一种令人惊讶的极化反质子的方法
A surprising method for polarising antiprotons
摘要：
我们提出了一种利用极化的正电子束平行于反质子运动来极化储存环中的反质子的方法。如果将相对速度调整为$v/c \approx 0.002$，自旋翻转的截面将大到大约$2 \cdot 10^{13}$ barn，如三重自旋截面的新QED计算所示。提出了两种提供具有足够通量密度的正电子源的可能性。利用放射性$^{11}$ C直流源，极化度为0.70，通量密度约为$1.5 \cdot 10^{10}$ /（mm $^2$ s）的极化正电子束似乎是可行的。一个更复杂的提议是通过与圆极化光子成对产生极化正电子。它产生0.76的极化，需要注入到一个小的存储环。这样的偏振器源可以在低（100 MeV）以及高（1 GeV）能量储存环下使用，提供约一小时的时间用于将约$10^{10}$反质子的偏振建立到约0.18的偏振。与其他建议的比较表明，在品质因数的增益约为10倍。
英文摘要：
We propose a method for polarising antiprotons in a storage ring by means of a polarised positron beam moving parallel to the antiprotons. If the relative velocity is adjusted to $v/c \approx 0.002$ the cross section for spin-flip is as large as about $2 \cdot 10^{13}$ barn as shown by new QED-calculations of the triple spin-cross sections. Two possibilities for providing a positron source with sufficient flux density are presented. A polarised positron beam with a polarisation of 0.70 and a flux density of approximately $1.5 \cdot 10^{10}$/(mm$^2$ s) appears to be feasible by means of a radioactive $^{11}$C dc-source. A more involved proposal is the production of polarised positrons by pair production with circularly polarised photons. It yields a polarisation of 0.76 and requires the injection into a small storage ring. Such polariser sources can be used at low (100 MeV) as well as at high (1 GeV) energy storage rings providing a time of about one hour for polarisation build-up of about $10^{10}$ antiprotons to a polarisation of about 0.18. A comparison with other proposals show a gain in the figure-of-merit by a factor of about ten.
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