W/Z Production at the LHC and the Parton Distributions C.S. Kim (w/ Y.S. Jeong, F. Halzen)

Outline Introduction Sea quark contributions W charge asymmetry, A(Y) B(Y) and B( ε ) for the charm quark. Summary

W and Z cross section X = W or Z  To test the standard model (SM)  To test pQCD  current prediction is known up to NNLO.  To determine the parton distribution functions (PDF) of the proton  Drell-Yan mechanism can produce W/Z bosons.

The PDF of proton can be investigated using the relation of the differential cross sections.

Tevatron vs. LHC  Initial status of collision (p-pbar vs. p-p) – different pattern of the rapidity distributions

Tevatron vs. LHC A. Kusina et al. Phys. Rev. D 85, (2012)  High energy of the LHC – large event rate – lower momentum fractions of the partons, where sea quarks dominate.

Valence and Sea quark contributions to the Cross Sections for W/Z production As energy increases, the relative contributions of the sea quarks become more important.

Valence and Sea quark contributions to the Differential Cross Section on Y The sea-sea contributions dominate at the central rapidity region while the valence-sea contributions are bigger in the forward and backward regions. The sea-sea contributions to W + and W - are the same.

Valence and Sea quark contributions to the Differential Cross Section on Y At higher energies, the relative contributions of sea-sea interactions are also increased. e.g.) W + : 75% at 7 TeV → 86% at 14 TeV

W Charge Asymmetry, A(Y)

 V ud 2 = V cs 2 ~ 0.95, V us 2 = V cd 2 ~ 0.05, V ub 2 ~ 10 -5, V cb 2 ~  ⇒ The W charge asymmetry is mainly from u-d quark interactions.

W Charge Asymmetry, A(Y)

The Reconstructed Rapidity K. Hagiwara et al. Phys. Rev. D 41, 1471 (1990) Definition of the rapidity The rapidity that can be experimentally reconstructed

W Charge Asymmetry with the Reconstructed Rapidity Fully calculated with all flavors. A(Y)=A(-Y) while A(Y)=-A(-Y) for p-pbar collisions. The results for the NLO and NNLO PDF sets are almost degenerated.

Charm Quark Distributions

Charm-quark contributions at the LHC The shaded area indicates the charm contributions. Like the sea contribution case, the charm contribution increases with the collision energy. At 7 TeV, (29%, 33%, 8%) for (W+, W-, Z) → (36%, 38%, 11%) at 14 TeV. (at Y=0)

Charm Quark Distributions

B(Y) in terms of ε ε of CTEQ6.6 and MSTW2008 PDF is between 0.5 – 0.75.

The quantity ε for CTEQ6.6 and MSTW2008 PDF sets - about 0.6 for 7 TeV, and 0.7 for 14 TeV.

Summary At the LHC energies, the sea quark contributions are co nsiderable. We investigated the ways to explore the parton dist ributions; W charge asymmetry and B quantities. The charge asymmetry is little affected by the heavy qu arks. Therefore, it is proper to investigate the u (v) (x) and d (v) (x). The quantities B(Y) and B(ε) can be used to determine the charm distribution with.