Research on the energy resolution of neutrinoless double beta decay experiment DCBA

双β衰变是原子中的原子核发出两条β射线并使其原子序数增加两个单位的现象。在这种情况下，2 v ββ意味着两个反电子中微子和两个β射线的发射，而0 v ββ代表没有中微子发射，因此它被称为无中微子双β衰变。到目前为止，已经观察到了几个原子的2 v ββ，并测量了它们的半衰期，但Ovββ的观察尚未得到证实。如果中微子是马约拉纳粒子，Ovββ应该发生。换句话说，Ovββ的观测意味着中微子是马约拉纳粒子，对其半衰期的测量可以确定中微子的绝对质量标度。这有助于构建超越旧标准模型的新基本粒子理论。此外，Ovf 3f 3的观测将支持被认为是早期宇宙情景的强有力候选者的稀薄起源理论。DCBA（漂移室β射线分析仪）实验通过漂移室跟踪探测器测量均匀磁场中每个β射线的动量。这是迄今为止在其他地方没有实现的独特方法。DCBA室只对带电粒子敏感，因此它可以从本质上消除伽马射线背景。由于磁场的存在，电子、正电子和α粒子之间的粒子识别变得容易，并且对带电粒子背景的排斥非常强大。这些已经在本研究中使用称为DCBA-T2的原型得到证实。DCBA-T2揭示了提高能量分辨率的方法，这是分离Ovββ事例和2 v ββ事例的关键。然后，新的原型DCBA-T3正在根据DCBA-T2的经验建造中。为了寻找具有大量衰变源的Ovββ事件，今后还计划扩大探测器模块。

Double beta decay is the phenomenon that the nucleus in an atom emits two beta rays and increases its atomic number by two units. In this case, 2vββ means the emission of two anti-electron-neutrinos together with two beta rays, and 0vββ stands for no neutrino emission therefore it is called the neutrinoless double beta decay. So far 2vββ's of several atoms have been observed and their halflives have been measured, while no observation of Ovββ has been confirmed yet. If neutrinos are Majorana particles, Ovββ should take place. In other words, the observation of Ovββ means that neutrinos are Majorana particles, and the measurement of its haifiife can determine the absolute mass scale of neutrinos. This contributes to constructing the new theory of elementary particles beyond the old standard modeL And also, the observation of Ovf3f3 will support the leptogenesis theory, which is considered as the strong candidate of early universe scenario. The DCBA (Drift Chamber Beta-ray Analyzer) experiment measures the momentum of each beta ray in a uniform magnetic field by drift chamber tracking detectors. This is the unique method not realized elsewhere so far. The DCBA chamber is only sensitive to charged particles therefore it can intrinsically eliminate gamma ray backgrounds. Particle identification among electron, positron and alpha particle is easy because of the magnetic field, and it is very powerful for rejecting charged particle backgrounds. These have been confirmed using the prototype called DCBA-T2 in the present research. DCBA-T2 has revealed the method to improve the energy resolution, which is the key issue of separating Ovββ events from 2vββ events. Then new prototype DCBA-T3 is now under construction based on the experiences of DCBA-T2. In the future, an enlarged detector module is planed in order to search for Ovββ events with a large amount of decay sources.