# Azimuthal asymmetries from $\theta$ Vacuum

## TL;DR

This paper analyzes azimuthal asymmetries in dihadron production during electron-positron annihilation, highlighting how a non-trivial $ heta$ vacuum induces parity violation and affects measurable asymmetries and polarization effects.

## Contribution

It introduces the role of $ heta$ vacuum in generating parity-odd fragmentation functions and their impact on azimuthal asymmetries in semi-inclusive electron-positron annihilation.

## Key findings

- Parity-odd fragmentation functions contribute to azimuthal asymmetries.
- Certain asymmetries vanish when summing over many events due to symmetry.
- Surviving asymmetries can be used to measure $ heta$ vacuum effects.

## Abstract

We present the complete azimuthal asymmetries at leading twist in terms of fragmentation functions in dihadron production semi-inclusive electron positron annihilation process. When the non-trivial $\theta$ vacuum is taken into consideration, the parity symmetry of quantum chromodynamics is violated. As a consequence of the $local$ $\mathcal{P}$-odd effects, $\mathcal{P}$-odd fragmentation functions would contribute to the azimuthal asymmetries. Azimuthal asymmetry coming from two interference terms with opposite signs vanishes when sum over many events. This symmetry only survives on the event-by-event basis. Azimuthal asymmetry coming from two interference terms with same signs survives and can be measured to extract the $\mathcal{P}$-odd fragmentation functions. We also present the hadron polarizations.