CMS-PAS-BPH-13-005

CMS-PAS-BPH-13-005
Measurement of the $\chi_{\mathrm{b}2} / \chi_{\mathrm{b}1}$ production cross section ratio in pp collisions at $\sqrt{s}$ = 8 TeV
CMS Collaboration
2013

Abstract: 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 $p_{\rm T}^\Y$ .
Links: CDS record (PDF) ; inSPIRE record ; Public twiki page ; CADI line (restricted) ; Figures are available from the CDS record. These preliminary results are superseded in this paper, PLB 743 (2015) 383.

Compact Muon Solenoid
LHC, CERN