A Study of Bhabha Scattering at the Z Resonance

Citation

Lu, Wenwen (1998) A Study of Bhabha Scattering at the Z Resonance. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/kyrx-3v72. https://resolver.caltech.edu/CaltechTHESIS:05172021-190748275

Abstract

In this thesis, I present a study on Bhabha scattering at the Z resonance using the 13 detector at 1EP. I have measured the cross section and forward-backward asymmetry measurement for the process e⁺e⁻ → e⁺e⁻(nγ) in the large angle region ( 44° < θe⁺e⁻ < 136°). The data used was collected during 1993 (3 energy points at the Z resonance) and 1994 (Peak point only), corresponding to a total of 66,000 e⁺e⁻ pairs. The results of my measurement are combined with those from other 13 measurements of Z production and decays to provide a precision test of the Standard Model. Electroweak parameters are determined with unprecedented precision.

The main results in this thesis are as follows:

• the cross section of e⁺e⁻ → e⁺e⁻(nγ) process at the Z peak: σ = 1.072 ± 0.005 (stat.) ± 0.002 (sys.) nb,
• the forward-backward asymmetry of e⁺e⁻ → e⁺e⁻(nγ) process at the peak: A_FB = 0.122 ± 0.006 (stat.) ± 0.003 (sys.),
• the mass of the Z boson: Mz = 91188.3 ± 2.9 MeV,
• the total width of the Z boson: Γz = 2499.8 ± 4.3 MeV,
• the partial decay width of the Z boson into electrons: Γe = 83.99 ± 0.26 MeV,
• the Z electroweak coupling constants to fermions: -ℓ/g_V, -ℓ/g_A = -0.5010 ± 0.0006,
• the effective weak mixing angle: sin² θ̅ _w = 0.2304 ± 0.0009,
• the mass of the top quark: M_t = 189⁺¹²_-13 ± 17 GeV,
• the mass of the Higgs boson: M_H = 91⁺²³⁰_-81 GeV; M_H < 645 GeV 95% CL.

All the results from different measurements yield consistent results. No indication of a deviation from the Standard Model has been observed.

Thesis Files