D$_s^+$ meson production at central rapidity in proton-proton collisions at $\sqrt{s}$ = 7 TeV

The pt-differential inclusive production cross section of the prompt charm-strange meson D$_s^+$ in the rapidity range |y|<0.5 was measured in proton--proton collisions at $\sqrt{s}$=7 TeV at the LHC using the ALICE detector. The analysis was performed on a data sample of 2.98 10$^8$ events collected with a minimum-bias trigger. The corresponding integrated luminosity is $L_{int}=4.8 nb^{-1}$. Reconstructing the decay $D_s^+ \to \phi\pi^+$, with $\phi \to K^-K^+$, and its charge conjugate, about 480 D$_s^{\pm}$ mesons were counted, after selection cuts, in the transverse momentum range 2<pt<12 GeV/c. The results are compared with the prediction of a model based on perturbative QCD. The ratios of the cross sections of four D meson species (namely D$^0$, D$^+$, D$^{*+}$ and D$_s^+$) were determined both as a function of pt and integrated over pt after extrapolating to full pt range, together with the strangeness suppression factor in charm fragmentation. The obtained values are found to be compatible within uncertainties with those measured by other experiments in $e^+e^-$, ep and pp interactions at various centre-of-mass energies.