Dark Matter Experiments with Noble Gases
Transcript of Dark Matter Experiments with Noble Gases
Dark Matter Direct Search:
the XENON Experiment
José A. Matias Lopes
Universidade de Coimbra, 4 de Dezembro, 2008
What is our Universe made of?
Dark Energy
Atoms
Dark
Matter
Dark Matter from Gravitational Lensing
Galaxy Cluster Abell 2218
SUSY and Dark Matter
• Super Symmetry theory (SUSY) predicts:
• the existence of Weakly Interacting Massive Particles (WIMP) of dark matter
• interaction rate as low as 1 event /ton/year for exposure of tens of millions per sec.
The Via Lactea WIMP Halo
WIMP Detection: Scattering off Atoms
WIMP M. Attisha
WIMP
Nuclear
recoil
nuclear recoil spectrum
WIMP velocity distribution
f (v)dv
4v 2
v03
ev2 /v0
2
d3v
WIMP Detection: Elastic Scattering off Atoms
<V> = 220 km/s
Nuclei recoil energy:
Event rate:
ER
rq2
2mN
2v 2
mN
(1 cos) 50 keV
mmN
m mN
Q
Predicted Rates in Different WIMP Targets
Recoil energy [keVr]
MWIMP = 100 GeV/c2
σWN=4×10-43 cm2
Eth = 2 keVr
Differential rates Cross sections (normalized to nucleons)
CMSSM
Challenges of Direct Detection Experiments
n produced by fission and (α,n)
n produced by µ
muonsG. Heusser, 1995
hadrons
• Low event rates ⇒ ton-scale detectors
• Small deposited energies ⇒ low (~ few keV) energy thresholds
• Low backgrounds
• shield against cosmic rays (deep underground laboratories → µ-spallation reactions)
• low intrinsic radio-activity (ultra-pure materials → (α,n)-reactions)
• shield radio-activity from
surroundings (Pb, PE, H2O, etc)
• Good background rejection
• Particle identification
• nuclear vs. electron recoils
• Position sensitivity/fiducialisation
• Self-shielding
World Wide Direct WIMP Searches
Direct WIMP Detection Experiments
ER
LightCharge
Phonons
ZEPLIN, XENON,
LUX, WARP, ArDM
CRESST
ROSEBUDCDMS
EDELWEISS
DAMA, LIBRA,
XMASS, CLEAN,
ANAIS, KIMSHDMS, DRIFT,
GERDA, MAJORANA
COUPP,
PICASSO
NR WIMP
WIMP
Why Noble Liquids?
• Good Nuclear versus Electron Recoil discrimination
➡pulse shape of scintillation signal
➡ratio of ionization to scintillation signals
• High Scintillation Light Yields; transparent to their own light
➡low energy thresholds can be achieved
• Large Detector Masses are feasible
➡self-shielding => low-activity of inner fiducial volumes
➡good position-resolution in TPC operation mode (use ionization signal)
• Ionization Drift >> 1 m achieved
➡ corresponding to << ppm electronegative impurities
• Competitive Costs and Practicality of large instruments
Noble Liquids as Detector Media
• Liquid noble gases yield both charge and light
• Scintillation is decreased (∼ factor 2) when drift field to extract charge is applied
Z (A)BP (Tb) at
1 atm [K]
liquid density at
Tb [g/cc]
ionization [e-
/keV]
scintillation
[photon/keV]
He 2 (4) 4,2 0,13 39 15
Ne 10 (20) 27,1 1,21 46 7
Ar 18 (40) 87,3 1,40 42 40
Kr 36 (84) 119,8 2,41 49 25
Xe 54 (131) 165,0 3,06 64 46
Noble Liquids as Dark Matter Detectors
Differential rates
Integrated rates
MWIMP = 100 GeV/c2
σWIMP-N=4×10-43 cm2
Dense, homogeneous targets/detectors
High scintillation/ionization yields
Commercially easy to obtain and purify
Scintillation
Light
Intrinsic
Backgrounds
Ne (A=20)
$60/kg
100% even-even
nucleus
85 nm
requires
wavelength
shifter
Low BP (20 K), all
impurities frozen out
No radioactive isotopes
Ar (A=40)
$2/kg
100% even-even
nucleus
128 nm
requires
wavelength
shifter
Natural Ar contains 39Ar
at 1Bq/kg, corresp. to
~150 events/kg/day/keV
at low energies
Xe (A=131)
$3500/kg
50% odd nuclei
(129Xe, 131Xe)
175 nm
UV quartz PMT
window
No long lived isotopes85Kr can be removed by
distillation to ppt level
Charge and Light in Noble Liquids
triplet singlet Excitation/Ionization depends on dE/dx!
(recombination is stronger for NR)
=> discrimination of signal (WIMPs=>NR)
and (most of the) background (gammas=>ER)!
hνhν
2Xe 2Xe
ER Ionization
Excitation
Xe+
+Xe
Xe2+
+e-
Xe**+XeXe*
+Xe
Xe2*
VUV light: λ depends on gas
(85 nm Ne, 128 nm Ar, 175 nm Xe)
time constants depend on gas
( few ns/15.4μs Ne, 10ns/1.5μs Ar, 3/27 ns Xe)
excited molecular states
Noble Liquid Detectors: Existing and Proposed
Experiments
Single Phase
(liquid only)
PSD
Double Phase
(liquid and gas)
PSD and Charge/Light
Neon (A=20) miniCLEAN (100 kg)
CLEAN (10-100 t)
SIGN
Argon (A=40)DEAP-I (7 kg)
miniCLEAN (100 kg)
CLEAN (10-100 t)
ArDM (1 ton)
WARP (3.2 kg)
WARP (140 kg)
Xenon (A=131)
ZEPLIN I
XMASS (100 kg)
XMASS (800 kg)
XMASS (23 t)
ZEPLIN II + III (31 kg, 8 kg)
XENON10, XENON100,
XENON1t
LUX (300 kg)
XENON detection principle: Dual Phase Detector
• detects prompt (S1) light signal after a particle interacts in the active xenon
• drifts the charge, extracts into the gas phase and detects as proportional light (S2)
hν
e- Ed
Eg
Liquid Xe
Gas Xe
PMT array
PMT array
ER
hν
hν
hν
PMT array
PMT array
drift time
WIMP
S1 S2
drift time
Gamma
S1 S2
WIMP
gamma
electron recoil (ER)
nuclear
recoil (NR)
XENON at the Gran Sasso Laboratory
• since March 2006, in ex-LUNA box
• ~3100 m.w.e; muon flux ≈ 1 m-2 h-1
Muon Inte
nsity [m
-2y
-1]
Depth [meters water equivalent]
The first phase: XENON10
• March 06: detector first installed/tested outside the shield
• July 06: inserted into shield (20 cm Pb, 20 cm PE, Rn purge)
• August 24, 2006 – February 14, 2007: WIMP search run
The XENON10 Detector
•22 kg of liquid xenon
➡15 kg active volume
➡20 cm diameter, 15 cm drift
•Hamamatsu R8520 1’’×3.5 cm PMTs
•bialkali-photocathode Rb-Cs-Sb,
•Quartz window; ok at -100ºC and 5 bar
•Quantum efficiency > 20% @ 175 nm
•48 PMTs top, 41 PMTs bottom array
➡x-y position from PMT hit pattern; σx-y≈ 1 mm
➡z-position from ∆tdrift (vd,e- ≈ 2mm/µs), σZ≈0.3 mm
•Cooling: Pulse Tube Refrigerator (PTR),
➡90W, coupled via cold finger (LN2 for emergency)
Typical XENON10 Low-Energy Event
• 4 keVee event; S1: 8 p.e => 2 p.e./keV
S1
S2
S1 S2
Hit pattern of top PMTs
8 p.e. 3000 p.e.
drift time: 65 µs
XENON10 Performance at LNGS
• Stable pressure, temperature, PMT gain, liquid level, cryostat vacuum, HV...
➡ over many months (continuously monitored with ‘slow control system’)
PMT gain < ±2%
December 8, 06
Pressure: ∆P < ±0.006 atm
Temperature: ∆T < ±0.005 ºC
Start of WIMP Search Run
XENON10 Backgrounds :
Data and MC Simulations
x-y position of WS data
r < 8 cm fiducial volume cut
Data
MC total
Steel
PMTs
Ceramic FTs
Single hits in fiducial mass (8.9 kg)
• Gamma BG: dominated by steel (inner vessel and cryostat) and ceramic FTs
• Neutron BG: subdominant for XENON10 sensitivity goal (MC: < 1 event/year from
(α,n) in materials and < 5 events/year from µ-induced n’s)
164 keV 236 keV
XENON10 Calibrations: Gammas and Neutrons
energy scale
(S1 in p.e)
Nuclear recoil spectrum
164 keV
236 keVn-activated Xe:
Combined
energy
spectrum
AmBe source
n-activated Xe:
Anti-correlation of
charge/light
signals
57Co source
Data and Monte Carlo agree well:⇒ NR response at low energies well understood
XENON10 Blind WIMP Analysis Cuts
dt [μs] ↔ z
r < 8 cm fiducial volume cut
Wimp
search
region
3s
XENON10 WIMP Search Data
• WIMP search run Aug. 24. 2006 - Feb. 14, 2007: ~ 60 (blind) live days
• 136 kg-days exposure = 58.6 live days × 5.4 kg × 0.86 (ε) × 0.50 (50% NR acceptance)
WIMP ‘Box’ defined at
50% acceptance of NRs
(blue lines): [Mean,-3σ]
10 events in ‘box’ after all cuts
7.0 (+1.4 -1.0) statistical leakage
expected from the gamma (ER) band
50% NR
acceptance
~ 1800 events
2 6 8 10
1
34
57
9
Spatial Distribution of Events
‘Gaussian events’: nr. 3, 4, 5, 7,9
‘Non-Gaussian events’: nr: 1, 2, 6, 8, 10
Ev. nr. 1: S1 due to noise glitch (a posteriori)
Ev. 2, 6, 8, 10 -> not WIMPs!
Likely explanation: reduced S2/S1-events due to
double scatters with one scatter in a ‘dead’ LXe
region => no S2 for 2nd scatter
e-e-
e-
e-e-e-
-12 kV
ground
S1
S1
15 cm
1.2 cm
e-e-e-
-12 kV
S1
S1
15 cm
1.2 cm
15 c
m
XENON10 WIMP-Nucleon Cross Sections upper
limits for SI Interactions (90% CL)
Upper limits in WIMP-nucleon cross
section derived with Yellin Maximal
Gap Method [PRD 66 (2002)]
No background subtraction:
8.8 × 10-44 cm2 at 100 GeV/c2
(4.5 × 10-44 cm2 at 30 GeV/c2)
5.5 × 10-44 cm2 at 100 GeV/c2
(known background subtracted, not
shown)
factor 6 below previous best limit
WIMP mass [GeV/c2]
WIM
P-n
uc
leo
n S
I c
ros
s s
ec
tio
n [
cm
2]
CDMS-II
XENON10
Phys. Rev. Lett. , 100 (2008) 21303
XENON10 WIMP Search Results for SD
Interactions
Phys. Rev. Lett., 101 (2008) 91301
The XENON10 Collaboration
• Columbia University Elena Aprile, Bin Choi, Karl-Ludwig Giboni, Sharmila Kamat, Yun Lin, Maria Elena Monzani,
Guillaume Plante, Roberto Santorelli and Masaki Yamashita
• University of Zürich Laura Baudis, Jesse Angle, Ali Askin, Martin Bissok, Alfredo Ferella, Marijke Haffke, Alexander Kish,
Aaron Manalaysay, Stephan Schulte, Eirini Tziaferi
• Brown University Richard Gaitskell, Simon Fiorucci, Peter Sorensen and Luiz DeViveiros
• Lawrence Livermore National Laboratory Adam Bernstein, Chris Hagmann, Norm Madden and Celeste Winant
• Case Western Reserve University Tom Shutt, Peter Brusov, Eric Dahl, John Kwong and Alexander Bolozdynya
• Rice University Uwe Oberlack, Roman Gomez, Christopher Olsen and Peter Shagin
• Yale University Daniel McKinsey, Louis Kastens, Angel Manzur and Kaixuan Ni
• LNGS Francesco Arneodo and Serena Fattori
• Coimbra University Jose Matias Lopes, Luis Coelho, Luis Fernandes and Joaquim Santos
XENON100 (2008-2009)
• US/EU new collaboration to build 170 kg (70 kg fiducial) LXe detector in
(conventional: Pb, PE) XENON10 shield at LNGS
• Start of WIMP search data: early 2009
XENON10 XENON100
+ UCLA recently joined (now >30)
• x10 fiducial mass:170 kg LXe
(vs. 20 kg in XE10); 50 kg
fiducial mass (vs. 5 kg in
XE10).
• Improved shield (additional
inner copper layer)
• 242 R8520 PMTs with lower
background and higher QE (vs.
89 in XE10)
• a factor of 100 lower
background: lower background
stainless steel cryostat and
inner chamber
Bell
Top PMTs
Grids
Structure
Active LXe Shield
Teflon
Panels with
HV
Racetracks
Shield PMTs
Vacuum Cryostat
Bottom PMTs
Active LXe Target
Cathode Mesh
XENON100: a new detector
Status of XENON100:
Commission Phase at LNGS
• Cryostat, cryogenics, TPC with active veto installed underground and tested
• high-purity, double walled stainless steel cryostat assembled and tested at LNGS
• 242 (R8520) PMTs (98 top, 80 bottom, 64 in active LXe shield) installed, tested
170 kg
3
• Low activity PMTs: Hamamatsu R8520-06-Al
• 98 on top - 80 on bottom - 64 in active LXe shield
• QE~23% for top array; QE~33% for bottom array
XENON100: PMTs
Bottom PMT ArrayTop PMT Array
New XENON100 material screening facility
• Ultra-low background, 100 % efficient (2 kg) HPGe-spectrometer
• Shield: 5 cm of OFRP Cu (Norddeutsche Affinerie); 20 cm Plombum Pb (inner 5 cm: 3 Bq/kg 210Pb), air-lock system and Nitrogen purge against Rn
• First background spectrum: < 1 event/kg/day/keV above 40 keV
• Goal: screen all XENON100 detector/shield components for a complete BG model
Gator LNGS background
30 kg days (October 2007)
Gator Soudan background
44 kg days
XENON100 Materials Screened at LNGS Facility
Material 238U 232Th 40K 60Co
Stainless Steel
1.5mm (316Ti,
Nironit)
<2 mBq/kg <2 mBq/kg 10.5 mBq/kg 8.5 mBq/kg
Stainless Steel
25mm (316Ti, Nironit)<1.3 mBq/kg <0.9 mBq/kg <7.1 mBq/kg 1.4 mBq/kg
PMTs (R8520-AL) 0.25 mBq/PMT 0.19 mBq/PMT 7.0 mBq/PMT 0.67 mBq/PMT
PMT Bases 0.16 mBq/pc 0.10 mBq/pc <0.16 mBq/pc <0.01 mBq/pc
XENON100: expected Neutron Background
• internal neutron BG from detector materials + shield, from (α,n) and fission reactions
• numbers based on detailed MC, taking into account the measured U/Th activities of
all the materials
MaterialTotal
n-rate [yr-1]
Single NR rate
[μdru]
Stainless steel 17,7 0,29
PMTs 7,0 0,32
Teflon 16,8 0,97
Copper 1,6 0,01
Poly shield 416,3 0,49
Total 2,08 background from
muon-induced
neutrons is currently
being modeled
• background from U/Th/K/Co in stainless steel cryostat & PMTs
• active LXe veto shield on sides, and top/bottom of target mass
• <1 gamma; <0.2 neutron events for 2 month operation
XENON100: expected Gamma Background
<10 mdru
rate of single scatters (0-100 keV)
before S2/S1 discrimination
XENON100
XENON10
XENON100: projected results (2009)
XENON100 purification system
Kr distillation column
(down to ppt level)
Storage rack
Purification unit
(<0.1 ppm volatile/organics)
The XENON100 Slow Control
Set of instruments that locally monitors, records and controls most of the physical
parameters of the experiment.
Slow Control
Instrumentation
Xenon100 Detector
Pressures
Temperatures
Vacuum
Gas flow
Xe liquid levels
Photomultipliers
Anode
Cathode
Grids
High Voltages
Slow Control Server(Underground Computer)
Measures, controls,
records to disk and
makes them available to
the clients.
Runs the alarms through
emails and SMS
The XENON100 Slow Control
The Slow Control Structure
Slow Control Server
Internet
Alarms
SMS and Email
Slow Control Clients
Alarm Redundancy Server
Gets data from server and sends
status reports and email alarms.
Laboratori Nationali del Gran Sasso
Underground Facilities
0,0
0,5
1,0
1,5
2,0
2,5
3,0
0 3 6 9 12 15 18 21 24
E/N (10-17
V cm2 atom
-1)
Y/N
(
x 1
0-1
7 p
ho
ton
s e
lec
tro
n-1
cm
2 a
tom
-1)
this work
Santos et al., Monte Carlo [7]
Fraga et al., Boltzmann [11]
Fonseca et al. [17]
Fonseca et al., -90ºC [17]
Parsons et al. [13]
Bolozdynia et al. [14]
Akimov et al. [15]
Aprile et al., -95ºC [16]
Ngoc et al. [12]
Xenon
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0.0 5.0 10.0 15.0 20.0 25.0 30.0
E/N (10-17
V cm2 atom
-1)
Y/N
(x
10
-17 p
ho
ton
s e
lec
tro
n-1
cm
2 a
tom
-1)
Ar experimental
Ar Monte Carlo
Ar WARP
Xe experimental
JINST 2 (2007) P05001 Phys. Lett. B 668 (2008) 167-170
Absolute Electroluminescence Yield Measurements
Argon
R&D on Photosensors: Avalanche Photodiodes and
Gaseous Photomultipliers
XENON1T: the next step
• Possible new design with full coverage of PMTs.
• 3T Xe, 1T fiducial mass
• A new PMT (QUPID) designed by UCLA with Hamamatsu is under development . Alternative photosensors also under study (Coimbra & Columbia).
From XENON10 to XENON1T
DetectorsXENON10
(2006-2007)
XENON100
(2007-2009)
XENON1T
(2010-2012)
Fiducial Mass (kg) 5 50 1000
Gamma background
(dru:
events/kg/keV/day)
1 10-2 goal: <10-4
Neutron background < 1 per year < 1 per year goal: < 1/two years
Exposure 2 months 2 months 2 year
Photodetectors R8520lower bkg, higher
QE R8520QUPID, APD, GPMs
WIMP Sensitivity
at 100 GeV9 x 10-44 cm2 2 x 10-45 cm2
(projected)
3 x 10-47 cm2
(projected)
Future projected results
Summary
95%68% 1 event/kg/yr
1 event/t/yr
CDMS-II, XENON100, COUPP,
CRESST-II, EDELWEISS-II, ZEPLIN-
III,...
SuperCDMS1t, WARP1t, ArDM
XENON1t, EURECA, XMASS, ...
Many different techniques/targets are being employed to search for dark matter particles
Sensitivities are now approaching the theoretically interesting regions!
Next generation projects: should reach the ≲ 10-10 pb level => WIMP (astro)-physics
Nature 448, July 19, 2007
Theory example: CMSSM (Roszkowski, Ruiz, Trotta)