KIT – Universität des Landes Baden-Württemberg undnationales Forschungszentrum in der Helmholtz-Gemeinschaft

Benjamin Schmidt, IEKP, KIT Campus North, EDELWEISS experiment

www.kit.edu

Photo by Böhringer Friedrich

Data analysis and background investigation in the EDELWEISS direct dark matter search

EDELWEISS, IEKP, KIT2

The corner of the dark we are looking at

Benjamin Schmidt

Earth moves through DM halo

ρDM = 0.3 GeV/cm3

ER ~ 10 keV

<v> ≈ 230 km/s

M ~ 100 GeV/c2

q q

t

t

tScattering

Annihilation P

rodu

ctio

n

EDELWEISS, IEKP, KIT3

WIMP() direct detection

ER ~ 10 keV, Count rate: < 1 evt / (kg·year)

Benjamin Schmidt

Heat

Ionization

Light

LXe, LAr

NaI, LXe, LAr

Ge, Si

CaWO4, BGO

Al2O3, LiF

1% energyfastest,no surface effects

10% energy

100% energyslowest,cryogenics

WIMP

Target

Ge, CS2, C3F8, He3

EDELWEISS, IEKP, KIT4

The EDELWEISS experiment

Benjamin Schmidt

Polyethylene shield

Pb shield

Cryostat with bolometers

µ-veto

µ-n counter

Sensitivity Goal: s-n = a few·10-45 cm2 (< 10-3 evt/kg.d)

Cryogenic installation (18 mK) :Can host up to 40 kg of bolometer

Shieldings : Clean room + deradonized airActive muon veto (>98% coverage)PE shield 50 cm Lead shield 20 cm

Background studies :Radon detector down to few mBq/m3

thermal neutron monitoring (He3 det.)Muon-veto – bolometer coincidencesStrong AmBe source calibrationsStudy of muon induced neutrons (liquid scintillator 1 m3 neutron counter)

Shielding: ~ 4850 mwe m-flux (lab): ~ 5 m / m2 / day

µ

EDELWEISS, IEKP, KIT5

Muon-induced background

Muons cause high energetic electron recoilsHowever, muon-induced secondaries and especially muon-induced neutrons constitute low energetic background that scatters off nuclei

Before veto: 0.008 (WIMPlike) evts/(kg·d)

Benjamin Schmidt

- All events- Fiducial events- Potential background for DM search

Muon induced bolometer events (1504 kg·d)

EDELWEISS, IEKP, KIT6

Quantification of muon flux and muon veto efficiency – measurements and MC simulation

Muon veto efficiency1st method: (Measurement only) ε = (candidates in bolos/ evts in muon veto system)

ε ≥ 92,8% (90%CL) (34/34 observed)

2nd method: (Measurement + MC simulation) Determine trigger efficiency of each muon veto module; Simulate experiment with measured efficiency curves

ε = (97.7 ± 1.5) %Irreducible background flux 2·10-4 evts/(kg·d) (MPV)

Muon flux (horizontal area)Measurement + MC simulation: (5.4 ± 0.2 +0.5 -0.9) m/m2/d

Benjamin Schmidt

EDELWEISS, IEKP, KIT9

Topography of muon-induced events

Benjamin Schmidt

Distance of muon track to detectors- All detected muons (scaled)- Muons with secondaries in

bolometers (coincidences)- Coincidences EBolo < 1 MeV- Coincidences EBolo > 1 MeV

Lead identified as main target for the production of muon-induced neutronsMuon induced events produce multiple hits – 2nd handle for rejectionBenefits from more detectors and new PE shield in EDW-3

EDELWEISS, IEKP, KIT10 Benjamin Schmidt

A: +4 VB: 1.5V

C: 4 VD: +1.5V

Nuclear recoil event discrimination & Surface event rejection- principle

Bulk/Fiducial eventCharge collected on electrodes A&C

Surface eventCharge collected on electrodes A&B

NTD Phonon/Heat sensor = calorimetric measurement of total energy (T=18 mK, DT 0.2 mK/keV )

Al electrodes Ionization measurement ( sub-keV resolution)

Ionization yieldQ = EI/ERec nuclear recoils have ~1/3 Q of e-recoils

Event discrimination via simultaneous charge and phonon measurement

Fiducial volume

Count rate:

< 1 evt/kg/year!

WIMP100 GeV/c2

Scatt. WIMP Recoil nucleus ER ~10 keV

A A AB B

D DC C

EDELWEISS, IEKP, KIT11

Outlook on data analysisTasks: 1st optimization of noise selection in optimal filter2nd adaptation of filtering techniques to new hardware

Benjamin Schmidt

Goal: improve stability and performance of optimal filterpotential gain in low mass WIMP region

Time domain

Frequency domain

EDELWEISS, IEKP, KIT12

Tasks: Investigation of potential of new hardware

Currently a new DAQ-system is being developed at KIT(talk by B. Siebenborn)

Features fast 40 MHz read-out of ionization channelsTime-resolved measurements of charge propagation Better understanding of detectors plus new possibilities for surface event discrimination

Benjamin Schmidt

Fiducial Volume> 600 g

EDELWEISS, IEKP, KIT13

Results expected for background free measurement

Benjamin Schmidt

EDELWEISS, IEKP, KIT14

While I have got the word:

The hike todayThe easy way - just follow me13.30 o’clock from the castle

There are also GPS-data and descriptions availablehttp://www.outdooractive.com/de/wanderung/nordschwarzwald/durch-das-wildromantische-monbachtal/1398559/download.html#axzz2COBW0Gc2

Benjamin Schmidt

EDELWEISS, IEKP, KIT15 Benjamin Schmidt