Estimate of the Branching Fraction of tau --> pi eta' nu_tau

TL;DR

This paper estimates the branching fraction of the tau decay to pi eta' nu, highlighting the dominant role of the a0(980) scalar meson and its potential to reveal the meson's quark structure or new physics.

Contribution

It provides a theoretical calculation of the tau to pi eta' nu branching fraction considering different meson structures, guiding future experimental tests.

Findings

Calculated branching fraction is below current experimental limits.

Dominant contribution from a0(980) scalar meson.

Potential to determine the nature of a0(980) through precise measurements.

Abstract

We calculate the expected branching fraction of the second-class-current decay tau --> pi eta' nu, motivated by a a recent experimental upper-limit determination of this quantity. The largest contribution to the branching fraction is due to the intermediate a0(980) scalar meson, assuming it is a $\bar ud$ state. Smaller contributions arise from a0(1450), rho(770), and rho(1450). Our calculated values are substantially below the experimental upper limit, and are smaller still if the a0(980) is a four-quark state, as often suggested. Thus, a precise measurement or tight upper limit has the potential to determine the nature of the a0(980), as well as search for new scalar interactions.