arXiv 1109.66892011-09-29hep-ex

一种新的百万分之一正μ子寿命测量方法和费米常数的测定

A new part-per-million measurement of the positive muon lifetime and determination of the Fermi Constant

David M. Webber

备注：: Proceedings for DPF 2011, on behalf of the MuLan collaboration. 7 pages, 8 figures

摘要：

费米常数G_F描述了弱力的强度，它是由正μ子的平均寿命τ_mu最精确地确定的。理论上的进步已经将G_F的理论不确定性从τ_μ计算到百万分之几（ppm）。直到最近，G_F的剩余不确定性完全是实验性的，并且由tau_mu的不确定性主导。我们报告了MuLan合作最近对正μ子寿命的1.0 ppm测量。这一测量比以往任何测量都精确15倍以上，是有史以来测量的最精确的粒子寿命。该实验使用了时间结构的低能μ子束和由波形数字化器读出的塑料衰减器阵列以及快速数据采集系统来记录超过2次10^{12} μ子衰变。两个不同的真空中μ介子停止目标被用于单独的数据采集期间。这两个数据采集期的结果非常一致。组合结果给出tau_{mu^+}（{MuLan}）=2196980.3（2.2）ps。μ子寿命的测量给出了费米常数的最精确值：G_F（{MuLan}）= 1.1663788（7）\times 10^{-5} {GeV}^{-2}（0.6 ppm）。寿命也被用来提取μ ^-p单重态俘获率，它决定了质子的弱诱导赝标耦合g_P。

英文摘要：

The Fermi Constant, G_F, describes the strength of the weak force and is determined most precisely from the mean life of the positive muon, tau_mu. Advances in theory have reduced the theoretical uncertainty on G_F as calculated from tau_mu to a few tenths of a part per million (ppm). Until recently, the remaining uncertainty on G_F was entirely experimental and dominated by the uncertainty on tau_mu. We report the MuLan collaboration's recent 1.0 ppm measurement of the positive muon lifetime. This measurement is over a factor of 15 more precise than any previous measurement, and is the most precise particle lifetime ever measured. The experiment used a time-structured low-energy muon beam and an array of plastic scintillators read-out by waveform digitizers and a fast data acquisition system to record over 2 times 10^{12} muon decays. Two different in-vacuum muon-stopping targets were used in separate data-taking periods. The results from these two data-taking periods are in excellent agreement. The combined results give tau_{mu^+}({MuLan})=2196980.3(2.2) ps. This measurement of the muon lifetime gives the most precise value for the Fermi Constant: G_F({MuLan}) = 1.1663788 (7) \times 10^{-5} {GeV}^{-2} (0.6 ppm). The lifetime is also used to extract the mu^-p singlet capture rate, which determines the proton's weak induced pseudoscalar coupling g_P.

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