Development of position sensitive Gamma-ray detector

对Λ（1405）辐射衰变的测量可以给出Λ（1405）结构的重要信息，它是否是Kbar-N束缚态。在本研究中，我们提出利用超子时间投影室研制一个位置灵敏的γ射线探测器来研究Λ（1405）的辐射衰变，在J-PARC强子实验装置上建立了一个用于研究H-重子和三体强子核子共振的实验装置，并对该装置的分辨率和可接受性进行了全面的模拟。基于GEANT 4工具包。基于重建的位置分辨率优化了伽马射线探测器的尺寸。采用64段探测器，对辐射衰减的接受度为83.3%，本底降低率大于85%。实验台采用13 mm^2 MPPC和2 x 1 x 80 cm^3塑料闪烁体。我们通过使用Sr-90的β射线获得了时序分辨率与ADC增益的关系。MIP的估计定时分辨率约为130 ps。但是，由于超导亥姆霍兹线圈的空间限制，需要薄的塑料闪烁体。我们新制作了新的MPPC板，以优化增益和光收集效率。该板正在进行测试，测试板将与TPC矢端镜共享。模拟和测试结果已于9月在东北大学举行的HYP 2015上展示。此外，该进展已在E42和E45合作会议上报告。

The measurement of radiative decay of the Λ(1405) can give important information of the structure of the Λ(1405), which is the Kbar-N bound state whether or not. In this research, we proposed to develop a position sensitive Gamma-ray-detector to study a radiative decay of the Λ(1405) by using Hyperon Time-Projection-Chamber, which is being built to explore an existence of the H-dibaryon and the 3-body hadronic nucleon resonances at the J-PARC hadron experimental facility.A full simulation was performed to estimate the resolution and acceptance of the Λ(1405) based on the GEANT4 toolkit. The size of the Gamma-ray-detector was optimized based on the reconstructed position resolution. By assuming the 64 segments of the detector, the acceptance of the radiative decay is estimated to be 83.3%, while the background reduction is obtained to be more than 85%.The test bench with 13 mm^2 size of MPPC and 2 x 1 x 80 cm^3 long plastic scintillator was performed. We obtained the timing resolution versus the ADC gain by using beta rays from Sr-90. The estimated timing resolution at MIP is about 130 ps. The thin plastic scintillator, however, is desired, because the space limitation of the super conducting Helmholtz-Coil was come. We newly fabricated new MPPC board to be optimize the gain and light collection efficiency. The board is being tested and the test board will be shared with the TPC hodoscope.The simulation and test results were presented at the HYP2015 at Tohoku University in Sep. In addition, the progress has been reported at the E42 and E45 collaboration meeting.