Cristina Cozzini (Oxford), IDM 2004, Edinburgh

CRESST-II background discrimination: detection of 180W natural

decay in a pure alpha spectrum

Paper submitted to Physical Review C

(also available on nucl-ex/0408006)

Cristina Cozzini (Oxford), IDM 2004, Edinburgh

C. Cozzini1, G. Angloher2, C. Bucci3, F. von Feilitzsch4, D. Hauff2, S. Henry1, Th. Jagemann4, J. Jochum, H. Kraus1, B. Majorovits1, V. Mikhailik1, J. Ninkovic2, F. Petricca2, W. Potzel4, F. Proebst2, Y. Ramachers1,*,

W. Rau2, M. Razeti4, W. Seidel2, M. Stark4, L. Stodolsky2, A. J. B. Tolhurst1, W. Westphal4, H. Wulandari4

1. University of Oxford, U.K. 2. MPI für Physik, Munich, Germany3. Laboratori Nazionali del Gran Sasso, Italy4. Technische Universität München, Germany5. Eberhard-Karls-Universität Tübingen, Germany

* Permanent address: University of Warwick, U.K.

Cristina Cozzini (Oxford), IDM 2004, Edinburgh

light reflector

300 g CaWO4 crystal separate cryogenic light detector

thermometer

Superconducting film as thermometer

simultaneous measurement of phonons and scintillation light to discriminate nuclear recoil signals from radioactive background

CRESST PhaseII detector module

Cristina Cozzini (Oxford), IDM 2004, Edinburgh

irradiation with e- and with e- und neutrons

Background Suppression: 98 % 10-20 keV 99.7% 15-25 keV 99.9% > 20 keV

Cristina Cozzini (Oxford), IDM 2004, Edinburgh

U-Th

>

Cristina Cozzini (Oxford), IDM 2004, Edinburgh

1E-3

0.01

0.1

1

10

100

Ni

CrPb

Lu

Yb

ErGd

Eu

Sm

Nd

La Ce

Ba

Y

Sr

ZnCu

Imp

uri

ty c

on

cen

tra

tion

, pp

m

Elements

Russia Ukraine

300 400 500 600 7000

5000

10000

15000

20000

25000

Er3+

Gd3+

Wavelength, nm

600 625 6500

500100015002000

ICP-MS (inductively coupled plasma mass-spectrometry) analysis of the impurities in CaWO4

300 400 500 600 7000

2000

4000

6000

8000

10000

12000

77 K 295 K

Wavelength, nm

X-ray luminescence of CaWO4

RE- impurities in Russian (Y, Nd, Gd and Er all >1 ppm) and Pb (~1 ppm ) in Ukrainian samples

Russian

Ukrainian

Cristina Cozzini (Oxford), IDM 2004, Edinburgh

147Sm

152Gd

144Nd 180W

Cristina Cozzini (Oxford), IDM 2004, Edinburgh

180W

Run 28 crystal D

Cristina Cozzini (Oxford), IDM 2004, Edinburgh

Half-life for the -decay of 180W obtained independently in four different runs

Counts Exposure Half-life

[kg days] [years]

Run 28 Crystal D 35±4.3 12.268 (1.7±0.2) 1018

Run 27 Crystal D 28.5±5.6 11.745 (1.9±0.4) 1018

Run 23 Crystal E 9 3.467 ≥1.1 1018 (90% C.L.)

Run 22 Crystal B 4 1.140 ≥6.7 1017 (90% C.L.)

Cristina Cozzini (Oxford), IDM 2004, Edinburgh

Half-life for the -decay of 180W obtained from the total exposure (28.62 kg days)

Half life T1/2 = (1.8±0.2) 1018 years

Energy Q = (2516.4±1.1 (stat.)±1.2(sys.)) keV

Previous indication (Danevich et al. Phys. Rev. C 67 (2003))

Half life T1/2 = ( (stat.)±0.3(sys.)) 1018 years8.04.01.1

Cristina Cozzini (Oxford), IDM 2004, Edinburgh

Lower limits (90% C.L) for the half-life times of the non-observed -decay on the other naturally occurring W isotopes (exposure 16.875 kg days)182W T1/2 ≥ 7.7 1021 years

183W T1/2 ≥ 4.1 1021 years

184W T1/2 ≥ 8.9 1021 years

186W T1/2 ≥ 8.2 1021 years

Cristina Cozzini (Oxford), IDM 2004, Edinburgh

Summary

• Strength of CRESST discrimination techniques

• High sensitivity (~1µBq/kg)• Detection of the alpha decay of 180W• 182W 183W 184W 186W: improving by a

factor of 50 the best previously published limits