First cosmic rays seen in the CMS Tracker Endcap

On March 14, 2006, first cosmic muon tracks have been measured in the Tracker EndCap TEC+ of the CMS silicon strip tracker. The end caps have silicon strip modules mounted onto wedge-shaped carbon fibre support plates called petals. Up to 28 modules are arranged in radial rings on both sides of these plates. One eighth of an end cap (called sector) is populated with 18 petals. The TEC+ endcap is currently being integrated at RWTH Aachen. 400 silicon modules with a total of 241664 channels, corresponding to one eighth of the endcap, are read-out simultaneously by final power supply and DAQ components. On the left is the TEC+ in Aachen, whilst on the right is a computer image of a cosmic ray traversing the many layers of silicon sensors. To understand the response to real particles, basic functionality testing was followed by a cosmic muon run. A total of 400 silicon strip modules are read out with a channel inefficiency of below 1% and a common mode noise of only 25% of the intrinsic noise.