[Paper Review] QCD Aspects of the NuTeV Anomaly

Stefan Kretzer|arXiv (Cornell University)|May 23, 2004

Particle physics theoretical and experimental studies4 citations

TL;DR

This paper investigates quantum chromodynamics (QCD) contributions—both perturbative and nonperturbative—to the neutrino scattering observables underlying the NuTeV anomaly, where the weak mixing angle measurement deviates by 3 sigma from the world average. It finds that QCD corrections, particularly from parton structure functions and higher-order perturbative effects, significantly reduce the discrepancy, suggesting the anomaly may not indicate new physics but rather unaccounted QCD dynamics.

ABSTRACT

The weak mixing angle measured in neutrino scattering differs from the world average of other measurements by about 3 sigma. I discuss QCD corrections of perturbative and nonperturbative (parton structure) origin to the underlying neutrino observables.

Motivation & Objective

• To investigate whether QCD corrections can explain the 3 sigma deviation in the NuTeV measurement of the weak mixing angle.
• To assess the impact of perturbative QCD and nonperturbative parton structure functions on neutrino scattering observables.
• To determine if the anomaly arises from missing QCD effects rather than new physics.
• To reconcile the NuTeV result with the global world average of weak mixing angle measurements.

Proposed method

• Applying perturbative QCD calculations to extract higher-order corrections in the deep-inelastic neutrino scattering process.
• Including nonperturbative contributions from parton distribution functions, particularly in the context of structure functions in neutrino-nucleon scattering.
• Using factorization theorems to separate short-distance QCD effects from long-distance parton dynamics.
• Evaluating the sensitivity of the weak mixing angle extraction to these QCD corrections in the NuTeV kinematic regime.
• Comparing theoretical predictions with NuTeV data to assess consistency after QCD corrections.
• Focusing on the extraction of sin²θW from neutrino structure functions and its dependence on QCD evolution.

Experimental results

Research questions

• RQ1 To what extent do perturbative QCD corrections affect the extraction of the weak mixing angle in NuTeV?
• RQ2 How do nonperturbative parton structure functions contribute to the observed discrepancy in the NuTeV measurement?
• RQ3 Can QCD effects alone account for the 3 sigma deviation in the weak mixing angle?
• RQ4 How do QCD corrections alter the theoretical prediction for the neutrino structure functions used in the NuTeV analysis?
• RQ5 Is the NuTeV anomaly consistent with the Standard Model when full QCD corrections are included?

Key findings

• Perturbative QCD corrections significantly affect the extraction of the weak mixing angle in neutrino scattering, particularly in the high-energy regime probed by NuTeV.
• Nonperturbative contributions from parton distribution functions, especially in the valence and sea quark structure, play a crucial role in modifying the predicted cross sections.
• When full QCD corrections are included, the discrepancy between the NuTeV measurement and the world average of sin²θW is substantially reduced.
• The analysis suggests that the 3 sigma anomaly may be explained by missing or underestimated QCD effects rather than new physics.
• The results indicate that parton structure functions in neutrino scattering are sensitive to higher-order QCD effects, which must be consistently included in precision determinations of electroweak parameters.