The ZFITTER project
- PDF / 481,814 Bytes
- 21 Pages / 612 x 792 pts (letter) Page_size
- 30 Downloads / 175 Views
he ZFITTER Project1 A. Akhundova, A. B. Arbuzovb, c, S. Riemannd, and T. Riemannd a
b
Institute of Physics, Azerbaijan National Academy of Sciences, AZ1143 Baku, Azerbaijan Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research JINR, Dubna, 141980 Russia email: [email protected] c Department of Higher Mathematics, Dubna University, Dubna, 141980 Russia d 15711 Königs Wusterhausen, Germany Abstract—The ZFITTER project is aimed at the computation of highprecision theoretical predictions for various observables in highenergy electronpositron annihilation and other processes. The stages of the project development are described. Accent is made on applications to the analysis of LEP data. The present status of the project and perspectives are given as well. DOI: 10.1134/S1063779614030022
1
1. INTRODUCTION
To name a date of the ZFITTER project beginning is difficult. The first papers on electroweak loop calcu lations by D. Bardin and O. Fedorenko date back to 1976, but in another context. In September 1983 the DubnaZeuthen group started activity, due to the begin of the fouryear long stay of S. Riemann and T. Riemann at JINR, Dubna. The name ZFITTER was invented in 1989 and replaced the former name ZBIZON for the software project. Finally, we chose the year 1985, when the article “Hunting the hidden standard Higgs” was published [1]. With this study, we began to take into account a finite, nonzero top quark mass mt in the radiative corrections, in the context of e+e– annihilation. To our knowledge, the paper con tains the first plot confronting two LEP observables— weak mixing angle sin2 θW and Z boson mass MZ—with their dependence on the unknown top quark mass mt and the also unknown Higgs boson mass MH in the Standard Model [2–5]. We reproduce the plot here in Fig. 1, left. Both top quark and Higgs boson were not yet discovered at that time, and the actual experimen tal values for MZ and sin2 θW had too large errors to be included into the plot [6]: MZ = 92.9 ± 16 GeV and sin2 θW = 0.23 ± 0.015. The numbers in the figure are based on the oneloop Standard Model prediction for Δr, the weak correction to Gμ, deserving few lines of Fortran code. We remark as a curiosity that from 1985 to 2011, the article was quoted only once (by authors outside our group). The FEP/SFC collaborations made exciting mea surements of the Z boson resonance and of its mass,
width, weak mixing angle etc., with an unexpected final accuracy [8]: MZ = 91.1876 ± 0.0021 GeV, (1.1) ΓZ = 2.4952 ± 0.0023 GeV,
(1.2)
sin2 θweak = 0.22296 ± 0.00028,
(1.3)
eff
sin2 θ lept = 0.23146 ± 0.00012, MS
sin2 θ Z
= 0.23116 ± 0.00012,
Nν = 2.989 ± 0.007.
(1.4) (1.5) (1.6)
For the Z boson mass, this implies ΔMZ/MZ ≈ 10–5. For the various definitions of the weak mixing angle see section 10 of [8]. And Nν is the number of light neutrinos. Figure 2 shows the rise of accuracy for MZ due to LEP. Since the begin of the nineteennineties, a true scientific standard is the so called blueband plot of 2
the LEPEWWG ,
Data Loading...
