A search for CP violation in Cabibbo-suppressed $D^{pm}rightarrow K^0_{mathrm{S}} K^{pm}$ and $D^{pm}_{s}rightarrow K^0_{mathrm{S}} pi^{pm}$ decays is performed using $pp$ collision data, corresponding to an integrated luminosity of 3~fb$^{-1}$, reco
rded by the LHCb experiment. The individual $CP$-violating asymmetries are measured to be begin{eqnarray*} mathcal{A}_{CP}^{D^{pm}rightarrow K^0_{mathrm{S}} K^{pm}} & = & (+0.03 pm 0.17 pm 0.14) % mathcal{A}_{CP}^{D^{pm}_{s}rightarrow K^0_{mathrm{S}} pi^{pm}} & = & (+0.38 pm 0.46 pm 0.17) %, end{eqnarray*} assuming that $CP$ violation in the Cabibbo-favoured decays is negligible. A combination of the measured asymmetries for the four decay modes $D^{pm}_{(s)}rightarrow K^0_{mathrm{S}} K^{pm}$ and $D^{pm}_{(s)}rightarrow K^0_{mathrm{S}} pi^{pm}$ gives the sum [ mathcal{A}_{CP}^{D^{pm}rightarrow K^0_{mathrm{S}} K^{pm}} + mathcal{A}_{CP}^{D^{pm}_{s}rightarrow K^0_{mathrm{S}} pi^{pm}} = (+0.41 pm 0.49 pm 0.26) %. ] In all cases, the first uncertainties are statistical and the second systematic. The results represent the most precise measurements of these asymmetries to date and show no evidence for CP violation.
The prompt production of charmonium $chi_{c}$ and $J/psi$ states is studied in proton-proton collisions at a centre-of-mass energy of $sqrt{s}=7$ TeV at the Large Hadron Collider. The $chi_{c}$ and $J/psi$ mesons are identified through their decays $
chi_{c}rightarrow J/psi gamma$ and $J/psirightarrow mu^+mu^-$ using 36 pb$^{-1}$ of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for $chi_{c}$ and $J/psi$, $sigma (chi_{c}rightarrow J/psi gamma)/ sigma (J/psi)$, is determined as a function of the $J/psi$ transverse momentum in the range $2 < p_{mathrm T}^{J/psi} < 15$ GeV/$c$. The results are in excellent agreement with next-to-leading order non-relativistic expectations and show a significant discrepancy compared with the colour singlet model prediction at leading order, especially in the low $p_{mathrm T}^{J/psi}$ region.
The prompt production of the charmonium $chi_{c1}$ and $chi_{c2}$ mesons has been studied in proton-proton collisions at the Large Hadron Collider at a centre-of-mass energy of $sqrt{s}=7$ TeV. The $chi_c$ mesons are identified through their decays $
chi_cto J/psi,gamma$ with $J/psi to mu^+ mu^-$ using 36 $mathrm{pb^{-1}}$ of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for the two $chi_c$ spin states, $sigma(chi_{c2})/sigma(chi_{c1})$, has been determined as a function of the $J/psi$ transverse momentum, $p_{mathrm{T}}^{J/psi}$, in the range from 2 to 15 GeV/$c$. The results are in agreement with the next-to-leading order non-relativistic QCD model at high $p_{mathrm{T}}^{J/psi}$ and lie consistently above the pure leading-order colour singlet prediction.
