Minijets and large hadronic backgrounds ate+e−supercolliders

We show that the hadronic structure of the photon, along with the beamstrahlung phenomenon, leads to a very large rate of γγ→jets at ${\mathit{e}}^{+}$ ${\mathit{e}}^{\mathrm{-}}$ supercolliders. At √s =1 TeV, for round, dense bunches, we expect ∼5–50 ‘‘minijet’’ events per bunch crossing, giving rise to an ‘‘underlying event.’’ Thus ${\mathit{e}}^{+}$ ${\mathit{e}}^{\mathrm{-}}$ supercolliders will be ‘‘messier’’ than expected, unless beamstrahlung can be kept under control.