B.SadouletAPS 2013 W.K.H Panofsky Prize 1
The Search for Weakly InteractingMassive Particle Dark MatterScience motivations and strategies
Is dark matter made of particles?What physics? Complementarity of experimental approaches
Two paradigmsWeak scale WIMP (≈ 100GeV): how this business started!A Dark Sector (low mass?, structure?): emerging ideas!
Experimental strategy for Direct DetectionVery low rate, small energy deposition, need for nuclear recoilComplementarity of approaches:
Noble Liquids may be more natural at high massesLow temperature detectors are essential if we want to explore low mass WIMP
Bernard SadouletDept. of Physics /LBNL UC BerkeleyUC Institute for Nuclear and ParticleAstrophysics and Cosmology (INPAC)UC Dark Matter Initiative
B.SadouletAPS 2013 W.K.H Panofsky Prize
W.K.H. Panofsky
Thanks to APSParticularly honored because Pief was one of the
important mentors of my youth!Very happy to share this prize with Blas Cabrera
Coordinated talks
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B.SadouletAPS 2013 W.K.H Panofsky Prize 3
Dark Matter: A Central Cosmology Question
The nature of dark matter is a central problem of cosmology!
≠ baryons ≠ light neutrinosIs it made of particles produced in
the early universe? If yes: evidence for physics beyond
standard model! Tev scale or totally different
origin?
B.SadouletAPS 2013 W.K.H Panofsky Prize 4
4 Complementary Approaches
Dark MatterGalactic Halo (simulation)
WIMP annihilation in the cosmos
GLAST
Fermi/GLAST
VERITAS, also HESS, Magic + IceCube (v)
WIMP production on Earth
LHC
CDMS
WIMP scattering on Earth:e.g. CDMS, Xenon 100,etc.
Cosmological Observations
Planck
Keck telescopes
B.SadouletAPS 2013 W.K.H Panofsky Prize
Two Paradigms
Weak scale WIMPs <= hierarchy problem
Dark Matter Hidden Sector: no necessarily weak scale
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B.SadouletAPS 2013 W.K.H Panofsky Prize 6
Weak Scale WIMP paradigm
Fantastic success of Standard Model but unstableWhy is h, W and Z at ≈100 Mp? Need for new physics at that scale supersymmetry additional dimensions, global symmetries In order to prevent the proton to decay, a new quantum number => Stable particles: Neutralino Lowest Kaluza Klein excitation, little Higgs
Particles in thermal equilibrium + decoupling when nonrelativistic
Cosmology points to W&Z scaleInversely standard particle model requires new physics at this scale => significant amount of dark matter
Weakly Interacting Massive ParticlesDark Matter could be due to TeV scale physics
Freeze out when annihilation rate ≈ expansion rate
⇒Ωxh2 =
3 ⋅10-27cm3 / sσ Av
⇒σ A ≈α 2
MEW
2
A remarkable concidence
B.SadouletAPS 2013 W.K.H Panofsky Prize
Weak scale WIMP: How It All Started!My subjective impression of key steps
Dark MatterB Lee and S. Weinberg 1977 annihilation rate-> densityArticle of Silk and Srednicki, 1984 annihilation in gamma rays
Low temperature detectors -> neutrinosDrukier and Stodolsky Dec 1984Cabrera, Krauss, Wilzcek, Dec 1984
Goodman and Witten Jan 1985Direct detection is possible!
Ionization and Nuclear recoil recognitionNuclear recoils will ionize! (Marv Cohen-> Lindhardt) ≈1986Germanium (Avignone, Caldwell) 1987-88
excluded Z0 Importance of nuclear recoil (CDMS) 1989 Low pressure TPC (Tao, ≈1990)DAMA (Bernabei) 1990-2000Liquid Xenon (Elena Aprile)1998-2002
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B.SadouletAPS 2013 W.K.H Panofsky Prize
An Active Field
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Credit: Joerg Jaeckel
Direct DetectionAn expanding community US≈ 270 physicists ≈70% FTE ≈ 40% of world
B.SadouletAPS 2013 W.K.H Panofsky Prize
Xe 100 (2012)
Direct Detection
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CMSSM≈mSUGRA Focal point regionNo threshold for Direct Detection
LHC Monojetsχγ µγ 5χ( ) qγ µγ 5q( )
B.SadouletAPS 2013 W.K.H Panofsky Prize
No Missing Energy at the LHC
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mSUGRA≈CMSSM 4 parameter + signUseful simplification but easy to eliminate
Natural supersymmetryDo only what you really need to solve
the hierarchy problem : light s-top Much more open
But other problems (mh, Bs->𝛾)
Simplified models ->600 GeV
mSUGRA ≈out except FPbut SUSY parameter space still very much open although -> larger mass
B.SadouletAPS 2013 W.K.H Panofsky Prize
Dwarfs
Dark Matter Annihilation (Fermi)
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Galactic Halo
Extragalactic Background
cf Alex Drlica-Wagner
No clear signalPresentation in terms of bb, 𝝉𝝉 ,WW channels is simpleBut realistic model is a mix -> less restrictive limits:
No strong limit on low mass
- - -
B.SadouletAPS 2013 W.K.H Panofsky Prize
Different Paradigm: Dark Sector
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WIMP-less DM (e.g., Feng Kumar)MSSM breaking through gauge mediation in SUSY breaking sector+ Hidden sectors
Thermal relic with WIMP-less miracle
⇒ Naturally σv ≈gx
4
mx2 ≈
gEW4
mZ2 but mX ≠ mZ
What if there were a hidden dark sector?In contact with ordinary sector at high temperature.Now shielded from ordinary sector
e.g., preventing production of low mass WIMp at accelerators
Three examples
Dark Photon (e.g., Arkani-Ahmed, Finkbeiner, Weiner)Light mediator -> interesting phenomenology: excited stated,
Sommerfeld enhancement etc..
Asymmetric Dark Matter (e.g., K. Zurek)What if dark sector was also asymmetric betweendark matter and anti-dark matter?Reasonable to have ≈ same asymmetryif MDM=6*Mp we get ΩDM≈6*Ωb as observedbut no idea about cross section, no indirect
B.SadouletAPS 2013 W.K.H Panofsky Prize
Fundamental Motivations?Weak: Make sense of a confused experimental situation
Just having more parameters to play with, to fit experiments which are probably plagued by misunderstood backgrounds, systematics, calibration and astrophysics problems
Stronger: Natural in many theoretical modelse.g., String theory inspiredNon necessarily related to weak scale
Hopefully: establish by solid observationsCurrent candidates
Serious failure of LCDM in dwarf galaxiesAstrophysics Or fundamental physics? e.g. self interacting
Direct detection signals at low energy????
Fermi-Glast GeV excess: unlikely that can distinguish from astrophysicsPamela,Fermi,AMS positron excess: difficult to distinguish from astrophysicsFermi-Glast 135 GeV gamma line in Fermi Glast if confirmed (no continuum -> internl structure of dark sector )
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B.SadouletAPS 2013 W.K.H Panofsky Prize
Dwarf Spheroidals
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2) The density profile: NFW or core?Basic degeneracy between velocity
anisotropy and density profileWalker and Penarrubia: break the
degeneracy for Fornax and Sculptor with two populations of stars -> Core!
2 distinct but related problems1) The number of satellitesbut we keep discovering small ones
Not enough large masssatellites: “Too big to fail problem”
Frenk et al.Bullock et al.
σm
≈ 0.1 g / cm2( )−1 ≈ 0.18 barns/ GeV/c2( ) (Bullock's group)
Is it astrophysics or particle physics?Extremely efficient ejection of baryons by repetition of SNsOr strongly interacting dark matter => would point to dark sector
B.SadouletAPS 2013 W.K.H Panofsky Prize
Low WIMP Mass Region (DD)
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Claims for Very large modulationsCDMS does not see modulation (but needs to go
below 5 keV if possible )Statistical significance of CoGeNT marginal (2.8
sigma) => more statistics. Malbeck does not see a modulationControl of systematics is essential
CoGeNTCDMS
Trying to make sense of the various claims
CoGeNT evolving (surface events): no more claimCRESST likely 206Pb CDMS Ge interpreted by Collar/Fields: Our only comment so far similar effect in multiples
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FIG. 3: Best-fit components of the null and alternative mod-els, overlapped on summed data, projected on Er and Ei.Red: ER and SE combined through the Crystal Ball PDF[15]. Green: ZC. Blue: NR. Black: sum of components. Thenull model requires a large deviation of the ZC centroid toEi ! 0.5 keVee, hard to reconcile with adequate Ei calibra-tions [12] and with the mean Ei of ZC events above ! 5 keVnr,a region where their true centroid can be assessed (Fig. 2).The separation between ZC and NR populations is noticeablefor data in the 5-11.9 keVnr analysis region used in [1].
stance, the addition of non-overlapping time periods [26]from detectors spanning an order of magnitude in back-ground rate within the signal box [14, 16], the negligibleoverlap with the CoGeNT spectral region containing aclear excess of events (Fig. 4), or unresolved issues relatedto CDMS’s energy scales [22]. However, we emphasizethat the choice of signal box boundaries, one that resultsin a poor signal-to-background ratio, is already su!cientto cripple its sensitivity.
In conclusion, we find that recently released 2007-2008CDMS data strongly support (5.7! C.L.) the presence ofa family of low-energy events concentrated in the nuclear
FIG. 4: Blue: best-fit NR component for CDMS summeddetector data, translated to ionization scale and overlappedon histogrammed CoGeNT data [4] after normalization tothe vertical scale. Neither is corrected for e!ciency nextto threshold. Dotted blue lines represent the 1! uncertaintyin the parameter A1 for NR. A dashed black line representsknown CoGeNT backgrounds (flat+cosmogenic, [4]), whichprovide an adequate fit to the data down to ! 1.2 keVee,the lower boundary of the CDMS annual modulation searchregion. Inset: 90% and 99% C.L. CDMS ROI in WIMP cou-pling vs. mass (see text), including all present uncertaintiesexcept for those related to CDMS’s energy scales [22]. ROI’sfor CoGeNT [4], CRESST [23] and DAMA [3] are from [6],and include the e"ect of a residual surface event contamina-tion in CoGeNT described in [4]. The DAMA ROI assumesa Maxwellian dark matter halo: deviations from it can dis-place it to lower WIMP couplings [5, 6, 24, 25]. Additionaluncertainties for DAMA exist [25].
recoil band. An origin in neutron scattering is highly un-likely. Their rate and spectral shape provides a matchto the majority of low-energy events unaccounted for byCoGeNT (Fig. 4). Both searches employ the same tar-get material, germanium, but perform orthogonal back-ground cuts [8], enhancing the possible meaning of thiscoincidence. If this excess is interpreted as a WIMP sig-nal, it falls in close proximity to other anomalies reportedby recent dark matter experiments (Fig. 4). The favoredregion of WIMP mass is also of present interest in indi-rect searches for dark matter [27]. We also determine thatthe recent search for an annual modulation signal by theCDMS collaboration is insu!ciently sensitive to excludea dark matter origin for this excess, due to an inadequateselection of analysis region. Unsupported quantitativestatements made in [7, 11] about background composi-tion in CDMS detectors are not compatible with ourfindings.
B.SadouletAPS 2013 W.K.H Panofsky Prize
New result for CDMS on Si K. McCarthy yesterday
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Analysis favors a WIMP region of interest ≈3σ
Most likely value at 8.6 GeV WIMP mass with 1.9x10-41 cm2 cross section
Consistent with earlier CDMS Ge and Si limits
Also consistent with a WIMP interpretation of the COGENT experiment
In tension with limits from Xenon 10, Xenon 100 experiments
DAMA
CRESST
CoGeNT-KelsoXENON100
CDMS-II Ge
DAMA
CRESST
XENON10
CDMS-II Ge
CDMS-II Si
CDMS-II Si
Data are insufficient to claim discovery of a WIMP signal, but does warrant further investigation
B.SadouletAPS 2013 W.K.H Panofsky Prize
How do we check?
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Still to be done with CDMS IIInvestigation of possible systematics, unsuspected backgroundGe+Si consistent likelihood analysisLow energy Si analysis in same style as Ge
SuperCDMS SNOLABLower noise in phonons and Ionization <-R&DSi towers?
SuperCDMS SoudanCDMS Lite 23eV rmsLow threshold
Si towers?
SuperCDMS Soudan low threshold
CDMS II limit
B.SadouletAPS 2013 W.K.H Panofsky Prize
Compatibility of Low Mass WIMP with LHC
LHC Monojets in effective contact operatorProbably means that if indeed there is light dark matter it does not couple to gluons (in most models it does not).
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q,g
q,g
X
X
jet
B.SadouletAPS 2013 W.K.H Panofsky Prize
Experimental Strategy
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log σ
log M50 GeV/c2
2 directions1. Improve
sensitivity at large mass
5 GeV/c2
2. Improve sensitivity at small mass
B.SadouletAPS 2013 W.K.H Panofsky Prize
2 frontiers: 1.High Mass FrontierGet as many events as possible
with no background=> convincing signal, enough statistics to do physicsWeak scale WIMP: natural scale if Higgs exchange 10-45 -10-46 cm2/nucleon+ push as down as possible if no signal
The smaller, the more fine tuned...≈ 10-48 cm2/nucleon: irreducible background from atmospheric coherent
neutrino scattering
What technology?Noble liquids most natural if they can control their background
=> several tons (e.g., LZ 7 tons)However Xe requires a factor 3000 improvement to get 10-48 cm2/
nucleon
But low temperature detectors can play a useful role for Weak scale WIMP:Current CDMS proposal 200kg -> 10-46 cm2/nucleonNeeded background rejection demonstrated within a factor of 2.Complementary: very different backgrounds and detection mechanism
Need a diversity of target e.g., isospin dependence (J. Kumar)
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B.SadouletAPS 2013 W.K.H Panofsky Prize
What technology?Low temperature detectors are most natural because of their large S/N Best: improved phonons and ionization (see next slide) Giving up rejection, you can go to very low threshold with luke phonons
but then background limited
2 frontiers: 2.Low Mass Frontier
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Need excellent signal to noiseEnergy deposition goes as square of the WIMP mass
Ed =2M χ
2MN
M χ + MN( )2 v2 1− cosθ*( ) ≈ 2M χ
2
MN
v2 1− cosθ*( ) for M χ << MN
Xenon with S2 only (Sorensen) could also be useful, but No rejection: will have to rely on self shielding Fiducialization difficult (no t0-> can we use diffusion?) Few 100eV/ electron? Single electron background from surface would have to be corrected
Both would need careful calibration of energy scale
B.SadouletAPS 2013 W.K.H Panofsky Prize
Importance of Discrimination
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How far can we go?Gamma level 1/210 CDMS, beta 200kg Phonon energy: ≈Tc3 σ=180 eV -> σ=10 eV More optimistic!Ionization: FET->HEMT σ=300 eV -> σ=150 eV+ noise environment not baseline!!
No electron recoil rejection
Electron recoil rejection
100 101 10210−47
10−46
10−45
10−44
10−43
10−42
10−41
10−40
WIMP Mass (GeV)
σ o (cm
2 )
WIMP Sensitivity
Likelihood sensitivityEstimate by M. PylePreliminary!
SuperCDMS SoudanMajorana Demonstrator
CDMS II 2013
DAMA
CRESSTSi
CoGeNT -Kelso
We may be even able to detect coherent scattering of 8B solar neutrino! L. Strigari
Important physics signal (30kg/yr) + sensitivity demonstration (if no Si)
8B
B.SadouletAPS 2013 W.K.H Panofsky Prize
WIMPs: ≥Two paradigms•Weak scale•Dark SectorPhenomenology (e.g., dependence on the target nucleus) may be more complex
than for the “vanilla” WIMP scenarios.
Conclusions
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Fascinating time4 prong approach=>
complementary coverageconstrain theory speculations
No convincing result so farBut both paradigms still in good shape
Other good DM candidates: axions and possibly sterile neutrinos
Strategy for Direct DetectionSeveral technologies with complementary capabilities 2 frontiers• high WIMP mass: natural region of noble liquids (background control)
• low WIMP mass: S/N of low temperature (target mass cost )Different susceptibility to background, energy scale uncertaintiesEnough sensitivity overlap to have at least a second experiment able to cross-check any claim.Several targets => physics, large target masses-> astrophysics
B.SadouletAPS 2013 W.K.H Panofsky Prize
DAMA
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Can it be instrumental?Unstability in threshold: modulation appears smaller in LIBRA than in DAMA? Delayed pulses from muons (not neutrons, but defects): problems single rate
+phaseAwkward to the community: What to do?
Lower threshold: LIBRA has changed Phototubes to high QE + background modelExperiment by other groups: DM-Ice,ANAIS,KIMS, Princeton
Clearly modulationalthough not blind
Is it a signal?incompatible with other
experiments (New: KIMs)Saturates single rate=>Unphysicallylarge modulation
If true important!
B.SadouletAPS 2013 W.K.H Panofsky Prize
LHC<-> Direct and Indirect Detection
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Monojets/MonophotonsTim Tait et al, Paddy Fox et al:Effective theory with various
operatorsBut: Physical interpretation? limits of formalism(e.g., E<<M)
B.SadouletAPS 2013 W.K.H Panofsky Prize
Complementarity Direct-Indirect
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pMSSM model scan (19-dimensional scan of the MSSM) shown in grayred = models which the LAT may be sensitive to over a 10 year mission
B.SadouletAPS 2013 W.K.H Panofsky Prize
Sterile Neutrinos?
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AnomaliesLSND antineutrinoMiniBoone
antineutrinos now similar to neutrinostwice as much statisticless fluctuation up in high energy
Now compatible with LSND3.6 sigma
Note: Karmen excludes large DM2
not keV neutrino! Best fit ≈ 1 eV Compatibility with cosmology???
Ignarra Oct 12 3+1
Deficit of reactor antineutrinosSage-GallexTension with µ disappearanceWe need probably ≥2 sterile neutrinos
B.SadouletAPS 2013 W.K.H Panofsky Prize 30
Axions
3 directionsCosmological axions
with RF cavitiesSolar axionsLight-through the wall
experiments
cavity: next year
cavity: 4-year
cavity: very challenging
helioscope: current
helioscope: 10-year
Laser: current
Laser: locked FP
Rosenberg
B.SadouletAPS 2013 W.K.H Panofsky Prize
What about the Galactic Center?
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2 independent analysis Hooper,LindenAbazadjian,Klapinghat
More or less agree on conclusionsCould be dark matter annihilation: spatial shape, cross section, spectrumBut could be Millisecond Pulsars or Cosmic rays interaction
How will we ever know whether astrophysics or Particle Physics?
Better spectrumHigher spatial resolution? Gamma 400?
Same type of remarks about TeV positron excess
B.SadouletAPS 2013 W.K.H Panofsky Prize
Fermi 135 GeV Gamma Line?
Very few events ≈15+ Fundamental difficulty: how do we determine the number of trials
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What could it be if it is real?Not ordinary WIMP (large cross section/absence of continuum)Dark Sector with light mediator or more generally structure (Weiner et al.)Decay of heavy right handed neutrino (Bergstrom)
Can it be instrumental?A priori smooth efficiency (MC) but
Use the limb as efficiency calibrator : 30 events; large error bars“Signal” appears toward the limb and the sun (Daniel Whiteson)Can it be due to change of reconstruction algorithm in this energy region?
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