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Although there is consensus that metal-rich stars in the Milky Way bulge areformed via secular evolution of the thin disc, the origin of their metal-poorcounterparts is still under debate. Two different origins have been invoked formetal-poor stars: they might be classical bulge stars or stars formed viainternal evolution of a massive thick disc. We use N-body simulations tocalculate the kinematic signature given by the difference in the meanGalactocentric radial velocity ($\Delta\rm V_{\rm GC}$) between metal-richstars ([Fe/H] $\ge$ 0) and moderately metal-poor stars (-1.0 $\le$ [Fe/H] $<$0) in two models, one containing a thin disc and a small classical bulge(B/D=0.1), and the other containing a thin disc and a massive centrallyconcentrated thick disc. We reasonably assume that thin-disk stars in eachmodel may be considered as a proxy of metal-rich stars. Similarly, bulge starsand thick-disc stars may be considered as a proxy of metal-poor stars. Wecalculate $\Delta\rm V_{\rm GC}$ at different latitudes ($b=0^\circ$,$-2^\circ$, $-4^\circ$,$-6^\circ$, $-8^\circ$ and $-10^\circ$) and longitudes($l=0^\circ$, $\pm5^\circ$, $\pm10^\circ$ and $\pm15^\circ$) and show that the$\Delta\rm V_{\rm GC}$ trends predicted by the two models are different. Wecompare the predicted results with ARGOS data and APOGEE DR13 data and showthat moderately metal-poor stars are well reproduced with the co-spatialstellar discs model, which has a massive thick disc. Our results give moreevidence against the scenario that most of the metal-poor stars are classicalbulge stars. If classical bulge stars exists, most of them probably havemetallicities [Fe/H] $<$ -1 dex, and their contribution to the mass of thebulge should be a small percentage of the total bulge mass.

Searching for a kinematic signature of the moderately metal-poor stars in the Milky Way bulge using N-body simulations