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A Study of Bhabha Scattering at the Z Resonance


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


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: AFB = 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/gV, -ℓ/gA = -0.5010 ± 0.0006,
  • the effective weak mixing angle: sin² θ̅ w = 0.2304 ± 0.0009,
  • the mass of the top quark: Mt = 189+12-13 ± 17 GeV,
  • the mass of the Higgs boson: MH = 91+230-81 GeV; MH < 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.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Physics
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Newman, Harvey B.
Thesis Committee:
  • Newman, Harvey B. (chair)
  • Filippone, Bradley W.
  • Frautschi, Steven C.
  • Porter, Frank C.
Defense Date:12 September 1997
Record Number:CaltechTHESIS:05172021-190748275
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14151
Deposited By: Kathy Johnson
Deposited On:17 May 2021 19:38
Last Modified:17 May 2021 19:39

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