Search for neutrinoless double beta decay with DCBA-T

中微子质量的存在已经通过对中微子振荡的观察得到了证实。下一个主要问题是测量中微子的绝对质量，并研究中微子是马约拉纳粒子还是狄拉克粒子。因为小的中微子质量可以用所谓的跷跷板机制自然地解释，所以理论上可以预期马约拉纳型中微子的质量。如果中微子是马约拉纳粒子，就会发生无中微子双衰变。在这种情况下，“用dba - t寻找中微子双β衰变”的研究被提出。一种被称为漂移室β射线分析仪（DCBA）的磁跟踪探测器，由微型射流型漂移室和一个电磁磁铁组成。由于这是国际上第一个将漂移室应用于双β衰变实验的计划，因此为了解决技术问题，我们建造了一台名为DCBA-T的测试装置。根据最近的中微子振荡实验结果，通过理论分析预计中微子的有效质量在0.05 eV左右，这取决于质谱。具有如此质量灵敏度的探测器需要逐步发展。dba - t是第一步，其质量灵敏度约为4 eV。由衰减源薄板发射的两条射线的轨迹由位于均匀磁场中的漂移室检测。每条射线的动量由螺旋轨迹的半径和俯仰角得到。每条射线的动能也由动量计算出来。衰减点由两条轨道确定。由于漂移室对伽马射线不敏感，伽马射线引起的背景事件被有效地消除了。dba - t证实(1)在1atm充满氦气混合物的漂移室中获得了1 MeV Br的转换电子径迹，(2)通过三维径迹重建获得的动量计算了电子能量。现在DCBA-T正致力于从含有5.6% ^<150>Nd的天然Nd_2O_3源中寻找中微子双β衰变事件。另一方面，继续提高能量分辨率，并研究大量源板（如600 kg ^<150>Nd和^<82>Se）的调节方法，以达到低至0.05 eV的质量灵敏度。少

The existence of neutrino mass has been confirmed by the observation of neutrino oscillations. The next major matter of concern is to measure the absolute neutrino mass and to investigate that neutrinos are Majorana or Dirac particles. Because the small neutrino mass is naturally explained by the so-called see-saw mechanism, Majorana-type neutrino mass is theoretically expected. If neutrinos are Majorana particles, neutrinoless double beta decay takes place. In this situation, the present study of "Search for neutrinoless double beta decay with DCBA-T" was proposed.A magnetic tracking detector, called Drift Chamber Beta-ray Analyzer (DCBA), consists of mini jet-type drift chambers and a solenoid magnet. Since this was the first plan to apply the drift chamber to double beta decay experiment in the world, a test apparatus called DCBA-T was constructed to solve technical problems. Effective neutrino mass, which is expected from the theoretical analysis based on the results of recent neut … More rino oscillation experiments, is in the order of 0.05 eV, depending on mass spectra. A detector having such mass sensitivity will require step-by-step processes in developing. DCBA-T is the first step, and having a mass sensitivity of about 4 eV. Tracks of two beta rays emitted from thin plates of decay source are detected by drift chambers, which are located in a uniform magnetic field. A momentum of each beta ray is obtained from a radius and a pitch angle of a helical track. Kinetic energy of each beta ray is also calculated from the momentum. A decay point is determined by two tracks. Since a drift chamber is insensitive to gamma rays, background events caused by gamma rays are effectively eliminated. DCBA-T confirmed that (1) the conversion electron track of 1 MeV from Br was obtained in the drift chamber filled with helium gas mixture at 1 atm, and (2) the electron energy was calculated from the momentum obtained from three dimensional track reconstruction. Now DCBA-T is engaged in searching for neutrinoless double beta decay events from the source of natural Nd_2O_3 containing 5.6% ^<150>Nd. On the other hand, improving the energy resolution is continued, as well as investigating the accommodation method for a large amount of source plates such as 600 kg of ^<150>Nd and ^<82>Se, in order to reach the mass sensitivity down to 0.05 eV. Less