The Study On The Spin Structure Of Nucleons And Evolution Effects

The study of the spin-related physical observables in high energy scattering processes has been and is still one of the most attractive issues in current Quantum Chromodynamics?QCD?spin physics.The investigation on this issue may shed light on the understanding of the internal spin structure of nucleons,as well as the QCD dynamics.Factorization theorem can serve as an important tool to investigate and calculate inclusive or semi-inclusive processes in which hadrons participate.Based on the factorization theorem,the cross section of the process can be separated into two parts:the short distance part,which can be calculated by perturbative QCD,and the long distance nonperturbative part.In this way,factorization theorem makes the most of the perturbative QCD.In this thesis,the two factorization frameworks:the collinear factor-ization and the transverse momentum dependent?TMD?factorization including TMD evolution effects are adopted to study the transverse-spin related observables.The two processes which involve at least two hadrons in the initial and final states,the semi-inclusive deep inelastic s-cattering?SIDIS?process and the?N dilepton production Drell-Yan process,are studied in this thesis.Based on the current experimental measurements and the development of theoretical re-search,we focus on the following subjects in this thesis.1.Within the collinear factorization frame at the tree level,we study the transverse single-spin asymmetry A_UT^sin?S in SIDIS,in which the unpolarized electron beam scatters off a transversely polarized nucleon producing charged and neutral pions in the final state. Particularly,we consider the case in which the transverse momentum of the final state hadron is integrated out.Since the asymmetry is merely contributed by the coupling of the wist-3 collinear fragmentation function?H?z?and the transversity distribution function ₁?x?,the twist-3 collinear fragmentation function?H?z?can serve as a“spin analyzer” o access the quark transversity of nucleons.Using the available parametrization of h₁?x? nd the recent extracted result for?H?z?,and including the leading-order QCD evolution ffect of the parton distribution functions and fragmentation functions,we predict the in?_Sasymmetry at a future Electron Ion Collider?EIC?,showing that the asymmetry is izable and could be measured.The prediction demonstrates that it is feasible to access he transversity distribution function via transverse SSA of single meson production in IDIS within the framework of collinear factorization.2.Within the collinear factorization at tree level,we investigate the longitudinal-transverse ouble-spin asymmetry with a cos?_Smodulation in SIDIS for charged and neutral pions roduction,in which a longitudinally polarized electron beam scatters off a transversely olarized nucleon target.We consider the particular case in which the transverse mo-entum of the final state hadron is integrated out.The corresponding asymmetry may be ontributed by two parts:one is the convolution of the twist-3 distribution function g_T?x? nd the unpolarized fragmentation function D₁?z?,the other one is related to the cou-ling of the twist-2 transversity distribution function h₁?x?and the collinear twist-3 frag-mentation function?E?z?.We take into account both contributions to predict the cos?_S symmetry at the kinematics of CLAS12 and future EIC.We consider the leading-order CD evolution effects for the parton distribution functions and fragmentation functions.We find it might be promising to access the twist-3 fragmentation function?E^q?z?via the easurement of the cos?_Sasymmetry at the kinematics of CLAS12 in the large-z region.3.We propose a prescription for the nonperturbative Sudakov form factor which is related to the TMD evolution of the unpolarized pion distributions.We study the transverse omentum dependent differential cross section using the TMD factorization up to the ext-to-logarithmic order of QCD and TMD evolution in the unpolarized?^-N Drell-Yan rocess.We extract the nonperturbative Sudakov form factor for the pion by fitting the xperimental data collected by the E615 Collaboration at Fermilab.With the extracted Su-dakov form factor,we calculate the transverse momentum spectrum of dilepton produced in the unpolarized?^-N Drell-Yan process and compare it with the recent measurement by the COMPASS Collaboration at CERN.The comparison shows that the extracted nonper- turbative Sudakov form factor is compatible with the COMPASS measurement at small q_?region with q_??Q,indicating that our approach can be used to study the unpolarized Drell-Yan process at COMPASS.Furthermore,the framework can also be extended to the study of the polarized processes.4.Utilizing the extracted nonperturbative Sudakov form factor for the pion meson and the formalism for unpolarized?^-N Drell-Yan set up above,we investigate the Sivers asymmetry in the transversely single polarized?^-N Drell-Yan process at the kinematics of COMPASS,under the theoretical framework of the TMD factorization.The effect of the energy-scale dependence of the Qiu-Sterman function T_q,F?x,x,??to the asymmetry is also studied.We find that our prediction on the Sivers asymmetry is consistent with the recent COMPASS measurement.The study shows that the scale dependence of the Qiu-Sterman function should also be considered in the future phenomenological studies.