A low mass pixel detector upgrade for CMS

The CMS pixel detector has been designed for a peak luminosity of $1\times 10^{34}~{\rm cm}^{-2}{\rm s}^{-1}$ and a total dose corresponding to 2 years of LHC operation at a radius of 4 cm from the interaction region. Parts of the pixel detector will have to be replaced by 2015. The detector performance will be degraded for two reasons: radiation damage of the innermost layers and the planned increase of the LHC peak luminosity by a factor of 2-3. Based on the experience in planning, constructing and commissioning of the present pixel detector, we intend to upgrade the whole pixel detector in 2015. The main focus is on lowering the material budget and adding more tracking points. We will present the design of a new low mass pixel system consisting of 4 barrel layers and 3 end cap disks on each side. The design comprises of thin detector modules and a lightweight mechanical support structure using CO2 cooling. In addition, large efforts have been made to move material from the services out of the tracking region.