Nuclear suppression at large pT and xF: Direct photons from RHIC to LHC

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Théâtre National (Centre Bonlieu)

Théâtre National

Centre Bonlieu

Board: 80
Poster Pre-equilibrium and initial state physics


Jan Cepila (Faculty of Nuclear Sciences and Physical Engineering (FNSPE)-Czech Technical University in Prague)


We discuss a common feature of all known reactions on nuclear targets - a significant suppression at large Feynman xF and large transverse momenta pT of produced particles. The main emphasis is devoted to production of prompt photons since they are not expected to be accompanied by any final state interaction, either energy loss or absorption. Therefore, besides the Cronin enhancement at medium pT and small isotopic corrections at larger pT, one should not expect any nuclear effects. However, data from the PHENIX experiment demonstrate a significant large-pT suppression in central d+Au and Au+Au collisions that cannot be induced by coherence phenomena. We demonstrate that such an unexpected result is subject to the energy sharing problem in multiple initial state interactions. Using the colour dipole approach we describe first the large-pT production of direct photons in the RHIC kinematic region in agreement with available data. We study also a rise of nuclear effects with rapidity(xF) caused besides corrections for energy deficit by an increasing onset of coherence phenomena. In the LHC energy range we analyze relative manifestation of these effects presenting predictions for large-pT suppression at different rapidities. We analyze also a contribution of gluon shadowing as a leading twist shadowing correction modifying nuclear effects especially at small pT.

Primary author

Jan Cepila (Faculty of Nuclear Sciences and Physical Engineering (FNSPE)-Czech Technical University in Prague)


Dr Jan Nemchik (IEP SAS Kosice & FNSPE CTU in Prague)

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