Long-lived magnons throughout the Brillouin zone of the strong-leg spin ladder (C${}_7$H${}_{10}$N)${}_2$CuBr${}_4$

Inelastic neutron scattering is used to measure spin excitations in fully deuterated single crystal samples of the strong-leg antiferromagnetic S=1/2 spin ladder compound (C${}_7$H${}_{10}$N)${}_2$CuBr${}_4$. Sharp resolution-limited magnons are observed across the entire one-dimensional Brillouin zone. The results validate the previously proposed {\it symmetric} spin ladder model and provide a reliable estimate of the relevant exchange interactions.