Dark Matter Overview

Harry Nelson

UCSB

INPAC

Oct. 4, 2003

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Outline Axions Massive Particles

Direct Detection Weakly Interacting No Strongly Interacting (interesting opportunities)

See talks of Dave Cline (ZEPLIN), Patrizia Meunier (CDMS-II)

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Usual Simplifications of Dark Matter Local energy density, speed of DM

Consists of one elementary particle (!)

ú0 ø 300cm3

MeVv0 ø 220

skm

(ì 0 ø 7â 10à 4)

0? (200-2000) (170-270)… from galactic astrophysics

, e,e- , p , n - 7 in our few percent of Univ.2 are composite… n ??

The DM particle that provides the clearest signal in a search might not be the most abundant – a strong argument for an eclectic mix of search techniques.

(ì 20 ø

21 â 10à 6)

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Advice of Dennis the Menace

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DM not baryons (CBR, BBN; Eros/MACHO) DM was once in thermal equibrium

Usual Simplifications of Dark Matter

mass > few keV (large scale structure)mass < 340 TeV (unitarity)

cross section with us weak (10-44-10-36 cm2)…little unknown missing energy at LEP, Tevatron… mass>10’s GeV

SUSY restored just above weak scale gives WIMPS

Weakly Interacting Massive Particles

DM at rest:vDM=0 (sun plowing through at v0 220 km/s)

vDM1/2 300 km/s… useful to approximate 02

…Attractive candidates (axions, `*zillas’, etc.) were never in thermal equilibrium…

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a axion, couples to … non- thermal, very light

Round up the Usual Suspects

e e- 0 p n -- Our Matter

0 (SUSY, neutralino, WIMP)

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Direct Detection Momentum Transfer

v0

Convert a to photon – detect it

axion

m v0 target

Cause target recoil – detect it

MassiveParticle

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Axions (and similar)

(Dark matter)axion models

1.9-3.4 eV (ADMX, LLNL-Florida-Berkeley-NRAO)

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Primakoff Conversion, Microwave Detection

Solenoid

Amplifier – power pours out of cavity when B0 applied

Cavity, `TM’ mode(E parallel to B0: 0- )

LB= 50 cm

Lower noise allows faster scanning….

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Signal Level and Noise10-17 W fromPioneer 10Spacecraft,1010 km away

HEMT 10-26 W

(s

/n)

(time)

Substantial improvements in Ts are on the horizon (X30) from increased cooling, SQUIDS

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Nuclear Recoil – Cross Section

A4

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WIMP Region Large Exposure, Background:DAMA (58K kg-days, NaI)ZEPLIN (230 kg-days, Xe)IGEX (276 kg-days, Ge Ioniz)

Small Exposure, Background:CDMS (28 kg-days, Ge P/I)Edelweiss (12 kg-days, Ge P/I)(DRIFT - gaseous, recoil dir.)

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Event Rates...

RickGaitskell

Xe Nuclear Form Factor

~ several 10-2 ev/kg/d/keV

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Compare with Common Background Rate

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

DRU

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vDM1/2 300 km/s2

vDM1/2 =0 km/s2

DAMA:Annual Modulation in Rate• `Usual Simplification’: Halo particles are at rest, on average• Sun moves through Halo - `apparent’ 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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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

I

3

4

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DAMA vs. Super-K Model dependent… but less so than I thought.

Spin-dependent (Sun)

Scalar (Earth)

Desai, IDM 02

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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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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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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

L. Chabert,EPS `03 Aachen

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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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CDMS-II Projections

~1cal year, initial deployment

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Some conclusions Axions searches about to become much more

sensitive WIMPs…

Next few years should get factor of 100 sensitivity High Mass, Bkgd versus Low Mass, Bkgd:

How well do very high mass detectors self shield?Can low mass, bkgd be mass produced with ever-lower

background requirements? Is Xe, with ionization, `middle way’?

INPAC...