Direct photons at low transverse momentum: a signal for quark-gluon plasma in pp collisions at LHC.

We investigate photon production in a scenario of quark-gluon plasma formation in proton-proton scattering at 7 TeV. It is shown that thermal photon yields increase quadratically with the charged particle multiplicity. This gives an enhanced weight to high multiplicity events, and leads to an important photon production even in minimum-bias events, where the thermal photons largely dominate over the prompt ones at transverse momentum values smaller than 10  GeV/c.