Measurement of the chib2/chib1 production cross section ratio in pp collisions at sqrt(s)= 8 TeV

The ratio of cross sections of $\chi_{\mathrm{b}2}(1\mathrm{P})$ and $\chi_{\mathrm{b}1}(1\mathrm{P})$ bottomonium states promptly produced in pp collisions at $\sqrt{s}= 8$\,TeV is measured by detecting their radiative decays $\chi_{\mathrm{b}1,2}(1\mathrm{P}) \rightarrow \Upsilon(1\mathrm{S}) + \gamma$ with the CMS experiment. The emitted photons are detected through their conversion to $e^+e^-$ pairs, with the electron trajectories accurately reconstructed in the silicon tracker, so that the two states can be resolved with a good mass resolution. The measurement is based on an event sample corresponding to an integrated luminosity of 20.7\,fb$^{-1}$ and is performed in a phase space region defined by selection cuts on the photon pseudorapidity and on the $\Upsilon$ transverse momentum and rapidity: $| \eta^\gamma | < 1.0$, $7 < p_{\rm T}^\Upsilon < 40$\,GeV, and $|y^\Upsilon | < 1.5$. The measured cross-section ratio is around 0.9, with no significant dependence on $p_{\rm T}^\Y$.