Armbruster B, Drexlin G, Eitel K, Jannakos T, Kleinfeller J, Maschuw R, Oehler C, Plischke P, Reichenbacher J, Steidl M, Zeitnitz B, Gemmeke H, Kleifges M, Eichner C, Ruf C, Bodmann B A, Finckh E, Hössl J, Jünger P, Kretschmer W, Wolf J, Booth N E, Blair I M, Edgington J A
Institut für Kernphysik, Forschungszentrum Karlsruhe, 76021 Karlsruhe, Germany.
Phys Rev Lett. 2003 May 9;90(18):181804. doi: 10.1103/PhysRevLett.90.181804.
We investigated mu(+) decays at rest produced at the ISIS beam stop target. Lepton flavor (LF) conservation has been tested by searching for nu(e) via the detection reaction p(nu(e),e(+))n. No nu(e) signal from LF violating mu(+) decays was identified. We extract upper limits of the branching ratio (BR) for the LF violating decay mu(+)-->e(+)+nu(e)+nu(-) compared to the standard model (SM) mu(+)-->e(+)+nu(e)+nu(mu) decay: BR<0.9(1.7) x 10(-3) (90% C.L.) depending on the spectral distribution of nu(e) characterized by the Michel parameter rho=0.75(0.0). These results improve earlier limits by one order of magnitude and restrict extensions of the SM in which nu(e) emission from mu(+) decay is allowed with considerable strength. The decay mu(+)-->e(+)+nu(e)+nu(mu) often proposed as a potential source for the nu(e) signal observed in the LSND experiment can be excluded.
我们研究了在ISIS束流终止靶产生的静止μ⁺衰变。通过检测反应p(νₑ,e⁺)n寻找νₑ来检验轻子味（LF）守恒。未发现来自违反LF的μ⁺衰变的νₑ信号。与标准模型（SM）的μ⁺→e⁺+νₑ+νμ衰变相比，我们提取了违反LF的衰变μ⁺→e⁺+νₑ+ν⁻的分支比（BR）上限：根据由米歇尔参数ρ = 0.75(0.0)表征的νₑ的能谱分布，BR < 0.9(1.7)×10⁻³（90%置信水平）。这些结果将早期的限制提高了一个数量级，并限制了允许μ⁺衰变以相当强度发射νₑ的SM扩展。常被提议作为在LSND实验中观测到的νₑ信号潜在来源的μ⁺→e⁺+νₑ+νμ衰变可以被排除。
