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
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
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
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
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.
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
• 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?
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
ZEPLIN IZEPLIN I
Xe*
+Xe
Xe2*
Triplet27ns
Singlet3ns
2Xe2Xe
175nm175nm
Xe** + Xe
Xe2+
+e-
(recombination)
Xe+
+XeIonisation
Excitation
Electron/nuclear recoil
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
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
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
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-
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
Z1 Energy CalibrationZ1 Energy Calibration
Geant4 Simulation of 57Co calibrationWith/without energy resolution
Multi-source calibrationVariation in yield commensurate with volume response matrix
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
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)
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
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)
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
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
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
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
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
• ‘‘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
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
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
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
Dual phase discriminationDual phase discrimination.. but still keeping some interesting pulse shape properties on primary
Active volume: 30kg LXe
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
Zeplin 3Zeplin 3
Active volume 6kgGas phaseInverse field region
… 31 PMTs
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
Projected limitsProjected limits
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
Zeplin Max - towards 1t ?Zeplin Max - towards 1t ?
Zeplin-1 type
Zeplin-2 type
Zeplin-3 type
Modular approach ?
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
• 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?
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
Gotthard experiment:5.3kg Xe TPC62.5% 136Xe
in in 136136XeXe
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
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 ??
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
Pulse Shape analysis at high
Energygammas
Alphas (from different
locations)
Z1: Background at high EZ1: Background at high E
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
‘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
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
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
UK HEP Forum, May 03UKDMC - roland lüscher - RAL/PPD
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