Transcript Document
Direct detection of WIMP
李金
IHEP/THU
2010.12.13 workshop in ITP
1.
Principle of detection 2，New results 3，Detection technique 4，Summary
Property of WIMP
Suppose : Element particle
• • • • •
stable, came from BB massive neutral speed very low weak interaction ?
WIMP WIMP mass : 10~100 GeV
（
or smaller) flux: 100,000/cm 2 /s
Detection of dark matter
WIMP nuclear elastic scattering
WIMP Cs
예상되는 사건 수
< 1/kg/day I Recoil nuclear
Detector / Target
recoil nuclear is normal particle , can be detected
核反冲事例率和能 谱
Ge is better
Ar is better
Comparison of different dark matter target ( WIMP 100GeV in mass 10e 6pb incross section) : Form factor for Ar,Xe, and Ge; Differential rate Integral rate over threshold
两种测量方法
WIMP 本底 来 源 电 子反冲和中子的核反冲 Gamma/betta Interaction difference between WIMP and gamma or electron but similar to neutron
Big challenges
Very low energy thresholds(<10 KeV) (“Quenching effect” ~1/10) Very low event rate (cross section σ < 10-45)
Long exposures (long term stability)
Big detector (large mass,100kg 1000kg … )
Stringent background control( Cosmogenic ,Radioactive, neutrons ) Underground & Shielding (passive , active , deep site, cleanness) Discrimination signal/background power
Measurement has to be in underground Passive shielding & Active shielding
Neutrino background
Passive shielding & Active shielding Passive shielding
PE, PE(B) neutron Lead –gamma Cu- gamma Ar gas –radon Active veto
本底来源-天然放射性（α,γ, n）
核素 含量
226 Ra 232 Th 1.8
±0.2 Bq/Kg （145.8 ppb）
<
0.27 Bq/Kg （<66.42 ppb） 锦屏地下岩石放射性含量
40 K <
1.1Bq/Kg （<35.53 ppm）
Background from Radon
222 Rn长期平衡下， 222 Rn 衰变一次平均放出0.0269个光子 探
测
器空
间
中吹 氮气减 少
氡
的影 响
中韩合作Y2L地下实验室KIMS实验屏蔽体和VETO 聚乙烯
.
中子屏蔽
/ μ
子探测 铅 高纯 无氧铜 LS 30cm 宇宙线Veto 中子屏蔽体 屏蔽外部 等 Pb 15cm : 30t 屏蔽外部材料的本底 OFHC Cu 10cm : 3t
TEXONO实验
。 屏蔽体从外到内： 5cm厚塑料闪烁体反符合； 15cm厚铅室， 25cm厚含硼聚乙烯， 5cm厚无氧铜， 紧贴高纯锗探测器外部的约5cm厚 的高纯CsI晶体反符合探测器
Direct detection techniques
Detector Techniques
-
Present Focus : Nuclear Vs Electron recoils WIMP
HPGe expts TEXONO CDMS II, EDELWEISS I CDMS II, EDELWEISS II
E phonons Ionization
10% energy ZEPLIN II/III/Max, XENON, LUX, WARP, ArDM Target DAMA/LIBRA KIMS ZEPLIN-I, DEAP, CLEAN, XMASS
Light
1% energy fastest no surface effects
Phonons/heat
100% energy slowest cryogenics CRESST II Picasso, Simple, Coupp (superheated)
WIMP E phonons
Future : Lower Threshold ; Direction Sensitive
New physics results
CDMS Dec09 Results
Plus, of course, many theory papers to explain a positive result which was not claimed ……
Calibration with Sources Y:Number of standard deviation from the mean recoil yield X: time relative to acceptance region
Official Conclusion: Spin-Independent Cross-Section How Probable is it to Detect N>=2 events at Mean=0.8 ??
~19% ~ 1.3
s
from Poisson Distribution in Gaussian Equivalence
i.e.
Very Likely to be Statistical Effects
CoG
ｅ
NT collaboration
２０１０．２．２５
1,
采用
PC Ge
探测器
2
，
2100m.w.e
的地下
3
，采用去除本底新技术
4
，
3KeV
附近有去不掉的多余事例
5
，有可能是
CDMS
，并在
DAMA/LIBRA
的区域内
1，做了效率修正，Cut后的低能能谱，有宇宙线的峰， Zn，Ge的EC峰 2. 点线： 触发效率， 虚线： 触发 + PSD cut 效率， 实线: trigger + PSD + rise time Cut 4, 电子学脉冲标定 5，7GeV/c 和10GeV/c 的WIMP的信号（ｓｉｇｍａ＝ 10e-4Pb） 1 ＤＡＭＡ，ＣｏＧｅＮＴ２００８，２０１０的结果 ２，不同理论模型的预言 ３，紫的区域支持ＣＤＭＳ ４，新结果偏向ＷＩＭＰ 质量在７－11GeV/C2，而不是本底 ５，axioelectric dark matter 的耦合系数（０.５－８.５ＫｅＶ)
XENON100
Comments&discussion on the results from Xenon 100
最新实验结果 高质量区 低质量区
Large mass Convenience Simple
Scintillation Crystal Detector
Backgound
WIMP nucleus fluorescence light wimp 晶体