The ALICE experiment at the LHC has studied $\jpsi$ 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 $L_{\rm {int}}$ = 5.6nb$^{-1}$. The fraction of $\jpsi$ from the decay of long-lived beauty hadrons was determined for $\jpsi$ candidates with transverse momentum $\pt$ > 1.3 GeV/$c$ and rapidity |$y$| < 0.9. The cross section for prompt $\jpsi$ mesons, i.e. directly produced $\jpsi$ and prompt decays of heavier charmonium states such as the $\psi$(2S) and $\chi_c$ resonances, is $\sigma_{{\rm {prompt}} \; \jpsi}$ ($\pt$ > 1.3 GeV/$c$, |y| < 0.9) = 8.3 $\pm$ 0.8 (stat.) $\pm$ 1.1 (syst.)$^{+1.5}_{-1.4}$ (syst. pol.) $\mu$b. The cross section for the production of b-hadrons decaying to $\jpsi$ with $\pt$ > 1.3 GeV/$c$ and |y|< 0.9 is $\sigma_{\jpsi \leftarrow {\rm {h_B}}} = 1.46 \pm 0.38$ (stat.) $^{+0.26}_{-0.32}$ (syst.) $\mu$b. The results are compared to QCD model predictions. The shape of the $\pt$ and y distributions of b-quarks predicted by perturbative QCD model calculations are used to extrapolate the measured cross section to derive the ${\rm {b\bar{b}}}$ pair total cross section and d$\sigma/$d$y$ at mid-rapidity.
JHEP11(2012)065
HEP Data
e-Print: arXiv:1205.5880 | PDF | inSPIRE
CERN-PH-EP-2012-132