Research for the development of the vertex detector using fully-depleted fine-pixel CCD

我们开展了用于线性对撞机(ILC)实验的全耗尽细像素CCD(FPCCD)顶点探测器的研制工作。研究内容包括基于FPCCD的顶点探测器预期性能的模拟研究、标准像素尺寸全耗尽CCDs的研制与表征、FPCCDs的辐射耐受性研究、FPCCDs抗辐射性能研究装置的研制以及薄膜化CCDs的力学研究。在模拟研究中，我们发明并验证了一种利用命中团形状有效抑制背景点击的方法，这是细像素的优势之一。随着全耗尽CCDs的发展，我们制作了几种不同厚度和不同外延层电阻率的背光CCDs样品。用宽度小于像素点宽度的线状激光照射这些CCDs。我们测量了信号传播到靠近前表面的势井的扩散。结果，我们发现具有24gm厚的高阻外延层的样品可以完全耗尽，而与栅极电压无关。我们还测量了磁场中的洛伦兹角，发现在3T磁场中使用不会出现严重的问题，有望在实际实验中使用。通过本研究，我们证明了FPCCD顶点探测器原则上可以用于ILC实验。在硬件研发方面，实现了样品面阵的完全耗尽。

We have carried out a study for the development of the vertex detector using fully-depleted fine-pixel CCDs (FPCCD) for the linear collider (ILC) experiments. The study issues are simulation studies of the expected performance of the vertex detector using FPCCD, development and characterization of standard pixel-size fully-depleted CCDs, study of radiation tolerance of FPCCDs, development of apparatus for the radiation hardness study of FPCCDs, and mechanical study of thinned CCDs.In the simulation studies, we invented and demonstrated the validity of a method of effective rejection of background hits by using the hit cluster shape, which is one of the advantages of the fine pixels. We also demonstrated the FPCCD vertex detector can satisfy the requirement for the tracking efficiency and the impact parameter resolution in the ILC experiment.As the development of fully depleted CCDs, we fabricated several kinds of sample back-illuminating CCDs which have different thickness and resistivity of the epitaxial layers. These CCDs were illuminated with LASER light focused in line shape which has the width less than the width of the pixels. We measured the spread of the signal which travels to the potential well near the front surface. As a result, we have found that a sample which has 24gm-thick high-resistive epitaxial layer can be fully depleted independent of the gate voltage. We also measured the Lorentz angle in the magnetic field, and found that there will be no serious problem when used in 3T magnetic field which is expected to be used in the actual experiment.Through this study, we demonstrated that the FPCCD vertex detector can, in principle, be used for the ILC experiment. As for the hardware R＆D, we have achieved the fully depletion of the sample CCD.