2—5GeV能区的R值测量

作为粒子物理中的一个基本参数，R值在发展粒子物理理论及检验标准模型（SM）方面起着重要的作用。在低能区精确测量R值的实验努力对于弱电精确物理是至关重要的。R值测量不仅对α(M^2Z)的计算及αu的解释是重要的，而且对强子产生机制和经e^ e^-湮没产生的粲偶素本身的理解也是必须的。文章简要报道了在北京正负电子对撞机（BEPC）和升级的北京谱仪（BES－Ⅱ）上完成的R扫描及其物理结果。

MEASUREMENT OF R AT ENERGIES BETWEEN 2-5GeV

Being one of the fundamental parameters in partic le physics,the R value plays an important role in the development of the the ory of particle physics and in testing the Standard Model(SM).Experimental effor ts to precisely measure R value at low energies are crucial for the electrow eak precision physics.The R measurements are not only important for the eval uation of α(M2Z) and for the interpretation of aμ,but also neces sary for the understanding of the hadron production mechanism and the charmonium itself produced via e+e- annihilation.This article briefly reports the R scan done with the upgraded Beijing Spectrometer(BES-Ⅱ) at the Beijing Electr on Positron Collider(BEPC) and its physics results.