Improvement in the reconstruction method for VAMOS spectrometer

The VAMOS spectrometer at GANIL is a large acceptance magnetic spectrometer employing a trajectory reconstruction technique to identify the reaction products. The spectrometer when coupled with the EXOGAM clover array provides a powerful tool for the spectroscopy of very weak reaction channels. Parameters are reconstructed using a numerical procedure with a polynomial relationship between the measured final coordinates and the quantities of interest. The coefficients of this polynomial function are determined from a numerical fit to the data generated from ray-tracing calculations using the ion optics code ZGOUBI. To reconstruct each parameter, a single polynomial is used with a set of coefficients that are valid across the full accepted phase space of the spectrometer. To further improve upon the reconstruction method, we developed an alternate procedure for reconstruction based on selecting an optimum set of trajectories and interpolating the data within these trajectories. For each detected event, a set of coordinates lying close to the measured trajectory are selected from the database and the target parameters of interest are determined by polynomial interpolation. The results for the reconstructed parameters using the two methods are presented.