GERDA and GeDet Project Review 2010 Fabiana Cossavella for GERDA - - PowerPoint PPT Presentation

GERDA and GeDet Project Review 2010

Fabiana Cossavella for GERDA & GeDet groups

Max-Planck Institut f¨ ur Physik, M¨ unchen

21 December 2010

Fabiana Cossavella GERDA and GeDet Project Review 2010 1/27

Director: Allen Caldwell Project leaders: B´ ela Majorovits (GERDA), Iris Abt (GeDet) Postdoc: Fabiana Cossavella, Josef Janicsko, Xiang Liu (03/10), Christopher O’Shaughnessy PhD: Neslihan Becerici-Schmidt, Sabine Dinter, Daniel Lenz (03/10), Oleksandr Volynets Diplomand: Hossein Aghaei-Khozani (11/10), Florian Faulstich, Sabine Hemmer (09/10), Annika Vauth (10/10) Group engineer: Hans Seitz, Franz Stelzer Engineering: Karlheinz Ackermann, Sven Vogt Many thanks to the Sonja Boisnel, Reinhard Sedlmeyer, Dominik Wamsler, Alex Wimmer, G¨ unter Winklm¨ uller and the colleagues from electronic & mechanic departments

Fabiana Cossavella GERDA and GeDet Project Review 2010 2/27

Search for 0νββdecay

Unknowns about Neutrinos:

• Nature of the Neutrino (Dirac - Majorana?)
• Absolute mass scale? Inverted/normal hierarchy?
• CP phases?

If neutrinoless double beta-decay is observed: Neutrino is a Majorana particle Information on absolute mass scale

1/ τ = G(Q,Z) |M nucl| 2 <mee>2

0νββ Decay rate Phase space factor Matrix element Effective Majorana Neutrino mass

Δm32 > 0 eV Δm32 < 0 eV degeneracy

F.Feruglio et al., Nucl.

• Phys. B 637(2002)

90% CL Δm32 > 0 eV Δm32 < 0 eV degeneracy

F.Feruglio et al., Nucl.

• Phys. B 637(2002)

90% CL

Evidence from Heidelberg- Moscow-Experiment

Δ L=2, beyond SM

• n

e e p n p

w- w-

Fabiana Cossavella GERDA and GeDet Project Review 2010 3/27

Search for 0νββdecay

Signature: Sharp peak at Q-value of the decay (2039 keV for 76Ge)

Fabiana Cossavella GERDA and GeDet Project Review 2010 4/27

The GERmanium Detector Array

Detector array Liquid argon Cryostat (steel + Cu) Water tank (steel) Muon veto (Č) Lock system Clean-room

Phase I: Use HdMo and IGEX detectors (18kg) Phase II: Use additional detectors from 37.5kg available enriched material

Fabiana Cossavella GERDA and GeDet Project Review 2010 5/27

Deployment of 1st string

◮ infrastructure completed in

May 2010

◮ 1st string of natGe installed in

June 2010 background measurement ongoing since June 2010

Fabiana Cossavella GERDA and GeDet Project Review 2010 6/27

Deployment of 1st string

500 1000 1500 2000 2500 3000 3500 10 10

2

10

4

Energy (keV) Counts 500 1000 1500 2000 2500 3000 3500 10 10

2

10

4

Energy (keV) Counts 500 1000 1500 2000 2500 3000 3500 10 10

2

10

4

Energy (keV) Counts 4.0 keV FWHM 4.2 keV FWHM 4.4 keV FWHM GTF 45 GTF 32 GTF 112

228Th calibration spectrum

Fabiana Cossavella GERDA and GeDet Project Review 2010 7/27

GERDA background

Distinct peak at 1525 keV

C

• n

t i n u

• u

s b a c k g r

• u

n d f r

• m

e l e c t r

• n

s

◮ background contributions due to 232Th, 238U:

< 1.2 · 10−2counts/(kg keV y)

Fabiana Cossavella GERDA and GeDet Project Review 2010 8/27

GERDA background

Distinct peak at 1525 keV

C

• n

t i n u

• u

s b a c k g r

• u

n d f r

• m

e l e c t r

• n

s

◮ 42K+ drift in the electric field ◮ Changing field configuration changes intensities → best

background: 8 · 10−2counts/(kg keV y) at Qββ

◮ further studies ongoing

Fabiana Cossavella GERDA and GeDet Project Review 2010 8/27

GERDA enriched material

Reduction in H 2 atmosphere

enrGeO 2 powder enrGe metal bars

Zone refinement

enrGe 6N metal bars suitable

for HP enrGe crystal growth

Reduction yield

98.5%

Zone refinement yield

95.3% , overall 93.9% Material reduced and purified with yield > 80% (target)

Fabiana Cossavella GERDA and GeDet Project Review 2010 9/27

Crystal pulling for n-type HPGe detectors

Cooperation with IKZ, Berlin: Czochralski puller procured, Refurbrished and electropolished. Many crystals grown. One crystal with few 10 10 per cm3 But most crystals with ~10 11 per cm3 Still one order of magnitude too high 6N Material from PPM is already very clean

Pulling HPGe crystals is not trivial! Worlwide only three companies.

Fabiana Cossavella GERDA and GeDet Project Review 2010 10/27

The final lock system

Outer Lock Inner Lock Cable Feedthrough Motor Feedthrough

assembly starts after delivery of the 3-string arm of c-lock

Fabiana Cossavella GERDA and GeDet Project Review 2010 11/27

GeDet Project

Development of segmented n-type Germaniun detectors for future applications

1 Ton initiative

◮ push further down sensitivity ◮ normal or inverted hierarchy? ◮ 1 Ton of enrGe ◮ background index = 10−5 cts

keV−1kg−1y−1

Properties of Ge detectors

◮ study of surface events

induced by α and β

◮ study of pulse shape details to

identify surface events and multiple interaction → background reduction

Fabiana Cossavella GERDA and GeDet Project Review 2010 12/27

Test Stands: detector characterization

K1 test stand: detector operated in vacuum cryostat (T from 90 K to 120 K), γ scans only task completed → prototype detector for a GERDA scale experiment

“Characterization of the first true coaxial 18-fold segmented n-type prototype detector for the GERDA project”, Iris Abt et al., Nucl.Instrum.Meth. A 577 (2007) 574 Fabiana Cossavella GERDA and GeDet Project Review 2010 13/27

Test Stands: detector characterization

Gerdalinchen II

◮ able to handle 3 HPGe detectors

in LN2 or LAr

◮ operation at 77 K

”Operation of an 18-fold segmented n-type HPGe detector in liquid nitrogen”, Iris Abt et al., J. Instrum. 4 (2009) p11008 Fabiana Cossavella GERDA and GeDet Project Review 2010 14/27

Pulse Shape simulation

Development of a complete package to simulate pulses. Shape of a pulse strongly influenced by:

impurity of the crystal

◮ impurities are not homogenous ◮ each crystal is individual ◮ uncertainty ∼ 20% − 30%

mobility

◮ e− reasonably well known ◮ holes → available measurements differ inside a factor 2

Fabiana Cossavella GERDA and GeDet Project Review 2010 15/27

Pulse Shape simulation

120 140 160 180 200 220 240 260 280 [degree] 10 5 5 10 <100> <110> <100>

(a) (b)

x [mm]

• 40
• 30
• 20
• 10

10 20 30 40 y [mm]

• 40
• 30
• 20
• 10

10 20 30 40 〉 1 〈 〉 010 〈 〉 110 〈 〉 110 〈

h, outward drift

◮ trajectories are bent due to the crystal structure ◮ charge carries slower in the < 110 > than in the < 100 >

direction → very clear for the holes trajectories

Fabiana Cossavella GERDA and GeDet Project Review 2010 16/27

Pulse Shape simulation

• 3

10

• 2

10

• 1

10 1 x [mm]

• 40
• 30
• 20
• 10

10 20 30 40 y [mm]

• 40
• 30
• 20
• 10

10 20 30 40

electron hole

A B C γ

(a) ◮ electric signals induced on the electrodes by cumulative

influence of moving electrons and holes

◮ pulse in segment B + mirror pulses in segments A and C ◮ kinks in core and segment B pulse when e− reach the core

Fabiana Cossavella GERDA and GeDet Project Review 2010 17/27

Pulse Shape simulation

Data Fitted Simulated Pulse Time scale factor = 0.90 ± 0.01 χ² /dof = 184/146

◮ simulated core pulses fitted to measured pulses → simulation

describe the general shape very well

◮ overall length of simulated pulse to be adjusted → ρimp, T, µ

Fabiana Cossavella GERDA and GeDet Project Review 2010 18/27

Pulse lenght: T dependence

Temperature [K] 80 90 100 110 120 130 Rise time [ns] 250 300 350 400 450 500 550 , <110> axis

• Core, 0

DS1 DS2 DS3 DS1, T=77.4 K DS2 shifted for 8.5 K DS3 shifted for 10.0 K /T)

2

exp(-p

1

+p Fit p Theoretical calculation

Expectation

◮ if E ∼ const. →

tr ∝ µeff −1

◮ µeff ∝ T −3/2

Data

◮ Boltzmann-like law:

tr ∝ e−k/T

◮ is something else

T-dependent?

◮ tr core = 290ns, simulation ◮ tr core = 287ns, data

→ T dependence will be included in PS simulation package!

Fabiana Cossavella GERDA and GeDet Project Review 2010 19/27

GALATEA

◮ analysis of surface effects with coaxial Ge detectors ◮ direct irradiation with α and β particles and IR laser

Fabiana Cossavella GERDA and GeDet Project Review 2010 20/27

GALATEA first measurements

◮ 60Co and 228Th on top of the

tank to test functionality

◮ alpha-(241Am), beta-(90Sr)

and gamma sources inside the tank for precision measurements

Fabiana Cossavella GERDA and GeDet Project Review 2010 21/27

GALATEA first measurements

energy in keV 500 1000 1500 2000 2500 3000 number of events 100 200 300 400 500 600

Th228

K40 FWHM @ 2.6MeV = 3.75 keV

Th spectrum of segment 7 with background

Fabiana Cossavella GERDA and GeDet Project Review 2010 22/27

Background reduction R&D

◮ singly Compton scattered γs

escaping detector → same event topology as signal-like events

◮ use scintillation light to

identify event as background

◮ normal PMTs contribute to

radioactive background!

Fabiana Cossavella GERDA and GeDet Project Review 2010 23/27

Background reduction R&D

◮ 12 SiPMs + 15 m wavelength

shifting fibers

◮ successfully operated in

anticoincidence with 6-fold segmented HPGe detector

◮ detection efficiency ≈ 90

p.e./MeV energy deposit

Fabiana Cossavella GERDA and GeDet Project Review 2010 24/27

Background reduction R&D

E [keV] 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800

2

10

3

10

4

10

Th228 spectrum Anti-Compton cut Anti-Compton + Single Segment

background suppression by factor 4.2 in the RoI (8.6 with segment anti-coincidence veto)

Fabiana Cossavella GERDA and GeDet Project Review 2010 25/27

Background reduction R&D

E [keV] 1500 1550 1600 1650 1700 1750 1800 1850 1900 1950 500 1000 1500 2000 2500 3000 3500 4000 4500

Th228 spectrum Anti-Compton cut Anti-Compton + Single Segment

DEP Bi212 1620

background suppression of the DEP (1593 keV) by a factor 6.2 (9.3)

Fabiana Cossavella GERDA and GeDet Project Review 2010 25/27

Summary: GERDA

◮ GERDA infrastructure finished, first commissioning detectors

deployed

◮ 42Ar background is being investigated ◮ Phase I start next year after delivery of 3-string arm and

mitigation of the 42Ar problems

◮ Enriched material has been purified with very high yield ◮ R&D on crystal pulling at IKZ is ongoing ◮ SiPM anti-compton veto looks promising

Fabiana Cossavella GERDA and GeDet Project Review 2010 26/27

Summary: GeDet

◮ characterization of 18-fold segmented Ge detectors completed ◮ power to suppress background with segmentation cut andor

PSA

◮ validation and improvement of the PS simulation package ◮ improvement of PSA package ongoing ◮ GALATEA test stand for 3D scan in operation! ◮ also ongoing: neutron screening studies for 1 Ton experiment

Fabiana Cossavella GERDA and GeDet Project Review 2010 27/27