雙光子交換對電子核子碰撞的貢獻

Abstract

對於核子波形因子的量測，近代的極化實驗所得的結果，和以前非極化實驗所得的結果對比時，雖在低動量交換時能夠一致，但在高動量交換時卻有巨大的不同。為要解決這個迷題，雙光子交換在彈性電子質子碰撞中的效應開始被注重起來。我們透過部份子的模型，計算雙光子交換的貢獻。我們發現，當加入雙光子交換的貢獻後，能很好的解決之前兩種實驗所得結果嚴重衝突的問題。如今我們明白，雙光子交換的效應，在量測核子的波形因子時伴演了很重要的角色。

When measuring the nucleon form factors, recent polarization experiments at the Thomas Jefferson Laboratory (JLab) have confirmed the earlier Rosenbluth measurements from SLAC at small Q2. However, at large Q2, a huge discrepancy appear between them. To solve this puzzle, the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer by using a quark-parton representation of virtual Compton scattering was estimated. And then we thus can relate the two-photon exchange amplitude to the generalized parton distributions which also enter in other wide angle scattering processes. We find that the interference of one- and two-photon exchange contribution is able to substantially resolve the difference between electric form factor measurements from Rosenbluth and polarization transfer experiments. Now we know higher-order QED effects can play an important role in precision measurements of nucleon elastic form factors in electron scattering.