Anomalous behavior of the nodal scattering rate of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ near the Fermi energy

The scattering rate as determined by the width of a band is a direct measure of the imaginary part of a particle's self-energy. Though the dispersion of a band can also used to extract the particle's self energy, the scattering rate is superior, because the ambiguity due to determining the underlying bare band is not included. The excellent momentum and energy resolution of low photon energy ARPES allows us to study the scattering rate of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+ \delta }$ near the Fermi energy. Our studies show an anomalous feature that warrants continued study.