# Münster 2017 – wissenschaftliches Programm

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# T: Fachverband Teilchenphysik

## T 89: Experimentelle Methoden 3

### T 89.8: Vortrag

### Mittwoch, 29. März 2017, 18:30–18:45, JUR 253

**Momentum transfer reconstruction for the P2 Experiment** — •Alexey Tyukin for the P2 collaboration — Institute for Nuclear Physics, Johannes Gutenberg University, Mainz

The P2 experiment at the future MESA accelerator in Mainz is designed to determine the Weinberg angle, a core parameter of the weak force, with great precision. It will require measuring a parity violating asymmetry of elastically scattered electrons from a liquid hydrogen target for different beam polarisations, which depends heavily on the momentum transfer *Q*^{2}. Therefore a reconstruction of the electron tracks in the inhomogeneous magnetic field of the P2 detector is essential. For this, the detector will have four tracking planes of thin high voltage monolithic active pixel sensors (HV-MAPS).

In this talk the method of *Q*^{2} reconstruction will be shown. A Geant4 simulation is used to produce electron tracks and hits in the detection planes. For track reconstruction the General Broken Lines fit is used, which requires propagating seed parameters to all planes in order to determine a good approximation of the real parameters at the first plane, which can then be extrapolated back to the target. The propagation is done by solving the equation of motion numerically with a Runge-Kutta method. In each step also the track parameter error matrix needs to be calculated by the Bugge-Myrheim method. Systematical effects producing offsets in the reconstructed values must be kept under control. The average *Q*^{2} value of 0.006 GeV^{2}/*c*^{2} can be reconstructed with about 4 % uncertainty for a single event, leading to a high overall precision due to large electron rates in the experiment.