摘要
BESⅢ合作组最近开始双光子物理研究,主要源于强子light-by-light散射对缪子反常磁矩的贡献有很大不确定性,电磁跃迁形状因子作为实验输入是改善计算精度的需要。在BESⅢ探测器上获得的质心能量3.77 Ge V到4.6Ge V的数据使得我们能够测量轻赝标量介子的跃迁形状因子。在动量转移低于2(Ge V/c)2时单标记技术测量的结果达到前所未有的精确,该区域对于αμ的计算十分重要,并且也首次开始了π介子跃迁形状因子的双标记测量。这是π~0跃迁形状因子模型无关参数化研究的第一步。另外,多介子末态测量也在进行中.
The BES Ⅲ Collaboration has recently embarked on a two-photon physics program. Its main motivation is given by the large uncertainty of the contribution of hadronic light-by-light scattering to the anomalous magnetic moment of the muon αμ,and the need of electromagnetic transition form factors( TFF) as experimental input to improve the calculations. Data acquired with the BESⅢ detector at center-of-mass energies from 3. 77 to 4. 6 Ge V allow for the determination of TFFs of light pseudoscalar mesons. The measurements are performed with a single-tag technique and result in unprecedented accuracy at momentum transfers below 2 Ge V2,the region of highest importance for the calculations ofαμ. Employing the same approach,the first double-tagged measurement of the pion transition form factor has been started. It is the first step towards a model independent parameterization of the TFF of the π0.Additionally,measurements of multi-meson final states have been engaged.
基金
Supported by the German Research Foundation DFG under Contract(CRC-1044)
