Development of thin CCD vertex detector

我们测量了滨松S7170 CCD的表面轮廓，其厚度仅为20μm。大面积薄型CCD中心弯曲约60μm，变形更大。当CCD温度从27.5℃变化到-13℃时，观察到相似大小的轮廓变化。精确的位置测量需要一个坚固的结构来支撑CCD。我们还研究了b/c夸克标记和JLC探测器的背景。仅使用拓扑顶点查找器和质量标记方法，我们发现b夸克的标记纯度为95%，效率为50%，c夸克的标记纯度为55%，效率为27%。为了提高性能，我们考虑了一种设计，其中束管半径减少一半，顶点探测器的厚度减少到1/3，并使用5个CCD层。在相同纯度的情况下，b夸克的标记效率提高了10%，而c夸克的效率和纯度都提高了10%。我们还估计，在十年的运行中，电子和中子的背景剂量分别为10^<12>e/cm^2和10^9n/cm^2。如果我们使用MPP模式CCD在近室温下工作，根据我们的辐射硬度测试，平带电压的位移约为1 V， VCTI约为2×10^<-4>。这种损坏是可以接受的，但对于高光度加速器的工作，更可取的是开发更多的辐射硬CCD。为了获得更好的顶点探测器性能，在选择标准但光度较低的加速器操作时，如果将探测器螺线管磁场从2特斯拉增加到3特斯拉，则束管半径可以从标准值2 cm减小到1.5 cm。

We have measured surface profile of Hamamatsu S7170 CCD, whose thickness is only 20μm. The central part of the CCD bowed about 60μm and more large deformation was seen in the case of large area thin CCD.When the temperature of CCD is changed from 27.5℃ to -13℃, similar size of change of profile were observed. A solid structure to support CCD is required for precise position measurement. We also studied b/c quark tagging and backgrounds of the proposed JLC detector. By using the topological vertex finder and the mass tagging method alone, we found b quark can be tagged with 95% purity and 50% efficiency and c quark can be tagged with 55% purity and 27% efficiency. For improved performance, we considered a design where the radius of the beam pipe is reduced by half, thickness of vertex detector is reduced to 1/3 and five CCD layers are used. In that design, b quark tagging efficiency increased by 10% with same purity, while, in the case of c quark, both efficiency and purity increased by 10%. We have also estimated electron and neutron backgrounds dose to be 10^<12>e/cm^2 and 10^9n/cm^2 for ten years of operation. If we use MPP mode CCD for near room temperature operation, shift of the flat band voltage is about 1 V and VCTI is about 2×10^<-4> according to our test of radiation hardness. This damage will be acceptable but a development of more radiation hard CCD is preferable for high luminosity accelerator operation. For the better vertex detector performance, the radius of the beam pipe can be reduced to 1.5 cm from the standard value of 2 cm if the detector solenoid magnetic field is increased from 2 Tesla to 3 Tesla when the standard but lower luminosity accelerator operation is selected.