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W/Z Production at the LHC and the Parton Distributions

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. Drell-Yan mechanism can produce W/Z bosons.

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W/Z Production at the LHC and the Parton Distributions

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

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

  3. W and Z cross section • Drell-Yan mechanism can produce W/Z bosons. 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

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

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

  6. Tevatron vs. LHC • High energy of the LHC • – large event rate • – lower momentum fractions of the partons, where sea quarks dominate. A. Kusina et al. Phys. Rev. D 85, 094028 (2012)

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

  8. Valence and Sea quark contributionsto 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.

  9. Valence and Sea quark contributionsto 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

  10. W Charge Asymmetry, A(Y)

  11. Vud2 = Vcs2 ~ 0.95, Vus2 = Vcd2 ~ 0.05, Vub2 ~ 10-5, Vcb2 ~ 10-3 • ⇒ The W charge asymmetry is mainly from u-d quark interactions.

  12. W Charge Asymmetry, A(Y)

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

  14. 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.

  15. Charm Quark Distributions

  16. 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)

  17. Charm Quark Distributions

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

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

  20. Summary • At the LHC energies, the sea quark contributions are considerable. • We investigated the ways to explore the parton distributions; W charge asymmetry and B quantities. • The charge asymmetry is little affected by the heavy quarks. 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 .

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