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 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/cm2/s

Detection of dark matter WIMP nuclear elastic scattering WIMP Cs I Recoil nuclear 예상되는 사건 수 < 1/kg/day 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

本底来源电子反冲和中子的核反冲 WIMP 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 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） 锦屏地下岩石放射性含量 核素 226Ra 232Th 40K 含量 1.8±0.2 Bq/Kg （145.8 ppb） < 0.27 Bq/Kg （<66.42 ppb） < 1.1Bq/Kg （<35.53 ppm） 锦屏地下岩石放射性含量

222Rn长期平衡下，222Rn 衰变一次平均放出0.0269个光子 Background from Radon 222Rn长期平衡下，222Rn 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 .中子屏蔽/μ子探测 铅 聚乙烯 高纯 无氧铜 LS 30cm 宇宙线Veto 中子屏蔽体 屏蔽外部等 屏蔽外部材料的本底 OFHC Cu 10cm : 3t Pb 15cm : 30t

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， 的高纯CsI晶体反符合探测器

Direct detection techniques

Detector Techniques - Present Focus : Nuclear Vs Electron recoils Target CRESST II CDMS II, EDELWEISS I Light 1% energy fastest no surface effects Phonons/heat 100% energy slowest cryogenics Ionization 10% energy WIMP ZEPLIN-I, DEAP, CLEAN, XMASS CDMS II, EDELWEISS II Ephonons Elight Background Signal Eionization HPGe expts TEXONO DAMA/LIBRA KIMS Picasso, Simple, Coupp (superheated) ZEPLIN II/III/Max, XENON, LUX, WARP, ArDM  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

Spin-Independent Cross-Section Official Conclusion: Spin-Independent Cross-Section How Probable is it to Detect N>=2 events at Mean=0.8 ?? ~19% from Poisson Distribution ~ 1.3s in Gaussian Equivalence i.e.Very Likely to be Statistical Effects

CoGｅNT 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

Scintillation Crystal Detector Large mass Convenience Simple PSD Backgound

WIMP nucleus fluorescence light 晶体