Higher Twist Effects In Polarized Structure Functions

Spin plays an important role during the process of particle interactions and in understanding the fundamental structure of matter, as well as the the stability of the world we live in. The spin distribution of nucleon has been investigated extensively since the fact that only a small fraction of spin is from quark and antiquark was observed in an experiment performed by European Muon Collaboration (EMC). A lot of information about quark-gluon interaction and momentum distribution have been obtained, via high energy lepton-nucleon deep inelastic scattering experiments. In recent 20 years, the experimental precision has been developed a lot, which can give us more information about nucleon spin, such as data about polarized structure function. Theoretically, investigations on the nucleon structure function are mostly based on twist-2 quantum chromodynamics linear evolution equation, which sums the Feynman diagrams by using the renormalization group theory. When considering the recombination phenomenon in small x region, linear evolution equation can not be used to describe the interactions of partons, and a nonlinear term must be added to amend the evolution equation. The reference[1] first brings forward the twist-4 modified evolution equation which this paper is mainly based on. At present the investigations on higher twist effects mostly concentrate on twist-3. The present paper firstly performed a calculation of polarized structure function when considering twist-4 effect.The purpose of this paper is to study the higher twist effects in structurefunction g₁(x,Q²) and asymmetry A₁(x,Q²). Here are the main contents of thepresent paper: A brief summary of deep inelastic scattering experiments and parton model; An introduction for 'proton spin crisis'; The computation result on parton evolution equations which considering twist-4 effect; An detailed analysis of higher twist effect on polarized structure function in the cases of leading order(LO) approximation.