  We consider the asymmetric simple exclusion process (ASEP) on $\mathbb{Z}$.
For continuous densities, ASEP is in local equilibrium for large times, at
discontinuities however, one expects to see a dynamical phase transition, i.e.
a mixture of different equilibriums. We consider ASEP with deterministic
initial data such that at large times, two rarefactions come together at the
origin, and the density jumps from $0$ to $1$. Shifting the measure on the KPZ
$1/3$ scale, we show that the law of ASEP converges to a mixture of the Dirac
measures with only holes resp. only particles. The parameter of that mixture is
the probability that the second class particle, which is distributed as the
difference of two independent GUEs, stays to the left of the shift. This should
be compared with the results of Ferrari and Fontes from 1994 \cite{FF94b}, who
obtained a mixture of Bernoulli product measures at discontinuities created by
random initial data, with the GUEs replaced by Gaussians.
