Slow and fast particles in shear-driven jamming: critical behavior and finite size scaling

We do shear-driven simulations of a simple model of non-Brownian particles in two dimensions. By examining the velocity distribution at different densities and shear rates we find strong evidence for the existence of two different processes, respectively dominated by the slower and the faster particles -- the slow process and the fast process. The leading divergence in the shear viscosity is governed by the fast process. An examination of height and position of the low-velocity peak in the distribution demonstrates that it is the slow process that is responsible for the correction-to-scaling term in the critical scaling analysis. We further find that the long range velocity correlations are primarily due to the slow process which implies that the diverging viscosity and the diverging correlation length are only indirectly related.