  Heavy ion collisions at the LHC facility generate a Quark-Gluon Plasma (QGP)
which, for central collisions, has a higher energy density and temperature than
the plasma generated in central collisions at the RHIC. But sufficiently
peripheral LHC collisions give rise to plasmas which have the \emph{same}
energy density and temperature as the "central" RHIC plasmas. One might assume
that the two versions of the QGP would have very similar properties (for
example, with regard to jet quenching), but recent investigations have
suggested that \emph{they do not}: the plasma "knows" that the overall
collision energy is different in the two cases. We argue, using a gauge-gravity
analysis, that the strong magnetic fields arising in one case (peripheral
collisions), but not the other, may be relevant here. If the residual magnetic
field in peripheral LHC plasmas is of the order of at least $eB\,\approx
\,5\,m^2_{\pi}$, then the model predicts modifications of the relevant
quenching parameter which approach those recently reported.
