Measurement of the cross-section ratio $\ddot{I}ƒ(\ddot{I}{‡}_{c2})/\ddot{I}ƒ(\ddot{I}{‡}_{c1})$ for prompt $\ddot{I}{‡}_c$ production at $\sqrt{s}=7$ TeV

Abstract

The prompt production of the charmonium $\ddot{I}{‡}_{c1}$ and $\ddot{I}{‡}_{c2}$ 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 $\ddot{I}{‡}_c$ mesons are identified through their decays $\ddot{I}{‡}_c\to J/\ddot{I}ˆ{\hat{I}}^3$ with $J/\ddot{I}ˆ\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}$ using 36 $\mathrm{p}{\mathrm{b}}^{-1}$ of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for the two $\ddot{I}{‡}_c$ spin states, $\ddot{I}ƒ(\ddot{I}{‡}_{c2})/\ddot{I}ƒ(\ddot{I}{‡}_{c1})$, has been determined as a function of the $J/\ddot{I}ˆ$ transverse momentum, $p_{\mathrm{T}}^{J/\ddot{I}ˆ}$, 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 $p_{\mathrm{T}}^{J/\ddot{I}ˆ}$ and lie consistently above the pure leading-order colour singlet prediction.

13 pages, 3 figures