Two-photon Exchange Effect In E~+e~-→π~+π~- At Small(?)

The electromagnetic form factors(FFs)of hadrons are important non-perturbative physical quantities which reflect the internal structure of hadrons.The precise measurements of the electromagnetic form factors have been a hot topic for decades.Experimentally,one can extract the FFs of proton and pion via the ep scattering,e+e-→pp,eπscattering,and e+e-→π+π-.In 2000 an experiment by JLab showed that the results by the traditional Rosenbluth method and the new polarized method give very different results for the ratio of proton form factors.In 2003 the theoretical studies showed that this difference can be partly explained by the two-photon-exchange(TPE)effect.Since then,the study of the TPE effects has become an important topic.Based on these facts,in this thesis we study the TPE effect in e+e-→π+π-.Specifically,we use the hadronic model to calculate the TPE corrections to the amplitude and the unpolarized cross section when(?)is small.The numerical results for the angle dependence of the TPE corrections are presented.The sensibility of the results on the parameter is also given.The final results show that the TPE effect gives nonnegligible contribution to the asymmetry of the unpolarized cross section.We find the contribution reaches about 4%when(?)GeV.We expect that our prediction can be compared with the coming experimental results,and these comparison can check and improve our understanding on the TPE effect...