The $p_{ \rm T}$-differential inclusive production cross section of the prompt charm-strange meson $\rm D_s^+$ 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 $2.98 \times 10^8$ events collected with a minimum-bias trigger. The corresponding integrated luminosity is $L_{ \rm int}=4.8$/nb. Reconstructing the decay ${ \rm D_s^{ +}\to \phi\pi^+}$, with $\phi\to { \rm K}^-{ \rm K}^+$, and its charge conjugate, about 480 ${ \rm D_s^{ \pm}}$ mesons were counted, after selection cuts, in the transverse momentum range $2<p_{ \rm T}<12$ Gev/$c$. The results are compared with predictions from models based on perturbative QCD. The ratios of the cross sections of four D meson species (namely ${ \rm D^0}$, ${ \rm D^+}$, ${ \rm D^{ *+}}$ and ${ \rm D_s^+}$) were determined both as a function of $p_{ \rm T}$ and integrated over $p_{ \rm T}$ after extrapolating to full $p_{ \rm T}$ 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 $\rm e^+e^-$, ep and pp interactions at various centre-of-mass energies.
Categories: hep-ex