氢气中μ子俘获率的测量及质子赝标耦合$g_P$的确定
Measurement of the Rate of Muon Capture in Hydrogen Gas and Determination of the Proton's Pseudoscalar Coupling $g_P$
摘要：
利用一种基于时间投影室的新实验技术，在超净贫氘氢气中，在1 MPa的压力下，测量了质子捕获核μ介子的速率。捕获率由测量的$μ^-$在氢气中的消失率与$μ^+$衰变率的世界平均值之间的差值获得。与液态氢相比，靶的低气体密度为1%，这是避免μ子分子形成引起的不确定性的关键。从$μp$原子的超精细单重基态的俘获率被测量为$Λ_S=725.0 \pm 17.4 s^{-1}$，由此提取核子的诱导赝标耦合$g_P(q^2=-0.88 m_μ^2)=7.3 \pm 1.1$。这一结果与基于QCD的近似手征对称性的$g_P$的理论预测是一致的。
英文摘要：
The rate of nuclear muon capture by the proton has been measured using a new experimental technique based on a time projection chamber operating in ultra-clean, deuterium-depleted hydrogen gas at 1 MPa pressure. The capture rate was obtained from the difference between the measured $μ^-$ disappearance rate in hydrogen and the world average for the $μ^+$ decay rate. The target's low gas density of 1% compared to liquid hydrogen is key to avoiding uncertainties that arise from the formation of muonic molecules. The capture rate from the hyperfine singlet ground state of the $μp$ atom is measured to be $Λ_S=725.0 \pm 17.4 s^{-1}$, from which the induced pseudoscalar coupling of the nucleon, $g_P(q^2=-0.88 m_μ^2)=7.3 \pm 1.1$, is extracted. This result is consistent with theoretical predictions for $g_P$ that are based on the approximate chiral symmetry of QCD.
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