Observation of the $B^{\pm}_c$ meson in the decay $B^{\pm}_c\to J/\psi(\mu^+\mu^-)\pi^{\pm}$ with the ATLAS detector at the LHC

The production of $B^{\pm}_c$ mesons is observed with the ATLAS detector at the LHC through their decay into $J/\psi(\mu^+\mu^-)\pi^{\pm}$, using 4.3 fb$^{-1}$ of data from 7 TeV $pp$ collisions. The resulting $B^{\pm}_c$ mass distribution is fitted with an unbinned maximum likelihood fit. The fit yields 82$\pm$17 (stat.) signal events after background subtraction, with a fitted mass of 6282$\pm$7 (stat.) MeV. The mass value is consistent with the world average value $m_{B_c}=$ 6277$\pm$6 MeV.