|The PAMELA experiment - Firenze|
The PAMELA tracking system
The PAMELA tracking system is designed to measure the curvature of crossing charged particles. The detector is exposed to the flux of the primary Cosmic Rays during its revolution in orbit around the Earth. The tracking system is composed of six equidistant planes (14x16 cm2) of double-sided, silicon microstrip detectors, inserted between five hollow modules of a permanent magnet. The cross section of the magnetic cavity corresponds to the plane dimensions and its full height is 44.5 cm.
The geometrical factor (or acceptance) of the tracker is 20.5 cm2sr. The resulting counting rate, averaged on the position along the orbit, is about 3 Hz for good events, except near the South Atlantic Anomaly where the flux is greatly enhanced, due to the trapped protons' contribution. A three-year-long data taking is expected.
On that side of the silicon detector which is used to measure the track curvature (bending view) the implantation and the read-out pitches are respectively 25 and 50 μm; during repeated beam tests Signal-to-Noise ratios greater than 50 have been measured resulting in less than 3.0 μm spatial resolution. The Maximum Detectable Rigidity is reached when the relative uncertainty in the momentum reaches 100%: this quantity has been estimated from beam test data as greater than 1 TV/c.