size

    9. A contributionfromCosmology Cosmic Microwave Background • Imprint of Recombination -> Phonon decoupling„fossil density fluctuations“ Allows measuring the total matter density of the Universe and the baryonic matter density , thus giving a value for the cold, non-baryonic Dark Matter Density. • Measured with COBE between 1989 and 1993. 2006 – Nobel Prize for G. Smoot and J. MatherAngular resolution 7° (approx. 14 full moons) -> only large anisotropies detected

    10. WMAP The COBE mapand … The improvedmap

    11. WMAP - results

    12. Energycontentoftheuniverse

    13. Alternative interpretations - MoND • What if Newtons law needs to be modified at large scales?Modified Newtonian Dynamics – introduces an ad-hoc correction to explain flat rotational curvesrecently fuelled by the discovery of the Pioneer-Anomaly where The constant adjuststhedeviationfromNewton‘slaw proposedby M. Milgrom

    14. A strong caseagainstMoND Bullet Cluster (1E 0657-558) Source ofgravitational Potential ≠ Visible Matter! MACS J0025.4-1222 published in ApJ, August 2008(Bradac, M. et al, 2008, ApJ)

    15. Can MoNDtake a bullet? • Possibly…In [arXiv:astro-ph/0606216v1] G. W. Angus, B. Famaey, H.S. Zhao conclude, that it could work but only with Dark Matter in addition to a modified Newtonian Law • So it seems we will have to start looking for Dark Matter …

    16. DM Particle Zoo Promising Candidates • Axions • Heavy Relics – produced by fluctuations during inflation – Mass in the range of GUT-Scale > 1014 GeV/c2 • Heavy Neutrinos – m > 45 GeV (LEP constraint) • Primordial Black Holes • Gravitons (worst case scenario) • Heavy Higgs • Kaluza-Klein Particles, Universal Extra Dimensions • SUSY-Particles e.g. Neutralino There are about 200 more, depending on the way you count them…

    17. The Quest – Dark Matter Search • Indirect Methodslooking for signatures of Dark Matter Annihilation: Gammas, Antiprotons, Positrons… • Direct MethodsMeasure Recoil or other signatures of the unknown Dark Matter Particles

    18. IndirectSearches • CGRO EGRET: Gamma flux, point sources,will be followed by GLAST (Fermi GST) • AMS, AMS II – Looking for Antimatter excess • PAMELA – detecting charged Particles, recently claimed evidence for Antimatter excess possibly linked to DM annihilation • ANTARES, IceCube, NESTOR – detecting high energy neutrinos, also looking for Kaluza-Klein Particles in the sun and others… More can be found on the Dark Matter Portal by Frédéric Mayet:

    19. DirectSearches • Recoil + Ionizitaion: EDELWEISS (Fréjus), CDMS (Soudan Mine) • Noble Gases:XENON10, WARP, ZEPLIN II • Recoil+ Light: ROSEBUD, CRESST II • Modulation in rate, puls-shape analyses, DAMA/Libra, NAIAD, ANAIS More can be found on the Dark Matter Portal by Frédéric Mayet:

    20. DirectSearchesConcept - Recoil Mass mχ ~ GeV to TeV Velocity <v χ > ~ 270 km/s Local densityρ χ~ 0.3 GeV/cm3 Recoil energies in the keV range! Cross section < 10-36 cm2  Rare events! < 0.1/day/kg And there‘s a lot of background…

    21. Reducingthebackground • Going underground – reducing Cosmic Ray flux(e.g. Gran Sasso: 1 muon/m2/h) • Passive shielding against Neutrons and charged Particles (e.g. Lead, PE, Copper + Radon Box) • Muon Veto • „Active“ Veto: implement discrimination on event-by-event basis

    22. CRESST CryogenicRare Event SearchwithSuperconductingThermometers Passive Shieldingof ~ 42 tons: PE, Lead, Copper, Radon Box Muon Veto Cryostatfor Low-Temperatures ~ 8 – 12 mK, decoupledby a Coldfinger Holder structurewithminimizedamountof material, UHP Cu, electropolished

    23. CRESST 300 g CaWO4 Absorber Crystal at ~8-12 mK RecoileventleadstodepositionofEnergy via Phonons Temperaturerise MeasureΔT ~ serveralμK TES – Thermometers CaWO4 isscintillating, thusyoucan detectHeat & Light simultaneously Light also measuredcalorimetrically 350 300 250 200 150 100 50 0 ∆R Thermometer resistance [mW] ∆T 15 16 17 18 19 20 21 MC temperature [mK]

    24. CRESST • Discrimination of γ and charged particles from recoil events • Good energy resolution e.g. 300 eV @ 8.05 keV

    25. Whatyouget… • As both, σW-N and mχ are unknown, one shows the results in a 2d-Plot • The region above the line is excluded at 90% C.L. arXiv:0809.1829v1 [astro-ph]

    26. Status report • Target masses of a few kg • Best limit at the moment XENON10, CDMS • CRESST has been upgraded and is running again, Limit of comissioning run has been published, best European experiment • The DAMA Collaboration has hardend the case for the existence of a 1 yr modulation signal , yet there are by now 5 experiments excluding their region of acceptance…

    27. A fewwords on DAMA • DAMA evidence • Annual modulation with • Due to DM Densitymodulationcausedbytheannualrevolutionofthe Earth aroundthesun?

    28. ? PossibleExplanations ? DAMA evidenceexcludedby CDMS, Xenon10, CRESST II, Zeplin II and EDELWEISS with 90% C.L. • No Dark Matter Signal? Problems: Onlylowestenergybinsused, noMuon Veto… • Dark Matter doesnot consistofSUSY particlesandis not interacting via recoils? E.g. Axion- Dark Matter? Wouldgive a signal in theElectromagneticchannel – COUPP andothersareabletotestthis… • Still an open discussion ?

    29. LHC and Dark matter? LHC can discover SUSY particles… but even if SUSY particles are discovered, it is hard to determine contribution to ‘Dark Matter’ Ωh2 with good accuracy  we need direct / indirect detection experiments to prove new particles ARE Dark Matter SUSY ‘Benchmark’ Parameter Sets Complementarity can explore different parameters Cryogenic DM Exp. 25 kg Target LHC E.Baltz et al., Phys.Rev.D 74, 103521 (2006)

    30. Wherewewouldliketoget • Cross Sectiontobereached: 10-8 – 10-9pb • What will weneedtogetthere? Increase Target Mass/Exposure Reduce BackgroundWeneed a ton scaledetector, e.g. EURECA European Rare Event CalorimenterArray

    31. Beyondthestandard model Dark Matter SearchesmighthelptoanswerthefollowingQuestions: • Are therenewparticles? • Is SUSYimplemented in nature? • Are therenewinteractions/forces? • Is Newtons Law valid on large scales?

    32. Christof Sailer - Universität Tübingen EUROGRAD WORKSHOP 2008 - BLAUBEUREN Thank you for your attention!

    33. Backup slides: WMAP explained