Mu3e experiment: a search for lepton flavour violation in the decay of a muon to three electrons.

Mu3e实验将研究大量的介子衰变。为此，该实验背后的团队将建造一种探测器，能够以前所未有的精度测量这些衰变过程中产生的子粒子。这项实验将寻找一种非常特殊的衰变类型，在这种衰变中，一个反Muon衰变到两个正电子和一个电子。最重要的是，在这个过程中，反介子失去了它的“味道”，变成了一个正电子。尽管夸克和中微子等其他粒子已知会这样做，但对于带电的轻子(电子、介子或介子)来说，从来没有观察到这样的味道变化。如果粒子物理学公认的标准模型(SM)是完整的故事，那么涉及到违反带电轻子味道守恒的过程将不会被观察到。然而，粒子物理学家预计，为了解决物理学中的一些大问题，比如为什么在我们的宇宙中，物质比反物质更重要，需要超越标准模型的新模型。已经制定了过多的这种模式，但仍然缺乏确证其中任何一种的实质性证据。到目前为止，以前的实验已经排除了涉及带电轻子味道违背的介子衰变，甚至每10亿次衰变中就会发生一次。Mu3e实验的结果将再一次变得更加敏感10000倍，可能会在这个已经非常令人印象深刻的结果上增加4个零；或者--更好的是--找到人们追逐的衰变过程的证据，并由此获得新物理的直接证据。粒子物理学家试图回答的另一个关键问题是理解神秘暗物质的本质。暗物质的存在从天文观测中得到了强有力的证实，但其性质仍不清楚。Mu3e实验可以非常精确地研究大量介子的衰变产物，这一独特的能力也允许建造和操作探测器的团队成员搜索假设的低质量暗物质候选粒子。到目前为止或计划中的任何其他实验中都不会看到这样的粒子。

The Mu3e experiment will study a very large numbers of muon decays. For this the team behind the experiment will build a detector that can measure with unprecedented accuracy the daughter particles produced in these decays. The experiment will look for a very specific type of decay in which an anti-muon decays to 2 positrons and an electron. Crucially, in this a process the anti-muon loses its "flavour" to become a positron. Although other particles such as quarks and neutrinos are known to do this, such a change of flavour has never been observed for the charged leptons (electrons, muons or taus). If the well-established standard model (SM) of particle physics is the complete story, processes involving the violation of the conservation of charged lepton flavour will not be observed. However, particle physicists expect that to address some big questions in physics, such as why in our universe matter dominates over antimatter, new models going beyond the standard model are needed. A plethora of such model have been formulated but substantive evidence to corroborate any of these remains absent. To date, previous experiments have excluded that muon decays involving charged lepton flavour violation occur even once in 1,000,000,000,000 decays. The results of the Mu3e experiment will be more sensitive by a factor 10,000 again, potentially adding 4 zeros to this already very impressive result; or - much better - finding evidence of the sought after decay process and with that, direct evidence of new physics. Another key question particle physicist are trying to answer is to understand the nature of the mysterious dark matter. The existence of dark matter is strongly established from astronomical observations, but its nature remains unknown. The unique capabilities of the Mu3e experiment to study with great precision the decays product of a very large number of muons, also allows the members of the team that will build and operate the detector to search for hypothetical dark matter candidate particles at low masses. Such particles would not have been be seen in any other experiment to date or planned.