lecture 3: direct dark matter detection
TRANSCRIPT
Lecture 3:
Direct Dark Matter Detection
Graciela Gelmini - UCLA
23d.Spring School, Tainan, Taiwan, 3/31-4/3 2010
Graciela Gelmini-UCLA
Content:
• WIMPs: Cross sections and rates
• Milky Way Halo Model
• WIMP’s: Annual modulation
• WIMP’s: Search and signal discrimination techniques
• WIMPs: Main experiments and best present bounds
• DAMA signal, compatible with other negative results?
• Axions
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Milky Way’s Dark Halo Fig. from L.Baudis; Klypin, Zhao and Somerville 2002
1010(GeV/mχ) WIMP’s passing through us per cm2 per second!
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WIMP DM searches:
• Direct Detection- looks for energy deposited within a detector by acollision of a WIMP is the halo of our galaxySignature: same σ and m seen by different experiments with different
nuclei + annual modulation and/or recoil direction
• Indirect Detection- looks for WIMP annihilation (or decay) products(Next lecture)
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Direct DM Searches:
• Small ERecoil ≤ 50keV(m/100 GeV)
• Rate: depends on WIMP mass,
cross section, dark halo model, nuclear
form factors...
typical... < 1 event/ 100 kg/day
(need to go underground underground to
shield from cosmic rays)
• Single hits: single scatters, uniform
through volume of detector
• Annual flux modulation (few % effect)
• Directional detection (daily modulation-
requires measuring the recoil direction)
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WIMPs vs photons
• WIMPs interact with nuclei and produce
phonons besides ionization/scintillation.
• Photons and electrons interact mostly
with atomic electrons.
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WIMP-Nucleous Interaction:
WIMPs are not relativistic: v ≃ 300km/s ≃ 10−3 c. Thus, for the typical momentum
exchanged q = µv/√
2 (µ = mM(m+M) is the reduced mass)
1
q> RNucleus ≃ 1.25 fm A1/3
or, using 1= 197 MeV fm (1 femtometre, fm = 10−15 m)
q ≃ MeV
„
mχ
GeV
«
< MeV
„
160
A1/3
«
WIMP interact coherently with all the nucleons in a pointlike nucleus.
For larger q and heavier nuclei- A large- the loss of coherence is taken into account with
a nuclear form factor F (E) =R
e−iqrρNucleon(r)dr. Conventional Helmi form factor:
F (E) = 3e−q2s2/2[sin(qr) − qr cos(qr)]/(qr)3,
with s = 1 fm, r =√
R2 − 5s2, R = 1.2A1/3 fm, q =√
2ME.
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WIMP-Nucleous Interaction:
For a non relativistic elastic collision, the maximum recoil energy impartedto a Nucleus by a WIMP moving at v is Emax = 2µ2v2/M and
dσ
dE=
(
σ
Emax
)
pointlike
|F (E)|2
Minimum WIMP speed required to produce a nuclear recoil energy E:
vmin =
√
ME
2µ2=
√
(m + M)2E
2Mm2
µ = mM(m+M): reduced mass, m: WIMP mass, M : is the nucleus mass.
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Event rate: events/(kg of detector)/(keV of recoil energy)
dR
dE=
∫
NT
MT× dσ
dE× nvf(v, t)d3v
=ρσ(q)
2mµ2
∫
v>vmin
f(v, t)
vd3v
-NTMT
= Avogadro’s number per mol = Number of atoms per gram
- ρ = nm, f(v, t):local DM density, ~v distribution depend on halo model
- spin-independent σ(q)= σ0F2(q), σ0 = A2(µ2/µ2
p)σp for fp = fn
- spin-dependent σ(q) =32µ2G2
F (JN+1)
JN
[
〈Sp〉ap + 〈Sn〉an
]2
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- spin-independent: σ(q)= σ0F2(q)
From scalar and vector couplings in the Lagrangian- fp,n effective couplings to p, n
σ0 =[
〈Zfp + (A − Z)fn
]2(µ2/µ2
p)σp = A2(µ2/µ2p)σp for fp = fn
- spin-dependent: σ(q) =32µ2G2
F (JN+1)
JN
[
〈Sp〉ap + 〈Sn〉an
]2
From axial couplings in the Lagrangian- ap,n couplings to p, n
〈Sp,n〉 expectation values of the spin content of p,n in the target nucleus
Example: 73Ge (JN = 9/2, 7.8% in isotopic composition) Single particle shell model:
〈Sn〉 = 0.5, 〈Sp〉 = 0 (Odd-group model: 0.23, 0; Shell Model 0.488, 0.011)
Need non zero nuclear spin JN . Examples:29Si (JN = 1/2, 4.7%), 129Xe (JN = 1/2, 26.4%), 131Xe (JN = 1/2, 21.2%)
- SD Form Factor is O(1) thus SI cross sections are A2 larger than SD
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Bounds on SI better that on SD Example: XENON collaboration
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Standard Halo Model (SHM) The of halo models
ρSHM = 0.3 GeV/cm3
Maxwellian ~v distribution
at rest with the Galaxy
v⊙ =220 km/s, vesc = 500 - 650 km/s
Local ρ and velocity could be very different if the Earth is within a DM clump or stream
or if there is a “Dark Disk”. Simulations advancing fast....
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Standard Halo Model (SHM) The of halo models
Maxwellian distribution truncated at the local Galactic escape speed vesc
fh(v, t) =
8
>
<
>
:
1
Nh(2πσ2h)
3/2e−|v+v⊙+v⊕(t)|2/2σ2
h if |v + v⊙ + v⊕(t)| < vesc = 650 km/s,
0 otherwise.
v: WIMP velocity relative to the Earth
v⊕(t): velocity of the Earth relative to the Sun (29.8 km/s tangent to orbit)
v⊙: velocity of the Sun relative to the Galactic Rest Frame (in which halo WIMPs assumed
to be stationary)= 232 km/s in direction λ⊙ = 340◦, β⊙ = 60◦ ecliptic coordinates ;
σh: velocity dispersion of WIMPs ( 220/√
2 km/s (in isothermal model),
Nh = erf(z/√
2) − (2/π)1/2ze−z2/2, with z = vesc/σh: normalization factor.
With this model: maximum possible heliocentric WIMP velocity is vesc +v⊙ = 882 km/s.
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The Actual Halo of the Milky Way
The Sagittarius (Sgr) Dwarf Galaxy is being eaten-up by the Milky Way.Using its tidal disruption leading and trailing streams (in stars) of the D.Law and S. Majewski and K. Johnson have modeled the shape of the DarkHalo (Jan 2010). It is a triaxial “beachball”.
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Possible Dark Halo profiles Important for indirect DM searches.
Cuspy profiles: fits to N-bodyDM only simulations
Cored profiles: Fits to observedrotation curves
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Rotation curves of the Milky Way (Fig from M. Weber)
v⊙ = 244 ± 10.2km/s ((Reid, Brunthaler, 0808.2870)
ρ⊙−DM = 0.3 ± 0.1 GeV/cm3((Honma et al
0709.0820)
Possible Inner Ring (at r ≃4 kpc) andOuter Ring (at r ≃13 kpc) of DM likelypart of a Dark Disk can explain betterthe curves, contributing to ρ⊙−DM < 1.0GeV/ cm3 ??? ((Weber, de Boer [0910.4272])
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Dark Disk: Read, Lake, Agertz, Debattista MNRA 389, 8/2008;Read, Mayer, Brooks, Governato, Lake 0902.0009
Read et al include baryons in
simulations: “A stellar/gas disc,
already in place at high redshift,
causes merging satellites to be dragged
preferentially towards the disc plane
where they are torn apart by tides.”
Dark Disk: equilibrium structure
ρD ≤ 2 × ρSHM
vlag ≃ 50 km/s with respect to Sun
vdisp ≃ 50 km/s
Threshold of XENON 10
Bruch, Read, Baudis, Lake Ap.J.696:920-923,2009 and arXiv:0811.4172
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State of the art non-linear N-body simulations No baryons!
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Dark halo substructure:
Haloes grow hierarchically incorporating
lumps and tidal streams from earlier
phases of structure formation.
Can the solar system be within a DM lump
or a stream?
“Via- Lactea II” simulations: “lots of
subhalos and tidal streams down to 8kp”
“fewer subhaloes in inner regions (but more
concentrated)”
Kuhlen Diemand Madau arXiv:0805.4416
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Dark halo substructure: VIRGO Collaboration-Aquarius Programme
Most subhaloes are at large distances
from the galactic center, far from the
Sun. Subhaloes are more effectively
destroyed near the center
The chance of a random point close
to the Sun lying in a substructure is
< 10−4
Local v distribution smooth (no
streams) but differs from Gaussian due
to the detailed assembly history of the
halo (rates may deviate by 10%)Vogelsberger et al. 0812.0362 [astro-ph]
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WIMP wind arrival direction to Earth
Standard halo
Extreme model with only streams(Sikivie)
Gelmini, Gondolo 2000
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Annual Modulation: sensitive to velocity distributionStandard: Std. halo and Maxwellian distribution, max. vel in June, min. vel in Dec.
Mod. Amplitude≃ (vEarth/vSun)2 ≃ (30km/sec/300km/sec)2 ≃ 0.01
Sikivie: Extreme analytic model with ONLY DM streams Gelmini, Gondolo 2000
Right: with just one stream Freese, Gondolo, Newberg 2003
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Direct DM Searches: Many experiments!
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Direct DM Searches:Fig. from KIMS
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WIMP vs. photons Many experiments!
• Single Channel Techniques:-Ionization (Ge, Si, CdTe): IGEX, HDMS, GENIUS, TEXONO, CoGeNT
-Scintillation (NaI, Xe, Ar, Ne, CsI): DAMA (2 keVee), NAID, DEAP, CLEAN, XMASS,
KIMS
-Phonons (Ge, Si, Al2O3, TeO2): CRESST-I (0.6 keV), Cuoricino, CUORE (5 keV)
-Threshold detectors: PICASSO (bubbles of C4F10),
COUPP (superheated bubble chamber)
• Hybrid detector techniques for discrimination:-Ionization + Phonons (Ge, Si): CDMS, SuperCDMS, EDELWEISS, EURECA
-Ionization + Scintillation(Xe, Ar, Ne): XENON, LUX, ZEPLIN, WARP, ArDM, XAX
-Scintillation+Phonons (CaWO4, Al2O3): CREST-II
• Very promising: (Liquid) Noble-Gas Detectors act as their own veto,
up-scalable to multi tonnes
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Noble Liquid detectors:
• Single-Phase: Scintillation
-XMASS - Xe (Japan, Kamioka)
-DEAP/CLEAN - Ar/Ne (US/Canada, SNOLab)
• Two-phase liquid and gas: Scintillation and ionizationBoth seen as light pulses (one delayed)
-XENON - Xe (US/Switzerland/Germany/France/
Portugal/Italy/Japan/China, LNGS)
-WARP - Ar (Italy/US, LNGS)
-ZEPLIN - Xe (UK/US, Boulby)
-LUX - Xe (US/UK, Sanford Lab- later DUSEL)
-ArDM - Ar (Switzerland/Spain/UK, Canfranc)
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WIMPs vs photons
• WIMPs interact with nuclei and produce
phonons besides ionization/scintillation.
• Photons and electrons interact mostly
with atomic electrons.
In crystals: quenching factor Q= fraction of ERecoil that goes into Ionization scintillator.
QGe = 0.4, QSi = 0.25, QNa = 0.3, QI = 0.09
In liquid/gas Xe: Leff=scintillat. efficiency of WIMP relative to a 122 keV γ ≃ 0.2.
Electron-equivalent energy Eee = QE or LeffE (in keVee) = Energy deposited in e to
have the same ionization/scintillation signal
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WIMPs vs photons
In CDMS (crystal)
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WIMPs vs photons
In XENON (liquid Xe)
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Present best bounds from CDMS and XENON 10
CDMS (Soudan Mine): 19 Ge detectors (4.75 kg) and 11 Si (1.1 kg) ZIPs in 5 towers
Rejection: ionization (Q= 0.3)-phonons and timing to discriminate surface vs bulk events
Recently 2 events
0.9 backg. expec-
ted, 612 kgday
(prior set: 0 ev.,
0.6 expected,
∼ 400 kg day)
Future: Super CDMS with 16 kg Ge
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Present best bounds from CDMS and XENON 10
XENON 10 at Gran Sasso: 22 kg of L Xe (15 kg in active volume), 136 kg day
Rejection: Prompt scintillation light (S1) - propagated light from charge drifted into gas
phase (S2)
(2-12 keVee = 4.5-27 keVr- 1800 events- in red 50%acceptance)
New bounds from Xenon 100 expected soon (100 kg active) + “Ugrade”
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Best SI: CDMS Dec/09, m > 30 GeV
Right: CDMS (diamonds), ZEPLIN-II (circles), KIMS
(triangles), NAIAD (squares), PICASSO (stars), COUPP
(pluses) and SuperK (crosses)
Best SD n-only:XENON-10 May/08
WIMP Mass [GeV/c2]
SD
pur
e pr
oton
cro
ss s
ectio
n [c
m2 ]
101
102
103
10−40
10−38
10−36
10−34
WIMP Mass [GeV/c2]
SD
pur
e ne
utro
n cr
oss
sect
ion
[cm
2 ]
101
102
103
10−40
10−38
10−36
10−34
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Best SD p-only bound:
COUPP at FNAL1.5 kg of CF3I, room-temperature
bubble chamber (60 Kg detector
under construction)
WIMP: single bubble,
n: multiple bubbles
and KIMS in Korea 4× 6kg CsI(Tl)-237d
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Low Threshold:TEXONO (4× 5 g of Ge) and CoGent (500g of PPC Ge)PRD79:061101,2009 arXiv:1002.4703 Excess events at low mass??
10-44
10-43
10-42
10-41
10-40
10-39
10-38
10-37
10-36
1 10 102
01234567
2 3 4 5 6 7
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Directional detectors: low density gas TPCsDRIFT at Boulby (CS2) and DM-TPC at MIT-WIPP (CF4)Measure direction of recoil- track reconstructed through drift of e
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Directional detectors: low density gas TPCsDRIFT at Boulby (CS2) and DM-TPC at MIT-WIPP (CF4)Measure direction of recoil- track reconstructed through drift of e
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DAMA/LIBRA
• The DAMA collaboration, has found an annual modulation in its datacompatible with the signal expected from dark matter particles boundto our galactic halo-which has been confirmed by DAMA/LIBRA inApr/2008
• All other experiments have not found any signal from WIMPs
• Are these results compatible?
For light usual WIMPs incompatible only to the 2-3 σ level...
possibly compatible also for inelastically scattering WIMPs (IDM)...
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DAMA/LIBRA 25 NaI (Tl) crystal of 9.5 kg each, 4y in LIBRA (11years total), 0.83 ton × year, 8.2σ modulation signal.
2-4 keV
Time (day)
Res
idua
ls (
cpd/
kg/k
eV) DAMA/NaI (0.29 ton×yr)
(target mass = 87.3 kg)DAMA/LIBRA (0.53 ton×yr)
(target mass = 232.8 kg)
Rate
0
2
4
6
8
10
2 4 6 8 10 Energy (keV)
Rat
e (c
pd/k
g/ke
V)
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Savage,Gelmini, Gondolo, Freese JCAP 0904:010,2009
36 bins (likelihood ratio 4 param. fits
100 101 102 10310-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
MWIMP HGeVL
ΣΧ
pHp
bL
spin-independent CDMS I SiCDMS II Ge
XENON 10
Super-K
CoGeNT
TEXONO
CRESST I
DAMA H3Σ�90%Lwith channeling
DAMA H7Σ�5ΣLwith channeling
DAMA H3Σ�90%L
DAMA H7Σ�5ΣL
With channeling, light usual WIMPs,
m ≃ 7 to 10 GeV
are still a possible explanation
(in conflict with CDMS and XENON at the
2-3σ level)
100 101 102 10310-4
10-3
10-2
10-1
100
101
102
103
104
MWIMP HGeVL
ΣΧ
pHp
bL
spin-dependentHan = 0, proton onlyL CDMS I Si
CDMS II Ge
XENON 10
Super-K
CoGeNT
TEXONO
CRESST I
DAMA H3Σ�90%Lwith channeling
DAMA H7Σ�5ΣLwith channeling
DAMA H3Σ�90%L
DAMA H7Σ�5ΣL
100 101 102 10310-4
10-3
10-2
10-1
100
101
102
103
104
MWIMP HGeVL
ΣΧ
nHp
bLspin-dependent
Hap = 0, neutron onlyL CDMS I SiCDMS II Ge
XENON 10
CoGeNT
TEXONO
CRESST I
DAMA H3Σ�90%Lwith channeling
DAMA H7Σ�5ΣLwith channeling
DAMA H3Σ�90%L
DAMA H7Σ�5ΣL
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Channeling effect: important for light WIMPs When ions move along
crystal axes and planes penetrate longer and give their energy to electrons, so Q = 1
instead of QI = 0.09 and QNa = 0.3 (Drobyshevki, 07; DAMA- Eur. Phys. J. C 53, 205-2313, 2008)
ER (keV)
frac
tion
Iodine recoils
Sodium recoils
10-3
10-2
10-1
1
0 10 20 30 40 50 60
However, here not taken into account that the recoiling nucleus starts froma lattice site (this reduces the channeling fraction) Bosognia, Gelmini, Gondolo in preparation
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Other possibilities to explain the DAMA signal:
• Very tuned DM stream (aligned with Sun motion-3% of local density) marginal solution
appears for 2 to 4 GeV WIMP (very unlikely)
• Light keV mass DM particles which interact only with e?
• MeV and above mass DM particles which interact with e-bound to nuclei (not at rest)?
• Inelastic DM scattering?
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Inelastic DM (IDM) Tucker-Smith, Weiner 01 and 04; Chang, Kribs, Tucker-Smith, Weiner 08;
March-Russel, McCabe, McCullough 08; Cui, Morrisey, Poland, Randall 09
In addition to the DM state χ with mass mχ there is an excited state χ∗
mχ − mχ∗ = δ ≃ 100keV
Inelastic scattering χ + N → χ∗ + N dominates over elastic.
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Inelastic DM (fig from T. Schwetz)
vinelmin =
√
MER2µ2 + δ√
2MER
velmin =
√
MER2µ2
Only high-velocity DM particles have enough energy to up-scatter, and vinelmin decreases
with increasing target mass M , thus targets with high mass are favored (better I than
Ge...). Notice no low ER events.
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Inelastic DM Tucker-Smith, Weiner 04 mχ = 50GeV, δ = 100keV
10 kev 50 kev 90 kev 130 kev
Recoil Energy
Rates
10 kev 50 kev 90 kev 130 kev
Spectrum in Ge
June December June
0.7
0.8
0.9
1
1.1
1.2
1.3
June December June
0.7
0.8
0.9
1
1.1
1.2
1.3
Annual modulation: elastic (dashed) and
inelastic (solid)
Leads to very different spectrum (no low ER events) The modulation of the signal is
enhanced (the number of WIMPs changes more rapidly at high v)
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Inelastic DM Chang, Kribs, Tucker-Smith, Weiner 08 mχ = 50GeV, δ = 100keV
DAMA, benchmarks, vesc = 500km/s Modulated fraction, mχ = 100GeV.
A spectrum with no low ER events and larger modulation (as δ increases) fit well the
DAMA/LIBRA data
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IDM Chang, Kribs, Tucker-Smith, Weiner 08
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IDM benchmarks, vesc = 500km/s Chang, Kribs, Tucker-Smith, Weiner 08
XENON-dataXENON- expected spectrum
-Different spectra: IDM events expected at higher energy. Xenon, Zeplin,CRESST, may have already seen DM events and taken then for background!
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IDM: fixed relative even rates for Ge, Xe, I, and W should test thisexplanation for the DAMA signal Chang, Kribs, Tucker-Smith, Weiner 08
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IDM: recent bound from the CDMS collaboration
New bounds from XENON 100 expected soon...
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Outlook: plenty of direct detection data to come!In the near future:
- Xenon 100 and Upgrade at Gran Sasso: almost finished 100 kg fiducial mass
- SuperCDMS at Soudan: 16 kg of Ge
- WARP at Gran Sasso: 3.2 kg L Ar prototype-140 kg under construction
- EDELWEISS at LSM (Modane-Frejus): 10 kg NbSi Ge
- LUX for DUSEL: 50 kg L Xe tested at CWRU -300 L Xe (100 kg fiducial)
- ArDM at CERN: 1 ton L Ar TPC/Calorimeter prototype
- COUPP at FNAL: 60kg module under construction
- KIMS at Yangynag Undeground Lab-Korea: in 2008 12× 6kg CsI(Tl) crystals (before 4)
- CRESST at Gran Sasso: 10 kg of 33 CaWO4
-XMASS at Kamioka: 3kg fiducial of Xe- 100 kg next step?
For DAMA/LIBRA: - DAMA/LIBRA is reducing its threshold to 1 keVee
A signal in another detector with other techniques is needed to confirm a DM discovery:
XENON, KIMS, CRESST II, can test IDM, and these + COUPP, TEXONO can test light
WIMPs - KIMS (100 kg CsI) should in a few years reproduce the statistics of DAMA?
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Further away:
- Directional detectors: gas TPC (DRIFT at Boulby; DM-TPC for DUSEL)
- Tonne to multi-tonne detectors: SuperCDMS 1t?, WARP 1t?, XENON 1t?, EURECA?,
XMASS?, XAX?
plenty to look-out for!
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AXION
• introduced to solve the “strong CP problem” in QCDPeccei & Quinn
• “invisible axion” (ma∼6µeV(1012GeV/fa) and gall ∼ 1/fa)Kim; Shifman, Vainshtein, Zakharov (KSVZ)
Dine, Fischler, Srednicki; Zhitnitsky (DFSZ)
• pseudo-Goldstone boson (SSB of a global U(1) at scale fa)
• produced “cold” (from a condensate |~p| ≃ 0 << ma)
• axion DM could soon be detected or ruled out experimentally!
• “Invisible axion” models have two Higgs doublets (plus a singlet but ata higher scale) whose components should be found at the LHC.
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Graciela Gelmini-UCLA
AXION
Good CDMcandidate for
1µeV ≤ m ≤ 1meV
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Graciela Gelmini-UCLA
AXION
ADMX (Axion DM eXperiment)
Microwave cavity: gaγγMany experimental searches (L. Rosenberg 2010)
ADMX Phase II is starting- “definitive” search
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Graciela Gelmini-UCLA
Axions: best present bounds(Duffy et al 2006)
Axion Dark Matter eXperiment
(ADMX) uses a Sikivie microwave
cavity detector to search for aγγ
“Medium Resolution” (MR) assumes
velocity dispersion is ≤ 10−3c (axion
escape velocity is 2 × 10−3c.)
“High Resolution” (HR) uses the
possible existence of discrete flows, or
streams (smaller velocity dispersion)
in Sikivie Halo Model 97.7% CL limits
ADMX Phase II is starting- “definitive” search
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