Context :

Aims : We present the analysis of the [ \alpha /Fe ] abundance ratios for a large number of stars at several locations in the Milky Way bulge with the aim of constraining its formation scenario .

Methods : We obtained FLAMES-GIRAFFE spectra ( R=22,500 ) at the ESO Very Large Telescope for 650 bulge red giant branch ( RGB ) stars and performed spectral synthesis to measure Mg , Ca , Ti , and Si abundances .
This sample is composed of 474 giant stars observed in 3 fields along the minor axis of the Galactic bulge and at latitudes b=-4 ^ { \circ } , b=-6 ^ { \circ } , b=-12 ^ { \circ } .
Another 176 stars belong to a field containing the globular cluster NGC 6553 , located at b=-3 ^ { \circ } and 5 ^ { \circ } away from the other three fields along the major axis .
Stellar parameters and metallicities for these stars were presented in Zoccali et al .
( 2008 ) .
We have also re-derived stellar parameters and abundances for the sample of thick and thin disk red giants analyzed in Alves-Brito et al .
( 2010 ) .
Therefore using a homogeneous abundance database for the bulge , thick and thin disk , we have performed a differential analysis minimizing systematic errors , to compare the formation scenarios of these Galactic components .

Results : Our results confirm , with large number statistics , the chemical similarity between the Galactic bulge and thick disk , which are both enhanced in alpha elements when compared to the thin disk .
In the same context , we analyze [ \alpha /Fe ] vs. [ Fe/H ] trends across different bulge regions .
The most metal rich stars , showing low [ \alpha /Fe ] ratios at b=-4 ^ { \circ } disappear at higher Galactic latitudes in agreement with the observed metallicity gradient in the bulge .
Metal-poor stars ( [ Fe/H ] < -0.2 ) show a remarkable homogeneity at different bulge locations .

Conclusions : We have obtained further constrains for the formation scenario of the Galactic bulge .
A metal-poor component chemically indistinguishable from the thick disk hints for a fast and early formation for both the bulge and the thick disk .
Such a component shows no variation , neither in abundances nor kinematics , among different bulge regions .
A metal-rich component showing low [ \alpha /Fe ] similar to those of the thin disk disappears at larger latitudes .
This allows us to trace a component formed through fast early mergers ( classical bulge ) and a disk/bar component formed on a more extended timescale .