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On the Effect of Asymmetric Strange Seas and Isospin-Violating Parton Distribution Functions on sin2thetaW Measured at NuTeV

NuTeV Collaboration, G. P. Zeller, K. S. McFarland

TL;DR

The paper addresses whether asymmetries in the strange sea and isospin-violating parton distributions can explain NuTeV's anomalous on-shell sin^2 theta_W measurement. It develops a formalism to propagate PDF-level asymmetries into NuTeV observables and uses CCFR/NuTeV dimuon data to constrain possible strange-sea asymmetries. It surveys several nonperturbative models of isospin violation and quantifies their potential impact, finding model-dependent shifts from negligible to a few times 10^-3. The results indicate that these asymmetries, while relevant, are not sufficient to fully resolve the NuTeV anomaly under current experimental constraints, and relaxing the strange-sea symmetry can even worsen the tension.

Abstract

The NuTeV collaboration recently reported a value of sin2thetaW measured in neutrino-nucleon scattering that is 3 standard deviations above the standard model prediction. This result is derived assuming that (1) the strange sea is quark-antiquark symmetric, s(x)=sbar(x), and (2) up and down quark distributions are symmetric under the simultaneous interchange of u<->d and p<->n. We report the impact of violations of these symmetries on sin2thetaW and discuss the theoretical and experimental constraints on such asymmetries.

On the Effect of Asymmetric Strange Seas and Isospin-Violating Parton Distribution Functions on sin2thetaW Measured at NuTeV

TL;DR

The paper addresses whether asymmetries in the strange sea and isospin-violating parton distributions can explain NuTeV's anomalous on-shell sin^2 theta_W measurement. It develops a formalism to propagate PDF-level asymmetries into NuTeV observables and uses CCFR/NuTeV dimuon data to constrain possible strange-sea asymmetries. It surveys several nonperturbative models of isospin violation and quantifies their potential impact, finding model-dependent shifts from negligible to a few times 10^-3. The results indicate that these asymmetries, while relevant, are not sufficient to fully resolve the NuTeV anomaly under current experimental constraints, and relaxing the strange-sea symmetry can even worsen the tension.

Abstract

The NuTeV collaboration recently reported a value of sin2thetaW measured in neutrino-nucleon scattering that is 3 standard deviations above the standard model prediction. This result is derived assuming that (1) the strange sea is quark-antiquark symmetric, s(x)=sbar(x), and (2) up and down quark distributions are symmetric under the simultaneous interchange of u<->d and p<->n. We report the impact of violations of these symmetries on sin2thetaW and discuss the theoretical and experimental constraints on such asymmetries.

Paper Structure

This paper contains 4 sections, 13 equations, 2 figures.

Table of Contents

  1. Introduction and Formalism
  2. Asymmetric Strange Sea
  3. Isospin Violating PDFs
  4. Conclusions

Figures (2)

  • Figure 1: The functionals describing the shift in the NuTeV $\hbox{$\sin^2\theta_W$}$ caused by not correcting the NuTeV analysis for isospin violating $u$ and $d$ valence and sea distributions or for $\langle{s(x)}\rangle\neq\langle\overline{s}(x)\rangle$. The shift in $\hbox{$\sin^2\theta_W$}$ is determined by convolving the asymmetric momentum distribution with the plotted functional.
  • Figure 2: The functionals describing the shifts in the NuTeV $(g_L^{\rm eff})^2$ and $(g_R^{\rm eff})^2$ caused by not correcting the NuTeV analysis for isospin violating $u$ and $d$ valence and sea distributions or for $\langle{s(x)}\rangle\neq\langle\overline{s}(x)\rangle$. The shifts in $(g_L^{\rm eff})^2$ and $(g_R^{\rm eff})^2$ are determined by convolving the asymmetric momentum distribution with the plotted functional.