Dark Matter search with ELEGANT VI CaF 2 detector

12 September '07 TAUP2007

Dark Matter search with ELEGANT VICaF2 detector

Introduction

ELEGANT VI detector

Photon counting

Analysis

Summary & Prospects

OGAWA Izumi (Osaka University)


CaF2 scintillation Detector

19F : Search for spin coupled Dark Matters large

48Ca : Search for 0 decay (talk by S. Umehara, on 14th )

highest Q-value least BG expected

Natural abundance 0.187%

Isotope 48Ca 76Ge 82Se 100Mo 116Cd 136Xe 150Nd

Q-value (MeV)

4.27 2.04 3.00 3.03 2.80 2.48 3.37

G0v×10-25

(year-1eV-2)2.44 0.244 1.08 1.75 1.89 1.81 8.00


ELEGANT VI

Surrounded by H3BO3 loaded-water tank

23 CaF2 modules ~3.5 kg 19F ~7.7 g 48Ca

Background reduction least material : non hygroscopic 4 active shield

CaF2(Eu)+CaF2(pure)

roll-off ratio

segmentation CsI(Tl) veto detector

passive shield OFHC Cu(t:5 cm), Pb(t:10 cm) air-tight box + N2 gas purge

Rn in the air

LiH + paraffin(t:15 mm), Cd sheet(t:0.6 mm), and H3BO3+H2O tank

neutron


C o sm ic ray:

N e u tro n flu x :

R n co n cen tra tio n :

4 .0× 1 0 -7 c m -2sec -1

4 .0× 1 0 -5 c m -2sec -1

10 B q m -3

The tunnel which is originally constructedfor the railway is 5 km long, and itsmaximum depth is about 470 m. Becauseof the natural ventilation due to therelatively strong wind inside the tunnel, theradon concentration is two or three ordersof magnitude lower than the Kamiokaunderground laboratory.

ELEGANT VI detectorCaF2 scintillator array

Spin-coupled DM search48Ca double beta decay search

Oto Cosmo Observatory

PICO-LON


CaF2(Eu) & CaF2(pure)

CaF2(pure) as light guide

active shield against PMT

CaF2(Eu) is not transparent for U.V. light

CaF2(Eu) : 　　 from BICRON catalogue CaF2(pure) : 　 measured value


Roll-off ratio

PMT PMT

CaF2(Eu)n = 1.44CaF2(pure)

n = 1.47 Quartz window

VL VR

RL VV

RL VV

Visible light

U.V. light

ROLL-OFFRATIO

ArbitaryUnit

RIGHT(channel)

LEFT(channel)

LR

LR

VV

VVR

VL, 　 VR : ADC channel from left & right PMT


Low energy signal by CaF2 scintillator

CaF2(Eu) long falling time (~ 1sec)

~0.5 keV/photoelectron

4 sec gate width

baseline fluctuation

one photoelectron signal fluctuation

noise

etc….

ADC


Flash Scaler

300 MHzDiscriminator

Flash scaler

PMT

FASTAmplifier

ADC

1 2 1 1 3 0 1 1

Flash scalerFlash scaler

–like multichannel scaler (MCS)like multichannel scaler (MCS)»dwell time : 50 – 100 nsecdwell time : 50 – 100 nsec

»each channel : 8 bits scalereach channel : 8 bits scaler

Signal from PMT

Discriminator output

Clock signal

Flash scaler output

CAMAC module

clock

keV 30


Single photon counting in low energy region

Improvement in energy resolution free from baseline fluctuations

single photoelectron

Reject the backgrounds fired at CaF2(pure) crystals

Roll-off spectrum by ADC

Fitting by simple binominal function

Roll-off cut pureEucut NBNAN

P : probability counted by left (right) PMT

N : total photon number counted

pure

Eu


Roll-off ratio by single photon counting

Fitting by Binominal functions for each Ntot

Nl,r : number of photoelectrons counted by left/right PMT

rPNBnrPNBnrPNBnrNF ,,,,,,, righttot*

rightEutot*

Eulefttot*

lefttot

N

N

N

Nr

ii

rPNB

rPNBrPNB 1

1

*

,,

,,,, : modified binominal function

(coincidence trigger)

tot

tot

N

NNr

NNN

lr

rl

PEu : determined by calibration run

rightleftrightEuleft , , , , PPnnn : fitting parameter

: roll-off ratio


Fitting

Fitting with binominal function for CaF2(#12) Live time 71.12 days 　 (Run-7)

Eupure


Obtained energy specrum

Single crystal, 71.12 days (Run-7)

Many BG events remains in low energy region

BG reduction using other information

Timing information ADC

(live time : 71.12 days)

Energy(keV)

rate

(dru

)

1

10

102

103

5 10 15 20


Time difference distribution

TL(1st p.e.) - TR(1st p.e.)

Horizontal axis: Tdiff=

T < 0T

N

RL

RLR

e)NN(

NN)T(P

T > 0 　 TN

RL

RLL

e)NN(

NN)T(P

BG run

Calibration run (241Am)

ex) Ntot=NL+NR=7In BG run,

•peaks at Tdiff= 0, ±500 nsec

•continuous events

Tdiff

coun

ts


PMT Noise

Measurement was done without scintillators

A peak around Tdiff = 0 nsec flushing at photocathode ?

continuous eventsaccidental coincidence

cannot identify peaks around Tdiff= ±500 nsec

with same DAQ system

Tdiff

cut


ADC cut

ADC vs. # of p.e.

BG run

Calibration run (241Am)ex) NL6, NR=1

# of p.e.

AD

C (

ch)

25 50

1000

500

0

ADC (ch)

coun

ts


Analysis

Run 1001 8ch Flash scaler for central CaF2 scintillators

mass : 0.29kg x 8 live time : 199.3 days

Analysis Time cut ADC cut roll-off cut : select single time bin which

corresponds to CaF2(Eu)

no binominal fit

1 2 3 4 56 7 8 9 10

11 12 13 14 1516 17 18 19 2021 22 23 24 25


Recoil Spectra for each crystal

0

100

200

300

400

500

3 4 5 6 7 8 9 10

0

100

200

300

400

500

3 4 5 6 7 8 9 10

0

100

200

300

400

500

3 4 5 6 7 8 9 10

0

100

200

300

400

500

3 4 5 6 7 8 9 10

0

100

200

300

400

500

3 4 5 6 7 8 9 10

0

100

200

300

400

500

3 4 5 6 7 8 9 10

0

100

200

300

400

500

3 4 5 6 7 8 9 10

0

100

200

300

400

500

3 4 5 6 7 8 9 10

#7 #8

#12

#9

#13

#17 #18

#19

Energy (keV)

cou

nts

/keV

/kg

/d

ay before cut

after cut


exclusion plots for each crystal

0.1

1

10

100

1000

1 10 100 1000

0.1

1

10

100

1000

1 10 100 1000

0.1

1

10

100

1000

1 10 100 1000

0.1

1

10

100

1000

1 10 100 1000

0.1

1

10

100

1000

1 10 100 1000

0.1

1

10

100

1000

1 10 100 1000

0.1

1

10

100

1000

1 10 100 1000

0.1

1

10

100

1000

1 10 100 1000

#7 #8

#12

#9

#13

#17

#18

#19

WIMP Mass (GeV)

WIM

P-pr

oton

cro

ss s

ectio

n (p

barn

)


Preliminarly result

this work


Summary & Prospects

ELEGANT VI detector CaF2 scintillators to search for SD dark matter Photon counting method by Flash scaler

Analysis without binominal fitting 460 kg ･ days of data exclusion plot for SD dark matter

In progress… Apply the binominal fit to reduce the CaF2(pure) ev

ents

expected to be ~1/2 – 1/3 in recoil rate


終


Recoil response calibration (f-value)

Calibration for our crystal 19F(n, n) elastic scattering

3.2 MV Pelletron (~2 A at 2 MHz)

Tid2 target

Deuteron beam~0.75 MeV

Heavy metal

paraffin

~3.7 MeV n

CaF2(Eu)

CaF2(pure)

NaI(Tl)

Neutron detectorf-

valu

e

recoil energy (keV)10 20 50 100 200 500

0.01

0.02

0.05

0.10

0.20

0.50

1.00

F recoilCa recoil

Result Result (R. Hazama, et al., NIM A482 (2002) 297)

Dark Matter search with ELEGANT VI CaF 2 detector

Documents

Transcript of Dark Matter search with ELEGANT VI CaF 2 detector