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 .