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.Lee H.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.Li Institute 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 conditioning system for a constant temperature and low humidity.

Radiation in the lab DepthMinimum 700 m Temperature20 ~ 25 o C Humidity35 ~ 60 % Rock contents 238 U less than 0.5 ppm 232 Th 5.6 +/- 2.6 ppm K 2 O 4.1 % Muon flux 4.4 x /cm 2 /s Neutron flux 8 x /cm 2 /s 222 Rn in air 2 ~ 4 pCi/liter

CSI P b 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 lab LS 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 30cm 11x11 =121 crystals  1.05 t ~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 ~40,000 Density(g/cm Decay Time(ns) ~1050 ~230 Peak emission(nm) Hygroscopicity slight strong

内部放射性 137 Cs :  1/2 = year (Artificial)  decay to 137 Ba* (Q = keV)  2 min life time, emitting keV gamma Hard to reject, serious background at low energy 134 Cs :  1/2 = year : Artificial+ 133 Cs(n,  )  to 134 Ba* (Q= keV)  immediate  emission Can be rejected easily : not a serious problem 87 Rb :  1/2 = 4.75 x year (27.8% natural abundance)  Beta deacy to 87 Sr (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 method of 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 Market Powder Selection Cs137 Reduction Using Pure water Rb87 Reduction by Re-crystallization

CsI(Tl) Crystal Detector CsI(Tl) Crystal Size 8* 8* 30 cm 3 Weight 8.7 kg 137 Cs reduction using purified water 87 Rb reduction by recrystalization 3” PMT QA 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 30cm 11x11 =121 crytals  1.05 t ~90 cm 30 cm 探测器 总体构造 kg kg 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 (2007). Crystals used in the analysis and amount of data Crystal Mass (kg) Data (kg. days) S0501A S0501B B0510A B0510B Total

WIMP search using ULEGe detector

Summary Y2L has been constructed for dark matter 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