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Cao Jun | Institute of High Energy Physics | P.R. China

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Dark Matter Signal Disappeared

I mentioned ATIC experiment in my blog last month. Many people has been excited by the possible dark matter evidence implicated by it for a while. Coming in May, HESS and Fermi/GLAST confuted it with higher precision data.

Have a rough count, there are quite a lot similar things in my no so long scientific career, such as lepto-quark, pendaquark, Heidelberg-Moscow neutrinoless double beta decay results, and many more. Most of them are based on serious analyses, just extend a little bit further with bold creativity. Some other analyses just like a joke.

Some experiments were suspectful at the beginning, e.g. Ray Davis’ solar neutrino experiment. The poor guy repeated his experiment for 30 years. Finally he became the oldest one when wining Nobel Prize. Some experiments lie between, e.g. the discovery of neutrino by Reines and Cowan. People believe they did observe neutrino. The measured cross section agreed with theoretical prediction very well, in 5%. In the next year, Lee and Yang revealed the parity nonconservation. Thus the theoretical prediction of the neutrino cross section was wrong. The actual value is twice larger. So they analyzed the data again, and the measured cross section was doubled, agreed with the new prediction very well again. Such an important discovery was not awarded Nobel Prize until 40 years later. The poorer Cowan couldn’t wait so long. For this reason, Zhizhong Xing often reminds us, “you should try to live long if you have done an important work.”

Science always advances in such debating of true or false. Kandice Carter wrote a review on the pendaquark, said “Even though the pentaquark seems to be illusory, at least in the form physicists have pursued so far, the alley leading toward it has been full of interesting revelations.”

暗物质信号又没了

上个月我在博客里提到了ATIC实验。不少人很是为它看到的可能是暗物质信号的结构激动了一阵。转眼进入五月,HESS和Fermi/GLAST两个实验就用更精确的数据否定了ATIC结果。
稍微数一数,在我短短的十几年研究生涯里,类似的事情已经不少:lepto-quark, 五夸克态, Heidelberg-Moscow的无中微子双贝塔衰变,还有不少。大部分还是基于严肃的数据分析,只是在解释上大胆地发挥了一下现象力。有些数据分析则像是开玩笑。

有的实验刚开始没人相信是对的,例如Ray Davis的太阳中微子实验,可怜的家伙就一直做了三十年,终于熬成了获奖时年龄最大的诺贝尔奖获得者。也有的实验介于两者之间,例如Reines和Cowan发现中微子的实验。大家相信他们发现了中微子,测得的反应截面也与理论符合得很好,只差5%。第二年,李杨发现宇称不守恒,这样原来的理论值不对,截面大了整整一倍。于是他们又重新分析了数据,测得的反应截面也大了一倍,又符合得很好。这么重要的发现,居然等了四十年才想起来发个奖。比Davis更可怜的Cowan终于没能熬过岁月,等到发奖的那一天。因此,邢志忠经常好心地提醒大家,假如你做出了重要的工作,一定要活得长。

科学总是在这些真真假假的争论中发展。Kandice Carter写过一篇五夸克态的回顾,说“尽管五夸克态看上去是个错觉,科学家行进的小巷里总是充满有趣的发现”。

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