Tests for the extraction of Boer-Mulders functions

TL;DR

This paper introduces two independent tests for the assumption that Boer-Mulders functions are proportional to Sivers functions, revealing potential unreliability in current extractions and successfully extracting Cahn contributions from experimental data.

Contribution

The study provides novel tests for the proportionality assumption of Boer-Mulders and Sivers functions, challenging existing analyses and extracting Cahn effects directly from experimental data.

Findings

Tests are satisfied if a universal proportionality constant is used across flavors.

Current Boer-Mulders function extractions may be unreliable due to flavor dependence issues.

First-time extraction and comparison of Cahn contributions with theoretical calculations.

Abstract

At present, the Boer-Mulders (BM) functions are extracted from asymmetry data using the simplifying assumption of their proportionality to the Sivers functions for each quark flavour. Here we present two independent tests for this assumption. We subject COMPASS data on semi-inclusive deep inelastic scattering on the $\langle\cos\phi_h\rangle$, $\langle\cos 2\phi_h\rangle$ and Sivers asymmetries to these tests. Our analysis shows that the tests are satisfied with the available data if the proportionality constant is the same for all quark flavours, which does not correspond to the flavour dependence used in existing analyses. This suggests that the published information on the BM functions may be unreliable. The $\langle\cos\phi_h\rangle$ and $\langle\cos 2 \phi_h\rangle$ asymmetries receive contributions also from the, in principle, calculable Cahn effect. We succeed in extracting the Cahn contributions from experiment (we believe for the first time) and compare with their calculated values, with interesting implications.