  We study the synchrotron radiation of gluons by fast quarks in strong
magnetic field produced by colliding relativistic heavy-ions. We argue that due
to high electric conductivity of plasma, time variation of the magnetic field
is slow and estimate its relaxation time. We calculate the energy loss due to
synchrotron radiation of gluons by fast quarks. We find that the typical energy
loss per unit length for a light quark at LHC is a few GeV per fm. This effect
alone predicts quenching of jets with $p_\bot$ up to about 20 GeV. We also show
that the spin-flip transition effect accompanying the synchrotron radiation
leads to a strong polarization of quarks and leptons with respect to the
direction of the magnetic field. Observation of the lepton polarization may
provide a direct evidence of existence of strong magnetic field in heavy-ion
collisions.
