  The top quark pair production cross section
($\sigma_{\mathrm{t}\overline{\mathrm{t}}}$) is measured for the first time in
pp collisions at a center-of-mass energy of 5.02 TeV. The data were collected
by the CMS experiment at the LHC and correspond to an integrated luminosity of
27.4 pb$^{-1}$. The measurement is performed by analyzing events with at least
one charged lepton. The measured cross section is $
\sigma_{\mathrm{t}\overline{\mathrm{t}}} = 69.5 \pm 6.1$ (stat) $\pm 5.6$
(syst) $\pm 1.6$ (lumi) pb, with a total relative uncertainty of 12%. The
result is in agreement with the expectation from the standard model. The impact
of the presented measurement on the determination of the gluon distribution
function is investigated.
