BEGe Detector studies update - Max Planck Society · BEGe Detector studies update Performance and...

BEGeBEGe Detector studies updateDetector studies update

Performance and analysisPerformance and analysis

DušanDušan BudjášBudjáš • • StefanStefan Schönert • Schönert • Mikael Hult*Mikael Hult*

MPI für Kernphysik • MPI für Kernphysik • HeidelbergHeidelberg* IRMM • Geel* IRMM • Geel

MMAXAX--PPLANCKLANCK--IINSTITUTNSTITUT

FFÜÜR R KKERNPHYSIKERNPHYSIK

OutlineOutline

1.1. BEGe publicationBEGe publication

2.2. BEGe pulseBEGe pulse--shape discrimination methodshape discrimination method

3.3. Update on recent resultsUpdate on recent results

4.4. Summary/OutlookSummary/Outlook

2

Dušan BudjášDušan BudjášDušan Budjáš

3

BEGe publicationBEGe publicationMPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDušan BudjášDušan BudjášDušan Budjáš

� submitted to JINST

� accepted for publication after some minor corrections

� ArXiv: 0909.4044 [nucl-ex]

� Contents:• charge collection

performance and stability

• PSD method and its calibration

• validation via coincident SCS and collimated 2.6 MeV beam

• experimental PSD results

� also: proceedings from CIPANP 2009 (4 pages, submitted to AIP)

� previously: IEEE 2008 proceedings arXiv: 0812.1735v1[nucl-ex]

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

distance from the read-out electrode, x [cm]

W

0

2

4

6

8

10

12

14

16

|Ew| [c

m-1

]

W(x)

|Ew(x)|

0

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0.8

1

0.5 1 1.5 2 2.5 3 3.5 4

r [cm]

W

0

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0.5

|Ew| [c

m-1

]

W(r)

|Ew(r)|

4

MPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDušan BudjášDušan BudjášDušan Budjáš

BEGe pulse shape discrimination methodBEGe pulse shape discrimination method

BEGe (hypothetical)

True coaxial

( ) ( ) ( ) vtxEqvtxEqtI h

W

he

W

e ⋅⋅+⋅⋅−= )()(

ee−−

hh++

+HV

read-out

Ramo's theorem ⇒

ref: Knoll

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1


W

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16

|Ew| [c

m-1

]

W(x)

|Ew(x)|

5



BEGe (hypothetical)


W

he

W

e ⋅⋅+⋅⋅−= )()(

-1000 -500 0 500 1000 1500 20000

200

400

600

800

Time after trigger [ns]

Am

plit

ud

e [a.u

.]

Interaction point distance from read-out electrode [mm]:

0

0.03

0.06

0.09

0.12

0.15

0.18

0 10 20 30 40 50 60 70 80 90 100

Time [ns]

Cu

rre

nt [a

. u

.]

0.4 1 2.5 4.5 6.5 8.2 9.7

ee−−

hh++

+HV

read-out

Ramo's theorem ⇒

simplified 1-dimensional calculation real recorded signal

0

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1

0 0.2 0.4 0.6 0.8 1


W

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|Ew| [c

m-1

]

W(x)

|Ew(x)|

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BEGe (hypothetical)


W

he

W

e ⋅⋅+⋅⋅−= )()(

-1000 -500 0 500 1000 1500 20000

200

400

600

800

Time after trigger [ns]

Am

plit

ud

e [a.u

.]

0

0.02

0.04

0.06

0.08

0.1

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0.14

0.16

0 10 20 30 40 50 60 70 80 90 100

Time [ns]

Cu

rre

nt [a

. u

.]

single site

multi site

energy normalised ~equal event energy

A A

ee−−

hh++

+HV

read-out

Ramo's theorem ⇒

simplified 1-dimensional calculation real recorded signal


7

PSD parameter distributionPSD parameter distribution

DEP events accepted

rejected

SSE band

MSE regionFEP

1620.7 keV

FEP

2614.5 keVSEP

FEP

1620.7 keV

DEP

1592.5 keVSEP

2103.5 keV

FEP

2614.5 keV

1400 1500 1600 1700 1800 1900 2000 2100 2200 2300

0.33

0.333

0.336

0.339

Energy [keV]

m

fitted curve

1400 1500 1600 1700 1800 1900 2000 2100 2200 2300

-5

-2.5

0

2.5

5x 10

-4

Energy [keV]

fit re

sid

uals

<A

/E>

SS

E

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PSD calibrationPSD calibration

Compton 1425 ± 25 keV

Compton 2245 ± 25 keV

DEP ± 1 σ

exponential tail

Gaussian

fit function

A/E [a.u.]

Nu

mber

of

cou

nts

<A

/E>

SS

E

DEPMSE

SSE

228Th

1400 1500 1600 1700 1800 1900 2000 2100 2200 2300

0.33

0.333

0.336

0.339

Energy [keV]

m

fitted curve

1400 1500 1600 1700 1800 1900 2000 2100 2200 2300

-5

-2.5

0

2.5

5x 10

-4

Energy [keV]

fit re

sid

uals

<A

/E>

SS

E

9



10



Assuming gaussian distribution (resolution dominated by noise):2 σ ⇒ 97.7% SSE acceptancearbitrary choice of "SSE identification probability"

SSE defined as events with charge cluster extent so small that the electric field doesn't change significantly across it's width

2 σ

228Th

11


Updated experimental results Updated experimental results

� cut at 2 σ from the SSE band mean

� simplified MC estimation of 0νββ acceptance: (89.4 ± 1.4)%

γ-lines

CC = Compton continuum (2039 ± 35 keV)

100%

10%

1%

0.1%

0νββ

12


PSD validation via coincident singlePSD validation via coincident single--Compton scatteringCompton scattering

SCS

⇒ double-escape peak (DEP) is a good representation of ββ events

⇒ validated our PSD calibration using DEP and Compton continuum events

A/E parameter histograms:

no effect ofevent topologyor spatial distribution

corrected forenergy depen-dence from Compton cont.

SSE line

MSE region

102

101.5

101

100.5

accepted

rejected

SSE band near-electrode events

13


PSD performance in dependence on spatial event distribution PSD performance in dependence on spatial event distribution

ee−−

hh++

Interaction point distance from read-out electrode [mm]:

0

0.03

0.06

0.09

0.12

0.15

0.18

0 10 20 30 40 50 60 70 80 90 100

Time [ns]

Cu

rre

nt [a

. u

.]

0.4 1 2.5 4.5 6.5 8.2 9.7

14


acceptance: DEP 1621 keV

uncollimated: 89% 10%

collimated (centre): 88% 23%

DEP

amplified current amplitude A

reject accept

228Th source

ee−−

hh++

∅ 6 mm collimated beam

PSD performance in dependence on spatial event distribution PSD performance in dependence on spatial event distribution

0%

5%

10%

15%

20%

25%

30%

35%

0 5 10 15 20

Collimator distance from centre [mm]

Fra

ction o

f events

above S

SE

band

.

4000V 3s

4250V 3s

4500V 3s

3750V 3s

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HV dependence of PSD performanceHV dependence of PSD performanceMPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDušan BudjášDušan BudjášDušan Budjáš

< 3% of total volume PSD ineffectiveComplementary PSD techniques effectivealso in this region (e.g. rise-time based)

� the extent of the insensitive region grows with HV

ee−−

hh++

electrode extent

beam size

� PSD tested on ∅ 6 cm BEGe (at IRMM Geel, Belgium)

� results: SEP survival 9.2% (∅ 8 cm: 7.1%)FEP survival 13.5% (∅ 8 cm: 10.2%)at 89% DEP acceptance

8000

7000

6000

5000

4000

3000

2000

1000

01560 1580 1600 1620 1640

232-Th spectrum

after 2 σ PSD cut

γ 1588 keV DEP

γ 1621 keV

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PSD performance in dependence on crystal sizePSD performance in dependence on crystal size


1%

10%

100%

1500 1700 1900 2100 2300 2500 2700

Energy [keV]

surv

iva

l pro

bab

ility

228-Th with MPIK BEGe (8 cm); 3.8 kV

232-Th with IRMM BEGe (6 cm); 3.5 kV

232-Th with IRMM BEGe (6 cm); 3.1 kV

DEP

γ 1588 keV

γ 1621 keVγ 2615 keV

SEP

� PSD tested on ∅ 6 cm BEGe (at IRMM Geel, Belgium)

� results: SEP survival 9.2% (∅ 8 cm: 7.1%)FEP survival 13.5% (∅ 8 cm: 10.2%)at 89% DEP acceptance

17

PSD performance in dependence on crystal sizePSD performance in dependence on crystal size


18


� PSD validated with SSE events of different topology (DEP vs. SCS), spatial distribution, and energy

� discovered < 3% loss of MSE rejection sensitivity near the read-out electrode (specific to our PSD method)

� no spatial dependence of SSE acceptance found

� no change of PSD sensitivity in dependence on HV (except for a slight growth of the MSE-insensitive volume)

� PSD performance in smaller crystals likely different only due to lower γ-ray absorption efficiency

Summary and conclusionsSummary and conclusions

19


� tests of FE electronics for bare BEGe operation in LAr

� optimisation of the PSD procedure and coordination with LNGS BEGe team in advance of acceptance testing of new BEGe's from depGe

� coordination with Zürich group (Francis) on definition of the Phase 2 calibration source from the point of view of PSD calibration requirements

OutlookOutlook

20


Backup slidesBackup slides

FWHM

1.5

1.6

1.7

1.8

1.9

2

2.1

2.2

2.3

2.4

2.5

3500 3700 3900 4100 4300 4500

HV

keV

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HV scanHV scan

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500 1000 1500 2000 2500 3000 3500 4000 4500

High voltage [V]

FW

HM

[keV

]

1.33 MeV (Co-60)

1.39 MeV (pulser)

0

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2600 3100 3600 4100 4600

V

co

un

ts

0

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7000

8000

ch

an

nel

peak intensity

peak position

22


HV scanHV scan

0

2000

4000

6000

8000

10000

12000

500 1000 1500 2000 2500 3000 3500 4000 4500

High voltage [V]

Num

ber

of

counts

0

1000

2000

3000

4000

5000

6000

7000

8000

Peak p

ositio

n [

channel]

1.33 MeV peak intensity

1.33 MeV peak position

Nu

mbe

r o

f co

un

ts [

pe

r 60

0 s

]

23


Charge collection characterisationCharge collection characterisation

59.4

59.42

59.44

59.46

59.48

59.5

59.52

59.54

-50 -40 -30 -20 -10 0 10 20 30 40 50

distance from center [mm]

pe

ak

po

sit

ion

[k

eV

]

0.4

0.5

0.6

0.7

0.8

0.9

1

FW

HM

[k

eV

]

peak position

FWHM

collimated 241

Am scan

59.3

59.35

59.4

59.45

59.5

59.55

59.6

0 5 10 15 20 25 30 35

distance from the top of crystal, d [mm]

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

FW

HM

[keV

]

peak position

FWHM

pe

ak p

ositio

n [ke

V]

gain variation: ≤ 0.055%

gain variation: ≤ 0.075%

� active mass: 836 g (95 % of total mass)

� dead layer:0.43 mm

59.5 keV

d

d

Energy [keV]

Co-60 (high rate)

Co-60 (high rate+pile-up reject)

Co-60 (low rate)

Num

ber

of

cou

nts

24


Charge collection losses: peak tailsCharge collection losses: peak tails

25


Charge collection stabilityCharge collection stability

-0.020%

-0.015%

-0.010%

-0.005%

0.000%

0.005%

0.010%

0.015%

22.12.08 29.12.08 5.1.09 12.1.09 19.1.09 26.1.09 2.2.09 9.2.09

Date

1333 keV

1174 keV

LN refilling

weekends

Re

lative p

eak p

ositio

n c

orr

ecte

d

for

puls

er

fluctu

ation

Setu

p

rearr

angem

ent

1st set 2nd set

Maximal variation: ≤ 0.015% ≈ 0.2 keV @ 1332.5 keV

26


Charge collection stability: count rateCharge collection stability: count rate

2.60

2.75

2.90

3.05

3.20

0 7 14 21 28 35 42 49

Days since 22.12.2008

2.0

2.1

2.2

2.3

2.4

59.5 keV

1333 keV

Co

un

ts p

er

3 h

r

Co

un

ts p

er

3 h

r (c

orr

ecte

d)

×104

×104

27


Coincident recordingCoincident recording

Struck SIS 3301

flash- ADC

14- bit, 100 MHz

pulse recording,

digital shaping

(τshaping = 10 µs)

1.6 µs

coincidence

window

software gate

Amplified raw signal

Canberra2002CSL

MPIKno shaping

TFACanberra2111

Time- filtered signal (10 ns differentiation and

10 ns integration time)

Amplified raw signal

Preamp

no shapingMPIK

228Th source(no collimator)

Pb/Cu shieldsolid

angle:~ 10°

25 c

m -

80 c

m

23.6 cm

28

HV dependence of PSD performanceHV dependence of PSD performanceMPIK HeidelbergMPIK HeidelbergMPIK HeidelbergDušan BudjášDušan BudjášDušan Budjáš

� current signal amplitude grows with HV => weighing field shape changes

� (the width of the SSE band seems to slightly increase with HV)

0.2

0.22

0.24

0.26

0.28

0.3

0.32

3500 3750 4000 4250 4500

V

<A

/E>

sse

0.005

0.0055

0.006

0.0065

0.007

sig

ma(A

/E_sse)

BEGe Detector studies update - Max Planck Society · BEGe Detector studies update Performance and...

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