  The medium-lived 44Ti isotope is synthesised by explosive Si-burning in
core-collapse supernovae. It is extremely sensitive to the dynamics of the
explosion and therefore can be used to indirectly probe the explosion scenario.
The young supernova remnant Cassiopeia A is to date the only source of
gamma-ray lines from 44Ti decay. The emission flux has been measured by
CGRO/COMPTEL, BeppoSAX/PDS and INTEGRAL/IBIS. The high-resolution spectrometer
SPI on-board the INTEGRAL satellite can provide spectrometric information about
the emission. The line profiles reflect the kinematics of the 44Ti in
Cassiopeia A and can thus place constraints on its nucleosynthesis and
potentially on the associated explosion process. Using 4 years of data from
INTEGRAL/SPI, we have searched for the gamma-ray signatures from the decay of
the 44Ti isotope. The overwhelming instrumental background noise required an
accurate modelling and a solid assessment of the systematic errors in the
analysis. Due to the strong variability of the instrumental background noise,
it has not been possible to extract the two lines at 67.9 and 78.4keV.
Regarding the high-energy line at 1157.0keV, no significant signal is seen in
the 1140-1170keV band, thereby suggesting that the line signal from Cassiopeia
A is broadened by the Doppler effect. From our spectrum, we derive a ~ 500km/s
lower limit at 2sigma on the expansion velocity of the 44Ti ejecta. Our result
does not allow us to constrain the location of 44Ti since the velocities
involved throughout the remnant, derived from optical and X-ray studies, are
all far above our lower limit.
