分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-10
摘要: A detailed theoretical derivation of the cross sections of e+e− → e+e− and e+e− → µ+µ− around the J/ψ resonance is reported. The resonance and interference parts of the cross sections, related to J/ψ resonance parameters, are calculated. Higher-order corrections for vacuum polarization and initial-state radiation are consid-ered. An arbitrary upper limit of radiative correction integration is involved. Full and simplified versions of analytic formulae are given with precision at the level of 0.1% and 0.2%, respectively. Moreover, the results obtained in the paper can be applied to the case of the ψ(3686) resonance.
分类: 物理学 >> 核物理学 提交时间: 2016-09-06
摘要: To measure the R value in an energy scan experiment with $\ee$ collisions, precise calculation of initial state radiation is required in event generators. We present an event generator for this consideration, which incorporates initial state radiation effects up to the second order accuracy, and the radiative correction factor is calculated using the totally hadronic Born cross section. The measured exclusive processes are generated according to their cross sections, while the unknown processes are generated using the LUND Area Law model, and its parameters are tuned with data collected at s√=3.65 GeV. The optimized values are validated with data in the range s√=2.2324∼3.671 GeV. These optimized parameters are universally valid for event generation below the DD¯ threshold.