  Prompt production of charmonium $\chi_{c0}$, $\chi_{c1}$ and $\chi_{c2}$
mesons is studied using proton-proton collisions at the LHC at a centre-of-mass
energy of $\sqrt{s}=7$TeV. The $\chi_{c}$ mesons are identified through their
decay to $J/\psi\gamma$, with $J/\psi\to\mu^+\mu^-$ using photons that
converted in the detector. A data sample, corresponding to an integrated
luminosity of $1.0\mathrm{fb}^{-1}$ collected by the LHCb detector, is used to
measure the relative prompt production rate of $\chi_{c1}$ and $\chi_{c2}$ in
the rapidity range $2.0<y<4.5$ as a function of the $J/\psi$ transverse
momentum from 3 to 20 GeV$/c$. First evidence for $\chi_{c0}$ meson production
at a high-energy hadron collider is also presented.
