  We examine the scattering behavior from a single non magnetic impurity in a
helical liquid. A helical liquid is a one dimensional system with a pair of
counter propagating edge states, which are time reversal partners. In the
absence of a magnetic field, time reversal symmetry is conserved and hence
single particle scattering is prohibited. However, multi particle processes are
possible. We examine the backscattering current and noise, and derive the
effective scattering charge. A magnetic field enhances the backscattered
current, but reduces the effective scattering charge. We find that the
scattering charge can vary between $e$ and $2e$, depending on the strength of
electron-electron interactions and the magnetic field.
