  The splitting function is a universal property of quantum chromodynamics
(QCD) which describes how energy is shared between partons. Despite its
ubiquitous appearance in many QCD calculations, the splitting function cannot
be measured directly since it always appears multiplied by a collinear
singularity factor. Recently, however, a new jet substructure observable was
introduced which asymptotes to the splitting function for sufficiently high jet
energies. This provides a way to expose the splitting function through jet
substructure measurements at the Large Hadron Collider. In this letter, we use
public data released by the CMS experiment to study the 2-prong substructure of
jets and test the 1 -> 2 splitting function of QCD. To our knowledge, this is
the first ever physics analysis based on the CMS Open Data.
