First measurement of charm production in fixed-target configuration at the LHC

The first measurement of heavy-flavour production by the LHCb experiment in its fixed-target mode is presented. The production of $J\mathrm{/}\psi$ and $D^0$ mesons is studied with beams of protons of different energies colliding with gaseous targets of helium and argon with nucleon-nucleon centre-of-mass energies of $\sqrt{s_{NN}}=86.6$ and $110.4$ $\mathrm{G}\mathrm{e}\mathrm{V}$, respectively. The $J\mathrm{/}\psi$ and $D^0$ (including charge conjugate) production cross sections in $p\mathrm{H}\mathrm{e}$ collisions in the rapidity range $[2,4.6]$ are found to be $\sigma_{J/\psi} = 652 \pm 33$(stat)$\pm 42$(syst)nb$/$nucleonand$\sigma_{D^0} = 80.8 \pm 2.4$(stat)$\pm 6.3$(syst)$\mu$b$/$nucleon, where the first uncertainty is statistical and the second is systematic. No evidence for a substantial intrinsic charm content of the nucleon is observed in the large Bjorken-$x$ region.