Double Beta Potential of Zeplin

UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD

Double Beta Potential of Zeplin

• Zeplin: brief summary of DM programme• Doing bb-search with a DM detector?

Can we do HDM search with CDM detectors?Very, very preliminary assessment

Roland Lüscher


Direct DetectionDirect Detection• Kinematics:Kinematics:

WIMPWIMPMD MT

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)

10

8

6

4

2

-2

0

0 5 10 15 20 25

Event Energy (keV)

Even

t Rat

e (e

vent

s/kg

/day

)

Raw spectrum

Noise corrected

Nuclear Recoil Limits

Predicted DM spectrum

Background rejection tools:(1) Nuclear recoil discrimination(2) Directional signal


Background DiscriminationBackground Discrimination• Nuclear recoil discriminationNuclear recoil discrimination

Signal Channel DifferencesGe, Si

40keV Nuclear RecoilM≈ 200GeVv = 230km/s

WIMP

Scintillation Ionisation Phonon

+ -

+ -

+ -+ -

Pulse Shape Differences

NaI, CsI, Xe Signal Channel Differences

Xe

Gamma ray(or beta decay)

40keV Electron Recoil

Different dE/dX, Range, etc.


• Heavy nuclei (A~130), sensitive to spin-independent interactions (Isi~A2).

• Isotopes with large spin-dependent factors, Isd~0.3 for 129Xe (23Na in NaI or 73Ge in Ge ~0.1) ...… as well as easier enrichement.

• Scintillation in UV (=175 nm), low visible energy threshold.

• Large quenching factor for Xe recoils g(A)>0.2 (I in NaI: g(A)=0.09, Na: g(A)~0.3), low recoil energy threshold.

• Low background• Scintillation properties enables Pulse-Shape

Discrimination (PSD) between background (electron recoil) and nuclear recoil events.

• Interesting ionisation properties …• Scale up possibilities (up to 1 ton ?)

LXe: Why using it?LXe: Why using it?


ZEPLIN IZEPLIN I

Xe*

+Xe

Xe2*

Triplet27ns

Singlet3ns

2Xe2Xe

175nm175nm

Xe** + Xe

Xe2+

+e-

(recombination)

Xe+

+XeIonisation

Excitation

Electron/nuclear recoil


ZEPLIN I InstallationZEPLIN I Installation

Pb shielding

Top of veto

Boulby stub 2 laboratory

xenon purification

Counts vs. time

Xe temp vs. time

room temp vs. time


ZEPLIN I Energy ResolutionZEPLIN I Energy Resolution

122 keV peak

136 keV peak (10%)

30 keV X-ray

92 keV recoil e-

Linear response 1.5 - 2.5 p.e./keV

(57Co calibration is effective point source)

Resolution

€

σ E( ) =1.24 E

57 Co Calibration

106 keV recoil e-


Z1 Energy CalibrationZ1 Energy Calibration

Geant4 Simulation of 57Co calibrationWith/without energy resolution

Multi-source calibrationVariation in yield commensurate with volume response matrix


Uniformity, light collectionUniformity, light collection

Scan through detector Scan through detector girthgirth

Scan through one PMT Scan through one PMT planeplane

Single PMT event

Trigger condition is set to ‘free-run’

Noise trigger

Bulk eventsTurret events

Double PMT event

Fiducial volume cut

• Part of detector response matrixPart of detector response matrix– 17% best, 14% bulk– Falls to 4% below Xe delivery pipe

• Light collection simulations allow S3 Light collection simulations allow S3 calculationscalculations

• S3 cut < 0.408 (66% on 1: S3 cut < 0.408 (66% on 1: 0.5 + 0.5/30.5 + 0.5/3))• Fiducial volume 3.1kg Fiducial volume 3.1kg

– (excluding turrets + ~1cm below)


cPCI DAQ systemcPCI DAQ system• Acqiris cPCI digitizers, 1ns sampling, 8 bitsAcqiris cPCI digitizers, 1ns sampling, 8 bits• Mean data rate: 2HzMean data rate: 2Hz• Max rate: 800 Hz (cal)Max rate: 800 Hz (cal)

Deadtime ~1 msDeadtime ~1 ms

• Dual Dual range DAQrange DAQ: : – one covers ‘high’ energy up to 150 keV (daily E cal)– 2nd is the dark matter interval, up to 40 keV.

(less digital noise at low E)(less digital noise at low E)


ZEPLIN I DiscriminationZEPLIN I Discrimination

0.00001

0.0001

0.001

0.01

0.1

1

1 10 100pulse time constant ns

0.00001

0.0001

0.001

0.01

0.1

1

1 10 100pulse time constant (ns)

• Using different fitting techniquesUsing different fitting techniques– Exp, Mean, mean to 90%, median

• Fitted ‘gamma’ density function in 1/Fitted ‘gamma’ density function in 1/• Surface calibrations data to 7keVSurface calibrations data to 7keV• Surface ambient neutrons to 4 keVSurface ambient neutrons to 4 keV

Gamma source

Neutron source

10-20keV

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0 5 10 15 20 25 30 35

observed energy keV


Statistical methodsStatistical methods

0.00001

0.0001

0.001

0.01

0.1

1 10 100fitted time constant ns

datagamma calGD fit

0.00001

0.0001

0.001

0.01

0.1

1 10 100fitted time constant ns

• 91 day livetime, 280kg.days data91 day livetime, 280kg.days data calibration from veto-ed eventscalibration from veto-ed events -density fit (actually in 1/-density fit (actually in 1/) as guide: smooth slope) as guide: smooth slope• Analysis: Analysis: 22 over signal region, poisson stat on tail over signal region, poisson stat on tail

2

Poisson


• ‘‘Standard’ DM modelStandard’ DM model• Nuclear physics: Nuclear physics: Quenching = 0.2, Form factorQuenching = 0.2, Form factor

ZEPLIN I limitZEPLIN I limit

Mass GeV

WIMP-Nucleon cross section pb

0.0000001

0.000001

0.00001

0.0001

0.001

1 10 100 1000 10000

EDELWEISS

ZEPLIN I

CDMS

IGEX

DAMA


Dual Phase XenonDual Phase Xenon

e- Applying an electric field

Electro-luminescence

Active,liquid phase

Gas phase

Primary-Scintillation

e- or nucl. recoil

• Prevents (part of) recombination• Measure both scintillation and

ionisation


Dual phase discriminationDual phase discrimination.. but still keeping some interesting pulse shape properties on primary

Active volume: 30kg LXe


Zeplin 3Zeplin 3

Active volume 6kgGas phaseInverse field region

… 31 PMTs


Projected limitsProjected limits


Zeplin Max - towards 1t ?Zeplin Max - towards 1t ?

Zeplin-1 type

Zeplin-2 type

Zeplin-3 type

Modular approach ?


• Low background• Scintillation properties enables Pulse-Shape

Discrimination (PSD) between background (alphas) and electron recoil events.

• Interesting ionisation properties …• Scale up possibilities (up to 1 ton ?)• 3 candidates to look at:

• 136Xe, with E0 = 2.48 MeV, 8.9% natural abundance• 134Xe, with E0 = 0.85 MeV, 10.4% natural abundance• 124Xe, with E0 = 0.82 MeV, 0.1% natural abundance

Phase-space factor, hence rate, is going with E05

World yearly of enriched 124Xe is … 5 liters!

-

-

+

+

LXe: Why using it?LXe: Why using it?


Gotthard experiment:5.3kg Xe TPC62.5% 136Xe

in in 136136XeXe


T 1/2 = (NA/0.136) A (M/(σB))1/2

A: Isotopic abundance 8.9% or 65%: Detector efficiency nearly 1M: Target mass 3.1 kg, 30kg, 250kgσ: Energy resolution 40 keV (p.e. statistics)

60 keV (extrapol. from low E, 1.2√E)

B: Background rate ? ? ?

What is it in Z1? Can I extrapolate to Z2? To Zmax?

Limit on Limit on 136136Xe Xe ??


Pulse Shape analysis at high

Energygammas

Alphas (from different

locations)

Z1: Background at high EZ1: Background at high E


‘Gamma-like’ background:~ exponential shape

Assuming a spectroscopic smearing due to the varying light collection efficiency through the active volume - a quick ‘back of the envelope’ estimate:

0.05 counts/kev/kg/yearT1/2 > 1.9 x 1024 yr (90%CL, assuming enrichment of 65%, 1yr data)

=> 0.9 - 2.5 eVDama, 6.5kg LXe DM detector, 68.8% 136Xe: T1/2 > 1.2 x 1024 yr

PLB, 546 (2002) 23

Gotthard, 5.3kg Gxe TPC, 62.5% 136Xe: T1/2 > 4.4 x 1023 yrPLB, 434 (1998) 407

Z1: possible limit on Z1: possible limit on


Zeplin 2: 30kg, same background rate (?)

> 5.9 x 1024 yr, < 0.5 - 1.4 eVZeplin Max: 250kg module, same background rate (?)

> 1.7 x 1025 yr, < 0.3 - 0.8 eVTo be compared with: < 0.1eV (Cuore), < 0.02 eV (Genius, EXO)

(for 1 ton, 1yr) 0.35 eV (Heidelberg-Moscow claim)

Competitive with large scale expt. … … but only if we can B (factor 10)

Extrapolation to Z2 and ZMaxExtrapolation to Z2 and ZMax


ConclusionConclusionCan we do HDM search with Zeplin?

May be, yes!Slight problem: isotopic enrichment would be needed …

……… buy one get, one free?!?Well, what about a free cookie?

WIMP spin in/dependant cross section studies -- would require some isotopic separation!

128Xe 129Xe 130Xe 131Xe 132Xe 134Xe 136Xe1.9 26.4 4.1 21.2 26.9 10.4 8.9

Odd Even

Documents

Double Beta Potential of Zeplin