Measurement of prompt J/ψ and beauty hadron production cross sections at mid-rapidity in pp collisions at $\sqrt{s}=7$ TeV

Abstract

The ALICE experiment at the LHC has studied J/ψ production at mid-rapidity in pp collisions at $\sqrt{s}=7$ TeV through its electron pair decay on a data sample corresponding to an integrated luminosity L _int = 5.6 nb⁻¹. The fraction of J/ψ from the decay of long-lived beauty hadrons was determined for J/ψ candidates with transverse momentum p _t > 1.3 GeV/c and rapidity |y| < 0.9. The cross section for prompt J/ψ mesons, i.e. directly produced J/ψ and prompt decays of heavier charmonium states such as the ψ(2S) and χ_c resonances, is σ_{prompt J/ψ} (p _t > 1.3 GeV/c, |y| < 0.9) = 8.3 ± 0.8 (stat.) ± 1.1 (syst.) $_{-1.4}^{+1.5 }$ (syst. pol.) μb. The cross section for the production of b-hadrons decaying to J/ψ with p _t > 1.3 GeV/c and |y| < 0.9 is ${\sigma_{{{J \left/ {{\psi \leftarrow {{\mathrm{h}}_{\mathrm{B}}}}} \right.}}}}$ (p _t > 1.3 GeV/c, |y| < 0.9) = 1.46 ± 0.38 (stat.) $_{-0.32}^{+0.26 }$ (syst.) μb. The results are compared to QCD model predictions. The shape of the p _t and y distributions of b-quarks predicted by perturbative QCD model calculations are used to extrapolate the measured cross section to derive the $\mathrm{b}\overline{\mathrm{b}}$ pair total cross section and dσ/dy at mid-rapidity.