The $a$SPECT experiment - an overview and latest results

The $a$SPECT retardation spectrometer measures the $\beta$-$\nu$ angular correlation coefficient $a$ in free neutron $\beta$-decay. This measurement can be used to determine the ratio $\frac{g_A}{g_V}$ of the weak coupling constants, as well as to search for physics beyond the Standard Model. In 2013 $a$SPECT had a successful beam time at the Institut Laue-Langevin. The goal of this beam time is to improve the current uncertainty of $a$ from $\Delta a$/$a\approx 5\%$ to about $1\%$. The data analysis is in its final stage and nearly finished. In order to achieve an uncertainty of $1\%$, the systematics of $a$SPECT have to be understood accordingly. This is achieved by systematic tests and measurements of $a$ with different parameter settings for the spectrometer during the beam time. Additionally, offline measurements have been performed to determine the effect on the systematics, e.g. work-function fluctuations of the electrodes. These measurements are used as input for on-going simulations of the spectrometer to understand and reduce the systematic uncertainties further. In this talk $a$SPECT will be introduced and the current status of the data analysis will be reported, including a preliminary error budget of the systematic uncertainties.