论文标题
搜索$μ^ - \ rightarrow e^+$ conversion：可以从金目标上的sindrum-ii正电子数据中学到什么
Search for $μ^- \rightarrow e^+$ conversion: what can be learned from the SINDRUM-II positron data on a gold target
论文作者
论文摘要
在其2006年论文中，将当前限制限制在金目标\ cite {sindrum_ii：bertl2006}上，sindrum-ii合作发布，以及电子动量分布，构造方源的动量分布。在正电子频谱端点附近，观察到的事件在预期的背景上存在统计学意义。我们估计在该地区88 MEV/C <P <95 MeV/c有13个事件，预期的背景约为1-1.5事件，作者尚未讨论。这13个事件形成了与实验分辨率一致的宽度的凸起，这使人们想到了$μ^ - \ rightarrow e^+$ conversion信号。但是，凸起的重建位置约为1 meV/c或$ \ sim \4σ_p$，低于预期的$μ^ - au \ rightarrow e^+ ir $信号，这强烈阻碍了异国情调的解释。但是，过剩可能是由于独家偶极子辐射muon捕获（RMC）过渡$^{197} au（gs）〜\ rightArrow〜^{197} pt（gs）$，分支分数约为$ 2 \ cdot 10^{ - 4} $。现有的RMC测量将无法解决此类过渡。我们得出的结论是，专属的RMC转变可以显着改变运动学终点附近的正电子光谱，以充分利用即将到来的实验的物理潜力，例如MU2E和Comet，这是对RMC Spectrum在核上的理论上更好的理解。必须对RMC光子光谱进行高分辨率测量。没有这些，搜索的敏感性$μ^ - \ rightArrow e^+$和$μ^ - \ rightArrow e^ - $可能会受到RMC过渡到女儿核独有的低较低状态的未知概率的严格限制。
In their 2006 paper setting the current limit on \mumemconv\ conversion search on a gold target \cite{sindrum_ii:Bertl2006}, the SINDRUM-II collaboration published, along with the electron momentum distribution, the momentum distribution of reconstructed positrons. Near the positron spectrum endpoint, there is a statistically significant excess of observed events over the expected background. We estimate that in the region 88 MeV/c < p < 95 MeV/c there are 13 events with an expected background of about 1-1.5 event, which has not been discussed by the authors. Those 13 events form a bump with a width consistent with the experimental resolution, making one think of a $μ^- \rightarrow e^+$ conversion signal. However, the reconstructed position of the bump is about 1 MeV/c, or $\sim\ 4σ_p$, lower than the expected $μ^- Au \rightarrow e^+ Ir $ signal, which strongly discourages the exotic interpretation. The excess, however, could be due to an exclusive dipole radiative muon capture (RMC) transition $^{197}Au(GS) ~\rightarrow~ ^{197}Pt(GS)$ with the branching fraction of about $2\cdot 10^{-4}$. Such a transition would not be resolved by the existing RMC measurements. We conclude that the exclusive RMC transitions could significantly modify the positron spectrum near the kinematic endpoint, to fully exploit the physics potential of the upcoming experiments such as Mu2e and COMET, a better theoretical understanding of the RMC spectrum on nuclei is needed. A high-resolution measurement of the RMC photon spectra has to be carried out. Without that, the sensitivity of the searches for $μ^- \rightarrow e^+$ and $μ^- \rightarrow e^-$ might be severely limited by unknown probabilities of RMC transitions to the exclusive low-lying states of the daughter nuclei.
