Parameterization-based tracking for the P2 experiment

The P2 experiment in Mainz aims to determine the weak mixing angle θ_W at low momentum transfer by measuring the parity-violating asymmetry of elastic electron-proton scattering. In order to achieve an unprecedented measurement accuracy within the planned 10 000 hours of data taking, the experiment has to run at event rates on the order of 10¹¹ per second. Whereas the tracking system is not required to operate at the full beam rate, every attempt is made to achieve the highest possible rate capability. At the full beam rate every reconstruction frame (45 ns long) will contain about 800 signal tracks, and 16 000 background hits from Bremsstrahlung photons. In order to cope with the extreme combinatorial background on-line, a parameterization-based tracking is considered as a possible solution. The idea is to determine the optimal hit search windows in every tracking plane for every possible positions of hits in the previous planes. Currently, the position and the size of the hit search windows are expressed as polynomial functions of hit coordinates. The coefficients of the polynomials are evaluated from a sample of reference tracks, reconstructed with a simple, exhaustive-search tracking in low-rate data. The implementation, as well as the estimated performance of the parameterization-based tracking is going to be presented.