本帖最后由 voyagerbb 于 2009-12-20 11:30 编辑
匆忙翻译的,也没有太斟酌语句.暗物质探测有两个主要的方向:直接探测和间接探测,间接探测更接近天文一些,不过现在看来似乎直接探测会先有突破了.
英文原文出处:
http://www.symmetrymagazine.org/breaking/2009/12/17/dark-matter-experiment-results-announced/
Dark matter experiment results announced
December 17, 2009 | 7:04 pm
暗物质实验结果发布
2009年12月17日,上午 7:04
In the analysis of new data, scientists from the Cryogenic Dark Matter Search experiment, managed by the Department of Energy’s Fermi National Accelerator Laboratory, have detected two events that have characteristics consistent with the particles that physicists believe make up dark matter.
在对新的数据的分析过程中,参与低温暗物质搜寻实验(Cryogenic Dark Matter Search experiment)的科学家已经探测到了两个事件,其特征与物理学家认为构成暗物质的粒子一致.该实验由能源部的费米国家加速器实验室(Fermi National Accelerator Laboratory)主持.
However, there is a chance that both events could be the signatures of background particles–other particles with interactions that mimic the signals of dark matter candidates. Scientists have a strict criterion when determining whether a discovery has been made. There must be less than one chance in 1000 that the observed events could be due to background. This result does not yet pass that test, so CDMS experimenters do not claim to have detected dark matter. Nevertheless, the result has caused excitement excitement in the scientific community.
然而,还有可能是所有的事件都是背景粒子----其它的有跟暗物质候选者类似信号的相互作用的粒子,在作怪. 当决定是否取得了一项发现的时候,科学家有一个严格的标准.观测到的事件是由背景导致的可能性要小于千分之一.这次的结果却没有通过这样的检验,所以CDMS实验并没有宣称已经探测到了暗物质.然而, 其结果已经在科学圈内引起了相当的兴奋.
CDMS Analysis Coordinator Jodi Cooley of Southern Methodist University said in a presentation at SLAC National Accelerator Laboratory that “our results cannot be interpreted as significant evidence for WIMP [dark matter] interactions. However, we cannot exclude either [of the two candidate events] as signal.”
CDMS实验的数据分析协调员 (Analysis Coordinator),来自南卫理公会大学(Southern Methodist University)的Jodi Cooley在SLAC国家加速器实验室 (SLAC National Accelerator Laboratory)的一次报告上说:”不能把我们的结果理解为WIMP 暗物质相互作用的重要证据,但是, 也不能认为这两个候选事件都不是信号而给排除掉”
She also said that, “the two events occurred during a time of nearly ideal detector performance–there was nothing suspicious going on. Both events passed all of our data quality checks.”
她还说道到,”这两个事件发生的时候正值探测器在几近理想的状态下工作的时间---没发生什么可疑的事情.所有的事件都通过了我们的数据质量核查.”
Lauren Hsu, a CDMS researcher at Fermilab, said in a presentation at Fermilab that “this is a very intriguing result. We really don’t know if this is a background or a signal. As an experimenter you always wish you had more data. I’m really interested to see what our next results will be.”
费米实验室的另一位CDMS研究者Lauren Hsu在费米实验室的一次报告上说:”这是一个非常引人入胜的结果,我们确实不知道这倒底是一个背景还是一个信号.作为一个实验家你总是期望有更多的数据.我对看看接下来的结果会是什么非常有兴趣.”
CDMS researchers announced their results in parallel talks at Fermilab and SLAC on Thursday, Dec. 17. The collaboration details the results in a paper “Results from the Final Exposure of the CDMS II Experiment,” that they have submitted to the physics preprint ArXiv for publication.
12月17日,也就是周二的时候,CDMS的研究者同时在费米实验室和SLAC举行的讨论会中发布了他们的结果.这项协作的细节在论文”Results from the Final Exposure of the CDMS II Experiment”中给出,这篇论文已被提交至物理学的预印本ArXiv上以便出版.
Astronomical observations from telescopes, satellites, and measurements of the cosmic microwave background have led scientists to believe that most of the matter in the universe neither emits nor absorbs light. This dark matter may have provided the gravitational scaffolding that allowed normal matter to coalesce into the galaxies we see today. In particular, scientists think our own galaxy is embedded within an enormous cloud of dark matter. As our solar system rotates around the galaxy, it moves through this cloud.
来自望远镜,卫星还有宇宙微波背景测量的天文学观测使得科学家们相信宇宙中的大多数物质既不发射也不吸收光.这些暗物质可能提供了引力,就像脚手架一样,以使得普通的物质能够合并到我们今天看到的星系里面去.特别是,科学家认为我们的银河系就嵌在一个巨大的暗物质云团中.随着我们的太阳系在绕着银河系公转的时候会穿行于其间.
Particle physics theories suggest that dark matter is composed of Weakly Interacting Massive Particles (WIMPs). Cooley said, “Both astrophysics and particle physics are pointing at the same thing. It’s what we call a happy coincidence.”
粒子物理理论指出,暗物质由大质量弱相互作用粒子 (Weakly Interacting Massive Particles, WIMPs)构成. Cooley说:”天体物理和粒子物理都指向同一个东西, 这就是所谓令人愉快的巧合.”
Scientists expect these particles to have masses comparable to, or perhaps heavier than, atomic nuclei. Although such WIMPs would rarely interact with normal matter, they may occasionally bounce off, or scatter from, an atomic nucleus like billiard balls, leaving a small amount of energy that is detectable under the right conditions.
科学家们期望这些粒子的质量跟原子核相当,或者还要重些.虽然这样的WIMPs很少跟普通物质发生相互作用, 它们偶尔会像台球一样被原子核给弹开或者散射,从而留下一点可以在适当的条件下被探测到的能量.
The CDMS experiment, located a half-mile underground at the Soudan mine in northern Minnesota, has been searching for WIMPs since 2003. The experiment uses 30 detectors made of crystals of germanium and silicon in an attempt to detect WIMP scatters. The detectors are cooled to temperatures very near absolute zero. Particle interactions in the crystalline detectors deposit energy as heat and as charges that move in an applied electric field. Special sensors detect these signals, which are then amplified and recorded for later study. By comparing the size and relative timing of these two signals, experimenters can distinguish whether the particle that interacted in the crystal was a WIMP or a background particle. Layers of shielding materials, as well as the half-mile of rock above the experiment, are used to prevent most of the background particles from reaching the detector.
CDMS实验位于明尼苏达州北部的Soudan矿井的地下半英里处,从2003年开始搜寻WIMPs.这个实验使用了30个锗硅晶体探测器来试图探测WIMP散射.这些探测器被冷却至非常接近绝对零度.晶体探测器中的粒子相互作用以加热和在电场中移动的电荷的形式沉积能量.特殊的传感器探测这些信号,并随后被放大和记录在案以备后续研究.通过比较两个信号的尺度和相对时长,实验家可以区分在晶体中反应的粒子到底是一个WIMP还是一个背景粒子.防护材料层和实验仪器上方半英里厚的岩石用来阻挡大多数的背景粒子,使其不能到达探测器.
Previous CDMS data did not yield evidence for WIMPs, but did assure physicists that the backgrounds have been suppressed to the level where as few as one WIMP interaction per year could have been detected.
先前的CDMS数据并未给出WIMP存在的证据,但是却使物理学家们相信其背景已经被抑制到足够低的程度,以致即使少到每年一次的WIMP相互作用都能被探测到.
CDMS collaborators are now reporting on their new data set, taken in 2007-2008, which approximately doubles the sum of all past data sets. With each new data set, collaborators must carefully evaluate each detector’s performance, excluding periods when the detectors were not operating properly.
CDMS的工作者们现在正在报道他们的新的数据,采集于2007-2008,这些数据量几乎是以前所有数据总和的2倍.对每一个新的数据集,工作者们必须仔细评估每个探测的性能,以排除掉探测器未正常运转的时间.
Physicists assess detector operation by frequently exposing the detector to sources of two types of radiation: gamma rays and neutrons. Gamma rays are the principal source of normal matter background in the experiment. Neutrons are the only known type of particle that will interact with germanium nuclei in the billiard ball style that WIMPs would. Neutrons frequently hit more than one of the CDMS detectors, while WIMPs would only hit one.
物理学家通过将探测器频繁地在两类辐射:伽玛射线和中子之下曝光来评定探测器的运转情况.伽玛射线是该实验中普通的背景物质的主要来源.中子则是仅知的可以跟锗核进行类似台球那样的弹开的反应的粒子,WIMP跟锗核也是这种类型的反应.中子频繁地跟不止一个的CDMS探测器发生撞击,而WIMP只撞击一个.
Experimenters use data from these studies as a baseline for determining how well a WIMP-like signal (produced by neutrons) is visible over a background (produced by gamma rays). Based on this information, physicists predict that no more than one background event will be visible in the data region where WIMP signals would appear. Since background and signal regions overlap somewhat, achievement of this background level required experimenters to throw out roughly 2/3 of the data that might contain WIMPs, because these data would contain too many background events.
实验者使用这些研究中的数据来作为基准,以确定一个类似WIMP的信号(由中子产生)在多好的程度上相对于背景(由伽玛射线产生)来说是可见的.基于这些信息,物理学家预言,在WIMP信号出现的范围之内,可见的背景事件不会多于一个.由于背景跟信号在某种程度上有些重叠,为了达到这样的背景程度,实验者们要扔掉大约2/3的可能包含WIMPs粒子的数据,因为这里面可能包含太多的背景事件.
CDMS experimenters do all of their data analysis without looking at the data region that might contain WIMP events. This standard scientific technique, sometimes referred to as ‘blinding’, is used to avoid the unintentional bias that might lead a scientist to keep events that have some of the characteristics of WIMP interactions but are really from background sources. After collaborators have made detailed estimates of background ‘leakage’ into the WIMP signal region, they ‘open the box’, or look in that region, and see if there are any WIMP events present.
CDMS的实验家在对所有的数据进行分析的时候都没有特意去关注可能包含WIMP时间的数据区域.这一标准的科学技巧,有时候被称为”盲法”,用来避免无意中的偏见,而这种偏见可能导致科学家保留那些事实上是来自背景源并具有某些WIMP反应特征的事件. 在协作者们对”泄露”进WIMP信号区域的背景进行过细致的评估之后,他们才”打开盒子”,或说把注意力转向那个区域,并查看是否有WIMP 事件存在.
A signal of about five events would meet criteria to claim a discovery. With only two events detected in this data set, there is about a one in four chance that these could be due to backgrounds. Therefore, CDMS experimenters do not claim to have discovered WIMPs. Previous results have established a rate of interaction between WIMPs and nuclei that varies depending on WIMP mass. The new result improves upon these limits for WIMPs with a large mass. Such upper limits are quite valuable in eliminating a number of theories that might explain dark matter. For examples, the results rule out some parameter values that the theory of supersymmetry could have.
大约五个事件可以产生一个信号满足宣布一项发现的标准.在这些数据里面只探测到2个事件,所以有四分之一的可能性它们是背景.因此,CDMS实验家并没有宣布已经发现了WIMPs.以前的结果已经确立了一个依赖于WIMP质量的WIMPs跟原子核之间的反应速率.这次的新的结果强化了对大质量的WIMPs的限制.这一上限对淘汰一大批解释暗物质的理论来说价值匪浅.例如,这次实验结果排除了一些超对称理论可以容许的参数值.
What comes next? While physicists could operate the same set of detectors at Soudan for many more years to look for more WIMP events, this would not take advantage of new detector developments and would try the patience of even the most stalwart experimenters (not to mention theorists).
接下来会是什么?物理学家可以将位于Soudan的探测器再运转多年以寻找更多的WIMP事件,但这并不会从新的探测器发展中获益,并且,对哪怕最坚定的实验家来说也是对其耐心的考验(更别说理论学家了).
Cooley said in her presentation that the CDMS experiment would need to run for about 2.5 times as long to reach discovery significance if the two candidate events were actual dark matter particles.
Cooley在其报告中说,如果这两个候选事件确实是暗物质粒子的话,CDMS实验需要再运转2.5倍的时间以确立真正的发现.
A better way to increase sensitivity to WIMPs is to boost the size of detectors that might see the particles, while still maintaining the ability to keep backgrounds under control. This is precisely what CDMS experimenters are now in the process of doing. By summer of 2010, collaborators hope to have about three times more germanium nuclei sitting near absolute zero at Soudan, patiently waiting for WIMPs to provide the perfect billiard ball shots that will offer compelling evidence for dark matter.
增加探测WIMPs的灵敏度的一个较好的办法就是增加可能看到粒子的探测器的尺寸,而同时依然将背景保持在可控的程度上.这正是CDMS的实验家们现在正在做的事情.到2010年的夏季,研究者们希望在Soudan拥有大约多3倍的冷至绝对零度附近的锗核,并耐心等待WIMPs给出像台球一样的完美撞击,以提供令人信服的暗物质存在的证据.
“While this result is consistent with dark matter, it is also consistent with backgrounds,” said Fermilab Director Pier Oddone. “In 2010, the collaboration is installing an upgraded detector (SuperCDMS) at Soudan with three times the mass and lower backgrounds than the present detectors. If these two events are indeed a dark matter signal, then the upgraded detector will be able to tell us definitively that we have found a dark matter particle.”
“尽管这次的结果跟暗物质一致,它同时也跟背景一致,”费米实验室的主任Pier Oddone说道:”在2010年,研究者们将会在Soudan安装一个升级了的探测器(超级CDMS,SuperCDMS),比现在的探测器重3倍,而噪音水平更低.如果这两个事件确实是暗物质信号,那升级后的探测器就可以肯定地告诉大家我们已经发现了暗物质粒子.”
The CDMS collaboration includes more than 59 scientists from 18 institutions and receives funding from the U.S. Department of Energy, the National Science Foundation, foreign funding agencies in Canada and Switzerland, and from member institutions.
CDMS的全体研究者包括来自18个研究所的超过59名研究人员,接受能源部,国家自然科学基金委,加拿大和瑞士的国外资助局以及成员单位的资助.
The paper is now available at the arXiv.
论文现在可以从arAiv上获取.
Background information:
背景知识参见:
http://www.fnal.gov/pub/presspas ... background2008.html
CDMS image gallery:
CDMS的图库:
http://www.fnal.gov/pub/presspas ... otos2008/index.html
CDMS home page:
CDMS的主页:
http://cdms.berkeley.edu/index.html
In these figures, the dotted red line divides events into those determined not to be WIMPs based on the relative timing of the heat to charge signals (left side) and those that could potentially be WIMPs based on that parameter (right side). The solid red box delineates the area of the graph in which WIMPs should occur based on both timing and the heat to charge ratio. Two events in separate detectors demonstrated the characteristics scientists predicted a WIMP would have.
在这些图中,红色的点线把事件分成两部分,从加热相对于电荷信号的时标来判断,一部分被认为是不是WIMPs(左侧),另一部分被认为具有潜在的可能是WIMPs(右侧).红色的实线方框勾画出了根据相对时间和加热电荷比WIMPs应该发生的区域.在独立的探测器中的两个事件展现了科学家预言WIMP应该具有的性质.
The curves dipping through this figure represent the results of several dark matter search experiments. The vertical scale represents the rate of WIMP scatters with nuclei while the horizontal scale is the mass of the WIMP. The gray line represents the 2008 results from the CDMS experiment. The blue line represents the most recent CDMS results. The solid black line represents the two results combined. The dotted black line represents the curve the combined results would have formed if CDMS had found no candidate events in 2009. The green and gray backgrounds represent areas that two theories of supersymmetry predict would contain dark matter.
图中的曲线代表几个暗物质搜寻实验的结果.纵轴表示WIMP跟原子核的散射率,横轴是WIMP的质量.灰线是CDMS 2008年的结果.蓝线是CDMS最近的结果.黑色的实线表示把两个结果合在一起.黑色的点线是在假设如果2009年CDMS没有发现候选事件的情况下的合并结果.绿色和灰色的背景表明两个超对称理论预言的会含有暗物质的区域. |
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