  The process responsible for the Chandra-detected X-ray emission from the
large scale jets of powerful quasars is a matter of ongoing debate. The two
main contenders are external Compton (EC) scattering off the cosmic microwave
background (CMB) photons (EC/CMB) and synchrotron emission from a population of
electrons separate from those producing the radio - IR emission. So far, no
clear diagnostics have been presented to distinguish which of the two, if any,
is the actual X-ray emission mechanism. Here we present such diagnostics based
on a fundamental difference between these two models: the production of
synchrotron X-rays requires multi - TeV electrons, while the EC/CMB model
requires a cutoff in the electron energy distribution (EED) below TeV energies.
This has significant implications for the gamma-ray emission predicted by these
two models, that can be tested through GeV and TeV observations of the nearby
bright quasar 3C 273. We show how existing and future GeV and TeV observations
can confirm or refute one or both of the above hypotheses.
