Development of position sensitive Gamma-ray detector

通过测量Λ（1405）的辐射衰减，可以得到Λ（1405）的结构的重要信息，无论是否为Kbar-N束缚态。在这项研究中，我们提出了一个位置敏感的伽玛射线探测器来研究Λ（1405）的辐射衰变，利用超子时间投影室，这是在J-PARC强子实验设施中用于探索h -重子和三体强子核子共振的存在。基于GEANT4工具包，对Λ（1405）的分辨率和接受度进行了全面模拟。基于重建的位置分辨率，优化了伽玛射线探测器的尺寸。通过假设探测器的64段，估计辐射衰减的接受度为83.3%，而背景衰减则大于85%。搭建了尺寸为13 mm^2的MPPC和2 × 1 × 80 cm^3长的塑料闪烁体的试验台。我们利用Sr-90的β射线获得了时序分辨率与ADC增益的关系。估计MIP的定时分辨率约为130 ps。然而，由于超导亥姆霍兹线圈的空间限制，需要薄塑料闪烁体。为了优化增益和光收集效率，我们制作了新的MPPC板。电路板正在测试中，测试板将与TPC hodoscope共享。9月，仿真和测试结果在日本东北大学举行的HYP2015上进行了展示。此外，在E42和E45合作会议上也报告了进展情况。

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.