Measurement of the branching fraction of $J\mathrm{/}\psi \to \rho \pi$ at KEDR

We present the study of the decay $J\mathrm{/}\psi \to \rho \pi$. The results are based on of 5.2~million $J\mathrm{/}\psi$ events collected by the KEDR detector at the VEPP-4M collider. The branching fractions are measured to be $\text{B}(J\mathrm{/}\psi \to \rho \pi )=(2.072\pm 0.017\pm 0.062)\cdot {10}^{-2}$ and $\text{B}(J\mathrm{/}\psi \to {\pi }^{+}{\pi }^{-}{\pi }^0)=(1.878\pm 0.013\pm 0.051)\cdot {10}^{-2}$, where the first uncertainties are statistical and the second systematic. Our results are more precise than the previous relative measurements.