Technical description

The Outer Detector (OD) is composed of 24 planks of 5 layers x 32 columns of 4.7 meters long drift tubes operating in the limited streamer mode (section 1.65x1.65 cm2). The electrons produced by a charged particle crossing a tube drift toward the wire (high voltage of 4.4 kV) and give a signal with short raise time and high amplitude (typically 3ns and 80mV). Situated at 2 meters from the beam axis, it makes up the precision of the momenta of charged particles measured by the TPC. 5800 electronic channels in total give 3 space points plus 2 r-phi points per track.

20% (contiguous channels in r-phi) of the plank 6 is known to be dead.

It looks like

Quantities measured

For each event, 3 types of information are produced :

Accuracy

Trigger:

Dedicated electronics is used to produce the local trigger results for the first and second level. ID trigger data are correlated with the OD ones in order to reduce the rate due to cosmic and beam gas events. The third level is done by software. The IDOD trigger is very useful to cover the cracks between the TPC sectors.