  To understand the formation and composition of planetary systems it is
important to study their host stars composition since both are formed in the
same stellar nebula. In this work we analyze the behaviour of chemical
abundances of Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd and Eu in the large and homogeneous
HARPS-GTO planet search sample ($R \sim$ 115000). This sample is composed of
120 stars hosting high-mass planets, 29 stars hosting exclusively Neptunians
and Super-Earths and 910 stars without detected giant planets. We compare the
[X/Fe] ratios of such elements in different metallicity bins and we find that
planet hosts present higher abundances of Zn for [Fe/H]$<$--0.1 dex. On the
other hand, Ba, Sr, Ce and Zr abundances are underabundant in stars with
planets, with a bigger difference for stars only hosting low-mass planets.
However, most of the offsets found can be explained by differences in stellar
parameters and by the fact that planet hosts at low metallicity mostly belong
to the Galactic thick disk. Only in the case of Ba we find a statistically
significant (3$\sigma$) underabundance of 0.03 dex for low-mass planet hosts.
The origin of these elements is quite complex due to their evolution during the
history of the Galaxy. Therefore, it is necessary to understand and
characterize the stellar populations to which planet hosts belong in order to
do a fair comparison with stars without detected planets. This work
demonstrates that the effects of Galactic chemical evolution and not the
presence of planets mostly account for the differences we find.
