Constraints for the nuclear parton distributions from Z and W production at the LHC

Abstract

The LHC is foreseen to finally bring also the nuclear collisions to the TeV scale thereby providing new possibilities for physics studies, in particular related to the electro-weak sector of the Standard Model. We study here the Z and W ± production in proton-lead and lead-lead collisions at the LHC, concentrating on the prospects of testing the factorization and constraining the nuclear modifications of the parton distribution functions (PDFs). Especially, we find that the rapidity asymmetries in proton-nucleus collisions, arising from the differences in the PDFs between the colliding objects, provide a decisive advantage in comparison to the rapidity-symmetric nucleusnucleus case. We comment on how such studies will help to improve our knowledge of the nuclear PDFs.

Nuclear PDFs in the beginning of the LHC era

“…The first experimental results from the LHC proton+lead run are now starting to become public [12], and are expected to conclusively test the universality of the nPDFs and hopefully serve as further constraints as well. For instance, different rapidity and transverse momentum distributions of charged leptons from electroweak gauge boson decays have been theoretically explored [45,46,47,48,49] and promise to probe various aspects of nPDFs. Direct photons, inclusive hadrons and jet observables [50,51,52,53,54,55] have been predicted to retain sensitivity to the nuclear modifications in PDFs as well.…”

Scaling properties of inclusive W $$^\pm $$ ± production at hadron colliders

“…This is in sharp contrast to hadronic observables (high-transverse momentum hadrons [29,30,31] and jets [32,33,34]) which are strongly suppressed as compared to p-p collisions. Thus, the leptons from W decays are valuable "messengers" from the initial state of heavy-ion collisions and could also be used to constrain the nPDFs [35,36,37].…”

Dimuons in pp and PbPb collisions with the CMS experiment

“…Predictions [5,6,7,8,9] indicate that the effects that can affect the Z boson production in heavy ion collisions are rather small. From these effects, shadowing is expected to have the biggest contribution ≈10 -20% [8].…”

“…Predictions [5,6,7,8,9] indicate that the effects that can affect the Z boson production in heavy ion collisions are rather small. From these effects, shadowing is expected to have the biggest contribution ≈10 -20% [8]. The isospin effect arises from the difference of quark content of protons and neutrons that collide in the PbPb case as opposed to pp, and is expected to contribute less tha 3% [8].…”

“…From these effects, shadowing is expected to have the biggest contribution ≈10 -20% [8]. The isospin effect arises from the difference of quark content of protons and neutrons that collide in the PbPb case as opposed to pp, and is expected to contribute less tha 3% [8]. Finally, scattering and energy loss of the initial partons should have an effect of the order of 2 % [7].…”