Recent Results from Direct Searches for Dark Matter with the...
Transcript of Recent Results from Direct Searches for Dark Matter with the...
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Recent Results from Direct Searches for Dark Matter with the
XENON100 Experiment
Institutstreff, 07 July 2011
Cyril Grignon
XENON group, JGU
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Evidence of Dark Matter
DM Halo surrounds our galaxy: good for detection !
NASA/WMAP
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Looking for Dark Matter
Particles collider (LHC): production and
detection (missing E)
Indirect detection: search products of an
annihilation
Direct detection: search for a WIMP-nucleus scattering within a
detector
Lots of candidates for Dark Matter : not in the standard model.
This candidate is: Long lived, Massive and undergo weak interaction
WIMP (weakly interacting massive particle), thermal relic
A popular candidate: the neutralino, as the lightest supersymetric particle (GeV-TeV)
Direct detection needed to prove that DM is coming from the Halo
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1 event/kg/yr
1 event/ton/yr
WIMP ExpectationsCMSSM: Trotta et al.CMSSM+LHC: Buchmueller et al.
WIMP Direct Detection
WIMP
v ~ 230 km/s
Recoil energy :
Events rate :
We need:- low E threshold- heavy nuclei- low background
Er < 100 keV
Rate from particle physics, nuclear physics and cosmology :
R < 0.01 evt/kg/day
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Backgrounds in Direct DM Search
Depth [meters water equivalent]Depth [meters water equivalent]
Muon inten sity [m
-2y-1]
Background Sources: α decays from Rn daughters..
and Decays (electron recoil) careful material selection, discrimination, shielding (Pb, Cu, Xe, Ar, water) Neutrons from (,n) in rocks neutron moderators (paraffin, poly, water) Neutrons from cosmic ray muons: Rate depending on depth. go deep underground
Electronic Recoils Nuclear Recoils(gamma, beta) (neutron, WIMPs)
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DM Direct detectors overview
Bubble FormationCOUPP, PICASSO
IonizationCoGeNT
ScintillationDAMA/LIBRAKIMS, XMASS,DEAP/CLEAN
Phonons
LAr: WARP, ArDMLXe: XENON, LUX, Zeplin
CDMS-II, Super-CDMSEDELWEISS-II
CRESST-II,ROSEBUD, EURECA
TrackingDrift, DM-TPC, NIT
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Liquid Xenonefficient, fast scintillator (178nm) high mass number A~131: SI: high WIMP rate @ low threshold high Z=54, high ~3 kg/l: self shielding, compact detector SD: 50% odd isotopes allows further characterization after detection by testing only SI or SD no long lived Xe isotopes, Kr-85 can be removed to ppt "easy" cryogenics @ –100°C scalability to larger detectors in 2-phase TPC: good background discrimination
M = 100 GeV, = 10-45 cm2
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The Liquid Xenon Dual Phase TPC Ionization + Scintillation
Wimp recoil on Xe nucleus in dense liquid (2.9 g/cm3) → Ionization + UV Scintillation
Detection of primary scintillation light (S1) with PMTs.
Charge drift towards liquid/gas interface.
Charge extraction liquid/gas at high field between ground mesh (liquid) and anode (gas)
Charge produces proportional scintillation signal (S2) in the gas phase (10 kV/cm)
3D position measurement: XY (from S2), Z (e- drift time): resolution ~ mmelectron recoil rejection to >99% via ionization/scintillation ratio (S2/S1)Multiple scatter rejection
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XENON100
161 kg LXe TPC 62 kg in target volume active LXe veto (≥4 cm) 242 PMTs (low radioactivity < 1mBq/PMT for U/Th) passive shield (Pb, Poly, Cu, H2O)
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XENON100 Background
Measured Background in good agreement with MC prediction.
At low energies: Lowest background ever achieved
in a Dark Matter Experiment!
Xenon keVee-Scale not precisely known below 9 keVee
30 kg fiducial mass active LXe veto not used for this plot exploit anti-correlation between light and charge for better ER-energy scale
No MC tuning!Values from
screening only.
PRD 83, 082001 (2011)
arXiv:1103.2125
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3D localization
164 keV electron recoil
S1
S2
3D reconstruction with mm resolution:- Fiducial cut to remove background- identify single/multiple scatter events
Phys.Rev.Lett.105:131302,2010
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Discrimination electron/nucleus recoils
99.75 % rejection @ 50% acceptance
definition of WIMP search region (ROI)
Co60
AmBe
-ray source
Neutron source
ER Band
NR Band
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Data analysis
Consistency Cuts: - S2 width cut (drift time ok? gas events) - position reconstruction - anomalous event rejection
single scatterinteraction
anomalousevent pattern
cathode
gate grid
blinded region
- data taken in first half of 2010- 100.9 life days- data blinded in ROI (Region Of Interest) defined with cuts optimized with calibration data
Data quality:- keep period with stable detector- remove period with electronic noise
Fiducial volume: - keep events inside the 48 kg
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Data analysis
S2 threshold
Energy window
Energy Cuts - low E region (S1) - S2 software threshold - require 2x S1 coincidence (against PMT dark current, noise)
Single Scatter Selection (WIMPs interact once !): - only one S2 peak - only one S1 peak - active veto cut - S1 PMT Pattern - S2 PMT Pattern (good xy reconstruction required)
NR calibration
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99.75 ER rejection
3 NR acceptance
Expected Background for - 48 kg fiducial mass - 100.9 live days - 99.75% ER rejection
Gaussian Leakage:1.14 ± 0.48
Anomalous Leakage:
0 .56 ± 0.25 Neutron Background:
0.11 ± 0.08
Total: 1.8 ± 0.6 events
prediction based on data and MC
prediction verified on high E sideband
Background prediction
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Observe 3 events likelihood for 3 or more events is 28% No observation of a WIMP signal !
calculate limit
Unblinding the data
Total expected background for the 100 days:
1.8 ± 0.6 events
arXiv:1104.2549, submitted to PRL
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XENON100 new limit
preliminary
90% CL
New Re
sult!
100.9 live days, exposure: 1471 kg×d Profile Likelihood limit based on side-bands from calibration Best SI limit over a large mass range. Minimum σs = 7.0×10-45 cm2 @ 50 GeV/c2 Strong tension with low mass WIMP interpretation for DAMA, CoGeNT, CRESST Inelastic DM as explanation for DAMA annual modulation ~ ruled out.
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Summary
XENON100
XENON1T
Dark Matter: One of the big unsolved puzzles
XENON100: the most sensitive experiment for WIMP direct detection
Best SI limit achieved : 7.0×10-45 cm2 @ 50 GeV/c2
Currently run 10 ongoing: 2.0×10-45 cm2 by the end of the year
Next step : XENON1T, goal of 10-47 reached by 2015
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Next step: XENON1T 2.4T LXe ("1m³ detector"), 1T fiducial mass 100x lower background (10 cm self shielding, QUPID) Timeline: 2010 – 2015 start construction end of 2011
See XENON posters !!
0.95 m
1.05 m
XENON1T @ LNGS
5 m water shield acting as active muon veto
10 m
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The XENON Collaboration
Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21