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Posts Tagged ‘ATIC’

I have thought that ultra-high energy cosmic particles always move straight forward. At most, they deflect a little bit under the giant gravity. However, a more accurate picture is that those particles, moving at almost light speed, float in the vast and violent universe like dust in sunlight, and diffuse all around without specified direction.

Recently I invited Prof. Hongbo Hu to give a seminar to the Daya Bay students, on the excess of cosmic ray electrons at 300-800 GeV observed by ATIC above the South Pole. Those excess could possibly be explained as an evidence of dark matter annihilation. Hongbo provides another possible explanation with the pair production in the remnant of supernova. My question is, supernova explosion in short distance happen 3 times every century in average. Each explosion lasts several days. So the excess should be short-lived. The answer is, 1) the supernova explosion lasts only several days but the remnant can exist for hundreds years. The mechanism for the pair production is still valid. 2) the high energy electrons will not fly to the Earth directly. They can be easily trapped by the strong magnetic field in the galaxy, circling there for million years. The propagation to the Earth is more like diffusion.

Some physicists could read the implications behind the complex mathematical expressions. Seems I am not good at it. I prefer to have a simple and straightforward physical picture at first. The excess of the electrons haven’t enough evidences to draw an exclusive conclusion now. It is not important to say it is due to dark matter or pair production. What’s important to me is that I have a more accurate picture on the propagation of cosmic ray particles in the universe.

像灰尘一样飞舞的超高能粒子

我总以为超高能的宇宙线粒子总是直线前进的,最多,在巨大星体的引力下稍微偏转一下。然而更加正确的图像是,这些几乎以光速前进的粒子,在浩渺狂暴的宇宙中,如阳光下的灰尘般飘飘荡荡,没有明确方向地四处扩散。

不久前请胡红波教授为大亚湾的学生做了一个关于南极高能电子(300-800GeV)超出现象的讲座。这些电子超出可能被解释为暗物质湮灭产生的信号,因此激发了新的暗物质研究的热情。红波提出了另一种可能的解释,即超新星遗迹中的对产生。我的问题是,近距离的超新星爆发平均一百年才三个,每次持续不过几天,那我们看到的高能电子超出应该是短暂的,稍纵即逝的现象。得到的回答是,1)超新星爆发只持续几天,但超新星遗迹可以存在数百年,仍能提供对产生需要的环境;2)产生出的超高能电子并不是直线飞到地球上,很容易被星系中的强磁场俘获,盘旋亿万年,因此电子飞到地球上更像是一种扩散过程。

有些人能够从数学表达式中得到隐藏的物理,我似乎不擅长这一点,而更喜欢首先建立一个简单直观的物理图像。南极电子超出现象还没有足够的证据做出排他性的解释,到底是暗物质还是对产生,对我来说并不重要,重要的是我对宇宙间粒子的飞行有了一个更正确的图像。

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