Yang Yang Underground Lab in Korea (Y2L)

Li Jin IHEP/ Tsinghua Beijing , China

OCPA 2008 , HongKong

Outline

• Yang Yang Underground Lab• Detector for dark matter search• Physics results• Other issues in Y2L• Summary

KIMS Collaboration Korea Invisible Mass Search collaboration

H.C.Bhang, J.H.Choi, S.C.Kim, S.K.Kim, S.Y.Kim, J.W.Kwak, M.J.LeeH.S.Lee, S.E.Lee, J. Lee, S.S.Myung, H.Y.Yang

Seoul National University

Y.D.Kim, J.I. Lee, U.G.Kang

Sejong University

H.J.Kim

Kyungpook National University

M.J.Hwang, Y.J.Kwon

Yonsei University

I.S.Hahn, I.H.Park

Ewha Woman's University

M.H.Lee, E.S.Seo

Univ. of Maryland

J.LiInstitute of High Energy Physics

J.J.Zhu, D. He, Q.Yue, X. Lee

Tsinghua University

(TEXONO : close relationship )

（襄阳）

The Korea Invisible Mass Search (KIMS) experiment is located at the Yangyang Underground Laboratory (Y2L) at a depth of 700 m under an earth overburden in South Korea.

The space of Y2L provided by the YangYang Pumped Storage Power Plant , ,

Access to the lab by car 2Km tunnel from gate, clean room with an air conditioni

ng system for a constant temperature and low humidity.

Radiation in the lab Depth Minimum 700 m

Temperature 20 ~ 25 oC

Humidity 35 ~ 60 %

Rock contents

238U less than 0.5 ppm

232Th 5.6 +/- 2.6 ppm K2O 4.1 %

Muon flux 4.4 x 10-7 /cm2/s

Neutron flux 8 x 10-7 /cm2/s

222Rn in air 2 ~ 4 pCi/liter

CSI

Pb shield (15cm)PE shield (5cm)

Copper shield (10cm)

Mineral Oil shield (30cm)

NMD

MUD

Diagram of detector & shielding

NMD Neutron Monitor Detector

CSI Cs(Tl) Crystal Detector

MUD Muon Detector - LS 5%

Active Detector

Passive shield

Copper : 10 cm PE : 5 cm Lead : 15 cm

Mineral Oil : 30 cm

Y2 Underground labY2 Underground labLS 30cm

Pb 15cm : 30t OFHC Cu 10cm : 3t

宇宙线 Veto中子屏蔽体

屏蔽外部等 屏蔽外部材料的本底

PE 5cm

8cm x 8cm x 30cm11x11 =121 crystals1.05 t

~90 cm

~ 90 cm

30 cm

CsI(Tl) Crystal Array

Advantage High light yield ~60,000/MeV Pulse shape discrimination Easy fabrication and handling High mass number(both Cs and I) Relatively easy to get large mass with an affordable cost

Disadvantages Emission spectra does not match with normal bi-alkali PMT

=> Effectively reduce light yield Inner radioactivity Cs137, Cs134 , Rb87

Why CsI(Tl) Crystal ?

CsI(Tl) NaI(Tl)Photons/MeV ~60,000 ~40,000Density(g/cm3 4.53 3.67Decay Time(ns) ~1050 ~230Peak emission(nm) 550 415Hygroscopicity slight strong

内部放射性137Cs : 1/2= 30.07 year (Artificial) decay to 137Ba* (Q = 1175.6 keV) 2 min life time, emitting 661.6 keV gamma Hard to reject, serious background at low energy

134Cs : 1/2 = 2.065 year : Artificial+ 133Cs(n,) to 134Ba* (Q=2058.7 keV) immediate emission Can be rejected easily : not a serious problem87Rb : 1/2 = 4.75 x 1010 year (27.8% natural abundance) Beta deacy to 87Sr (Q=282.3 keV) no emission Hard to reject => potentially a serious problem => reduction technique in material is known

Backgrounds of CsI(Tl) crystal

We investigated the contamination process and the reduction methodof 137Cs. By using purified water, succeeded in reducing the 137Cs in the final powder and the crystal. The reduction technique of Rb, a repeated recrystallization process, has been widely known

Best available Crystal at MarketBest available Crystal at MarketPowder SelectionPowder SelectionCs137 Reduction Using Pure waterCs137 Reduction Using Pure waterRb87 Reduction by Re-crystallizationRb87 Reduction by Re-crystallization

CsI(Tl) Crystal Detector

CsI(Tl) Crystal Size 8* 8* 30 cm3 Weight 8.7 kg 137Cs reduction using purified water 87Rb reduction by recrystalization 3” PMT - 9269QA Quartz window RbCs photocathode

CsI crystal detector module

CSI

NMD

MUD

Electronics

PREAMPLIFIER- FOR CSI

- 2 CHANNELS / BOARD

- x10 FOR DIGITIZER

- x100 FOR DISCRIMINATOR

- PSEUDO CHARGE SESITIVE

OUTPUT FOR PEAK SENSING

ADC

- 200MHz BANDWIDTH

ANALOG SUM- FOR MUD

- 3 IN - BNC

- 2 OUT- BNC,REMO

- 2 CHANNELS / BOARD

- SEPARATE INPUT GAIN & OFFSET ADJUSTMENT

- SUM OUT GAIN ADJUSTMENT

500MS/s DIGITIZER- 2 CHANNELS / BOARD

- 32us RECORDED/EVENT

- 16us DT / EVENT

- DOUBLE BUFFERER SRAMs (4Mbit/ CH)

- TRIGGER LOGIC IMPLEMENTED

VME CONTROLLER- USB2 INTERFACE

- OPTIONAL HD

Typical low energy r signal from one PMT obtained by Compton event from Cs137 source

8cm x 8cm x 30cm11x11 =121 crytals1.05 t

~90 cm

~ 90 cm

30 cm

探测器总体构造

2005 24kg

2007 100kg

2009

Exclusion plot for the SD interaction of pure proton coupling (R)

& pure neutron coupling (L) at the 90% confidence level .

Exclusion plot for the SI interaction

at the 90% confidence level Published in PRL 99 091301(2007)

. Crystals used in the analysis and amount of data Crystal Mass (kg) Data (kg . days)S0501A 8.7 1147S0501B 8.7 1030B0510A 8.7 616B0510B 8.7 616Total 34.8 3409

WIMP search using ULEGe detector

Summary Summary • Y2L has been constructed for dark matt

er search ,double beta decay and ….in Korea

• Low radiation background CsI(Tl) detector has built with large mass

• The physics result obtained and new result will coming using larger data sample.

Thanks