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Investigation of the muon-induced background of the EDELWEISS-II experiment. Astrid Chantelauze KIT – Karlsruhe Institute of Technology Université Blaise Pascal. Evidences of dark matter Strategies of detection Direct detection: EDELWEISS-II experiment

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slide1

Investigation of the

muon-induced background

of the EDELWEISS-II experiment

Astrid Chantelauze

KIT – Karlsruhe Institute of Technology

Université Blaise Pascal

1 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

overview
Evidences of dark matter

Strategies of detection

Direct detection: EDELWEISS-II experiment

Investigation of the muon-induced background:

Muon veto performances

Muon veto – bolometer coincidence analysis

Overview

2 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

since 6 centuries

Eppur si muove

Hello!

Barred Spiral Milky Way Illustration, Credit: NASA/JPL-Caltech/R. Hurt (SSC)

Since 6 centuries…

3 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

rotation of spiral galaxies using movement to measure mass
Rotation of spiral galaxiesUsing movement to measure mass

Vera Rubin (70s) showed that observation of rotation of

disks in their outer parts required a lot of invisible mass …

M33, Orange Observatory

E. Corbelli & P. Salucci MNRAS, 311, 441 (1999)

4 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

gravitational lensing

Image 1

Object

Cluster

Image 2

Gravitational lensing

ΩM= 1

ΩM= 0.3

Galaxy Cluster Abell 2218

as seen by the observer

Observer

N. A. Bahcall et al.,

Astrophysical Journal, 447, L81(1995)

5 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

new order of the universe

LCDM

ΩΛ

Ωnon-b

Ωb

ΩΛ

ΩM

New order of the universe:

Ωtot = ΩΛ + ΩM + Ωk

Ωk = 0.01 flat universe

G. Hinshaw et al., Astrophysical Journal, 170, 288 (2007)

S. Perlmutter, Physics Today, 56, 53 (2003)

6 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

new order of the universe1

LCDM

ΩΛ

Ωnon-b

Ωb

ΩΛ

ΩM

S. Perlmutter, Physics Today, 56, 53 (2003)

New order of the universe:

Ωtot = ΩΛ + ΩM + Ωk

Ωtot = ΩΛ + ΩM + Ωk

= 1.011 ± 0.012

7 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

slide8

4%

20%

as new unknown particles !

8 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

dark matter particle
4 main facts about its nature:

non-baryonic

weakly interacting

essentially stable, or at least have a life time long compared to the present age of the universe

cold = read slow-moving. More precisely, a cold dark matter candidate must be non-relativistic throughout the formation of largescale structure

Dark Matter particle

freeze-out of a weakly interacting massive (WIMP) when reaction rate drops below expansion rate

time t (t ~ T-2)

increasing <sAv>

thermodynamic

equilibrium

x = mc / T

Tfreeze-out~ 1/20· Mc

E. W. Kolb & M. S. Turner, The Early Universe, Frontiers in Physics, Vol. 69 (1990)

9 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

galactic wimp halo

Dark Matter in a cloud around the milky way

WIMP

WIMP

200 cm³

Galactic WIMP halo

≈72 Ge

  • Lightest Supersymmetric Particle (LSP)
  • mass 50 GeV to ~ 1000 GeV
  • relative speed 270 km/s (~ our orbital velocity around galactic center)
  • only a few keV of recoil energy
  • cross section
  • local WIMP-density

sc < 10-42cm2

rc 0.3 GeV/cm3 (1 per cup)

  • very very rare scattering events

(< 1 / week / kg)

in the same cup 60.000 ν

10 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

dark matter search

c

72Ge

Dark Matter search

Indirect DM search (cc annihilation)

cc ff needs astrophysical overdensities:

1. galactic center excess of cosmic rays (g´s & antimatter)

2. the Sun  energetic “solar” neutrinos (ne, nm, nm)

3. the Earth  “upward-going” muons from (nm, nm)

Production at Accelerators

Heavy strongly-interacting SUSY states (squarks, gluinos)

produced copiously in p-p collisions

 missing transverse momentum

Direct dark matter

elastic scattering on a nucleus

1. annual modulation

2. event-by-event discrimination

12 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

direct dm search detection schemes

WIMP

Direct DM search – detection schemes

…via elastic scattering off nuclei

Ge, CF3I, C4F10

Ge, Si

Ionization

CoGeNT

COUPP

Picasso

Edelweiss,

CDMS

10% energy

WArP, ArDM

Heat

Al2O3, LiF

liquid Xe/Ar

Target

100% energyslowestcryogenics

CRESST-1

Zeplin-3 , LUX,

Xenon-10/100

Light

NaI, liquid.Xe

1% energyfastestno surface effects

CaWO4, BGO

DAMA, Libra, Zeplin-1,

XMASS, KIMS, ANAIS

CRESST-2

WIMP

13 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

slide14

EDELWEISS @ Laboratoire Souterrain de Modane

FRANCE

ITALIE

Altitudes

1228 m

1263 m

1298 m

Distances

6210 m

12 868 m

0 m

14 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

germanium bolometers

300

Heat

200

100

0

0 100 200 300 400 500

t (ms)

Ionisation

100

0

0 2 4 6 8 10

t (ms)

Germanium bolometers

Guard ring

NTD sensor

m = 320g

Center electrode

  • Simultaneous measurement
  •  Heat @ 17 mK with Ge/NTD thermometer
  •  Ionization @ few V/cm with Al electrodes
  •  Evt by evt identification of the recoil by ratio Q = Eionization / Erecoil
    • Q = 1 for electronic recoil
    • Q  0.3 for nuclear recoil

15 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

standard q plot
Standard Q-plot

calibration of a 320g Ge bolometer with 252Cf

73Ge(n,n’g) 68.8 keV

13.3 keV

n/g discrimination > 99.9%

for Er >15 keV

Recoil threshold

20 keV

Ionization threshold 3.7 keV

O. Martineau et al., NIM A, 530, 426 (2004)

16 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

the edelweiss experiment
The Edelweiss experiment

One Germanium detector

Some layers of detectors

The cryostat when it’s closed

The shielding of the experiment

17 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

edelweis ii muon veto system
EDELWEIS-II muon veto system
  • 42 modules covering 100 m2

98% coverage

  • energy, timing

µ tracking capability

  • modular structure
  • read at both side

18 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

muon veto life time
Muon veto – Life time

position known thanks to user

position known via laser meas.

“veto closed”

“veto open”

July 2006 – July 2009:

835.9 live days = 76%; 85% of data “closed”

19 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

muon candidates
Muon candidates
  • Muon candidates:
  • Internal coincidence within a module
  • strictly more than one module hit
  • coincidence of two modules of different levels (module #4 and lower level)

m

20 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

muon rate
Muon rate

Geant-4 simulation

M.Horn, PhD thesis

21 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

through going muons
Through going muons

m

High multiplicity events → showers

  • expected time difference (vertical tracks):

Dt = 5.2m / 3×108 m/s ≈ 17 ns

  • obtained from the fit: Dt ≈ 19 ± 2 ns

→Δl = 5.7 ± 0.6 → non vertical

  • but still “downward going muons”

22 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

coincidence analysis
Coincidence analysis

Muon track

Ionization / Heat

removed !

Heat

Region of interest for WIMP signals

Heat

23 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

coincidence analysis with run 8
Coincidence analysis with Run 8

24 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

run 8 distribution of the time
Run 8 – Distribution of the time

as viewed in the muon veto

Time restarts with each run…

… perfectly continuous during a run

Connect correct veto period to run of s2 + same uncorrelated structure for other comput. → reconstrution of continuous a time line for all sub-systems

25 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

run 8 bolometer event building
Run 8 – Bolometer event building

∆tbolo > 500 ms

26 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

muon veto bolometers coincidences
Muon veto-bolometers coincidences

∆tbolo > 500 ms

> 1 veto module hit

Define an interval at

tveto - tbolo = +25 ± 10 ms

27 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

run 8 systematics of the muon veto bolometers coincidence interval

∆tbolo > 500 ms

Run 8 – Systematics of the muon veto-bolometers coincidence interval

> 1 veto module hit

Time interval

Low energy

High energy

Total excess

coincidence interval for Run 8

tveto - tbolo in [+15, +35] ms

28 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

run 8 coincidences at e r 250 kev

Erecoil < 250 keV

Erecoil ≥ 250 keV

measured events

16

28

expected accidentals

3.7 ± 0.2

2.9 ± 0.2

excess coincidences

12.3 ± 4.2

25.1 ± 5.5

signal/background

3.3 ± 1.4

8.7 ± 2.4

∆tbolo > 500 ms

Run 8 – Coincidences at ER < 250 keV

> 1 veto module hit

4 events at low Er, low Q:

(Er = 19 keV, Q = 0.26) (Er = 23 keV, Q = 0.17) (Er = 26 keV, Q = 0.23) (Er = 36 keV, Q = 0.31)

Erecoil < 250 keV

Muon-induced event rate: 0.04 events/kg.d

29 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

run 8 comparison with the simulation
Run 8 – Comparison with the simulation
  • 16 bolometers non compact
  • 15 keV < Edep < 250 keV
  • Single bolometer events

Erecoil < 250 keV

Measured: 0.04 events/kg.d

Expected from Geant4 simulation: ~ 0.03 events/kg.d

Geant-4 simulation

M.Horn, PhD thesis

hits/crystal (1/keV/day)

  • Compact geometry 120 bolometers
  • 1 keV < Edep < 250 keV
  • Multi hits

30

Energy deposit in bolometers/hit (keV)

30 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

run 8 coincidences at e r 250 kev1

∆tbolo > 500 ms

Run 8 – Coincidences at ER ≥ 250 keV

> 1 veto module hit

Erecoil ≥ 250 keV

coincidences with ● multi(bolo) = 1 ■ multi(bolo) > 1

and if multi(bolo) > 1 ∆ individual bolometer

3 events at low Er, low Q:

(Er = 16 keV, Q = 0.22) (Er = 34.9 keV, Q = 0.47) (Er = 35 keV, Q = 0.33)

Erecoil ≥ 250 keV

Muon-induced event rate: 0.1 events/kg.d

31 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

slide33

Run 8

Run 10

33 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

characteristics of run 8 and run 10
Characteristics of Run 8 and Run 10

34 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

new time stamp from the opera box
New time stamp from the OPERA box

as viewed in the muon veto

almost perfect

Removing time mismatches:

10-3 jumps

35 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

characteristics of run 8 and run 101
Characteristics of Run 8 and Run 10

36 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

run 10 events in the ntp file biplot heat vs ionization
Run 10 - Events in the ntp file: Biplot heat vs ionization

s1

Events which pass the adaptative threshold

Events which pass the adaptative threshold

Events which have ΣEH > 30 keV and ΣEI > 30 keV

37 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

characteristics of run 8 and run 102
Characteristics of Run 8 and Run 10

0.0107 Hz

38 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

run 10 bolometer event building
Run 10 – Bolometer event building

Events with ΣEH > 30 keV and ΣEI > 30 keV

∆tbolo > 500 ms

39 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

run 10 muon veto bolometers coincidences
Run 10 – Muon veto-bolometers coincidences

Events with ΣEH > 30 keV and ΣEI > 30 keV

∆tbolo > 500 ms

> 1 veto module hit

Define an interval at

tveto - tbolo = -5 ± 5 ms

40 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

run 10 evaluation of the muon veto bolometer coincidence interval
Run 10 – Evaluation of the muon veto-bolometer coincidence interval

Time interval

Low energy

High energy

Total excess

coincidence interval for Run 10

tveto - tbolo in [-15, +5] ms

Events with ΣEH > 30 keV and ΣEI > 30 keV

∆tbolo > 500 ms

> 1 veto module hit

41 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

run 10 coincidences at e h 250 kev
Run 10 – Coincidences at EH < 250 keV

Events with ΣEH > 30 keV and ΣEI > 30 keV

∆tbolo > 500 ms

> 1 veto module hit

Signal / Background = 2.4

Quality of coincident events

Erecoil < 250 keV

0 events at low EH, low Q !

Muon-induced event rate: 0.023 events/kg.d

42 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

run 10 coincidences at e h 250 kev1
Run 10 – Coincidences at EH ≥ 250 keV

Events with ΣEH > 30 keV and ΣEI > 30 keV

∆tbolo > 500 ms

> 1 veto module hit

EHeat ≥ 250 keV

coincidences with ● multi(bolo) = 1 ■ multi(bolo) > 1

and if multi(bolo) > 1 ∆ individual bolometer

EHeat ≥ 250 keV

1 event at low EH, low Q:

(EH = 294,2 keV, Q = 0.41)

in coincidence with (EH = 151.1 keV, Q = 1.08)

Muon-induced event rate: 0.1 events/kg.d

Signal / Background = 9.1

43 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

summary
Muon veto allows to access the muon event topology (tracking in time and energy) and the muon flux

Firstcombined analysis of both muon veto and bolometers

Identification of muon-induced events:

ER< 50 keV …………. dominated by neutrons

50 < ER < 250 keV …. electron like single hits

ER > 250 keV ……….. multi-bolometer events with single low-Q hits

Muon-induced events at ER<250 keV, for the EDW-II experiment:

G = 0.04 events/kg.d

New EDW bolometer (ID) – e/gbackground free

EURECA: joint effort of CRESST and EDW – 1 ton scale

Non vetoed µ-induced bg would be the limiting background

Summary

44 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

slide45

Investigation of the

muon induced background

of the EDELWEISS-II experiment

Astrid Chantelauze

KIT – Karlsruhe Institute of Technology

Université Blaise Pascal

45 | Astrid Chantelauze | PhD defense | Université Blaise Pascal | 04/11/09

slide46

25 ms

46 | Astrid Chantelauze | IK-Institutsseminar | KIT | 17/11/09