Prompt photons produced in a hard reaction are not accompanied with any final state interaction, either energy loss or absorption. Therefore, besides the Cronin enhancement at medium transverse momenta pT and small isotopic corrections at larger pT,
one should not expect any nuclear effects. However, data from PHENIX experiment exhibit a significant large-pT suppression in central d+Au and Au+Au collisions that cannot be accompanied by coherent phenomena. We demonstrate that such an unexpected result is subject to the energy sharing problem near the kinematic limit and is universally induced by multiple initial state interactions. We describe production of photons in the color dipole approach and find a good agreement with available data in p+p collisions. Besides explanation of large-pT nuclear suppression at RHIC we present for the first time predictions for expected nuclear effects also in the LHC energy range at different rapidities. We include and analyze also a contribution of gluon shadowing as a leading twist shadowing correction modifying nuclear effects at small and medium pT.
Data from E772 and E866 experiments on the Drell-Yan process exhibit a significant nuclear suppression at large Feynman xF. We show that a corresponding kinematic region does not allow to interpret this as a manifestation of coherence or a Color Glas
s Condensate. We demonstrate, however, that this suppression can be treated alternatively as an effective energy loss proportional to initial energy. To eliminate suppression coming from the coherence, we perform predictions for nuclear effects also at large dilepton masses. Our calculations are in a good agreement with available data. Since the kinematic limit can be also approached in transverse momenta pT, we present in the RHIC energy range corresponding predictions for expected large-pT suppression as well. Since a new experiment E906 planned at FNAL will provide us with more precise data soon, we present also predictions for expected large-xF nuclear suppression in this kinematic region.
We study a significant nuclear suppression of the relative production rates (p(d)+A)/(p+d(p)) for the Drell-Yan process at large Feynman xF. Since this is the region of minimal values for the light-front momentum fraction variable x2 in the target nu
cleus, it is tempting to interpret this as a manifestation of coherence or of a Color Glass Condensate. We demonstrate, however, that this suppression mechanism is governed by the energy conservation restrictions in multiple parton rescatterings in nuclear matter. To eliminate nuclear shadowing effects coming from the coherence, we calculate nuclear suppression in the light-cone dipole approach at large dilepton masses and at energy accessible at FNAL. Our calculations are in a good agreement with data from the E772 experiment. Using the same mechanism we predict also nuclear suppression at forward rapidities in the RHIC energy range.
