Kinematic constrains on interacting nucleons in $Pb+Pb$ collisions at   $\sqrt{s_{NN}}=2.76$ TeV within the HIJING code
  The kinematic constrains on interacting nucleons in Large Hadron Collider (LHC) heavy-ion collisions are investigated in the framework of the Heavy Ion Jet Interaction Generator (HIJING) code incorporated with a collective cascade recipe. The latter is used to implement energy-momentum conservation constrains on both primary and secondary interacting nucleons. It is found that the energy-momentum conservation constrains on the interacting nucleons affect the whole charged particle pseudo-rapidity density distribution $(\frac{dN_{ch}}{d\eta})$, at different centralities (from central (0-5\%) to peripheral (70-80\%) collisions), in Pb+Pb collisions at $\sqrt{s_{NN}} =2.76$ TeV. In particular, the kinematic constrains on interacting nucleons are shown to reduce $(\frac{dN_{ch}}{d\eta})$ yield at mid-pseudorapidity $(\lvert\eta\rvert<2)$ in all centrality intervals, which is consistent with the LHC data. In addition, the model predicts an enhancement of the hadron production at $\lvert\eta\rvert>8$, which could be checked in future ALICE Zero Degree calorimeter. Such an enhancement is found to be mainly due to the interactions of protons at the spectator parts of the collision. This indicates that the kinematic constrains are important for a correct geometrical treatment of Pb+Pb collisions at LHC energies. 
Khaled Abdel-Waged and Nuha Felemban
nucl-th nucl-ex