July 2001 Neil Spooner WIMP LIMITS Update on WIMP Direct and Indirect Searches Neil Spooner, University of Sheffield Direct Results Towards 1 Ton and why

July 2001 Neil Spooner

WIMP LIMITSWIMP LIMITSUpdate on WIMP Direct and Indirect SearchesUpdate on WIMP Direct and Indirect Searches

Neil Spooner, University of Sheffield

Direct ResultsTowards 1 Ton and why

Indirect Results

Xenon

Directional


WIMP DIRECT DETECTION WIMP DIRECT DETECTION

WIMPWIMPMD MT

Expected featureless differential nuclear recoil energy spectrum for stationary detector ---> looks like electron background

• KinematicsKinematics

dRdE R

=Ro

Eore -ER/Eor

recoil energy

incident energy

kinematic factor = 4MDMT/(MD + MT)2

event rate per unit mass

total event rate (point like nucleus)

1 2 3 4 5 6 7 8 9 100

(Eor

/Ro)

*dR

(vE,v

esc)

/dE

R

E/(E0r)

0123456789

10

• Observed spectrumObserved spectrumdRdE = Ro S(E) F2(E) I(A)

obs

(1) Nuclear recoil discrimination(2) Directional signal


WIMP ModulationWIMP Modulation

6

600

~30 kms-1

~220 kms-1Sun

Earth

Jun 2nd

WIMPWIMP

Directional - diurnal

(Eor

/Ro)

dR/d

E

Annual modulation

E/(Eor)SMALL

BIG


Many ExperimentsMany Experiments

USC-PNL-ZaragozaNeuchatel-Caltech-PSIUCSB-UCB-LBLHDMS (Heidelberg-Moscow)GENIUS (Heidelberg)TANDAR-USC-PNL-ZaragozaGEDEON (MOZA collaboration)UKDMC (IC-Sheffield-RAL)NAIAD (UKDMC)DAMA (Rome)ELEGANTSSACLAYUSC-PNL-ZaragozaANAIS (Zaragoza)DAMA (Rome)ELEGANTS VI (Osaka, Otho)CASPAR (Sheffield)DAMA (Rome)MACHe3

ZEPLIN I (UKDMC)ZEPLIN II (UK-UCLA-Torino)DRIFT (UK-UCSD-Oxy-Temple)SIMPLE (Paris VII-Lisbon)PICASOSIMPLECRESST-I (MPI-TUM-Oxford)CUORCINO(Italy-US collab)CUORE (Italy-US collab)ROSEBUD (IAS-IAP-Zaragoza)PASS (UBC-Bayreuth)ORPHEUS(Bern)SALOPARD(Lisbon-Paris-Zaragoza)CDMS-I (US collaboration)CDMS-II (US collaboration)EDELWEISS-I (French collab)EDELWEISS-II (French collab)CRESST-II (MPI-TUM-Oxford)

Recent progress in WIMP dark matter detection reviewed by speakers at workshop on the Identification of Dark Matter (IDM2000) held in York, UK (18-22 September). 94 talks on Dark Matter

Ionisation

Thermal

Scintillation

Dual Techniques

Superheated Droplets

Directional


RESULTS - Spin DependentRESULTS - Spin Dependent

Limits on WIMP-proton cross-section.DAMA limits, PLB 1996;UKDMC limits, PRL 1996;CRESST, 2001;EDELWEISS, 1996

From CRESST


RESULTS - Spin IndependentRESULTS - Spin Independent

Limits on WIMP-nucleon cross-section.DAMA positive signal, PLB 2000;DAMA limits, PLB 1996;CDMS at Stanford, PRL 2000;CRESST, 2001;EDELWEISS, 2001


IONISATION DETECTORSIONISATION DETECTORS

• Ge (natural / enriched) ionisation detectors used by several collaborations.

• Detectors of high radiopurity and ultra-low visible energy threshold.

• Quenching factor ~ 25%.

• Ge isotopes moderately heavy (A~73) and reasonably sensitive to spin-dependent interactions.

• However…electron recoil background rejection impossible using this technique alone (although Compton veto possible).


HDMSHDMS

• Heidelberg Dark Matter Search (HDMS) use different approach.

• Active Ge shield surrounded by high purity Pb and Cu.

• Compton background events in inner detector vetoed by outer.

Prototype Parameters


HDMS ResultsHDMS Results

Current limits for 9.9 kgdays

New set up with Inner detector from enriched 73Ge, use of ultra high purity copper etc.

Experiment was installed at Gran Sasso in August 2000.

projected sensitivity but no discrimination, no identification of a signal possible.

IGEX, COSME…...


SCINTILLATION DETECTORS SCINTILLATION DETECTORS

• Established technique.

• Well-suited to large target masses (search for annual modulation).

• Detectors of high radiopurity (although not as pure as Ge).

• Often contain heavy nuclei (I, Xe) and nuclei sensitive to spin-dependent interactions (Na, F).

• Quenching factor often low (e.g. ~ 9% for I in NaI) and visible energy threshold higher than for bolometers => relatively high recoil energy threshold.

• BUT…..electron recoil background rejection possible using scintillation Pulse-Shape Discrimination (PSD).


DAMA - NaI Annual ModulationDAMA - NaI Annual Modulation

• New NaI 3/4 -38475 kg.days.• Total 4 years annual modulation - 57986

kg.days• Annual modulation few% of signal

-0.10

-0.05

0.00

0.05

0.10

300 600 900 1200 1500 1800

DAMA Annual Modulation 2-6 keV Bin

ResidualDAMA Fit

Residual (kg

-1

day-1

keV-1

)

Day Number

Residuals from 2-6 keV

INFN/AE-00/01

No recoil discrimination


DAMA RegionDAMA Region

Our estimated PSD limit that would be obtainable by DAMA

DAMA/NaI-0 - 4123.2 kgdays -pulse-shape analysis, limits;DAMA/NaI1-4 - 57986 kgdays -annual modulation, signal;Predictions for PSA for the wholedata set (DAMA/NaI0-4):improvement of limit by a factor of√[(57986+4123.2)/4123.2]=3.9

UKDM+Saclay paper, sub Astro-p


UKDMC NAIAD - Pulse Shape Dis.UKDMC NAIAD - Pulse Shape Dis.

low activity silica

light guides & PMT shield

double zone refined NaI(Tl) crystalPMT

Example time constant distributions for new crystal DM72 showing log

gauss neutron and compton fits and data.

E - 12-15 keV

neutron

Compton1996 limit from DM46 spin-independent

Schematic of early NaI detector e.g. DM46

NaI(Tl) Integrated Pulse-Shape


• Following improvement in DM46 (5 kg) - discovery of fast events in NaI

Data (E 35-40 keV)

calibration

Example histogram for DM46 showing anomalous events

Typical fast event energy distributions in various crystals of different geometry

Many tests performed on different crystals/configurations

NaI Anomalous Events (1998)NaI Anomalous Events (1998)

Anomaly


UKDMC NaI + SaclayUKDMC NaI + Saclay

• very similar spectrum of fast events seen again

RESULT

• this despite very different manufacture and geometry

• Collaboration with Saclay to run a “DAMA” crystal at Boulby

anomalous event spectra in NaI

Saclay (“DAMA”) spectrum

UKDMC spectrum


UKDMC spectrum


DM74 limit onfast event spectrum

UKDMC spectrum


DM74 limit onfast event spectrum

anomalous event spectra in NaI

• anomalous events reduced in NaIRESULT

• BUT at least 3-4 months exposure to Rn would be needed! - difficult to explain

• Confirmed with unencapsulated NaI (DM74)

distribution for pre-polished unencapsulated crystal DM74 after 5 mns operation

no fast eventswithin stat

Identification of the eventsIdentification of the events

Are the fast events in any way related to the DAMA result?


NAIAD - unencapsulated arrayNAIAD - unencapsulated array• 40-50 kg Unencapsulated surface controlled NaI

• 10 kg Saclay crystal

NaI unencapsulatedcraneglove

box

OFHC boxOFHC box PTFE PTFE crystal crystal cagecage


NAIAD Preliminary ResultsNAIAD Preliminary Results

ELEGANT CaF2,ELEGANT V, Canfranc… (annual modulation and inelastic scattering used)


CRYOGENIC BOLOMETERSCRYOGENIC BOLOMETERS

• Detect small temperature rise in solid caused by recoil energy deposit.

• Have advantage that almost any crystalline material can be used => possible target nuclei with high mass / spin-dependent coupling.

• Detectors of high radiopurity and ultra-low visible energy threshold.

• Quenching factor ~ 100% as most energy released as heat.

CRESST I, ROSEBUD, ELEGANT LiF, Milan TeO2…...

No background rejection with this technique alone.


COMBINED DETECTORSCOMBINED DETECTORS

• Discrimination between nuclear recoil signal events and electron recoil background possible by measuring relative pulse-heights in several different read-out channels of combined detectors.

• Retain benefits of individual techniques (low threshold, low background etc.)

• Very powerful technique used by many new experiments.

• Possibilities include:

– Ionisation / thermal (Ge or Si cryogenic bolometers).

– Scintillation / thermal (cryogenic scintillator crystals).

– Ionisation / scintillation (double-phase Xe detectors).


CDMS I (Ion/Therm)CDMS I (Ion/Therm)

• 1998 - 1.6 kg.days Si ZIP (4 recoil events observed)• 1999-2000 - 10.6 kg.days Ge BLIP (17 nuclear recoil events observed)

Present experiment - Ge and Si ionisation + thermal at Stanford SitePresent experiment - Ge and Si ionisation + thermal at Stanford Site

See a total of 13 recoil candidates events > 10 keV

event rate is in region of DAMA signal

electrons


CDMS limitCDMS limit

13 single NRs similar to that expected for DAMA

BUTstrong evidence that these events are

caused by neutrons --> 4 multiple scatter recoils observed in

Ge in same data

DAMA and CDMS experiments are incompatible at 99.76% CL

Although problem with neutrons due to shallow site

New analysis, new run at Sanford

Move to Soudan

CDMS 90% limits on WIMP-nucleon cross-section.

CDMS sensitivity because the number of multiple scatters observed is larger than expected, the limit is lower than the median simulated sensitivity

ConclusionConclusion


EDELWEISS (Ion/Therm)EDELWEISS (Ion/Therm)

320 g Ge detectorHeat and ionisation5.03 kgdays of exposureDashed vertical line - energythreshold


EDELWEISSEDELWEISS

New limit


CRESST-II (Scint./Therm)CRESST-II (Scint./Therm)

• CRESST propose use of CaWO4 cryogenic scintillator crystals.

• Detect light with existing Al2O3 thermal absorber technology.

• Tests show 99.7% discrimination at 15 keV recoil energy threshold!

• Propose 10 kg detector with 1 /keV/kg/day background.


CRESST II - PredictionsCRESST II - Predictions

CRESST, phase II

WIM

P-n

ucle

on [

pb]

Predictions for CRESSTPhase II30 kgyears of CaWO4

99.7% backgroundrejection above 15 keV

CRESST IIprediction


• To reach 10-10 pb

MotivationMotivation

• Ionisation - Germanium: GENIUS proposal for 100kg --> 1 ton ?

PossibilitiesPossibilities

• Scintillation - NaI: LIBRA (DAMA) 250 kg under construction

Intrinsic low background but NO discrimination and expensive (mainly )

• Ionisation/thermal - CDMS - Cryo-array ?:

Annual modulation (what if DAMA region ruled out), PSD not sensitive enough

Good discrimination but difficult technology and expensive

• XENON - ZEPLIN-MAX proposal for 1 ton - BDMC (UKDMC, US, Europe)

Good discrimination, world expertise, simpler technology(?), less expensive

TOWARDS 1 TON?TOWARDS 1 TON?

• Community needs to grow up ---> much larger collaborations

ImplicationsImplications• Detector needs recoil discrimination at scaleable cost


XENON XENON

• High-A target (Xe~130) for WIMP masses 50-500 GeV/c2 to reach 0.01/kg/d, and ultimately 0.0001 kg/d

Motivation for a big Xe programmeMotivation for a big Xe programme

--> Complements NaI low-A, q(A) > 0.2

--> satisfies basic requirement for:(i) recoil identification (ii) diagnostic array capability

• Powerful discrimination (typically x100 better than NaI) with different techniques and geometry possible

• Big scale-up potential (yet retains recoil identification)

• Lower cost than alternatives? (low temperature, Ge..)

--> experience of ICARUS, UCLA, Suzuki, Aprile,

• Prospects for isotopic enrichment better than Ge…...

• ICARUS-UCLA • ITEP• Doke group (Japan) • DAMA

World expertise

• UKDMC• Columbia


1 Ton Xe - ZEPLIN-MAX1 Ton Xe - ZEPLIN-MAX

ZEPLIN-Isingle phase

PSD4 kg

ZEPLIN-IIion-scint

two phase Xe30 kg

ZEPLIN-IIIIon-scint

two phase Xehigh field

6 kg

ZEPLIN array

under construction

existing ZEPLIN-MAXion-scint

two phase Xe1000 kg

MULTINATIONAL

concept

Larged staged programme towards 1 ton by the BDMC

UCLA, Columbia

UK DMC: Sheffield, ICSTM, RAL

European:

US:

Growing collaboration

ZEPLIN I,II,III

ITEP, CERN/Padova,Torino, Coimbra,

Boulby Dark Matter Collaboration (BDMC)

UKDMC


Pb shielding

Top of ZEPLIN I veto

Boulby stub 2 laboratory

xenon purification

XENON - ZEPLIN I,I,III (UKDMC et al)XENON - ZEPLIN I,I,III (UKDMC et al)

ZEPLIN I undergroundBOULBY stub 2 lab


ZEPLIN - 1 ton ConceptZEPLIN - 1 ton Concept

ZEPLIN-MAX A BDMC multinational programme

• Final design by mid 2002• Recoil Discrimination• Construction 2004+

Options being explored:(I) single unit, (II) 4 units, (III) modular(IV) mass + low threshold units

RESULT: (a) attain 0.0001/kg/d, (b) diagnostic array with complementary techniques

3 modules

80 kg target

4 sub- units

shielding

One possibility


ZEPLIN-XENON Predictions ZEPLIN-XENON Predictions

NaI 1996 limit

ZEPLIN 2002/3

ZEPLIN I/II 2003

ZEPLIN II/III 2004

10-3

10-4

10-5

10-6

10-7

10-8

10-9

10-10

10 100 1000

WIMP-nucleoncross-section, pb

WIMP mass GeV

CDMS II

CRESST II

ZEPLIN-MAX 2006

ZEPLIN predictionsbased on prototype tests and operation of ZEPLIN I

Other Xe: DAMA,

KAMIOKA (also plan 1 ton Xe)


DIRECTIONALDIRECTIONAL

• Q: What else can we do to identify a WIMP signal?

• A: We can be more cleverWe can be more clever: S(A,E: S(A,ERR) )

is in fact also function of recoil is in fact also function of recoil direction due to earth’s motion direction due to earth’s motion through DM halo. => through DM halo. => Search for diurnal modulation to signal in directional detector.

6

600

~30 kms-1

~220 kms-1Sun

Earth

Jun. 2nd

WIMPWIMP

S(A,ES(A,ERR) => S(A,E) => S(A,ERR,,) ~ exp(-((v) ~ exp(-((vEEcoscos - v - vminmin)/v)/v00))22))

D.N. Spergel, Phys. Rev. D 37 (1988) 1353


DRIFT ConceptDRIFT Concept

Negative Ion Drift

An old idea revisited by J. Martoff

E.W McDaniels et al., RSI 28 (1957) 864H.R. Crane et al., RSI 32 (1961) 953

E

CS2-

ions drift

Xe

WIMP

anode MWPC readout

cathode

• Longitudinal and transverse diffusion of ions is much less than for electrons

--> typically < 1mm per m

• No need for magnet

• Readout by conventional MWPC

• Use CS2 + Ar, Xe at 10-80 Torr• Electrons from ionised tracks reversibly attach to CS2 and drift to anode

gammas

recoil discrimination

C recoils

S recoils

gammas

recoil discrimination gammas

alphas

S recoil region (>90%)

alpha discrimination

1 foot cube detector @6keV: 99.9% gamma rejection, 95% alpha rejection (from wires)

(UKDMC collaboration with US - Oxy, Temple, LLNL)


DRIFT-1 Integration at SheffieldDRIFT-1 Integration at Sheffield

The first ever direction sensitive dark matter detector

A BDMC multinational programme


DRIFT 1 site

Installation Aug 01

DRIFT 1 - Installation Aug 01 DRIFT 1 - Installation Aug 01

Part of 1500 m2 new facility at Boulby - 3000 mwe depth


DRIFT-1 Predicted limitsDRIFT-1 Predicted limits

Full background audit for DRIFT-1 completed (tests and MCs)

a background of ~ 5 counts per year per m3 is feasible

• DRIFT-1 can yield a limit below DAMA

CONCLUSION

• DRIFT-1 could just detect a directional signal at 10-5 pb


Other Techniques - DropletsOther Techniques - Droplets• The peculiar requirements of direct search dark matter experiments also

lend themselves to the use of many other novel techniques…….

• Superheated liquid droplets sealed in gel matrix.• Nuclear recoil causes liquid to boil creating bubble.• LET of electron recoils insufficient to trigger bubble formation.• Widely used in nuclear industry for neutron dosimetry.

Superheated Droplet Detectors

SIMPLE PICASO

Detect bubble formation via piezo-electric transucers


SDD - ResultsSDD - Results

SIMPLE:0.19 kgdays - blue curve (limit)25 kgdays - red curve (projected sensitivity)

PICASO:CCl2F2, C3F8, C4F10, C2ClF5

1.34 g of freon117 days of data taking


Other Techniques - 3He - MACHe3Other Techniques - 3He - MACHe3

• Use 3He cell => recoil energy converted to quasi-particles which damp vibrating wires.

• Hole allows diffusion of excitations.

• Tag neutrons with inelastic excitation.

• Low Compton cross-section => low background rate.

• Ultra-low recoil energy threshold.

• Propose matrix of 1000 cells of 125 cm3 each!

Abstract 622, F. Mayet


Summary Direct LimitsSummary Direct Limits

• Current sensitivity ≈ 10-6 pb

– DAMA: NaI annual modulation of rate

– UKDMC: NaI ‘anomalous’ events seen also Saclay

– CDMS: needs neutron subtraction

– EDELWEISS: new result

http://cdms.berkeley.edu/limitplots/

-

-

-

-

-

New high mass, high discriminaiton detectors needed

XENON?

EDELWEISS

CDMS

DAMA


INDIRECT DETECTIONINDIRECT DETECTIONAnnihilation in Halo, Earth, Sun or Galactic Centre

WW,ZZ , ,gg , ... e

, p, ,, ..Halo: positron, antiproton, gamma secondary decay products,

mono-energetic gamma lines

Earth, Sun, Galactic centre: High energy neutrinos

Signature Experiment

Halo annihilationPositron, Antiproton

Gamma rays Z

BESS, CAPRICE, AMS, ..GLAST, VERITAS, MILAGRO,….

Earth, Sun, GC

NeutrinoSuperK, Baksan,IMB, MACROAMANDA, ANTARES, Baikal, …

• High degree of complementarity between direct and indirect searchesE.g. high m => low direct detection rate but substantial annhilation rate


Indirect Searches - ResultsIndirect Searches - ResultsMuons from Sun and Earth: SuperK, AMANDA B10, MACRO, Baksan

DAMA ann. mod si

Possible contradiction with DAMA?

Earth

Earth muon predictions - Bergstrom et al., Phys. Rev. D (1998)

SuperK00

limits

DF CowanSUN

MACRO99

Bergstrom, Edsjo, Gondolo 1998

SuperK00

Astro-ph/0007003 Astro-ph/9905021IDM2000


Indirect Searches - ResultsIndirect Searches - ResultsMuons from Sun, Erath and Galactic Centre: Super-Kamiokande

From Super-K contribution to ICRC2001

Super-K limit

CDMS limit

3 allowed region fromDAMA

Combined Sun, Earth and GC, from opposite plot, using Kamionkowski et al. (1995) conservative neutrino spectra to convert from muon flux limit to WIMP-nucleon cross section


Indirect Searches - FutureIndirect Searches - FutureFuture sensitivity: estimated comparison of CRESST, UKDMC, ANTARES

Predicted sensitivity ofunderwater/under-iceneutrino telescopes tospin-dependentWIMP-proton interactionsin comparison with directWIMP searches.

0.1 km2 x 3 yrs

CRESST

UKDM-Xe

ANTARES


Indirect Searches - HaloIndirect Searches - Halo

BESSCAPRICE

Antiproton flux at top of atmosphere: e.g. CAPRICE98, BESS balloon• In principle sensitive to neutralinos (high mass) but predictions difficult• Signal is featureless and depends on Solar wind/galactic propagation models • Background, from CRs on the ISM, also featureless including sub-100 MeV• Difficult to distinguish pure CR background from CR + neutralino Annihilation

upper and lower limit predictions for secondary antiprotons by Simon et al. (1998). (i.e. Background)

secondary antiproton flux predictions by Bergstrom and Ullio From CRs (1999).

Primary antiproton flux from 964 GeV neutralino annihilations in the halo. Ullio Astro-PH/9904086

Example comparison with specific model

Positron detection also suffers from lack of a clear signature

Positron fraction from HEAT

Best fit to excess 380 GeV neutralinos


Indirect Searches - HaloIndirect Searches - HaloGammas in the halo: e.g. ACTs and Space-borne - GLAST, VERITAS….

Bergstrom, Buckley, Ullio 1998

Example predictions

Z

• Advtg: directional information (like , unlike antiproton) and lines

• Most likely e.g. E = m

• But rates difficult to predict (SUSY param, halo profile)

• Recent MSSM calculations: • (i) ATCs (large areas) potential at highest

predicted rates, • (ii) GLAST (high resolution) potential <250

GeV

Needs cusp!


SummarySummary• DAMA NaI annual modulation as objective

WIMP or fluctuating low energy noise?

• UKDMC NaI ‘anomalous events’

Seen in Saclay (DAMA) crystal!

• CDMS recoil limit (almost) excludes DAMA

Subtraction of neutron signal

• Several detectors becoming sensitive at 10-6 pb

• Need 1 ton with high recoil discrimination to get enough counts …XENON very promising

• Indirect searches reaching sensitivities to exclude models

Documents

July 2001 Neil Spooner WIMP LIMITS Update on WIMP Direct and Indirect Searches Neil Spooner, University of Sheffield Direct Results Towards 1 Ton and why