Measurement of the $D^\pm$ production asymmetry in 7 TeV $pp$ collisions

The asymmetry in the production cross-section $\sigma$ of $D^{\pm}$ mesons, \begin{equation*} A_{\mathrm{P}} = \frac{\sigma(D^+) - \sigma(D^-) }{ \sigma(D^+) + \sigma(D^-) }, \end{equation*} is measured in bins of pseudorapidity $\eta$ and transverse momentum $p_{\mathrm{T}}$ within the acceptance of the LHCb detector. The result is obtained with a sample of $D^+ \to K^{0}_{S}\pi^+$ decays corresponding to an integrated luminosity of 1.0~fb$^{-1}$, collected in $pp$ collisions at a centre of mass energy of 7~TeV at the Large Hadron Collider. When integrated over the kinematic range $2.0< p_{\mathrm{T}} < 18.0$~GeV/$c$ and $2.20 < \eta < 4.75$, the production asymmetry is $A_{\mathrm{P}} = (-0.96\pm0.26\pm0.18)\%$. The uncertainties quoted are statistical and systematic, respectively. The result assumes that any direct \emph{CP} violation in the $D^+ \to K^{0}_{S} \pi^{+}$ decay is negligible. No significant dependence on $\eta$ or $p_{\mathrm{T}}$ is observed.