GEM Tracker

Contact:  Bernd Voss, Radoslaw Karabowicz

A set of large area planar Gaseous Electron Multipliers detectors forms a GEM-Tracker, which will be used as a first forward tracking detector after the central tracker. The exact number of planes and their positions are yet to be determined based on the simulation studies performed using the PandaRoot package. Current implementations include 3 or 4 GEM-Discs depending on the length of the central tracker. The discs cover polar angles from 3 to 20 degrees and are placed at (81), 117, 153 and 189 cm from the target.

Located in the middle of each GEM-Disc is a double-sided read-out pad plane which allows particle track position measurement in four projections. In the front and back of the pad plane stacks of three GEM foils are used for electron amplification. The disc volume is closed with one cathode plane and one window foil per side. On the perimeter of the disc a ring of Front-End electronics, cooling, support, voltage supply and shielding is formed. In order to achieve enough stability of a disc as well as to read-out some of the channels, a vertical bar is introduced to the setup.


The high number of projections per GEM-Disc allows unambiguous determination of the particle trajectory position with a resolution of better than 100 μm.

Station no. 1 2 3 4
Weight [kg] 20 20 30 40
Distance to target [mm] 810 1170 1530 1890
Outer diameter [mm] 900 900 1120 1480