Prompt charm production in $pp$ collisions at $\sqrt{s}$ = 7 TeV

Open charm production in inelastic $pp$ collisions at a centre-of-mass energy $\sqrt{s}$ = 7 TeV has been studied with the LHCb detector at the LHC using an integrated luminosity 1.81 nb$^{-1}$. Cross-sections have been determined for $D^0/\overline{D}^0, D^{*\pm}, D^{\pm}$, and $D_s^{\pm}$ in bins of transverse momentum and rapidity in the region 0 < $p_T$ < 8 GeV/$c$ and 2 < $y$ < 4.5. The results are compared with theoretical predictions and with expectations from the LHCb tuning of the PYTHIA generator. Good agreement both in shape and absolute normalisation is found. A direct comparison of $D_s^{\pm}$ and $D^{\pm}$ gives the cross-section ratio integrated over 2.0 < $y$ < 4.5 as $\sigma(D^{+})$ = 2.32 $\pm$ 0.27 (stat) $\pm$ 0.26 (syst). We find a total $c\overline{c}$ cross-section to produce $c$-flavoured hadrons in the range 0 < $p_T$ < 8 Gev/$c$ and 2 < $y$ < 4.5 of 1.23 $\pm$ 0.19mb. Using PYTHIA to extrapolate the measurement to full phase space, a total cross-section $\sigma(pp \rightarrow c\overline{c}X)$ = 6.10 $\pm$ 0.93 mb is obtained.