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Hadrons emitted by the pre-surface layer of quark-gluon plasma (QGP) before phase transition into hadronic gas are considered as possible source of direct information about QGP. It is shown that these hadrons dominate at soft p t if QGP is created in ultrarelativistic heavy ion collisions.

Yield of direct photons in Pb+Pb collisions at SpS and LHC energy is evaluated with emphasis on estimate of possible uncertainty. Possibility of experimental observation of direct photons at LHC is discussed. Predictions of several models at SpS energy are compared with experimental data.

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