Six 'beyond Collins and Sivers' transverse spin asymmetries at COMPASS

摘要

COMPASS is a fixed-target high energy physics experiment at the SPS at CERN\cite{Abbon:2007pq}. One of the important objectives of the experiment is theexploration of the transverse spin structure of the nucleon via spin dependentazimuthal asymmetries in single-hadron production in deep inelastic scatteringof polarized leptons off transversely polarized target. For this purpose aseries of measurements were made in COMPASS, using 160 GeV/c longitudinallypolarized muon beam and transversely polarized $^6LiD$ (in 2002, 2003 and 2004)and $NH_3$ (in 2007 and 2010) targets. Till now main attention was focused on Collins and Sivers asymmetries andobtained results play an important role in the general understanding of thethree-dimensional nature of the nucleon in terms of Transverse MomentumDependent (TMD) Parton Distribution Functions (PDFs) and FragmentationFunctions (FFs). In addition to these two measured leading-twist effects, the SIDIScross-section counts six more target transverse spin dependent azimuthaleffects, which have their own well defined leading or higher-twistinterpretation in terms of QCD parton model. So far COMPASS presentedpreliminary results for these asymmetries from deuteron\cite{Parsamyan:2007ju},\cite{Kotzinian:2007uv} and "proton-2007" data\cite{Parsamyan:2010se}. In this contribution we review the results obtainedwith the last "proton-2010" data sample.