Dark Matter Overview Harry Nelson UCSB INPAC Oct. 4, 2003

UCSBHNN 10/4/03 INPAC 2 Outline Axions Massive Particles  Direct Detection  Weakly Interacting  No Strongly Interacting (interesting opportunities) See talks of Dave Cline (ZEPLIN), Patrizia Meunier (CDMS-II)

UCSBHNN 10/4/03 INPAC 3 Usual Simplifications of Dark Matter Local energy density, speed of DM Consists of one elementary particle (!) 0? ( )( ) … 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.

UCSBHNN 10/4/03 INPAC 4 Advice of Dennis the Menace

UCSBHNN 10/4/03 INPAC 5 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 ( cm 2 )… little unknown missing energy at LEP, Tevatron… mass>10’s GeV SUSY restored just above weak scale gives WIMPS W eakly I nteracting M assive P articles DM at rest:  v DM  =0 (sun plowing through at v 0  220 km/s)  v DM  1/2  300 km/s… useful to approximate  0 2 …Attractive candidates (axions, `*zillas’, etc.) were never in thermal equilibrium…

UCSBHNN 10/4/03 INPAC 6 a axion, couples to  … non- thermal, very light Round up the Usual Suspects  e   e -  0 p n -- Our Matter  0 (SUSY, neutralino, WIMP)

UCSBHNN 10/4/03 INPAC 7 Direct Detection Momentum Transfer v0v0 Convert a to photon – detect it axion m v0v0 target Cause target recoil – detect it Massive Particle

UCSBHNN 10/4/03 INPAC 8 Axions (and similar) (Dark matter) axion models  eV ( ADMX, LLNL-Florida-Berkeley-NRAO )

UCSBHNN 10/4/03 INPAC 9 Primakoff Conversion, Microwave Detection Solenoid Amplifier – power pours out of cavity when B 0 applied Cavity, `TM’ mode (E parallel to B 0 : 0 - ) L B = 50 cm Lower noise allows faster scanning….

UCSBHNN 10/4/03 INPAC 10 Signal Level and Noise W from Pioneer 10 Spacecraft, km away HEMT W   (s/n)  (time) Substantial improvements in T s are on the horizon (X30) from increased cooling, SQUIDS

UCSBHNN 10/4/03 INPAC 11 Nuclear Recoil – Cross Section A4A4

UCSBHNN 10/4/03 INPAC 12 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.)

UCSBHNN 10/4/03 INPAC 13 Event Rates... Rick Gaitskell Xe Nuclear Form Factor ~ several  ev/kg/d/keV

UCSBHNN 10/4/03 INPAC 14 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

UCSBHNN 10/4/03 INPAC 15  v DM  1/2  300 km/s 2  v DM  1/2 =0 km/s 2 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 Peak-to-peak up to 40% DAMA at Gran Sasso Fig. from DRIFT

UCSBHNN 10/4/03 INPAC 16 through 2000 … 4  DAMA Background and Signal through 2003 … 6.3  Bernabei et al., astro-ph/ Energy Spectrum Bkgd  1 cpd/kg/keV 2-6 KeV 8-24 KeV Na(23) KeV I(127)   cpd/kg/keV

UCSBHNN 10/4/03 INPAC 17 DAMA noise... >1 pe threshold <10 -4 cpd...

UCSBHNN 10/4/03 INPAC 18 DAMA Allowed Regions through 2003through 2000 (standard halo)  p (cm 2 ),  =  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3 44

UCSBHNN 10/4/03 INPAC 19 DAMA vs. Super-K Model dependent… but less so than I thought. Spin-dependent (Sun) Scalar (Earth) Desai, IDM 02

UCSBHNN 10/4/03 INPAC 20 00 v/c  7  Nucleus Recoils Dense Energy Deposition v/c small; Bragg Discrimination of Recoils Signal ErEr  v/c  0.3 Electron Recoils Background Sparse Energy Deposition ErEr Differences the Basis of Discrimination

UCSBHNN 10/4/03 INPAC 21 Simulation (by DRIFT) 40 keV Ar in 1/20 atm Ar13 keV e - in 1/20 atm Ar 5 cm Ar pushes other Ar atoms, none go very far. Electron pushes other electrons, all go far

UCSBHNN 10/4/03 INPAC 22 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

UCSBHNN 10/4/03 INPAC 23 Edelweiss (depth: 4500 mwe) 0.32 kg/ Ge detector 3×0.32kg Germanium Detectors Roman Lead L. Chabert, EPS `03 Aachen

UCSBHNN 10/4/03 INPAC 24 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 ● kg.d (fiducial) ● Good phonon channel 300 eV (FWHM) resolution during most of the runs ● Noisy charge channel ● 30 keV threshold Bolometer 1Bolometer 2 Bolometer 3   L. Chabert, EPS `03 Aachen

UCSBHNN 10/4/03 INPAC 25 Betas... Germanium Electrode Implants 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

UCSBHNN 10/4/03 INPAC 26 CDMS-II Projections ~1cal year, initial deployment

UCSBHNN 10/4/03 INPAC 27 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...