QED interference in charge asymmetry near the Z resonance at future electronpositron colliders
Abstract
The measurement of the charge asymmetry A_{FB}(e^{}e^{+}→μ^{}μ^{+}) will play an important role at the highluminosity circular electronpositron collider FCCee considered for construction at CERN. In particular, near the Z resonance, √{s }≃M_{Z}±3.5 GeV , A_{FB} will provide a very precise value of the pure electromagnetic coupling constant α_{QED}(M_{Z}) , which is vitally important for overall tests of the Standard Model. For this purpose, A_{FB} will be measured at the FCCee with an experimental error better than δ A_{FB}≃3 ×1 0^{5} , at least a factor of 100 more precisely than at past LEP experiments! The important question is whether the effect of interference between photon emission in the initial and final state (IFI) can be removed from the A_{FB} data at the same precision level using perturbative QED calculations. A first quantitative study of this problem is presented here, with the help of the KKMC program and a newly developed calculation based on soft photon resummation, matched with NLO and NNLO fixedorder calculations. It is concluded that a factor of 10 improvement with respect to the LEP era is obtained. We also present a clear indication that reducing the uncertainty of charge asymmetry near the Z peak due to IFI down to δ A_{FB}≃3 .1 0^{5}, i.e. the expected experimental precision at FCCee, is feasible.
 Publication:

Physical Review D
 Pub Date:
 July 2019
 DOI:
 10.1103/PhysRevD.100.013002
 arXiv:
 arXiv:1801.08611
 Bibcode:
 2019PhRvD.100a3002J
 Keywords:

 High Energy Physics  Phenomenology
 EPrint:
 51 pages, 46 figures. Version 3 is updated to agree with the final version to appear in Phys. Rev. D. There are minor corrections to some equations