A cylindrical GEM detector with analog readout for the BESIII experiment

A cylindrical GEM detector with analog readout is under development for the upgrade of the Inner Tracker of the BESIII experiment at IHEP (Beijing). The new detector will match the requirements for momentum resolution (sigma(pt) /p(t) similar to 0.5% at 1 GeV) and radial resolution (sigma(xy) similar to 120 mu m) of the existing drift chamber and will improve significantly the spatial resolution along the beam direction (sigma(z) similar to 150 mu m) with very small material budget (less than 1.5% of X-0). With respect to the state of the art the following innovations will be deployed: a lighter mechanical structure based on Rohacell, a new XV anode readout plane with jagged strip layout to reduce the parasitic capacitance, and the use of the analogue readout inside a high intensity magnetic field to have good spatial resolution without increasing the number of channels.