Development of thin CCD vertex detector

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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.