Contents Introduction Dual Lightemitting Cs INa crystals Status

Contents • • Introduction Dual Light-emitting Cs. I(Na) crystals Status of the experiment Summary 2

What to look for? Signal：nuclear recoil events <0. 01 events/kg. day @0 -100 ke. V Background：e α μ γ n（U Th K cosmic rays） Bg suppress： Underground shieldingn/γ separation Challenge: Background rejection at ~10 ke. Vee 3

Detection Technology Two channels technology: Cresst 2 Scintillation-Phonon Panda. X Scintillation-Ionization CDMS Ionization-Phonon background rejection power is good, but relatively complex. One channel technology: DAMA Scintillation CDEX Ionization Cresst 1 Phonon are relatively simple, but the ability to identify the bg presents weak. a proposal by IHEP Dual Light-emitting Cs. I(Na) Crystal Only scintillation channel background rejection by range 4

The Main Differences: Range l. Nuclear recoil has higher d. E/dx, the small rang l. Electron recoil has lower d. E/dx, the large rang 10 ke. V Dual Light-emitting Crystals can reflect the different ranges by the ratio of different scintillation components. 5

The Ratio is Different Average spacing of doped Na ions is 77Å Øelectron recoils cover more Na due to large range ~ n*1000Å ØNuclear recoils cover less Na due to small range ~ n*100Å 6

The Transmittance Cs. I(Na) crystal is transparent for the scintillation of pure Cs. I, but Cs. I(Tl) is not. So there are two components of light for Cs. I(Na), but Cs. I(Tl) not. 7

Separation by Waveform Pulse Shape Discrimination (PSD) technique could be used for n/γ separation based on different waveforms of nuclear recoils and γ-rays Define: ADC is the integration of the total component 2 us ADC 2 is the integration of the fast component 100 ns the ratio ADC 2/ADC can used for n/gamma separation neutron gamma 8

Separation by Wavelength different wavelength of the two components can also be used for separation, Na+ is 420 nm slow pure Cs. I is 310 nm fast we use a filter to test. Experimental Set-up PMT 1 Cs. I(Na) PMT 2 filter Transmittance of the wavelength filter as a function of wavelength Scatter plot of ADCfilter/ADC for γ and surface-α. 9

The Light Yield 2. 5 x 2. 5 cm Cs. I(Na) Test by PMT R 8778 ~30% QE @ 300 -400 nm -120 C Balance of alpha and gamma LY 4 p. e. /ke. Vee 36% QF: 10% Light collection: 25% ~0. 28 p. e. /ke. Vnr Threshold is 10 p. e. /35 ke. Vnr with 10 -6 rejection power light yield as a function of temperature for gamma and alpha 10

The waveform variety 5µs

400µs Waveform compare @120 C gamma alpha 12

Rejection Power 13

Separation @-120 C 1. 26µs/40µs separation for gamma /alpha 14

Detector concept design First Stage 1 module Water tank: To shield environment l. Funded by IHEP 2013 -2014 neutrons l. One module 43 kg trace cosmic ray by l. Daya Bay laboratory Cherenkov light Hall 5 ~100 m overburden Copper low. Water tank 5 m x 6 m temperature box: To provide a lowtemperature environment -120℃ Shield environment gamma Background rejection: PSD Next stage Ton scale l. Ton scale proposal 2015 l 50 modules 2000 kg l. Gran Sasso or Jingping 50 modules 2 T scale End read out 15

Key Technical and Physics Challenges • • Ultra-low controlled background Surface deliquescence remove Uniform of Na doped in crystal QF measurement Understanding of detector response Calibrate energy scales Efficiency calibration (background, signal) 16

The Low background Crystals have been received, Stored in the vacuum oven Close to the best level radioactive content Dr. Ezio Previtali from University of Milano Bicocca 850 USD/kg 17

Crystal Package Crystal size： 180 x 300 mm 43. 8 kg Shell size： 270 x 360 thick 40 118 kg Oxygen-free copper shielding shell, quartz-glass window, silicone coupling, TEFL reflecting layer, each side 5 PMT, positive seal against deliquescence. LC 1011 from LUOYANG COPPER CO. , LTD Ingredient: Cu+Ag >99. 98 18

Glove box Deliquescent crystals, 160 kg, assembly is a challenge. Vacuum glove box: 4 stations, heating chamber, transition chamber, Ball transfer, lifting hatch, Electrode and the vacuum channel interface reserved Moisture meter monitoring inside moisture content, Liquid nitrogen cold well for removing water vapor 19

Cryostat Temperature control system: Vacuum insulation structure, GM refrigerator, PT 100 temperature sensors, ceramic heater, lakeshore temperature controller, Detector using lifting structure, the upper is waterproof cover, Cable through the pipe to the surface. 20

PMT HAMAMATSU PMT have been delivered R 11065 MOD, R 8778 70100 m. Bq/PMT voltage divider has been designed, Positive high voltage, Voltage and signal separation, 21

Electronics FADC and trigger system developed by IHEP is expected finished this month 22

Calibration PMT Calibration： LED+Optical fiber for PMTs PS Si. PMT Cu Am 241 X Cs. I(Na) Gamma/neutorn： Cs 137 gamma, Cf 252 neutron, Rejection power calibration: Am 241 plastic scintillator source for gamma rejection power calibration. 23

QF measurement IHEP neutron experiment setup: DT, DD neutron tube, BC 501 A liquid scintillation have been installed and tested, Cryostat has arrived, is being assembled. Low temperature neutron scattering experiments ¥ 1 million funds condition is ready. Supported by National Natural Science Foundation of China 2014 QF measurements for Cs. I(Na), Cs. I(Tl), Na. I(Tl) will be carried out. 24

QF new results PHYSICAL REVIEW C 88, 035806 (2013) Na. I(Tl) Cs. I(Na) y expectedneutron gamm a QF is 4% for I recoil, consistent with our expectations. Cs. I(Tl)? ? ar n i lim pre Flight time peaks delayed than expected, indicating a small QF at room temperature. 25

G 2 Concept Design If G 1 successful, G 2 will be proposed 2015 8 m 2 m water tank: Φ 8 x 8 m Cryostat: Φ 2 x 2 m Detector array: 5 x 5 x 2 50 modules 2. 15 T The budget PMT: ￥ 20 million 500 x 40000/PMT Cs. I(Na): ￥ 10 million 2000 kg x 5000/kg Electronics: ￥ 5 million 500 x 10000/ch DAQ: ￥ 5 million Total ~￥ 40 million 26

Summary l Cs. I(Na) Crystals are proposed for WIMPs searches Ø One scintillation channel Ø background rejection by range l Some tests of Cs. I(Na) has been done Ø waveforms of n/gamma/alpha are different Ø wavelengths of fast and slow light are different Ø low temperature better performance l One module are under construction Ø 2013 -2014, 40 kg, water shielding, Low temperature, Daya bay Hall 5 Ø 2015 2 T 27

Thanks for your attention 28

Cs. I(Na) vs LXe Cs. I(Na) Advantages： Good n/γ separation by PSD; Cheap，price is 1/5 of LXe，Cs. I(Na) 850 USD/kg，Lxe 4200 USD/kg; Stable，suitable for long-term operation to observe the annual modulation effect; Modular，Easy to build large-scale detector; Cs. I(Na) Disadvantages： Cs 137 not easy purification (2 m. Bq/kg is best) ; Doping uniformity is difficult to measure, depends on the quality of the crystal growth; Volume is limited, Single crystal difficult to achieve 3 D measurement; Surface deliquescence, assembling and testing complex; LXe Advantages： Continuous purification , Kr 85 can purify from 5 -20 ppm to 1 ppb; Easy to implement 3 D measurements (TPC/4π); LXe Disadvantages： Expensive; Complex (precise temperature/pressure control, purification and recovery system); Scale limited by high drift voltage 29

backgrounds IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 55, NO. 3, JUNE 2008 PHYSICAL REVIEW D 83, 082001 (2011) 30