Isovector EMC effect explains the NuTeV anomaly

TL;DR

This paper demonstrates that the isovector EMC effect, caused by neutron or proton excess in nuclei, accounts for a significant part of the NuTeV anomaly, suggesting medium modifications of bound nucleons.

Contribution

It introduces a model-independent correction to the NuTeV measurement based on the isovector EMC effect, providing a new interpretation of the anomaly.

Findings

The isovector EMC effect accounts for about two-thirds of the NuTeV anomaly.

The correction is largely model independent.

Supports the idea of medium modification of bound nucleon wavefunctions.

Abstract

A neutron or proton excess in nuclei leads to an isovector-vector mean-field which, through its coupling to the quarks in a bound nucleon, implies a shift in the quark distributions with respect to the Bjorken scaling variable. We show that this result leads to an additional correction to the NuTeV measurement of sin^2(Theta_W). The sign of this correction is largely model independent and acts to reduce their result. Explicit calculation within a covariant and confining Nambu--Jona-Lasinio model predicts that this vector field correction accounts for approximately two-thirds of the NuTeV anomaly. We are therefore led to offer a new interpretation of the NuTeV measurement, namely, that it is further evidence for the medium modification of the bound nucleon wavefunction.