Predictions for p+Pb at 4.4A TeV to Test Initial State Nuclear Shadowing at energies available at the CERN Large Hadron Collider

Understand

Collinear factorized perturbative QCD model predictions are compared for p+Pb at 4.4A TeV to test nuclear shadowing of parton distribution at the Large Hadron Collider (LHC).

• The nuclear modification factor (NMF), R_{pPb}(y=0,p_T<20 GeV/c) = dn_{p Pb} /(N_{coll}(b)dn_{pp}), is computed with electron-nucleus (e+A) global fit with different nuclear shadow distributions and compared to fixed Q^2 shadow ansatz used in Monte Carlo Heavy Ion Jet Interacting Generator (HIJING) type models.
• Due to rapid DGLAP reduction of shadowing with increasing Q^2 used in e+A global fit, our results confirm that no significant initial state suppression is expected (R_{pPb} (p_T) = 1 \pm 0.1) in the p_T range 5 to 20 GeV/ c.
• In contrast, the fixed Q^2 shadowing models assumed in HIJING type models predict in the above p_T range a sizable suppression, R_{pPb} (p_T) = 0.6-0.7 at mid-pseudorapidity that is similar to the color glass condensate (CGC) model predictions.