First Measurement of Charged Current Cross Sections with Longitudinally Polarised Positrons at HERA

The analysis presented in this thesis concerns the $e^{+}p$ deep
inelastic charged current scattering cross sections measured with
the H1 detector at HERA. The analysed data were taken in the years
2003-04 at a centre-of-mass energy $\sqrt{s} = 319 \ GeV $ and
comprise two periods of positron beams with positive and negative
longitudinal polarisation, corresponding to an integrated
luminosity of 26.9 $pb^{-1}$ and 20.7 $pb^{-1}$, respectively. The
cross sections are measured in a kinematic region of four-momentum
transfer squared $Q^2 \geqslant 300 \ GeV^2$ and inelasticity $y
\leqslant 0.9$. \\ From the analysed data the polarisation
dependence of the total charged current cross section is determined
for the first time at high $Q^2$. The results are compared with
predictions of the Standard Model and found to be in agreement,
i.e. possible contributions from non-standard right-handed currents
are consistent with zero.