Transverse-spin-dependent azimuthal asymmetries of pion and kaon pairs produced in muon-proton and muon-deuteron semi-inclusive deep inelastic scattering

TL;DR

This paper reports measurements of azimuthal asymmetries in pion and kaon pair production during deep-inelastic scattering, providing insights into transversity distribution functions and di-hadron fragmentation, with results from COMPASS experiments on proton and deuteron targets.

Contribution

It presents new experimental data on azimuthal asymmetries in di-hadron production, enhancing understanding of transversity and fragmentation functions in nucleons.

Findings

Significant asymmetries observed for proton target indicating non-zero transversity.

Small asymmetries on deuteron target suggest cancellation of u and d quark transversity.

Results agree with some model predictions and previous measurements.

Abstract

A set of measurements of azimuthal asymmetries in the production of pairs of identified hadrons in deep-inelastic scattering of muons on transversely polarised $^6$LiD (deuteron) and NH$_3$ (proton) targets is presented. All available data collected in the years 2002-2004 and 2007/2010 with the COMPASS spectrometer using a muon beam of 160 GeV/$c$ at the CERN SPS were analysed. The asymmetries provide access to the transversity distribution functions via a fragmentation function that in principle may be independently obtained from $e^+e^-$ annihilation data. Results are presented, discussed and compared to existing measurements as well as to model predictions. Asymmetries of $\pi^{+}\pi^{-}$ pairs measured with the proton target as a function of the Bjorken scaling variable are sizeable in the range $x> 0.032$, indicating non-vanishing transversity distribution and di-hadron interference fragmentation functions. As already pointed out by several authors, the small asymmetries of $\pi^{+}\pi^{-}$ measured on the $^6$LiD target can be interpreted as indication for a cancellation of $u$ and $d$-quark transversity distributions.