Searches for Dark Matter (the Quest) Harry Nelson UCSB 2003 SLAC Summer Insitute Aug. 5-6 2003

Searches for Dark Matter(the Quest)

Harry Nelson

UCSB

2003 SLAC Summer Insitute

Aug. 5-6 2003

8/6/03 SLAC Summer Institute 2

UCSBHNN

Recap - Direct Detection

• Shield (shield radioactive too!)… 1 ev/(kg d keV) typical • Reduce the background… HDMS , IGEX , Genius • Exploit astron. propert. (year cycle, directionality) DAMA, DRIFT • Devise detectors that can distinguish nuclear recoil from electron recoil… Edelweiss, CDMS, Xenon..

How to dredge the small (0.01 DRU= ev/(kg d keV)) up out of a bigger background (1 DRU typical) of recoil electrons from comptons?

Indirect Detection(milli-) Charged Massive ParticlesClosing


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vDM1/2 300 km/s2

vDM1/2 =0 km/s2

Annual Modulation in Rate• Ùsual Simplification’: Halo particles are at rest, on average• Sun moves through Halo - àpparent’ wind• Earth modulates `wind’ velocity yearly

vk = 15 km/s

Peak-to-peak up to 40%DAMA at Gran Sasso

Fig. from DRIFT


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Daily Modulation in Direction• Recoiling Nucleus Follows the Initial WIMP Direction… the `wind’

• Detector gaseous to reconstruct recoil direction• DRIFT at Boulby (Spooner)

Fig. from DRIFT


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DAMA – 100 kg of NaI

Iodine, A=127Eobs(KeVee)0.09 Erecoil (KeV)

Sodium, A=23Eobs(KeVee)0.25 Erecoil (KeV)

Erecoil Light

NaI

PM

T

PM

T

CopperLead

Poly


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through 2000 … 4

DAMA Background and Signal

through 2003 … 6.3

Bernabei et al., astro-ph/0307403

Energy Spectrum

Bkgd 1 cpd/kg/keV

2-6 KeV

8-24 KeV Na(23) 20-70 KeV I(127)

0.01950.031 -0.00010.019 cpd/kg/keV


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DAMA noise...

>1 pe threshold<10-4 cpd...


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DAMA Allowed Regions

through 2003through 2000(standard halo)

10-42

10-44

p (cm2), =0 /

• Variation mainly due to changes in halo parameters• two plots not directly comparable (different halos used)• With new result, DAMA ceases to employ `standard Maxwellian halo’ - comparisons challenging

Na

I

3

4


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Halo Variation

Kamionkowski and Kinkhabwala (1997)


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Perhaps WIMP couples not to nucleons, but to their spin S,V,T,A,P S,A non-relativistic (V too)

S - `nucleon, SI’ (or V) … A - `spin or SD’(also, could break isospin… np)A2 2 J(J+1)

DAMA

J0 unpaired nucleon, odd A

NAIAD (Boulby)(couple to proton spin)

10-36

10-34

p (cm2)Couple to neutron spin

LIBRA 250kg, NAIAD continues, ANAIS in Spain...


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0

v/c 710-4

NucleusRecoils

Dense Energy Depositionv/c small; Bragg

Discrimination of RecoilsSignal

Er

v/c 0.3

ElectronRecoils

Background

Sparse Energy Deposition

Er

Differences the Basis of Discrimination


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Simulation (by DRIFT)

40 keV Ar in 1/20 atm Ar 13 keV e- in 1/20 atm Ar

5 cm

Ar pushes other Ar atoms,none go very far.

Electron pushes otherelectrons, all go far


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dE/dx for different recoils http://www.srim.org/SRIM/SRIM2003.htm

Strategies

Detector insensitiveto small dE/dx(track etch, SDD)

Convert E to two distinct measured quantities that look different depending on whether nuclear recoil or electron.


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Track Etch Detectors

Mica,CR39

StruckNucleus

Large dE/dx

100 Å

Corrosive Etch

http://moedal.web.cern.ch/moedal/moedal_track.htm

Ancient Mica0.5109 yrExposure

fraction mm2

area


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Mica Result

58% 16O16% 28Si12% 27Al5% 39K

p (cm2) 10-37cm2

SD: 10-33cm2

Snoden-Ifft, Freeman, Price (1994)


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Superheated Droplet Detector (SDD)

10 m

Gelatin

Target, C2ClF5 (Liquid): Temp. > Boiling

0

Spin Dependent

15 gm

Collar et al., (2000)

10-36 cm2


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Lose the Gelatin… get all Target

Really a bubble chamber...CF3Br

Juan Collar and

Andrew Sonnenschein(poster session)


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NaI

Distinct Quantities to Measure

t

Gerbier et al., 1998

0.00001

0.0001

0.001

0.01

0.1

1

1 10 100

pulse time constant ns

0.00001

0.0001

0.001

0.01

0.1

1

1 10 100

pulse time constant (ns)

10-20keVLiquid XenonAlso a scintillator

(Spooner)

e- recoils from ’s

Nuclear recoils From neutrons

t (ns)1 10 100

’s

(50-100 keV ER)

Width of pulse

DAMA doesnot use this

NaI

ER: 130-150 KeV (I)

1) Time Structure of the Pulse2) Pulse Height/Area via:

a) Ionization (like Ge)b) Scintillation (like NaI)c) Heat/Phononsd) Physical Size of Ionization


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to electronsto electrons

Distinguishing Nuclear Recoil Nuclear recoil energy lost

mainly to collisions with other nuclei Nuclear recoils deposit lots of

energy in lattice excitations: phonons... heat

Nuclear motion poor at causing electronic excitation, ionization


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Simultaneous Measurement of Phonons(Heat) + Ionization

Temperature-20 mK Temp)/(Energy)

Temp)NTD Ge Slow (10’s ms)

Ionization - E applied

E

Background (e- from ) … strong ionization signal… equal phonon signal (!)

Nuclear recoil… reduced (by 1/4) ionization signal, strong phonon signal

Edelweiss


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Separation of Nuclear Recoil from e- Recoil

Shutt et al., 1992

Nuclear recoils (induced by a neutron source)

Electron recoils (induced by a source)

Slope really 1!

IonizationPhonons

=1 (bkgd)1/3 (sig)

Egap = 3/4 eVw = 3 eV


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Edelweiss (depth: 4500 mwe)

0.32 kg/ Ge detector

3×0.32kg GermaniumDetectors

Roman Lead

L. Chabert,EPS `03 Aachen


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Edelweiss Data: ’s Suppressed by 1000

● 7.51 kg.d exposure(fiducial volume)● Best charg. channel : 1 keV (FWHM)● 20 keV threshold

● 3.72 kg.d (fiduc.)● Smaller exposure due to electronics problems● 30 keV threshold

● 10.86 kg.d (fiducial)● Good phonon channel300 eV (FWHM) resolution during most of the runs● Noisy charge channel● 30 keV threshold

Bolometer 1 Bolometer 2 Bolometer 3



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Betas...

GermaniumElectrodeImplants

E

External Ionization electrons get trapped in this electrode

Those electrons never drift over to the other electrode… ionization signal reduced… but, all the phonons/heat still present… (ionization)/(phonons) < 1

z

CDMS effort: measure z


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Edelweiss and other’s results

CDMS no background subtraction hep-ex/030600128 kg-days (Ge, phonon/ion.)CDMS with background subtraction hep-ex/030600128 kg-days (Ge, phonon/ion.)

ZEPLIN I (preliminary)230 kg-days (Liq Xe)

EDELWEISS 2003no background subtraction31 kg-days (Ge, phonon/ion.)


DAMA/Edelweiss inconsistent at 99.9%...

... not accounting for differential systematics


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CDMS: not as deep… neutron background

17 mwe

Detectors Inner Pb shieldPolyethylene

Pb Shield

Active Muon Veto

Fridge

Copper

nn

n

R. Schnee... Experiment moved to

Soudan, 2100 mwe depth


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CDMS Layout, Data

ZIP 1 (Ge)ZIP 2 (Ge)ZIP 3 (Ge)ZIP 4 (Si)ZIP 5 (Ge)ZIP 6 (Si)

SQUID cards

FET cards

4 K0.6 K0.06 K0.02 K

4 Germanium Detectors (0.66 kg total) 2 Silicon Detectors (0.2 kg total) Small DM rate, high neutron rate

Nuclear Recoils

Surface electrons Z1 () or Z5 (+)

1/5000 ’s misid’ed as nuclear recoils

R. Schnee

8 cm


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Technology of `ZIP’s (Z for z)

Al

quasiparticle trap

Al Collector W Transition-Edge Sensor (TES)

Si or Ge

quasiparticlediffusion

phonons

Very different from Edelweiss, although the objective is the same… the `phono-cathode’

Cooper Pair

superconducting

normal

T (mK)Tc ~ 80mK

RTES

()

4

3

2

1

~ 10mK

• Signal much faster - microseconds

• 3-d imaging (Z)

R. Schnee


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The ZIP Phono`cathode’...

1 tungsten 380 x 60 aluminum fins

• 4 segments + timing to get x,y on the face• rise time to get z, into the face

R. Schnee


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ZIP Surface Electron Rejection

Neutrons from 252Cf source

(Single-scatter)

photons from60Co Source

Surface-electron recoils (selected via nearest-neighbor multiple scatters from 60Co source)

Accept

Reject

Surface electrons still likely to be the limiting background

R. Schnee


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CDMS Expected Background Levels

CDMS-II Proposal

0.0024

In DRU, ev/kg/kev/day

a bit dated; nowX10 better, surfaceelectron X2 better

0.000140.0005

0.00074


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Catalog of Recoil Experiments

Rick Gaitskell


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Future Performances R

ick

Gait

skell


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Prognostication


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A Proposal… 5 billion years ago…(indirect DM detection)

Get 1057 protons in a sphere (ignite to enable a neutrino program)Wait for WIMPs to collect (spin-dependent cross section - proton’s spin)Detect on a nearby iron ball via the annihilation of WIMPs (with themselves) to neutrinos

Review Panel’s Recommendations/Queries:1)What if WIMP’s don’t self annihilate… no answer 2) Hey, you’re ìron ball’ is great for collecting WIMPS via spin-independent scattering, since A of Iron is big (54)! (thanks)3) Funding for preliminary studies...


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Study Results...For SUSY WIMPs… 1) Sun, rate bottleneck is capture not annihilation 2) Earth, situation reversed 3) `Relative Efficiency’ function of WIMP mass

Earth… best whenWIMP mass same as Iron mass… same reason hydrogen is the best neutron moderator

Sun lower masses… little capture


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Solar/Earth Comparison

Annihilation Rate in Earth is Earth Bottleneck

Capture Rate in Earth is Earth Bottlneck (

for

dete

ctor

on

Ear

th)

(WIMP models for spin/scalar comparison)


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Super-Kamiokande’s Results... Upward going muons

Desai, IDM 02


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Transcribe to the Direct Detection Plot Model dependent… but less so than I thought.

Spin-dependent (Sun)

Scalar (Earth)

Desai, IDM 02


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Future Indirect Detectors (neutrino)

Feng, Matchev, Wilczek 2000


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Cosmic Positrons - Halo WIMP annililation HEAT… terrific balloon experiment… saw an excess

Edsjo, IDM 02


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Positron Future… ’s too

Feng, Matchev, Wilczek 2000


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m (

GeV

)

1

103

106

109

1012

10-3

10-6

10-9

1015

1018

1021

Davidson, Hannestad, Raffelt, hep-ph/0001179 Charge Fraction

Excluded Regions

Milli-CHAMP Limits

Overclose Universe(Thermal)


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Stable CHAMPs in Matter

Perl et al., hep-ph/0102033

DM, stop in earth


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Some conclusions Rutherford/Chadwick hunted neutron for 12 years

Hints first seen on continent, interpreted as photons… Neutrino studies started about 90 years ago…

Masses? Majorana? Still not fully nailed down... Dark Matter…

Prepare for a long ride… no physical law guarantees that discoveries happen within any human’s lifetime

The only guarantee: if we fail to look, we will fail to find.

Documents

Searches for Dark Matter (the Quest) Harry Nelson UCSB 2003 SLAC Summer Insitute Aug. 5-6 2003