The Study On The Polarization Effects Of Hadrons In Electron-Positron Annihilation

Understanding the internal structure of hadrons and the interaction of quarks within hadrons has always been the focus in particle physics.In recent decades,the lepton-nucleon elastic and inelastic scattering,the Drell-Yan process,as well as the e+e-annihilation processes have been studied experimentally and theoretically,in order to explore the information about the PDF,EMFFs as well as the parton fragmentation functions of hadrons.Electron-positron annihilation process is an important tools to study the internal structure of hadrons and their internal interactions,which is mainly reflected in the following two aspects.Firstly,the study on the semi-inclusive production in the electron-positron annihilation:e+e-?h1h2X,one can obtain the parton fragmentation functions of hadrons.Particularly,the azimuthal asymmetry of the final-state hadron pair in this process has been measured,which provides the opportunity for extracting the polarized fragmentation functions,such as the Collins function.Besides the Collins effect,the contribution from the perturbative quantum chromodynamics(pQCD)cannot be ignored.Thus,it is necessary to perform more detailed quantitative study on this process from the view point of pQCD.Secondly,the study on the exclusive production of hadron pair can help us to understand the electromagnetic form factors of hadrons,particularly the charge and magnetic moment inside the hadrons.In recent years,the Born cross section and the ratio |Ge/Gm| of the exclusive production of baryons(such as the ?,?,and ?c)have been measured,and the strong enhancement effects near threshold are observed.These also need to be interpreted from theoretical studies.Based on the above two points,two important aspects of electron-positron annihilation will be studied in this thesis.Firstly,the contribution of Collins effect as well as the acoplanarity to the azimuthal asymmetry due to the digluon radiation correction effect will be taken into accout to study the transverse momentum dependent cos 2? azimuthal asymmetry in e+e-??+?-X process.Secondly,the data obtained from experiment to analyse the EMFFs of the ?c hyperon in e+e-??c+?c-process is applied to analyze the electromagnetic form factor of the ?c.The main content of the thesis are organized as follows:1.The transverse momentum dependent cos 2? azimuthal asymmetry in e+e-??+?-X process is studied.Particularly,the contribution of the acoplanarity to the azimuthal asymmetry due to the digluon radiation correction effect is taken into account.As a comparison,the contribution from Collins effect within the transverse momentum dependence factorization is also considered.We perform the calculation at(?)=10.58 GeV,accessible at Belle and BaBar Collaborations;and we choose in the Gottfried-Jackson frame,which is more convenient in comparing theoretical calculations with current experimental measurement.In the calculation we apply a recent parametrization on the Collins function.We adopt the Drell-Yan parametrization for the mean value of cos We find that in the qT?Q region,the asymmetry is dominated by the Collins effect,while the acoplanarity effect dominates in the large qT region(qT/Q>0.5)and is negligible in the small qT region.In the intermediate region the two contributions are comparable.II.We use two models to analyse the electromagnetic form factors(EMFFs)of the ?c hyperon in the time-like reaction e+e-??c+?c-.In the QCD inspired parameterization,we extend the model with two parameters of nucleon EMFFs to the case of ?c hyperon,and obtain the parameters of the model by fitting the experimental data of the Born cross sections from the Belle and BESIII Collaborations.Using the fitted parameter values,we calculated the Born cross section and compared it with the experimental data.The result shows that except the enhancement effect near the ?c+?c-threshold region,our model can describe the experimental data well.We also calculated the double polarized observables.In the VMD model,we included the contributions from the vector mesons ?(782),?(1420),?(1650),?(1020),?(1680)and ?(2170),as well as the charmed mesons ?(1S),?(2S),?(3770),?(4040),?(4160)and?(4415),which are related to cc quark.We perform the combined fit to the time-like Born cross section and the electromagnetic form factor ratio |GE/GM| of the ?c hyperon from the Belle and BES? Collaborations to obtain the model parameters.Our results show that the vector meson dominance model can simultaneously describe these observables.With the fitted parameters,we predict the relative phase ??.Moreover,we also predict the single and double polarization observables in e+e-??c+?c-reactions,which will be experimentally accessible in the polarized process.After analytic continuation of the electromagnetic form factors,we extend the time-like form factors to space-like region and discuss some properties of the space-like form factors of ?c hyperon.