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

UCSBHNN 8/6/03 SLAC Summer Institute 2 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 Particles Closing

UCSBHNN 8/6/03 SLAC Summer Institute 3  v DM  1/2  300 km/s 2  v DM  1/2 =0 km/s 2 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 8/6/03 SLAC Summer Institute 4 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

UCSBHNN 8/6/03 SLAC Summer Institute 5 DAMA – 100 kg of NaI Iodine, A=127 E obs (KeV ee )  0.09 E recoil (KeV) Sodium, A=23 E obs (KeV ee )  0.25 E recoil (KeV) E recoil  Light NaI PMT Copper Lead Poly

UCSBHNN 8/6/03 SLAC Summer Institute 6 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 8/6/03 SLAC Summer Institute 7 DAMA noise... >1 pe threshold <10 -4 cpd...

UCSBHNN 8/6/03 SLAC Summer Institute 8 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 Na I 33 44

UCSBHNN 8/6/03 SLAC Summer Institute 9 Halo Variation Kamionkowski and Kinkhabwala (1997)

UCSBHNN 8/6/03 SLAC Summer Institute 10 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… n  p) A 2   2 J(J+1) DAMA J  0  unpaired nucleon, odd A NAIAD (Boulby) (couple to proton spin)  p (cm 2 ) Couple to neutron spin LIBRA 250kg, NAIAD continues, ANAIS in Spain...

UCSBHNN 8/6/03 SLAC Summer Institute 11 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 8/6/03 SLAC Summer Institute 12 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 8/6/03 SLAC Summer Institute 13 dE/dx for different recoils Strategies Detector insensitive to small dE/dx (track etch, SDD) Convert E to two distinct measured quantities that look different depending on whether nuclear recoil or electron.

UCSBHNN 8/6/03 SLAC Summer Institute 14 Track Etch Detectors Mica, CR39 Struck Nucleus Large dE/dx 100 Å Corrosive Etch Ancient Mica 0.5  10 9 yr Exposure fraction mm 2 area

UCSBHNN 8/6/03 SLAC Summer Institute 15 Mica Result 58% 16 O 16% 28 Si 12% 27 Al 5% 39 K  p (cm 2 )  cm 2 SD: cm 2 Snoden-Ifft, Freeman, Price (1994)

UCSBHNN 8/6/03 SLAC Summer Institute 16 Superheated Droplet Detector (SDD) 10  m Gelatin Target, C 2 ClF 5 (Liquid): Temp. > Boiling 00 Spin Dependent 15 gm Collar et al., (2000) cm 2 

UCSBHNN 8/6/03 SLAC Summer Institute 17 Lose the Gelatin… get all Target Really a bubble chamber... CF 3 Br Juan Collar and Andrew Sonnenschein (poster session)

UCSBHNN 8/6/03 SLAC Summer Institute 18 NaI Distinct Quantities to Measure tt Gerbier et al., keV Liquid Xenon Also a scintillator (Spooner) e - recoils from  ’s Nuclear recoils From neutrons  t  (ns)  ’s ( keV E R ) Width of pulse DAMA does not use this NaI E R : KeV (I) 1)Time Structure of the Pulse 2)Pulse Height/Area via: a)Ionization (like Ge) b)Scintillation (like NaI) c)Heat/Phonons d)Physical Size of Ionization

UCSBHNN 8/6/03 SLAC Summer Institute 19 to 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

UCSBHNN 8/6/03 SLAC Summer Institute 20 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 8/6/03 SLAC Summer Institute 21 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! Ionization Phonons =1 (bkgd)  1/3 (sig) E gap = 3/4 eV w = 3 eV

UCSBHNN 8/6/03 SLAC Summer Institute 22 Edelweiss (depth: 4500 mwe) 0.32 kg/ Ge detector 3×0.32kg Germanium Detectors Roman Lead L. Chabert, EPS `03 Aachen

UCSBHNN 8/6/03 SLAC Summer Institute 23 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 8/6/03 SLAC Summer Institute 24 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 8/6/03 SLAC Summer Institute 25 Edelweiss and other’s results CDMS no background subtraction hep- ex/ kg-days (Ge, phonon/ion.) CDMS with background subtraction hep- ex/ kg-days (Ge, phonon/ion.) ZEPLIN I (preliminary) 230 kg-days (Liq Xe) EDELWEISS 2003 no background subtraction 31 kg-days (Ge, phonon/ion.) L. Chabert, EPS `03 Aachen DAMA/Edelweiss inconsistent at 99.9% not accounting for differential systematics

UCSBHNN 8/6/03 SLAC Summer Institute 26 CDMS: not as deep… neutron background 17 mwe Detectors Inner Pb shield Polyethylene Pb Shield Active Muon Veto Fridge Copper   n n n R. Schnee... Experiment moved to Soudan, 2100 mwe depth

UCSBHNN 8/6/03 SLAC Summer Institute 27 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 K 0.6 K 0.06 K 0.02 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

UCSBHNN 8/6/03 SLAC Summer Institute 28 Technology of `ZIP’s (Z for z) Al quasiparticle trap Al Collector W Transition-Edge Sensor (TES) Si or Ge quasiparticle diffusion phonons Very different from Edelweiss, although the objective is the same… the `phono-cathode’ Cooper Pair superconducting normal T (mK) T c ~ 80mK R TES (  ) ~ 10mK Signal much faster - microseconds 3-d imaging (Z) R. Schnee

UCSBHNN 8/6/03 SLAC Summer Institute 29 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

UCSBHNN 8/6/03 SLAC Summer Institute 30 ZIP Surface Electron Rejection Neutrons from 252 Cf source (Single-scatter) photons from 60 Co Source Surface- electron recoils (selected via nearest- neighbor multiple scatters from 60 Co source) Accept Reject Surface electrons still likely to be the limiting background R. Schnee

UCSBHNN 8/6/03 SLAC Summer Institute 31 CDMS Expected Background Levels CDMS-II Proposal In DRU, ev/kg/kev/day a bit dated;  now X10 better, surface electron X2 better

UCSBHNN 8/6/03 SLAC Summer Institute 32 Catalog of Recoil Experiments Rick Gaitskell

UCSBHNN 8/6/03 SLAC Summer Institute 33 Future Performances Rick Gaitskell

UCSBHNN 8/6/03 SLAC Summer Institute 34 Prognostication

UCSBHNN 8/6/03 SLAC Summer Institute 35 A Proposal… 5 billion years ago… (indirect DM detection) Get 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 `iron ball’ is great for collecting WIMPS via spin-independent scattering, since A of Iron is big (54)! (thanks) 3) Funding for preliminary studies... 

UCSBHNN 8/6/03 SLAC Summer Institute 36 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 when WIMP mass same as Iron mass… same reason hydrogen is the best neutron moderator Sun lower masses… little capture

UCSBHNN 8/6/03 SLAC Summer Institute 37 Solar/Earth Comparison Annihilation Rate in Earth is Earth Bottleneck Capture Rate in Earth is Earth Bottlneck (for detector on Earth) (WIMP models for spin/scalar comparison)

UCSBHNN 8/6/03 SLAC Summer Institute 38 Super-Kamiokande’s Results... Upward going muons Desai, IDM 02

UCSBHNN 8/6/03 SLAC Summer Institute 39 Transcribe to the Direct Detection Plot Model dependent… but less so than I thought. Spin-dependent (Sun) Scalar (Earth) Desai, IDM 02

UCSBHNN 8/6/03 SLAC Summer Institute 40 Future Indirect Detectors (neutrino) Feng, Matchev, Wilczek 2000

UCSBHNN 8/6/03 SLAC Summer Institute 41 Cosmic Positrons - Halo WIMP annililation HEAT… terrific balloon experiment… saw an excess Edsjo, IDM 02

UCSBHNN 8/6/03 SLAC Summer Institute 42 Positron Future…  ’s too Feng, Matchev, Wilczek 2000

UCSBHNN 8/6/03 SLAC Summer Institute 43 m (GeV) Davidson, Hannestad, Raffelt, hep-ph/ Charge Fraction Excluded Regions Milli-CHAMP Limits Overclose Universe (Thermal)

UCSBHNN 8/6/03 SLAC Summer Institute 44 Stable CHAMPs in Matter Perl et al., hep-ph/ DM, stop in earth

UCSBHNN 8/6/03 SLAC Summer Institute 45 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.