Research On Parton Distributions And Structure Functions In The Nucleon

In1911, Rutherford developed the nuclear model of atom from a series of a-scattering experiments. Since then, physicists always use scattering processes to in-vestigate the structure of matter. In1969, the SLAC-MIT experiments showed that nu-cleon is made of point-like particles called partons. Then Feynman introduced parton distribution functions (PDFs) to describe the properties of the nucleon in high-energy scattering processes. From them on, many famous theoretical and experimental groups such as GJR, MSTW, CTEQ etc., have been engaged in research of the PDFs, and got their own PDFs. However, marked differences in gluon and sea quark distributions from these three groups show that the gluon and the sea quark distributions have not been well confirmed yet.DGLAP equations are the standard QCD dynamical equations which describe the Q2dependence of parton distributions. According to DGLAP equations, the gluon density will become so large at very small x region that the unitarity of cross section will be violated. In view of this fact, we shall introduce higher twist effects (shadowing and anti-shadowing effects) to DGLAP equations. Nowadays, GLR-MQ and ZRS evolution equations are the well-known nonlinear equations considering higher twist effects. In this article, we mainly use the ZRS equations to discuss higher twist effects.In the early1990s, the experiments conducted by New Muon Collaboration at CERN first indicated a marked asymmetry between up and down sea quarks. In the frame of perturbation theory, the asymmetry of the up and down sea quarks in nucleon will not exceed1%. People proposed many explanations, but still have not found a generally acceptable answer to it. In this article, we also do some research on it.In this thesis, we mainly work on following points.1. We compare the parton distributions at leading order (LO) coming from GJR, MST-W, and CTEQ parton sets detailly, and discover marked differences exist in their gluon and sea quark distributions at small x region. We conclude that more precise data at small x region are needed to constrain the gluon and sea quark distributions.2. We analysis the influence of higher twist effects, i.e., shadowing effects and anti-shadowing effects, on parton distributions.3. We present a detailed analysis of how the proton’s momentum is shared among various parton flavors, and find that the difference in momentum carried by various partons is obvious for different parton sets. Also, we use different parton sets includ-ing twist-4parton distributions to calculate electromagnetic structure function F2P and longitudinal structure function FL. All these parton sets fit the data well within the uncertainty range to some extent.4. The research into light quark asymmetry is full of interest to many people. After calculating twist-4parton distributions, we find that HT-ZRS is more reasonable than GJR08LO and GJR08NLO when comparing with the measurement of d/u.