WIMP暗物质的直接探测

WIMP 暗物质

根据大爆炸核合成的计算,人们对非重子暗物质的期望在理论上是成立的,这表明宇宙中丢失的质量可能并不是重子物质.超对称的标准模型(SUSY)为人们提供了一个颇有希望的理论框架,在这个框架下人们可以期望一些粒子满足观测到的暗物质的性质.暗物质粒子最有希望的SUSY候选体是最轻的超对称粒子(LSP),中性超对称粒子(nentralino) X^0_1,这种粒子是希格斯粒子的费米性超对称伴随子跟中性规范波色子的叠加.为了能够跟宇宙早期的湮灭速率相一致,以便得到合适的残留丰度,这种粒子跟普通物质的作用截面应该比较小,但又足以为人们所测量到.特别是,中性超对称粒子跟普通物质的核子在弱电尺度的作用截面,应该与其在宇宙学上扮演的角色相一致.期望中的这种参与弱相互作用且质量范围在10Gev到1000Gev之间的中性超对称粒子,即被缩写为”WIMP”:大质量弱相互作用粒子.拜其参与弱相互作用所赐,WIMPs可以通过其跟普通物质的反应而被直接探测到.需要注意的是,并不是因为中性超对称粒子很特殊才能被探测到的--事实上任何具有类似质量和散射界面的WIMP粒子都能通过这个性质被探测到.

直接探测 WIMPs粒子

根据宇宙学中的结构形成的理论,星系的发光物质被引力束缚在一个更大的延伸的暗物质晕里面.假设宇宙的暗物质真是由这些尚未被识别的粒子组成的话,我们的太阳系和我们的行星就会在暗物质粒子的流里穿行,这些粒子构成了我们银河系所在的暗晕.既然这样的话,WIMP就可以直接被探测到(当然要把一些仪器埋在地表下才行).如果给定中性超对称粒子-核子的弱相互作用强度,银河系里的WIMPs粒子就会在具有合适的灵敏度的探测器的里留下一定量的能量.当一个WIMP粒子跟一个核子恰好在探测器感应材料的基准体积(fiducial volume)内发生弹性散射的话,这个过程就会发生. CDMS实验(当然还有很多其它的实验)就致力于探测中性超对称粒子通过跟核子碰撞而传递给它的反冲能量,这个探测是由跟低温的锗和硅晶体耦合在一起的灵敏的声子探测器做到的.探测器晶体产生的声子信号经处理后可用已知的背景反应速率解释.如果识别出了一个可信的高于背景速率的事件,就可以通过对其进行分析来确定与这个事件相对应的反应的性质--从而可能证认出WIMPs.保守点来说,即使没有测到任何的WIMP-核子反应,对可能的中性超对称粒子的反应截面大小的限制,也是很大的促进.

原文:

  WIMP Dark Matter  

  Expectations for non-baryonic darkmatter are founded principally in Big Bang nucleosynthesiscalculations, which indicate that the missing mass of the universe isnot likely to be baryonic. The supersymmetric standard model (SUSY)offers a promising framework for expectations of particle species whichcould satisfy the observed properties of dark matter. The most likelySUSY candidate for a dark matter particle is the lightestsupersymmetric particle (LSP), the neutralino χ01,which is a superposition of the fermionic superpartners of the Higgsand neutral gauge bosons. In order to be consistent with anearly-universe annihilation rate leaving proper relic abundances, sucha particle should have a small but measureable interaction crosssection with ordinary matter. Specifically, a cross section forinteraction between a neutralino and a nucleon in ordinary matter ofthe order of the electro-weak scale would be consistent with ameaningful cosmological role for the particle. This expectation of aweak interaction together with the expected mass range of theneutralino, 10 to 1000 GeV, produce the acronym "WIMP": WeaklyInteracting Massive Particle. By virtue of their weak-scaleinteraction, WIMPs should be able to be observed by directly detectingtheir interactions with ordinary matter. Note that this detectionprocedure is not specific to neutralinos - any WIMP with comparablemass and scattering cross section is detectable in this manner.

  Direct Detection of WIMPs

                               
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  Accordingto models of cosmological structure formation, the luminous matter ofgalaxies is gravitationally bound to a more massive, sprawling halo ofdark matter. Should the dark matter of the universe consist ofunidentified particles, our solar system and our planet would bepassing through a flux of these dark matter particles which constitutethe dark halo of the Milky Way galaxy. WIMP dark matter could then bedetected directly as the Earth (and some detection apparatus beneathits surface) pass through our galaxy's DM halo. Given the expected weakinteraction scale of the neutralino-nucleon scattering, galactic WIMPsshould deposit a measurable amount of energy in an appropriatelysensitive detector apparatus. This can occur through elastic scatteringbetween an incident WIMP and a nucleus in the fiducial volume of somemonitored detector material. The CDMS experiments (and many others)aim to measure the recoil energy imparted to detector nuclei throughneutralino-nucleon collisions by employing sensitive phonon detectionequipment coupled to arrays of cryogenic germanium and siliconcrystals. The phonon signals generated within the crystal detectors canbe processed and interpreted with information about known backgroundrates. If found, a confidently identified above-background event ratewould be analyzed to determine the nature of the responsibleinteraction -- perhaps enabling an identification of WIMPs. Conversely,a null WIMP-nucleon scattering find can be used to improve greatlycurrent limits on the possible neutralino interaction cross section.
    原文出自:

http://cdms.berkeley.edu/Education/DMpages/science/essays/science/essays/science/directDetection.shtml

楼主翻译的再标准不过了哈,因为这是你研究的领域哈!赞!

2# rjxie

千万别这么说啊,呵呵.
我翻译肯定有不好或者不足的地方,欢迎大家指正呢,呵呵.

楼主是强人！！！！

1# voyagerbb

“这些粒子构成了我们银河系所在的暗晕” "which constitute the dark halo of the Milky Way galaxy"
这句译的似乎不妥，银河系所在的暗晕？银河系的暗晕？

原来LZ早先在另一贴中提到的WIMP指的是超对称粒子，5月份刚开超对称的课程，刚学了一点点东西，对这个奇怪东西还不太了解，感谢LZ译的这篇文章。

另外，超对称理论还没有任何实验证据证明其正确性，而且现在超对称的模型太多，算出的结果也不太一样。这类实验还能对超对称理论进行验证。

从这个角度，清华还真野心勃勃，如果能让清华先给出了一些证据，对众多的超对称模型进行初步的筛选，居功至伟啊。

建议楼主翻译时一段段对应的翻，这样看起来方便。
欢迎专业人士的翻译作品。