CIRCULAR DICHROISM IN THE PHOTO DOUBLE IONIZATION OF HELIUM INVESTIGATED BY

{\bf COL}D {\bf T}ARGET {\bf R}ECOIL {\bf I}ON {\bf M}OMENTUM {\bf
S}PECTROSCOPY 
({\bf COLTRIMS})

V. Mergel$^{1}$, 
M. Achler$^{1,2}$, 
R. D\"orner$^1$, 
L. Spielberger$^1$,
T. Kambara$^2$,
Y. Awaya$^2$,  \\[-1pt]\normalsize 
J. Berakdar$^3$,
T. Koide$^4$, 
Y. Azuma$^4$, 
Schmidt-B\"ocking$^1$

$^1$Institut f\"ur Kernphysik der Universit\"at Frankfurt,
August-Euler-Str.6, D-60486 Frankfurt, Germany.
$^2$The Institute for Physical and Chemical Research, RIKEN, Japan.
$^3$Max-Planck-Institut, Halle, Germany.
$^4$Photon Factory, IMSS, KEK, Tsukuba, Ibaraki, 305, Japan. 

COLTRIMS has been used for the photo double ionization of helium by
circularly polarized photons of an excess energy of 10 and 20eV. We map the
complete square of the 9-dimensional final state momentum wave function of
the process, by measuring all angles and all energies of one electron and
the recoiling ion simultaneously.