Top quark production in the forward region in proton-proton collisions is observed for the first time. The $W!+!b$ final state with $Wtomu u$ is reconstructed using muons with a transverse momentum, $p_{rm T}$, larger than 25 GeV in the pseudorapidity range $2.0<eta<4.5$. The $b$ jets are required to have $50 < p_{rm T} < 100$ GeV and $2.2 < eta < 4.2$, while the transverse component of the sum of the muon and $b$-jet momenta must satisfy $p_{rm T} > 20$ GeV. The results are based on data corresponding to integrated luminosities of 1.0 and $2.0$ fb$^{-1}$ collected at center-of-mass energies of 7 and 8 TeV by LHCb. The inclusive top quark production cross-sections in the fiducial region are $sigma({rm top})[7rm{TeV}] = 239pm53({rm stat})pm33({rm syst})pm24({rm theory}),{rm fb}$ and $sigma({rm top})[8rm{TeV}] = 289pm43({rm stat})pm40({rm syst})pm29({rm theory}),{rm fb}$. These results, along with the observed differential yields and charge asymmetries, are in agreement with next-to-leading order Standard Model predictions.
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