WIMPs search project with highly segmented NaI(Tl) scintillators - PowerPoint PPT Presentation

WIMPs search project with highly segmented NaI(Tl) scintillators Ken-Ichi Fushimi Faculty of Integrated Arts and Sciences The University of Tokushima

CONTENTS � Signal Selection by Spatial and Time Correlation � Thin NaI(Tl) plate for WIMPs search � Performance of thin NaI(Tl) � Plan for Underground Experiment � Summary

Collaboration � The University of Tokushima � K.F, H.Kawasuso, M.Toi, K.Yasuda, E.Matsumoto, E.Aihara, R.Hayami, S.Nakayama, N.Koori � Osaka University � K.Ichihara, S.Umehara, S.Yoshida, M.Nomachi, H.Nakamura, R.Hazama � ICU � H.Ejiri

WIMPs search by scintillators � Large Mass (~100kg) � Good Target Nuclei � 23 Na for SD (NaI) � 127 I for SI,SD,EX (NaI, CsI) � 19 F for SD (CaF 2 ) � 129 Xe for SD,SI,EX (Xe) � Low Cost

Sensitivity for WIMPs χ χ σ ∝ 2 A SI N N J J σ ∝ C λ + 2 SD J ( J 1 ) N N J ’ + 2 J ' 1 1 J J σ ∝ * A M 1 A EX + 2 J 1 g M N N

Signal selection by Spatial and Timing Correlation � SSSC analysis � Signal Selection by Spatial Correlation � Signal � 57.6keV γ + Low energy recoil � Localized event � Background � High energy γ and β � Diffused event

� SSTC analysis � Signal Selection by Time Correlation � Signal � Timely localized � T 1/2 =0.9ns (57.6keV excited state) � Background � Timely correlated � 214 Bi � 214 Po (T 1/2 =164 µ s) � 210 Pb � 210 Bi(T 1/2 =5days)

Segmented NaI(Tl) plate for DM search � 23 Na & 127 I 57.6keV 7/2 � Sensitive to SD and SI � 100% natural abundance � 127 I 0keV 5/2 � Sensitive to EX 127 I � Low energy excited state Experimentally obtained 2 = M 0 . 1 M 1 � Expect: 3.60 × 10 -3 /day/kg (Higgsino) � Limit: 4.98 × 10 -2 /day/kg (ELE V NaI)

Previous technique χ χ 1 0 8 6 (Arb. Unit) 4 2 γ 127 I 0 - 2 dR dE 0 2 0 4 0 6 0 8 0 1 0 0 Recoil ENERGY(keV) Difficult to identify BG and Signal.

Signal identification by segmentation 1 0 χ 8 χ 6 4 2 0 - 2 0 2 0 4 0 6 0 8 0 1 0 0 E N E R G Y ( k e V ) 1 0 8 γ 127 I 6 4 Recoil 2 0 0 2 0 4 0 6 0 8 0 1 0 0 E N E R G Y ( k e V )

Estimation of signal selectivity � Monte Carlo simulation (GEANT4) � 57.6keV gamma ray from one module � γ is detected the another module � Next module to the emitter module The fraction which is detected both sides of emitter

Fraction of detected g by neighboring modules Thickness of NaI(Tl) Thickness of NaI(Tl) Coincidence probability Coincidence probability 0.5mm 0.5mm 0.21 0.21 0.75mm 0.75mm 0.18 0.18 1.0mm 1.0mm 0.15 0.15 1.5mm 1.5mm 0.11 0.11

Specification of thin NaI array � 0.05cmX5cmX5cm NaI(Tl) � 0.05cmX6cmx0.5cm Acrylic Light Guide � ESR reflector � 16modules (phase 1) � 256modules (phase 2) � 1024, 2176 (phase 3,4)

MC simulation for BG � Radioactive contamination � Uniformly contaminated in NaI(Tl) crystal � 210 Pb 0.1mBq/kg (1/100 of present value) � 214 Pb, 214 Bi 10 µ Bq/kg (present value)

Condition of SSSTC � 214 Pb, 214 Bi � SSSTC analysis � Delayed Coincidence Δ T<1ms � Reduction factor=0.03 � SSSTC 1s< Δ T<60min (3 T 1/2 ) � Reduction factor=0.003 � 210 Pb, 210 Bi � SSSTC analysis � Successive β ray in 12.5 days (2.5 T 1/2 ) � Reduction factor=0.177

Expected BG 1 T O T A L ( S ) / d a y / k g T O T A L ( C ) / d a y / k g - S S T C 0 . 1 SINGLES 0 . 0 1 g k / y a d / 0 . 0 0 1 S T N E V E 0 . 0 0 0 1 - 5 1 0 SSSTC - 6 1 0 0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 E N E R G Y ( k e V )

Energy window of analysis T O T A L ( S ) / d a y / k g T O T A L ( C ) / d a y / k g - S S T C 1 Coincidence 0 . 1 event rate 0 . 0 1 g k / y a ≤ ≤ d 2 keV E 10 keV / 0 . 0 0 1 S ee T N E V E 0 . 0 0 0 1 - 5 1 0 - 6 1 0 0 1 0 2 0 3 0 4 0 5 0 E N E R G Y ( k e V )

T O T A L ( S ) / d a y / k g T O T A L ( C ) / d a y / k g - S S T C 1 0 . 1 0 . 0 1 g k / y a d / 0 . 0 0 1 S T N E V E 0 . 0 0 0 1 - 5 1 0 - 6 1 0 0 1 0 2 0 3 0 4 0 5 0 E N E R G Y ( k e V )

Upper limit on BG rate N a I ( T l ) t h i c k n e s s = 0 . 0 5 U p p e r 4 l i n e s E t h = 2 k e V , L o w e r 4 l i n e s E t h = 4 k e V 1 モジュ ー B G U p p e r U p p e r B G r a t e # o f T o l a l E V E N T S / E R R O R / y ルの質量 l i m i t / y e a r l i m i t ( / k g / d / k g / d a y m o d u l e s m a s s ( k g ) y e a r e a r ( k g ) ( 9 0 % C . L . ) a y ) 1 . 7 2 E - 0 2 0 . 0 0 4 5 8 8 1 6 0 . 0 7 3 4 4 . 5 1 E - 0 1 0 . 6 7 1 5 5 6 1 . 4 1 7 5 0 . 0 5 2 8 7 3 1 . 7 2 E - 0 2 0 . 0 0 4 5 8 8 2 5 6 1 . 1 7 4 4 7 . 2 2 E + 0 0 2 . 6 8 6 2 2 4 3 . 4 6 5 2 2 9 0 . 0 0 8 0 7 8 1 . 7 2 E - 0 2 0 . 0 0 4 5 8 8 1 0 2 4 4 . 6 9 7 6 2 . 8 9 E + 0 1 5 . 3 7 2 4 4 8 6 . 9 3 0 4 5 8 0 . 0 0 4 0 3 9 1 . 7 2 E - 0 2 0 . 0 0 4 5 8 8 2 1 7 6 9 . 9 8 2 4 6 . 1 3 E + 0 1 7 . 8 3 1 6 2 2 1 0 . 1 0 2 7 9 0 . 0 0 2 7 7 1 1 . 2 7 E - 0 2 0 . 0 0 4 5 8 8 1 6 0 . 0 7 3 4 3 . 3 1 E - 0 1 0 . 5 7 5 3 4 1 0 . 7 4 2 1 9 0 . 0 2 7 6 8 4 1 . 2 7 E - 0 2 0 . 0 0 4 5 8 8 2 5 6 1 . 1 7 4 4 5 . 3 0 E + 0 0 2 . 3 0 1 3 6 3 2 . 9 6 8 7 5 8 0 . 0 0 6 9 2 1 1 . 2 7 E - 0 2 0 . 0 0 4 5 8 8 1 0 2 4 4 . 6 9 7 6 2 . 1 2 E + 0 1 4 . 6 0 2 7 2 6 5 . 9 3 7 5 1 7 0 . 0 0 3 4 6 1 . 2 7 E - 0 2 0 . 0 0 4 5 8 8 2 1 7 6 9 . 9 8 2 4 4 . 5 0 E + 0 1 6 . 7 0 9 5 6 9 8 . 6 5 5 3 4 4 0 . 0 0 2 3 7 4 N a I ( T l ) の厚さ 0 . 1 c m 1 モジュ ー 全モジュ ー 計数値上 モジュ ール 1 年間の 1 年間の B G 上限値 B G 計数率 ルの質量 ルの質量 限値 数 計数値 計数誤差 ( 9 0 % C . L . ) ( k g ) ( k g ) ( / k g / d a y ) 2 . 7 4 E - 0 2 0 . 0 0 9 1 7 5 1 6 0 . 1 4 6 8 1 . 4 4 E + 0 0 1 . 1 9 7 9 3 3 3 . 0 6 0 . 0 5 7 0 7 2 . 7 4 E - 0 2 0 . 0 0 9 1 7 5 2 5 6 2 . 3 4 8 8 2 . 3 0 E + 0 1 4 . 7 9 1 7 3 2 2 . 9 1 E + 0 1 0 . 0 3 3 9 6 9 2 . 0 1 E - 0 2 0 . 0 0 9 1 7 5 1 6 0 . 1 4 6 8 1 . 0 5 E + 0 0 1 . 0 2 4 9 6 4 2 . 4 5 7 0 . 0 4 5 8 2 4 2 . 0 1 E - 0 2 0 . 0 0 9 1 7 5 2 5 6 2 . 3 4 8 8 1 . 6 8 E + 0 1 4 . 0 9 9 8 5 8 2 . 2 1 E + 0 1 0 . 0 2 5 7 5 8

Calculation of Exclusion plot � Upper limit on R lim (Experimental result) � Upper limit on Cross section σ lim � Local halo density ρ 0 =0.3GeV/cm 3 � Mean velocity < v >=230km/sec � Target number density N T =4.013X10 24 /kg m χ σ = R lim, EX lim ρ 2 ε N v f F ( q ) T 0 Th Coinc p = f f p i

Exclusion plot for σ EX s _ l i m ( 1 6 m o d ) s _ l i m ( 1 0 2 4 m o d ) f u r o s h i k i 4 s _ l i m ( 2 5 6 m o d ) s _ l i m ( 2 1 7 6 m o d ) 4 1 0 1 0 0 0 1 0 0 1 0 1 0 0 1 0 0 0 M A S S ( G e V )

Calculation of limit on σ p-x Using the relation, 2 2   2 + * m m p 2 J 1 M ∑   χ σ ∝ ∆ T f 3 M 1 T q   + + µ EX q 2 1 m m J p   χ q T p i 2 2   m m ∑   χ σ ∝ λ + ∆ T 2 3 J ( J 1 ) T q   + SD q m m   χ q T The Upper limit on proton-WIMPs cross section 2   + + 2 * m m m 2 J 1   χ σ = λ + σ p p 2 J ( J 1 )   χ − + + lim, p lim, EX 2 m m m 2 J 1   χ T T

Parameters [ ] λ + = 2 J ( J 1 ) 0 . 75 p 5 7 = = * J , J 2 2 = 0 . 938 GeV m p 127 = m 118 . 18 GeV I

Expected sensitivity for WIMPs s x - p ( 1 6 ) s x - p ( 1 0 2 4 ) f u r o s h i k i 4 s x - p ( 2 5 6 ) s x - p ( 2 1 7 6 ) 0 . 0 1 Stringent limit will be obtained by 1year measurement 0 . 0 0 1 0 . 0 0 0 1 - 5 1 0 1 0 0 1 0 0 0 M A S S ( G e V )

SD Exclusion plot

Performance of thin NaI(Tl) � Thickness of NaI(Tl) � 0.05cm � Energy resolution � Energy threshold � Photon number/keV � Position selectivity � PMT : Hamamatsu R329P

Development of thin NaI(Tl) � Collaboration with Horiba Ltd. � Production of thin NaI plate � Selection of reflector � ~2004/Feb. � Design and production method � 2004/Apr. � First module was completed!! � 2004/May~ � Performance, stability test.