  The production cross-sections of B mesons are measured in pp collisions at a
centre-of-mass energy of 7 TeV, using data collected with the LHCb detector
corresponding to a integrated luminosity of 0.36 fb-1. The B+, B0 and Bs0
mesons are reconstructed in the exclusive decays B+ -> J/psi K+, B0 -> J/psi
K*0 and Bs0 -> J/psi phi, with J/psi -> mu+ mu-, K*0 -> K+ pi- and phi -> K+
K-. The differential cross-sections are measured as functions of B meson
transverse momentum pT and rapidity y, in the range 0 < pT < 40 GeV/c and 2.0 <
y < 4.5. The integrated cross-sections in the same pT and y ranges, including
charge-conjugate states, are measured to be sigma(pp -> B+ + X) = 38.9 +- 0.3
(stat.) +- 2.5 (syst.) +- 1.3 (norm.) mub, sigma(pp -> B0 + X) = 38.1 +- 0.6
(stat.) +- 3.7 (syst.) +- 4.7 (norm.) mub, sigma(pp -> Bs0 + X) = 10.5 +- 0.2
(stat.) +- 0.8 (syst.) +- 1.0 (norm.) mub, where the third uncertainty arises
from the pre-existing branching fraction measurements.
