Transverse-spin-dependent Azimuthal Asymmetries of Pion and Kaon Pairs Produced in Muon-Proton and Muon-Deuteron Semi-Inclusive Deep Inelastic Scattering

A set of measurements of azimuthal asymmetries in the production of pairs of identified hadrons in deep-inelastic scattering of muons on transversely polarised (LiD)-Li-6 (deuteron) and NH3 (proton) targets is presented. All available data collected in the years 2003-2004 and 2007/2010 with the COMPASS spectrometer using a muon beam of 160GeV/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 (LiD)-Li-6 target can be interpreted as indication for a cancellation of u and d-quark transversity distributions.(c) 2023 Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).