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The Strange Parton Distribution of the Nucleon: Global Analysis and Applications

H. L. Lai, P. Nadolsky, J. Pumplin, D. Stump, W. K. Tung, C. -P. Yuan

TL;DR

The paper addresses the poorly known strange-quark content of the nucleon by performing a global QCD analysis with the Collins general-mass formalism, extending the CTEQ6.5 framework to allow independent s_+(x) and s_−(x) components. It develops a new central set, CTEQ6.5S0, and explores ranges of magnitude and shape for the symmetric strange sea, as well as the possible strangeness asymmetry, using diverse DIS, DY, jet, and NuTeV dimuon data. The results show that s_+(x) has a distinct shape from the isoscalar non-strange sea and constrain its magnitude to 0.018–0.040, while s_−(x) remains weakly constrained with a small allowed range around zero. The work highlights practical implications for W+c and charged Higgs production at hadron colliders, and provides PDF sets and guidance for future measurements (e.g., W+c, Z+c) to further pin down strange content.

Abstract

The strangeness degrees of freedom in the parton structure of the nucleon are explored in the global analysis framework, using the new CTEQ6.5 implementation of the general mass perturbative QCD formalism of Collins. We systematically determine the constraining power of available hard scattering experimental data on the magnitude and shape of the strange quark and anti-quark parton distributions. We find that current data favor a distinct shape of the strange sea compared to the isoscalar non-strange sea. A new reference parton distribution set, CTEQ6.5S0, and representative sets spanning the allowed ranges of magnitude and shape of the strange distributions, are presented. Some applications to physical processes of current interest in hadron collider phenomenology are discussed.

The Strange Parton Distribution of the Nucleon: Global Analysis and Applications

TL;DR

The paper addresses the poorly known strange-quark content of the nucleon by performing a global QCD analysis with the Collins general-mass formalism, extending the CTEQ6.5 framework to allow independent s_+(x) and s_−(x) components. It develops a new central set, CTEQ6.5S0, and explores ranges of magnitude and shape for the symmetric strange sea, as well as the possible strangeness asymmetry, using diverse DIS, DY, jet, and NuTeV dimuon data. The results show that s_+(x) has a distinct shape from the isoscalar non-strange sea and constrain its magnitude to 0.018–0.040, while s_−(x) remains weakly constrained with a small allowed range around zero. The work highlights practical implications for W+c and charged Higgs production at hadron colliders, and provides PDF sets and guidance for future measurements (e.g., W+c, Z+c) to further pin down strange content.

Abstract

The strangeness degrees of freedom in the parton structure of the nucleon are explored in the global analysis framework, using the new CTEQ6.5 implementation of the general mass perturbative QCD formalism of Collins. We systematically determine the constraining power of available hard scattering experimental data on the magnitude and shape of the strange quark and anti-quark parton distributions. We find that current data favor a distinct shape of the strange sea compared to the isoscalar non-strange sea. A new reference parton distribution set, CTEQ6.5S0, and representative sets spanning the allowed ranges of magnitude and shape of the strange distributions, are presented. Some applications to physical processes of current interest in hadron collider phenomenology are discussed.

Paper Structure

This paper contains 13 sections, 6 equations, 8 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Global Analysis with Focus on the Strange Sector
  3. The Symmetric Strange Sea $\mathbf{s_{+}(x)}$
  4. The Number of New Shape Parameters
  5. New Central PDF set, CTEQ6.5S0
  6. Constraints on the Magnitude of $s_{+}$
  7. Constraints on the Shape of $s_{+}(x)$
  8. The Strangeness Asymmetry $\mathbf{s_{-}(x)}$
  9. Significance of non-zero Strangeness Asymmetry:
  10. Range of Allowed Strangeness Asymmetry:
  11. Physical Applications
  12. Summary
  13. Acknowledgment

Figures (8)

  • Figure 1: Comparison of neutrino dimuon data to fits using CTEQ6.5M (left panel) and the new set CTEQ6.5S0 of Sec. \ref{['sec:c65s0']} (right panel). The data points are sorted in $y$-bins, and within each $y$-bin, by $x$ value, and then $Q$ value.
  • Figure 2: The new CTEQ6.5S0 $s_+(x)$ and $\bar{u}(x)+\bar{d}(x)$ PDFs at $\mu=1.3\ \mathrm{GeV}$ compared to those of CTEQ6.5M.
  • Figure 3: $\chi^{2}$ per data point vs. $\langle x\rangle _{s_{+}}$ for the full data set (3542 points) and for the $\nu$ and $\bar{\nu}$ dimuon production data (149 points).
  • Figure 4: The strangeness distribution $s_{+}(x)$ at the initial scale $\mu =1.3\,\mathrm{GeV}$ for the five PDF sets CTEQ6.5Si, $i=0,\dots,4$.
  • Figure 5: Examples of strangeness asymmetry function $s_-(x)$ that are consistent with existing experimental data (left panel); and the corresponding momentum distribution $x\,s_-(x)$ (right panel).
  • ...and 3 more figures