Measurement of the $X$(3872) mass with first LHCb data

The mass of the $X$(3872) meson is measured using approximately 35 pb$^{-1}$ of data collected with the LHCb detector during the 2010 physics run of the LHC. Inclusively produced $X$(3872) mesons are reconstructed and selected in the $X$(3872) $\to J/\psi \pi^+ \pi^-$, $J/\psi \to \mu^+\mu^-$ decay mode. To verify that the momentum scale is well understood the kinematically similar decay $\psi$(2$S$)$\to J/\psi \pi^+ \pi^-$ is used. The preliminary result is \begin{align}M_{X(3872)} = 3871.96 \pm 0.46 {\rm (stat)} \pm 0.10 {\rm (syst)}~{\rm MeV}/c^{2}.\end{align}