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University of Oxford, Oxford, United Kingdom.
University of Liverpool, Liverpool, United Kingdom.
Phys Rev Lett. 2021 Apr 9;126(14):141801. doi: 10.1103/PhysRevLett.126.141801.
We present the first results of the Fermilab National Accelerator Laboratory (FNAL) Muon g-2 Experiment for the positive muon magnetic anomaly a_{μ}≡(g_{μ}-2)/2. The anomaly is determined from the precision measurements of two angular frequencies. Intensity variation of high-energy positrons from muon decays directly encodes the difference frequency ω_{a} between the spin-precession and cyclotron frequencies for polarized muons in a magnetic storage ring. The storage ring magnetic field is measured using nuclear magnetic resonance probes calibrated in terms of the equivalent proton spin precession frequency ω[over ˜]{p}^{'} in a spherical water sample at 34.7 °C. The ratio ω{a}/ω[over ˜]{p}^{'}, together with known fundamental constants, determines a{μ}(FNAL)=116 592 040(54)×10^{-11} (0.46 ppm). The result is 3.3 standard deviations greater than the standard model prediction and is in excellent agreement with the previous Brookhaven National Laboratory (BNL) E821 measurement. After combination with previous measurements of both μ^{+} and μ^{-}, the new experimental average of a_{μ}(Exp)=116 592 061(41)×10^{-11} (0.35 ppm) increases the tension between experiment and theory to 4.2 standard deviations.
我们展示了费米实验室国家加速器实验室（FNAL）μ子g-2实验针对正μ子磁矩反常a_μ≡(g_μ-2)/2的首批结果。该反常由两个角频率的精确测量确定。μ子衰变产生的高能正电子的强度变化直接编码了磁存储环中极化μ子的自旋进动频率和回旋频率之间的差频ω_a。使用在34.7°C的球形水样中根据等效质子自旋进动频率ω[]_p^'校准的核磁共振探头测量存储环磁场。比率ω_a/ω[]_p^'，连同已知的基本常数，确定a_μ(FNAL)=116 592 040(54)×10^-11（0.46 ppm）。该结果比标准模型预测值大3.3个标准差，并且与先前布鲁克海文国家实验室（BNL）的E821测量结果高度一致。在与先前对μ^+和μ^-的测量结果合并后，新的实验平均值a_μ(Exp)=116 592 061(41)×10^-11（0.35 ppm）将实验与理论之间的差异扩大到4.2个标准差。
