Hadron Structure And The Application Of Collinear Higher-twist Factorization In High Energy Recations

This thesis is devoted to the study of hadrons and nuclei internal structure by investigating spin or nuclei dependent phenomena in high energy reactions, within collinear higher twist factorization framework. High energy reactions provide us precious chance to study the internal structure of nu-cleon or nuclei, the feature of strong interaction, and to develop the reliable QCD based calculation technique as well, in which spin and nuclei dependent effects play the very important roles. The work presented in this thesis mainly focus on investigating several relevant processes, such as deep inelastic lepton scattering off nucleon or large nuclei, lepton pair production in pp collision.Higher twist effects and related higher twist correlations have been attracting a lot of attention recently in studying the nuclear structure with the great progress made from both experimental and theoretical sides. Within the collinear higher twist factorization framework, differential cross section of high energy reactions can be factorized into the calculable partonic hard scattering cross section convolved with the universal nonperturbative collinear twist-3 or twist-4 correlation functions. Based on this formalism, the following subjects have been addressed in this thesis:1) The single transverse spin asymmetries in heavy quark and anti-quark production from the quark-antiquark annihilation channel contribution is studied by taking into account the initial and final state interactions effects. Because of the different color charges, the final state interaction effects lead to about a factor of 3 difference in the spin asymmetry for heavy quark over that for the anti-quark in the valence region of low energy pp collisions. The experimental study of this model-independent prediction shall provide a crucial test for the underlying mechanism for the single spin asymmetry phenomena.2) Transverse polarization in the Hyperon production in the unpolar-ized deep inelastic scattering and pp collisions is studied in the twist-three approach, considering the contribution from the quark-gluon-antiquark correlation distribution in nucleon. We further compare our results for deep inelastic scattering to a transverse momentum dependent factorization approach, and find consistency between the two approaches in the intermediate transverse momentum region.3) We study the azimuthal asymmetry cos(2φ) in the Drell-Yan lepton pair production in hadronic scattering processes at moderate transverse momentum region, taking into account the contributions from the twist-three quark-gluon correlations from the unpolarized hadrons. The contributions are found to dominate the asymmetry, and are not power suppressed by q⊥/Q at small q⊥where q⊥and Q are the transverse momentum and invariant mass of the lepton pair. Accordingly, the Lam-Tung relation will be violated at this momentum region We also study the angular distribution of Drell-Yan lepton pair production in the polarized nucleon- nucleon scattering at moderate and large transverse momentum using the same approach. By extrapolating our result to intermediate transverse momentum region, it turns out the the two approaches: collinear higher twist factorization approach and TMD factorization appraoch in this case match each other again at the moderate transverse momentum region.4) We study the QCD evolution for the twist-three quark-gluon correlation functions associated with the transverse momentum odd quark distributions. Different from that for the leading twist quark distributions, these evolution equations involve more general twist-three functions beyond the correlation functions themselves.5) We show that the gauge-invariant transverse-momentum-dependent (TMD) quark distribution function can be expressed as a sum of all higher- twist collinear parton matrix elements in terms of a transport operator. From such a general expression, we derive the nuclear broadening of the transverse momentum distribution. Under the maximal two-gluon correlation approximation, in which all higher-twist nuclear multiple-parton correlations with the leading nuclear enhancement are given by products of twist-two nucleon parton distributions, we find the nuclear transverse momentum distribution as a convolution of a Gaussian distribution and the nucleon TMD quark distribution.6) Within the framework of a generalized collinear factorization for multiple parton scattering in nuclear medium, twist-4 contributions to DIS off a large nucleus can be factorized as a convolution of hard parts and two-parton correlation functions. The hard parts for the quark scattering in the light-cone gauge correspond to interaction with a transverse (physical) gluon in the target, while they are given by the second derivative of the cross section with a longitudinal gluon in the covariant gauge. We provide a general proof of the equivalence of the hard parts in the light-cone and covariant gauge. We further demonstrate the equivalence in calculations of twist-4 contributions to semi-inclusive cross section of DIS in both lowest order and next leading order.