Flavour and spin of the proton and the meson cloud

Abstract

We present a complete set of formulas for longitudinal momentum distribution functions (splitting functions) of mesons in the nucleon. It can be applied in the framework of convolution formalism to the deep-inelastic structure functions (quark distributions) of the nucleon viewed as a system composed of virtual 'mesons' and 'baryons'. Pseudoscalar and vector mesons as well as octet and decuplet baryons are included. In contrast to many approaches in the literature the present approach ensures charge and momentum conservation by the construction. We present not only spin averaged splitting functions but also helicity dependent ones, which can be used to study the spin content of the nucleon. The cut-off parameters of the underlying form factors for different vertices are determined from high-energy particle production data. We find an universal cut-off parameter for processes involving octet

Strange-quark asymmetry in the proton in chiral effective theory

“…(4), with the PV regulator, is qualitatively similar to the splitting functions found in the literature which have been computed in terms of form factors at the N KY vertex [57]. A comparison of the f (on) Λ splitting functions computed with PV regularization with the results obtained using t-dependent [17,[77][78][79][80] or s-dependent [28,55,81,82] form factors for the function F (on) is shown in Fig. 5.…”

“…1(a)] and hyperon rainbow [ Fig. 1(c)] diagrams [55,81]. Namely, because of the kine- longitudinal and transverse boosts).…”

“…For large values of the produced Λ momentum (1 − y 0.7) and small k ⊥ 100 MeV, the dominant contribution to the production process is expected to be from the exchange of a single K + meson. At larger kaon momenta y (smaller 1 − y) multiple meson exchanges and contributions from heavier meson and baryon intermediate states will become more important [55,66]. These, however, cannot be computed within the chiral effective theory framework and will not be considered here.…”

Do the E866 Drell-Yan data change our picture of the chiral structure of the nucleon?

“…The so-constructed model was perfectly consistent with the NA51 experiment at CERN [8,9], which measured thē u −d-asymmetry at x = 0.18 [8]. Furthermore, after the incorporation of the NA51 result, the global parton model analyses have produced parametrizations which were practically indistinguishable from the results of the meson cloud dynamical calculations in [6].…”

“…In Ref. [6] the effect of heavier vector mesons has been evaluated in an extended Fock state decomposition of the nucleon light-cone wave function into meson-baryon, including N ρ, N ω, ∆ρ in addition to πN, π∆ and ηN which are known to be important at low and intermediate energy hadron scattering.…”