High-pT hadrons in pA and AA collisions: Impact of energy conservation

The Cronin effect, which is nuclear enhancement of high-pT hadron production in pA collisions was successfully predicted prior the measurements at RHIC and LHC. The restrictions imposed by energy conservation lead to spectacular effects. Energy deficit becomes an issue for hadron production in pA collisions at large xL and/or large xT towards the kinematic bounds xL,T = 1. It leads to a suppression, which has been indeed observed for hadrons produced at forward rapidities and large pT. Intensive energy dissipation via gluon radiation by a highly virtual parton produced with large pT, makes impossible this process to continue long. Color neutralization and creation of a colorless dipole must occur promptly. When this happens inside a hot medium created in AA collisions, attenuation of dipoles, rather than induced energy loss, becomes a dominant mechanism for suppression of high-pT hadrons.