Dark Matter detection with the XENON Experiment · SSI 2012 R. Budnik, Columbia University 10...

R. Budnik, Columbia University 1SSI 2012

Dark Matter detection with the XENON Experiment

Ranny BudnikColumbia University

On behalf of the XENON100 collaboration


N

χ

χNumber of targets

WIMPmass

WIMPdensity

Interactioncross section

NuclearForm factor

WIMPvelocity distribution

Only those WIMPs with velocity above threshold will contribute to signalFor Spin Independent interactions the cross section is enhanced by a factor A2 (coherent scattering)

Dark Matter Direct Detection

Expected interaction rate

Goal: Observe WIMP interactions with some target material

Reminder:


Liquid Xenon for Dark Matter Search

● Large atomic number A~131 best for SI interactions (σ~A2).Need low threshold.

● ~50% odd isotopes: SD interactionsIf DM detected: probe physics with the same detector using isotopically enriched media.

● No# long-lived Xe isotopes.But control Kr-85, Rn-222. #Xe-136 2νββ

● High Z (54) and density: compact & self-shielding

● Scalability to large mass.

● “Easy” cryogenics (-100°C).

● Efficient and fast scintillator.

● Good ionization medium, long drift.

● Background discrimination in TPC.

– Ionization/Scintillation

– 3D imaging of TPC

WIMP Scattering Rate


XENON100

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 (12 kV/cm)

● 3D position measurement

– X/Y from S2 signal. Resolution few mm.

– Z from electron drift time (~0.3 mm).


TimeA

mpl

itude

S1 S2

S1

S1

S2

S2

neg HVE~1 kV/cm

pos HVE~10 kV/cm

E

TPC = time projection chamber

Dual Phase TPC


Dual Phase TPC

151 µs

PR

L 107, 131 302 (2011)

Astropart. Phys. 35, 573 (2012)

NR

ER

ER

NR

3d Vertex Reconstruction Signal/Background Discrimination


The XENON program

Columbia Rice UCLA U Zürich Coimbra LNGS Mainz SJTU

Bologna MPIK NIKHEF Purdue Subatech Münster WIS

2005-2007:XENON10

XENON R&D

XENON: A phased WIMP search program 2010-2015: XENON1T

2008-201x: XENON100


XENON100

Goal (compared to XENON10):● increase target ×10● reduce gamma background ×100 material selection & screening detector design

Quick Facts:

● 161 kg LXe TPC (mass: 10 × Xe10 )

● 62 kg in target volume

● active LXe veto (≥4 cm)

● 242 PMTs

● passive shield (Pb, Poly, Cu, H2O, N2 purge)

Astropart. Phys. 35, 573 (2012)

161 kg LXe, 62 kg in target242 1'' x1'' PMTs

R. Budnik, Columbia UniversitySSI 2012

Laboratori Nazionali del Gran Sasso (LNGS)

LNGS: 1.4km rock LNGS: 1.4km rock (3700 mwe)(3700 mwe)


(spin-independent) WIMP Limit 2011

PRL 107, 131302 (2011)

XENON100 sets the most sensitivelimit over a large WIMP mass range

Challenges the CoGeNT, DAMA, CRESST-II signals as being due to light mass WIMPs

already cited 362x

Limit derived with Profile Likelihood methodPRD 84, 052003 (2011)

CRESST (2011)

SIMPLE (2011)

CRESST (2007, reanalysis)


(spin-independent) WIMP Limit 2011

PRL 107, 131302 (2011)

XENON100 sets the most sensitivelimit over a large WIMP mass range

Challenges the CoGeNT, DAMA, CRESST-II signals as being due to light mass WIMPs

already cited 362x

Limit derived with Profile Likelihood methodPRD 84, 052003 (2011)

CRESST (2011)

SIMPLE (2011)

CRESST (2007, reanalysis)

O U T D A T E D !!!


XENON100 :

new results for 2012


Data Taking

run_08

Data Collection Stability

Data taking over 13 monthsfrom Feb 28, 2011 to March 31, 2012→ full annual cycle

3 interruptions for maintenance

224.56 live days of dark matter data

To our knowledge, no largeLXe detector has ever been operated under such stable conditions for that long


Improvements● Exposure more than doubled

● Lower thresholdS2>150 PE, S1>3 PE (6.6 keVr)

● Lower Background

● Much more calibration data 35x more ER calibration in ROI AmBe before and after run

● Higher LXe purity → smaller corrections


Selected CalibrationsPosition dependent Corrections: Cs137, AmBe inelastic (40 keV), Xe* (164 keV)Kr83m (planned)

Agreement better than 3%

Electron Lifetime: Cs-137

375 – 610 µs (average 514 µs)

Electron Recoil Band (Background):Co60, Th232

Nuclear Recoil Band (Signal):Neutrons: AmBe

definition of WIMP search region, discrimination

P R E L I M I N A R Y

arXiv:1107.2155


ER/NR Discrimination

Discrimination comparable to previous runs: ~99.5% ER rejection @ 50% NR accpetance


Background of this Run


Data Analysis: All data

More information on XENON100 data analysis in arXiv:1207.3458

Blinded ROI


Basic Quality Cuts


Single Scatter Selection


Threshold and Fiducial Volume


Consistency Cuts

S2 Width:


Select Energy Range


ER Rejection

99.75%


WIMPs are Nuclear Recoil-like

„Benchmark Region“


Background Prediction

Neutron background:- (,n)+sf and muon induced neutrons- MC simulation using the exact XENON100 geometry and measured contaminations

Expect: (0.17 +0.12 –0.07) events

ER background:- activity of the detector and shield- intrinsic radioactivity in the LXe (→ lowered this run)- use ER calibration to model background by scaling it to the observable DM data

Expect: (0.79 +-0.16) events

Sum: (1.0 +- 0.2) events

The same background model is implemented in the PL analysis


During ...


… and after ...


… Unblinding

(1.0 0.2) events expected 2 events observed

→ 26.4% probability that background fluctuated to 2 events→ PL analysis cannot reject the background only hypothesis

No significant excess due to a signal seen in XENON100 data.


The new XENON100 Limit

2.0 x 10 – 4 5 cm² @ 55 GeV/c²Theory region combined from:Strege et al., JCAP 1203, 030(2012)Fowlie et al., arXiv:1206.0264Buchmueller et al., arXiv:1112.3564

ArXiv:1207.5988 PRL submitted


LNGS, Italy

XENON1T(2011-2015)

● Liquid xenon TPC to explore σ ~ 2×10-47 cm2

● Detector size: ~ 1 m3, ~ 3 t LXe, ~ 1 t fiducial mass

● Water Cerenkov Muon Veto● Approved by INFN.

● Funded.● Construction start: fall 2012.

XENON1T in Hall B (next to Icarus) @ LNGS

Next on the agenda:


The Future of Direct Dark Matter Searches(next ~5 years, the XENON perspective...)

Spin-independent sensitivity


… but we hope for a detection

For a WIMPwith 10-45 cm2

~100 events

(Assuming standard isothermal halo, 220 km/s, escape vel. 540 km/s)


XENON1T design challenges

Background* Xe purity (e- lifetime)

HVTotal Rn/Kr

XENON100 ~5∙10-3 dru (events/kg/keV/day)

Kr: ~20 pptRn ~65 μBq/kg

160 kg @ ~400 µs In several months

30 cm @0.53 kV/cm

XENON1T essentials

~5∙10-5 dru(Events/kg/keV/day)

Kr: 0.5 pptRn: ~1 μBq/kg

~3 tons @ ~1000 μsIn ~2 months

100 cm @ 1 kv/cm

By how much should we improve?

X 100Kr: X 40Rn: X 50

X 3 (purity)X 50 (purification

speed)X 6

* In FV, including Veto, before discrimination


Summary● XENON100 was continuously running for more than 1

year in reduced background conditions

● Observed 2 events with a background expectation of 1, set a 90% CL limit in the WIMP-nucleon cross section of 2.0x10-45cm2 for a 50GeV WIMP

● Next on the agenda for XENON100:

– More analyses of the data, e.g. SD, annual modulation and more

– Continue running XENON100 with lower Kr and Rn

● We begin construction of XENON1T and reach a sensitivity of ~2x10-47 cm2 by 2017


Backup

38SSI 2012

Impact of Leff● As an excersise, we have computed the same limit with the

approximation that Leff is 0 below 3 keVnr (red line in the figure)

● The impact on the limit is below 5% for all the relevant mass range


Energy Scale

Enr=S1

Ly⋅Leff

⋅Se

Sr

Measured signal

Light quenching due to electric field

for gammas @122keV

Scintillation eff.for nr at 0 field

Light quenching due to electric

fieldFor nuclear

recoilsLight yieldfor gamma @122 keV

40SSI 2012

Low mass WIMP in XENON100

m = 8 GeV/c 2 σ=1.0x10 – 40 cm2

41SSI 2012

CRESST-like WIMP in XENON100

m = 25 GeV/c 2 σ=1.6 x10 – 40 cm2


Events in Benchmark Region● visual inspection:

valid waveforms

● at 7.1 keVr and 7.8 keVrboth events between 3 and 4 PE

● rather low wrt the NR calibration data

● no low S2/S2-events below threshold

Dark Matter detection with the XENON Experiment · SSI 2012 R. Budnik, Columbia University 10...

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Transcript of Dark Matter detection with the XENON Experiment · SSI 2012 R. Budnik, Columbia University 10...