New Ideas for Transverse Spin Asymmetries in Inclusive Reactions

sometimes also denoted by ATT . Clearly, it is legitimate to ask why these spin observables are important at high energy and what is the appropriate kinematic region xF , pT , where they should be best investigated, both theoretically and experimentally. For the SSA in pp → πX , there are interesting data at √s = 19.4GeV from FNAL [1] and for π production at √ s = 200GeV from BNLRHIC [2]. We will briefly recall the QCDmechanisms which have been proposed to explain these data. We will also consider the case of the W production and we will show the usefulness of positivity for spin observables.