Measurement of the production cross section ratio σ(χ_b2(1P))/σ(χ_b1(1P)) in pp collisions at s=8TeV

A measurement of the production cross section ratio σ(χ_b2(1P))/σ(χ_b1(1P)) is presented. The χ_b1(1P) and χ_b2(1P) bottomonium states, promptly produced in pp collisions at s=8TeV, are detected by the CMS experiment at the CERN LHC through their radiative decays χ_b1,2(1P)→ϒ(1S)+γ. The emitted photons are measured through their conversion to e⁺e^- pairs, whose reconstruction allows the two states to be resolved. The ϒ(1S) is measured through its decay to two muons. An event sample corresponding to an integrated luminosity of 20.7fb^-1 is used to measure the cross section ratio in a phase-space region defined by the photon pseudorapidity, |η^γ|<1.0; the ϒ(1S) rapidity, |y^ϒ|<1.5; and the ϒ(1S) transverse momentum, 7<pTϒ<40GeV. The cross section ratio shows no significant dependence on the ϒ(1S) transverse momentum, with a measured average value of 0.85±0.07(stat+syst)±0.08(BF), where the first uncertainty is the combination of the experimental statistical and systematic uncertainties and the second is from the uncertainty in the ratio of the χ_b branching fractions.