We present a first QCD analysis of next-to-next-leading-order (NNLO) contributions of the spindependent parton distribution functions (PPDFs) in the nucleon and their uncertainties using the Jacobi polynomial approach. Having the NNLO contributions of the quark-quark and gluon-quark splitting functions in perturbative QCD (Nucl. Phys. B 889 (2014) 351-400), one can obtain the evolution of longitudinally polarized parton densities of hadrons up to NNLO accuracy of QCD. A very large sets of recent and up-to-date experimental data of spin structure functions of the proton g p 1 , neutron g n 1 , and deuteron g d 1 have been used in this analysis. The predictions for the NNLO calculations of the polarized parton distribution functions as well as the proton, neutron and deuteron polarized structure functions are compared with the corresponding results of the NLO approximation. We form a mutually consistent set of polarized PDFs due to the inclusion of the most available experimental data including the recently high-precision measurements from COMPASS16 experiments (Phys. Lett. B 753 (2016) 18-28). We have performed a careful estimation of the uncertainties using the most common and practical method, the Hessian method, for the polarized PDFs originating from the experimental errors. The proton, neutron and deuteron structure functions and also their first moments, Γ p,n,d , are in good agreement with the experimental data at small and large momentum fraction of x. We will discuss how our knowledge of spin-dependence structure functions can improve at small and large value of x by the recent COMPASS16 measurements at CERN, the PHENIX and STAR measurements at RHIC, and at the future proposed colliders such as Electron-Ion collider (EIC).

In this article, we present our global QCD analysis of leading neutron production in deep inelastic scattering at H1 and ZEUS collaborations. The analysis is performed in the framework of a perturbative QCD description for semi-inclusive processes, which is based on the fracture functions approach. Modeling the nonperturbative part of the fragmentation process at the input scale Q 2 0 , we analyze the Q 2 dependence of the leading neutron structure functions and obtain the neutron fracture functions (neutron FFs) from next-toleading order global QCD fit to data. We have also performed a careful estimation of the uncertainties using the "Hessian method" for the neutron FFs and corresponding observables originating from experimental errors. The predictions based on the obtained neutron FFs are in good agreement with all data analyzed, at small and large longitudinal momentum fraction x L as well as the scaled fractional momentum variable β.

We have utilized the concept of valon model to calculate the spin structure functions of proton, neutron, and deuteron. The valon structure itself is universal and arises from the perturbative dressing of the valence quark in QCD. Our results agree rather well with all of the relevant experimental data on g p,n,d 1 and gA gV , and suggests that the sea quark contribution to the spin of proton is consistent with zero. It also reveals that while the total quark contribution to the spin of a valon, ∆Σ valon , is almost constant at Q 2 ≥ 1 the gluon contribution grows with the increase of Q 2 and hence requiring a sizable negative orbital angular momentum component L z . This component along with the singlet and non-singlet parts are calculated in the Nextto-Leading order in QCD . We speculate that gluon contribution to the spin content of the proton is about 60% for all Q 2 values. Finally, we show that the size of gluon polarization and hence, L z , is sensitive to the initial scale Q 2 0

Using repeated Laplace transform, We find an analytical solution for DGLAP evolution equations for extracting the pion, kaon and proton Fragmentation Functions (FFs) at NLO approximation. We also study the symmetry breaking of the sea quarks Fragmentation Functions, D h q (z, Q 2 ) and simply separated them according to their mass ratio. Finally, we calculate the total Fragmentation Functions of these hadrons and compare them with experimental data and those from global fits. Our results show a good agreement with the FFs obtained from global parameterizations as well as with the experimental data.

Within the framework of the so-called valon model, We argue that a substantial part of the nucleon spin, about 40%, is carried by the polarized valence quarks. The remaining is the result of cancelations between gluon polarization and the orbital angular momentum, where the gluon polarization is the dominant one. It is shown that the sea quark contributions to the spin of any hadron is simply marginal and consistent with zero. Our findings point to a substantially smaller value for a 8 than inferred from hyperon -β decay, suggesting that full SU (3) symmetric assumption needs to be reconsidered. New and emerging experimental data tend to support this finding. Finally, we show that within the model presented here the experimental data on the polarized structure functions g p,n,d 1 are reproduced. *