Neutron single spin asymmetries from semi-inclusive deep inelastic scattering off transversely polarizedHe3

Abstract

A study of semi-inclusive deep inelastic scattering off transversely polarized 3 He is presented.The formal expressions of the Collins and Sivers contributions to the azimuthal single spin asymmetry for the production of leading pions are derived, in impulse approximation, and estimated in the kinematics of forth-coming experiments at JLab. The AV18 interaction has been used for a realistic description of the nuclear dynamics; the nucleon structure has been described by proper parameterizations of data or suitable model calculations. The initial transverse momentum of the struck quark has been properly included in the calculation. The crucial issue of extracting the neutron information from 3 He data, planned to shed some light on the puzzling experimental scenario arisen from recent measurements for the proton and the deuteron, is thoroughly discussed.It is found that a model independent procedure, widely used in inclusive deep inelastic scattering to take into account the momentum and energy distributions of the bound nucleons in 3 He, can be applied also in the kinematics of the planned JLab experiments, although fragmentation functions, not only parton distributions, are involved. The possible role played by final state interactions in the process under investigation is addressed. * sergio.scopetta@pg.infn.it

Transverse momentum distributions and nuclear effects

“…As shown in Fig. 1, in the Bjorken limit the extraction procedure through the formula successful in DIS works nicely for the Sivers SSA and the same was shown to occur for the Collins SSA [4]. The generalization of Eq.…”

“…The nuclear effects are hidden in the proton and neutron "effective polarizations", p p(n) . With the AV18 nucleonnucleon interaction [18] the values p p = −0.023, p n = 0.878 were obtained [4]. The quantities f p (n) 3 He asymmetry taking into account the nuclear structure through Eq.…”

“…The quantities f p (n) 3 He asymmetry taking into account the nuclear structure through Eq. (1) (after [4]). …”

“…In Sect. II the possibility to extract the neutron SSAs from 3 He SSAs in plane wave impulse approximation (PWIA) [4] is briefly summarized; in Sect. III preliminary results about the effects of FSI are illustrated [9,10]; in Section IV the possibility to study the relativistic effects through a light-front (LF) spin-dependent speca e-mail: pace@roma2.infn.it tral function for 3 He is outlined [11][12][13], and eventually in Sect.…”

“…In particular the single spin asymmetries (SSAs) allow one to experimentally distinguish the Sivers and the Collins asymmetries [2,3], expressed in terms of different TMDs and fragmentation functions (ff) [1,4]. A large Sivers asymmetry was measured in → p(e, e ′ π)x [5] and a small one in → D(e, e ′ π)x [6], showing a strong flavor dependence of TMDs.…”