The Tokai-to-Kamioka (T2K) long-baseline neutrino experiment
made the first discovery of electron neutrino appearance
in a beam of primarily muon neutrinos in 2013.
Based on this discovery it is now possible to probe neutrino
CP violation by comparing the oscillations of neutrinos and antineutrinos
using this appearance channel.
In order to realize such a measurement T2K has been accumulating data
from an antineutrino-enhanced beam since 2014.
Since the electron antineutrino appearance probability depends heavily on
on the muon antineutrino disappearance probability, measurements of the latter
represent not only the first step towards a CP violation measurement
but also provide a means of testing CPT symmetry when compared to similar measurements
done with the neutrino enhanced beam.
This presentation will discuss the first physics results from T2K's antineutrino beam
running, focusing on measurements of muon antineutrino disappearance.