Direct Dark Matter Searches Elements of a Strategy

Transcription

1 Bernard Sadoulet Dept. of Physics /LBNL UC Berkeley UC Institute for Nuclear and Particle Astrophysics and Cosmology (INPAC) Direct Dark Matter Searches Elements of a Strategy Inputs from Cosmology and Particle Physics Non baryonic cold dark matter Axions: a dynamic way to restore CP invariance WIMPs: a generic consequence of new physics at TeV scale Axions WIMPs We need three approaches: accelerators, direct detection and indirect detection The direct detection challenges Current status Results DAMA: tension with other experiments 1

2 Tomorrow The road to larger mass Comparison of the various technologies Importance of discrimination/ fiducial volume => zero background Need for directional detectors Challenges A roadmap for the future 2 phases: Next 5 years exploration of technology+ push science frontier By 2014 converge on 2 technologies (maybe 3 world wide) +directional detector as soon as we have a discovery 2

3 Relationship with other talks Complementary to Talk this afternoon by Gabriella Sciolla: She will focus on individual experiments and their current results I will focus on the overall picture, providing today background to her talk and elaborating on the overall strategy of the field tomorrow. Lectures by Max Tegmark Neil Weiner Jan Conrad Even if there is overlap, the differences in perspective may be interesting. 3

4 What generic class(es) to look for? Fundamental Physics in particular 2 justifications experimental consequences What approach? Privilege unambiguous information minimize gastrophysics Complementary approaches e.g. Direct detection Indirect detection Colliders What sensitivity goals? Identify natural scale + fine tuning Previous results Cross checks What technology? Highly discriminative Large amount of information: rare events pathological configuration Identification of background Highly iterative Strategies 4

5 1.Input from Cosmology and Particles Physics A surprising but consistent picture Standard Model of Cosmology Ω Λ Ω matter Not ordinary matter (Baryons) Ω m >> Ω b = ± from Nucleosynthesis WMAP NASA/WMAP Science Team 2006 χ + internally to WMAP Ω m h2 Ω b h 2 15 σ's Mostly cold: Not light neutrinos small scale structure 5

6 1.Input from Cosmology and Particles Physics Dark Matter is cold Cold Non relativistic when comes out of the horizon time of galaxy formation Tegmark,Zeldarriaga Astro-ph/ light neutrinos = Hot erase density fluctuations at small scale baryonic Neutrinos Recurrent appeal to warm dark matter or mixed (Cold +hot) to soften spectrum Severely limited by Lyman alpha systems 6

7 c1.input from Cosmology and Particles Physics Large Scale Structure Non baryonic dark matter is an essential ingredient of our understanding of structure formation Galaxy scale: disk + halo Intermediate scale: hierarchical merging Power spectrum Amazing first approximation HST Ultra Deep Field Great increase in numerical accuracy particles e.g.halo substructure and merging history Hydrodynamics (although still course feedback mechanisms) 7

8 1.Input from Cosmology and Particles Physics Challenges Too peaked a distribution in center of galaxies Cusp problem :Navaro-Frenk-White profile density r -1 Dwarf spheroidals : mostly underestimate of beam smearing Low surface brightness galaxies (Blitz); when no radial motion r -1 Non-circular motions could be caused by nonspherical halos (Navarro & Hayashi). Large galaxies? Halo substructure <=Merging histories missing satellites Problems with simulatiion: e.g. Loss of gas => agreement with data. Angular momentum problem Catastrophic loss of angular momentum in current hydrodynamics simulations => difficulty to form spiral galaxies Formation and role of AGN? A long history of overcoming challenges 8

9 1.Input from Cosmology and Particles Physics Standard Model of Particle Physics Fantastic success but Model is unstable Why is W and Z at 100 M p? Need for new physics at that scale supersymmetry additional dimensions Flat: Cheng et al. PR 66 (2002) Warped: K.Agashe, G.Servant hep-ph/ In order to prevent the proton to decay, a new quantum number => Stable particles: Neutralino Lowest Kaluza Klein excitation QCD violates CP Dynamic stabilization by a Peccei-Quinn axion? Gravity is not included and we do not understand vacuum energy Always the danger of a failure of General Relativity and that dark matter is part of a new set of epicycles that we invent to adjust theory to increasingly accurate data 9

10 1.Input from Cosmology and Particles Physics Variety of candidates L. Roszkowski 10

11 Method of detection Axions Invented to save QCD from strong CP violation Current experimental limits are such that if they exist, they have to be cosmologically significant Window: ev Produced out of equilibrium Theoretical discussion if Peccei Quinnn symmetry breaking occurs after inflation => global strings which radiate axions. Technically difficult to compute (Shellard Sikivie) Loss mass region may be not favored m a = 0.62eV 107 GeV L aγγ = α em 2π f a f a E. B O 1 ( ) Tunable cavity: Most suitable for low mass region 11

12 Axions Microwave technology Reaching cosmologically interesting range With new SQUID microstrip amplifier (nearly quantum limited) -> lowest range of coupling ADMX will cover lowest decade of 3 decades still open 12

13 Galactic Axion DAMA: An axionic type particle of 3 kev converting its mass into electromagnetic energy in detector Modulation by flux Can be in principle checked by other detectors: being done by CDMS+ CoGeNT! arxiv: Assumes that σ A v 13

14 Solar Axions Emitted by Sun Convert in a magnet : Helioscope: Tokyo, CAST Crystal: Bragg condition Make you own GAMEV (Fermilab) Pay the price of g 4 14

15 WIMPs Bringing both fields together: a remarkable concidence Particles in thermal equilibrium + decoupling when nonrelativistic Freeze out when annihilation rate expansion rate Ω x h 2 = cm 3 / s σ A α 2 σ A v 2 M Generic Class EW Cosmology points to W&Z scale Inversely standard particle model requires new physics at this scale (e.g. supersymmetry or additional dimensions) => significant amount of dark matter Weakly Interacting Massive Particles 2 generic methods: Direct Detection= elastic scattering Indirect: Annihilation products + Large Hadron Collider 15 γ s e.g. 2 γ s at E=M is the cleanest ν from sun &earth elastic scattering dependent on trapping time e +, p

16 3 Complementary Approaches CDMS Halo made of WIMPs 1/2 shown for clarity WIMP scattering on Earth: e.g. CDMS : currently leading the field WIMP production on Earth HESS GLAST GLAST/Fermi Launched 11 June 2008 WIMP annihilation in the cosmos 16

17 We need all three approaches Direct detection May well provide a detection + cross section and mass But what is the fundamental physics behind it? What can we learn about the galaxy? LHC May well give rapidly evidence for new physics: missing energy But is it stable? => need direct or indirect detection Ambiguity in parameters: mass/cross section Indirect detection May well provide smoking gun for both dark matter and hierarchical structure formation (subhalos) But possible ambiguity in interpretation => need direct detection Complementary sensitivity to different parameter space region 17

18 Complementarity msugra/cmssm Taking as a guide msugra/constrained Minimum SuperSymmetric model (4 parameters +1 sign) (but take with grain of salt!) Direct Detection: Bulk +Focus point LHC low energy 1 fb -1 Fermi Focus + Higgs funnel 100/pb Take with grain of salt

19 If Maxwellian in galaxy rest frame f ( v' )d 3 v' = 1 v o 3 π exp v'2 3 / 2 v o 2 d 3 v' Annual modulation ±4.5% 19 Elastic Scattering Rates Energy deposition cf J.D Lewin and P.F. Smith AstroPart. Phys. 6(1996) 87 Simple non relativistic calculation E d = q2 m 2 χ m N = 2m N ( m χ + m N ) 2 v2 1 cosθ * s-wave scattering: ( ) = m 2 r ( ) m N v 2 1 cosθ * for given velocity v, flat between 0 and E d max = 2m r v 2 m N Convolution with velocity distribution in the halo differential rate per unit mass dr = σ oρ o 2 F 2 de d 4v e m χ m r dr de d ( q ) erf v min + v e erf v min v e v o v o where 4m dσ ( q = 0) 2 r v σ o = 2 d( q d q 0 2 ) 2 ρ o = local density of halo v min = E 2 dm N 2 2m r 2π t 2ndJune v e = v o cos 2 ( ) = independent of v ( ) 1yr E d

20 Elastic scattering Nearly Exponential Continuous full calculation Dotted=exponential dsigma/der !1 10!2 10!3 WIMP spectra e+03 1e+04 Ge MWIMP= GeV/c 2 10!4 10!5 Difference between electron and nucleus recoil energy deposition True for ionization and scintillation Little effect on phonons (measure total energy) 10! Recoil energy (kev) 20

21 Coherent Scattering The energy transfer is small compared to inverse size of nucleus Conventionally Spin independent : additive quantum number is mass, number of protons or neutrons! Usually scalar interaction dominates Cross sections A 2 + filled sphere form factor Spin dependent : additive quantum number is spin First order interaction of Majorana spin 1/2 particle is axial vector -> spin at low energy depends on spin content of the nucleus (Most nuclei spinless) Spin is never very large: usually <2nd order Uncertainties on spin content of nucleon + Peripheral form factor 21

22 Direct Detection Elastic scattering Expected event rates are low (<< radioactive background) Small energy deposition ( few kev) << typical in particle physics Signal = nuclear recoil (electrons too low in energy) Background = electron recoil (if no neutrons) dn/de r Expected recoil spectrum Signatures Nuclear recoil Single scatter neutrons/gammas Uniform in detector Linked to galaxy Annual modulation (but need several thousand events) Directionality (diurnal rotation in laboratory but 100 Å in solids) E r 22

23 Challenges Three General Challenges Understand/Calibrate detectors Be background free much more sensitive than background subtraction (eventually limited by systematics) Increase mass while staying background free log sensitivity sensitivity MT sensitivity MT sensitivity constant log(exposure=target mass M time T) 23

24 1. Particle Cosmology and WIMPs 2. WIMPs: current status 3. The road to high target mass Experimental Approaches A blooming field Direct Detection Techniques Xe, Ar, Ne NaI, Xe, Ar, Ne ZEPLIN II, III XENON WARP ArDM SIGN NAIAD ZEPLIN I DAMA XMASS DEAP Mini-CLEAN Scintillation Few % of Energy Ge, CS 2, C 3 F 8 DRIFT IGEX COUPP ~20% of Energy Ionization Heat - CRESST II ROSEBUD!"#$ % &'()$ Phonons *+#$ % &',-. $ / 0 ~100% of Energy CDMS Ge, Si EDELWEISS CRESST I Al 2 O 3, LiF As large an amount of information and a signal to noise ratio as possible At least two pieces of information in order to recognize nuclear recoil extract rare events from background (self consistency) + fiducial cuts (self shielding, bad regions) 24

25 Detection Techniques Method Detection Electron recoil Nuclear recoil Discrimination Groups Scintillation e.g. NaI Light 200eV/ photoelectron I: 1600eV/ photoelectron Pulse shape DAMA, UK NaI, Elegant nitrogen Electrons + holes 3eV/carrier 9eV/carrier No Heidelberg-Moscow Gas Ionization electrons 20eV/electron 60eV/electron Track Length DRIFT/MIMAC Cygnus /DMTPC High pressure gas electrons+light 20eV/electron 60eV/electron Ionization +Scintillation UCLA/Texas Liquid Xe Scintillation Light 200eV/photo electron 1600eV/photo electron Pulse shape 22ns 4ns/ Rome, ZEPLIN I, XMASS Liquid Xe Ionization+ Scintillation electrons 15eV/electron 200eV/p.e. 45eV/electron 1600eV/p.e. Ionization Yield Pulse shape ZEPLIN II-II-IV XENON Liquid Ar Scintillation Light 500eV/p.e ev/p.e? Pulse shape 6ns/ 1.6µs MiniClean Deap Clean Liquid Ar Ionization+ Scintillation electrons 20eV/electron 500eV/p.e. 60eV/electron ev/p.e? Ionization Yield Pulse shape WArp ARP Phonon mediated phonons 100µeV/phonon 100µeV/phonon No Cuerocino (2β) CRESST I low temperature Electrons + holes Phonons 3eV/carrier 100µeV/ phonon 9eV/carrier 100µeV/ phonon Ionization yield Phonon timing/shape CDMS,SCDMS Edelweiss low temperature Light Phonons 100eV/ photoelectron on O 900eV/ photoelectron Scintillation yield at least on O CRESST II Superheated Droplets Sound not sensitive 10keV-100keV tunable energy density sensitive to alphas Simple Picasso Bubble chamber CCD camera not sensitive 10keV-100keV tunable energy density sensitive to alphas COUPP 25

26 Natural scale? cm 2 Bulk (5 < tan β < 45) Focus Point (tan β~10) χ 2 0, χ 1 ± Coannihilation Higgs Funnel (50 < tan β < 60) Stau Coannihilation (tan β ~ 10) Low cross sections correspond to fine tuning The Higgs funnel and stau coannihilation are fine tuned to enhance annihilation The lower the elastic cross section, the finer the tuning! cm 2 is a natural scale Bulk (LSP= pure Bino: Higgs dominant) Focus region /split supersymmetry (LSP higgsino component: high annihilation+ elastic σ) 26

27 Spin Dependent? Taking again as a guide msugra/constrained Minimum SuperSymmetric model (but take with even more a grain of salt than spin independent!) Roughly proportional Spin dependent 1000x spin independent But no A 2 enhancement factor Two complementary approaches Spin independent experiments Spin dependent but have to get from current to cm kg COUPP 27

28 Where are we? January 09 Scalar couplings: Spin independent cross sections latest compilation by Jeff Filippini Gray=DAMA 2 regions(na, I) from Savage et al. WIMP nucleon σ SI [cm 2 ] Ellis 2005 LEEST Roszkowski 2007 (95%) Roszkowski 2007 (68%) DAMA/LIBRA EDELWEISS WARP 2006 ZEPLIN III 2008 XENON CDMS all Si CDMS all Ge WIMP mass [GeV/c 2 ] 28

29 Spin dependent couplings Where are we? January WIMP proton σ SD [cm 2 ] Roszkowski 2007 (95%) Roszkowski 2007 (68%) DAMA/LIBRA 2008 COUPP 2008 KIMS 2006 XENON SuperK 2004 CDMS all Ge WIMP mass [GeV/c 2 ] WIMP neutron σ SD [cm 2 ] Roszkowski 2007 (95%) Roszkowski 2007 (68%) DAMA/LIBRA 2008 XENON CDMS all Si CDMS all Ge WIMP mass [GeV/c 2 ] a p vs a n at mass of 60GeV/c a p DAMA/LIBRA KIMS 2006 XENON SuperK 2004 CDMS all Ge a n

30 Claim of DAMA/LIBRA 08 If WIMPs exist, we expect a modulation in event rate Sun Earth dn de Dec 2 June 2 E DAMA claims 3 kev peak cannot be fully explained by 40 K escape peak 5.5% Clearly a modulation Not a WIMP: incompatible with other experiments 30

31 Spin independent interactions Tension with Other Expts. DAMA WIMP nucleon σ SI [cm 2 ] Ellis 2005 LEEST Roszkowski 2007 (95%) Roszkowski 2007 (68%) DAMA/LIBRA EDELWEISS WARP 2006 ZEPLIN III 2008 XENON CDMS all Si CDMS all Ge WIMP mass [GeV/c 2 ] Spin dependent DAMA WIMP proton σ SD [cm 2 ] Roszkowski 2007 (95%) Roszkowski 2007 (68%) DAMA/LIBRA 2008 COUPP 2008 KIMS 2006 XENON SuperK 2004 CDMS all Ge WIMP mass [GeV/c 2 ] WIMP neutron σ SD [cm 2 ] Roszkowski 2007 (95%) Roszkowski 2007 (68%) DAMA/LIBRA 2008 XENON CDMS all Si CDMS all Ge WIMP mass [GeV/c 2 ] 31

32 What could it be: Physics? An axionic type particle of 3 kev converting its mass into electromagnetic energy in detector Modulation by flux Electron recoil line at 3 kev Checked by other detectors: CoGeNT, CDMS! 3 kev peak excluded cf. CDMS arxiv: kev peak in DAMA single rate is not physical (if Z 2 scaling) Probably 40 K escape (1.46MeV missed) Excludes as modulation signal as big as DAMA (even in optimistic case of ±6%) Note that cross sections of exothermic radiations tend to be inversely proportional to velocity => modulation very much suppressed (Pospelov et al. 2008) 55Fe Ga modulated rate ±6% Unmodulated rate 32

33 What could it be? Most likely very subtle detector problem Modulation is basically summer-winter Example of the cosmic muon rate which is modulated with the same phase (decay path of the pions change with temperature) Many things change: temperature, water in mountain, humidity, electric voltage What seems excluded Neutron from muons Direct effect of muons on detector Examples of effects which have not been excluded convincingly Modulation of the efficiency e.g. of the PM noise rejection algorithm Modulation of the 40 K 1.46 MeV gamma detection efficiency (e.g. varying humidity in purge gas=> modulation of dead layer=> 3 kev escape) Not blind analysis! Sociological problem: Nobody finds the result plausible enough to repeat the experiment! However, as a field we need to cross check the only claim. A different team has to redo the experiment in Southern Hemisphere e.g. NaI detectors in a hole in Antarctic Ice (Stubbs, Fisher, IceCube, B.S.) 33