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李淼的博客

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2009-12-13 14:22:14|  分类: 默认分类 |  标签: |举报 |字号 订阅

  下载LOFTER 我的照片书  |

1、一个具有纪念意义,但并没有实质意义的事情是,LHC在12月8号实现了两束相对运动的能量为1.18tev质子束。ATLAS展示了一个含有两个喷注的事例:2-jets event at 2.36Tev,这个能量超过了Tevatron。

Tommaso Dorigo写道

Well, as you know I cannot say anything about internal matters of the CMS experiment at the LHC, but I know that other sites will have information pretty soon on the matter. So my advice for tonight is to browse the web, and possibly the site of less discreet bloggers than myself. The CERN twitter feed might also be a good idea… All I can say is that LHC is working like a charm these days!

CERN的 twitterfeed没有说什么。

2、当然,另一件吸引眼球的事件是关于暗物质的谣言,我上次写博客时在comment里提了。

现在再转一个Sean Carroll的说法。

Not too much point in speculating — we’ll find out next week! There was some misplaced excitement about a Nature paper, but it is true that CDMS has scheduled simultaneous talks at CERN, Fermilab, SLAC, and elsewhere. Steinn did the citizen-journalist detective work and dug up the abstract for Priscilla Cushman’s talk at CERN:

I will present new results from the recent blind analysis of 612-kg days (before cuts) of data using the CDMS germanium detectors at Soudan. CDMS uses ionization and athermal phonon signals to discriminate between candidate (nuclear recoil) and background (electron recoil) events in Ge crystals cooled to ~ 50 mK. Timing, yield and position information allows us to tune our expected background leakage into the signal region to 0.5 events. I will report on what we saw when we “opened the box”, whether we have seen WIMPs or not, and implications for future dark matter direct experiments.

It would seem unlikely to me that CDMS would be able to announce a cut-and-dried discovery of dark matter; that would require collecting an awful lot of data. (But what do I know?) It’s more plausible that they would see some kind of provocative signal, but without quite enough significance to be definitive. With many different competing experiments, several of which have been working for quite some time now, it seems like the kind of result that you would gradually sneak up on, rather than dramatically capture in one fell swoop. Or maybe they’re just updating us on their best limits, and some rumor-mongering has spiraled a bit out of control. We’ll see.

Adrian Cho表示谨慎的怀疑:

In January, however, the CDMS collaboration also published results from data taken with the same array from October 2006 to July 2007 and saw no evidence for WIMPS, says Richard Gaitskell, a physicist at Brown University. Since then, he estimates, CDMS has taken about enough data to double its sensitivity. If so, the researchers probably haven’t seen a signal so strong that it couldn’t have resulted from a few background events. “You’d be lucky to see one event,” Gaitskell says. “It’s just not enough of an increase in sensitivity to have one of these ‘Oh my God!’ moments.” The researchers might have a shot at incontrovertible sighting of dark matter had they taken enough data to increase their sensitivity by a factor of 10, he says.

Still, researchers say that searching for dark matter in this way makes perfect sense–Gaitskell himself is working on such an experiment–and many hope such efforts will pay off within years. Whatever it might be, the rumored CDMS signal could be a hint of more decisive observations to come. But in all likelihood, it won’t by itself be enough convince physicists that dark matter has been spotted.

3、变换光学。

英文学名是transformation optics。我过去提到很多次了,就是和隐身斗篷、超颖材料联系在一起的一门学问。据陈焕阳说,从06年两篇Science的开创文章到现在,已经有了一千篇文章了。

每天,我在浏览hep-th,astro-ph,gc-gr以及hep-ph之余,还得看一眼physics的optics部分,因为那里几乎每天有一篇关于超颖材料的文章,有时还得看一眼cond-mat里的materials science。

原因很简单,最近我决心推动用超颖材料模拟引力场特别是宇宙学的研究,我相信这是一个很快要热起来的方向。

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