Theoretical Studies On The Spin Structure Of Nuclear At Subleading Twist

The spin-related asymmetry appearing in high-energy scattering process is a powerful tool to probe the spin structure and the flavor dependence of the nucleon. One of the important goals of QCD spin physics is to understand the origins of these spin-related asymmetries, since the study on these spin-related asymmetries can help us to understand more information of the correlation between quark spin and orbit inside the hadrons. Substantial spin asymmetries at leading twist have been measured by the experimental collaborations, but these leading-twist asymmetries cannot exhaust all possible spin polarized effects. Therefore, exploring the sources of the spin asymmetries at subleading twist that appearing in high energy scattering process is not only an important method to probe the spin structure of the nuclear, but also the main goal of this work. Based on the transverse momentum dependent (TMD) factorization, this work will give a study on these spin-related asymmetries at subleading twist in the semi-inclusive deep inelastic scattering (SIDIS), by focus on the contributions from the twist-3 distribution functions.For the SIDIS process, according to the different polarizations of the beam and target, theo-retically there are seven different angular modulations of the the spin asymmetries at subleading twist, that is, the beam single spin asymmetry (SSA) AsLUsiφh, the target longitudinal SSA AULsinφh the target transverse SSAs AUTsinφs and AUT(2φh-φs), target longitudinal double spin asymmetry (DSA) ALLcosφh, target transverse DSAs ALTcosφs and ALTcos(2φh-φs). Except the target longitudinal SSA AULsinφh that has been studied, this work will give a complete discussion on the above six left spin asymmetries. Under the transverse momentum dependent (TMD) factorization, from the phenomenological point of view, in the partonic picture, the leading twist asymmetries can be explained by the convolution of the leading-twist (twist-2) transverse momentum dependent distribution functions and fragmentation functions, while the subleading twist asymmetries can be explained by the convolution of various twist-3 TMD distribution/fragmentation functions with twist-2 TMD fragmentation/distribution functions. These TMD distribution functions are general physical observers that cannot be calculated by a perturbation way and are independent on the process, so far they are mainly calculated by model or parametrization, in this work we will adopt the quark-spectator diquark model under the field-theoretical frame to obtain them.The six azimuthal angle-dependent spin asymmetries at subleading twist that are discussed in this thesis refer to twelve different twist-3 TMD distribution functions, and six of them are time-reversal even (T-even) while the other six distributions are time-reversal odd (T-odd). With this model results for the twist-3 TMD distribution functions that obtained by the SU(6) quark-spectator diquark model under the field theoretical frame and the kinematical cuts at HERMES, Jefferson Lab (JLab) and COMPASS, one can estimate their contributions to the corresponding spin asymmetries at subleading twist. By comparing the results with the measured experimental data, one can examine the reliability of our theory calculation. Also, by extracting the spin asymmetries, we can obtain the information of the spin structure of the nucleon in the parton distribution functions; thereby we can probe the roles of the quark initial transverse quantum in the high-energy processes. Besides, our predictions on the future experiments can provide theoretical references, while the future experimental measurements can test the validity of our theory predictions. Both the theoretical and experimental studies will shed light on the sources of the spin asymmetries to deep our understanding on the nucleon internal structure in three dimensions. The main contents of this thesis are summarized as follows:1) Beam single spin asymmetry ALUsinφh. First, by considering the contribution from the T-odd twist-3 TMD distribution function g⊥(x, kT2) and the kinematical cuts at CLAS with the beam energy 5.776GeV and HERMES, we estimate the to the beam single spin asymmetry for π0 production, as well predict the asymmetry at CLAS 12. Second, by taking the contributions from both the twist-3 TMD distribution functionse.(x, kT2) and g⊥(x,kT2) into consideration, also with the kinematics at HERMES and CLAS 12, we calculate the beam single spin asymmetries for charged pion productions, and give the results with two different sets of the TMD distribution functions which are obtained by applying two different spectator diquark models. Third, we also give the beam single spin asymmetries for charged hadrons by using two different sets of the distribution functions and both the proton and deuteron targets. The comparisons with the experimental measurements show that our theoretical results agree with the experimental data very well within the statistical uncertainty, which indicates that our theoretical calculation method are valid and our model results are reliable.2) Target transverse single-spin asymmetries AUTsinφs and AUTsin(2φh-φs). Considering the contributions from the twist-3 TMD distribution functions fT(x,kT2), hT(x,kT2) and hT⊥(x,kT2) to the sin φ2 modulation and the contributions from the distributions fT⊥(x,kT2), hT(x,kT2) and hT⊥(x, kT2) to the sin (2φh-φs) modulation, together with the kinematical cuts at HERMES, JLab5.5, JLabll and COMPASS, we predict the two target transverse SSAs for π+、π-and π0 productions to provide theoretical references for the future experimental measurements. Our theoretical predictions show that these target transverse SSAs at subleading twist are quite ob-servable, and the T-odd twist-3 TMD distribution functions play important roles in these spin asymmetries.3) Target longitudinal double-spin asymmetry ALLcosφh. Taking the contributions from the twist-3 TMD distribution functionse L(x, kT2) and gL⊥(x,kT2) into account, we predict the target longitudinal DSA for three different pion productions. By using two different sets of the TMD distribution functions that obtained by applying two different spectator diquark models, we give our predictions at CLAS with a proton target at beam energy 5.5GeV and with a He3 target at beam energy 12GeV, as well at HERMES with a proton target, respectively. Furthermore, we also give asymmetries at COMPASS with a deuteron target for h+and h-productions, and compare the results with the experimental data. We find that different beam energies and different scattering targets will affect the sizes of the spin asymmetry.4) Target transverse double-spin asymmetries ALTcosφs and ALTcos(2φh-φs).Considering the contributions from the twist-3 TMD distribution functions gT(x,kT2), eT(x, kT2) and eT⊥(x, kT2) to the cos φs asymmetry and the contributions from the distributions gT⊥(x, kT2), eT(x, kT2) and eT⊥(x, kT2) to the cos (2φh-φs) asymmetry, together with the kinematical regions at HERMES, JLab5.5 and COMPASS, we give our predictions on the two target transverse DSAs for three different pions to enrich and complete our theoretical studies, as well provide related theoretical reference for the future experimental measurements. The predictions show that the target trans-verse DSAs are observable at HERMES and JLab, but almost unobservable in the kinematical regions at COMPASS.