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In ATLAS, the magnetic field is parallel to the 3D Electrodes in the EndCap region and perpendicilar in the barrel region. The testbeam will therefore test the ATLAS barrel configuration.

Expected effects due to the magnetic field

In the barrel region, given the direction of the E and B fields, charges will be drifted to the surface of the sensor, and will be trapped, recombined, etc... in the p-spray layer (or the oxide layer?).  What happens there is not fully understood (by me!). Some charges will be collected by the read-out electrodes (some in-time but some delayed), and some won't. The effect is therefore a loss of efficiency. In the barrel region, contrary to planar sensors, there is no charge sharing effect.

Question: do we need to understand what happens when charges are drifted to the surface of the sensor, and what measurement could we do to quantity the effect?

As Chris pointed it out, the effect will of course depend on the magnitude of the field but also on the sensor itself. That's why it important to test the sensors for various magnetic field (at least 1.9T and 0T, but also possibly with one or two more points in between).

Proposed Run Plan

1. Measurements to be performed at each setting: