Hard Probes in Heavy Ion Collisions at the

This manuscript is the outcome of the subgroup ``PDFs, shadowing and $pA $ collisions' ' from the CERN workshop ``Hard Probes in Heavy Ion Collisions at the LHC''. In addition to the experimental parameters for $pA $ collisions at the LHC, the issues discussed are factorization in nuclear collisions, nuclear parton distributions (nPDFs), hard probes as the benchmark tests of factorization in $pA $ collisions at the LHC, and semi-hard probes as observables with potentially large nuclear effects. Also, novel QCD phenomena in $pA $ collisions at the LHC are considered. The importance of the $pA $ program at the LHC is emphasized