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

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