We present a measurement of the left-right cross-section asymmetry (A LR ) for Z boson production by e + e − collisions. The measurement includes the final data taken with the SLD detector at the SLAC Linear Collider (SLC) during the period 1996-1998. Using a sample of 383,487 Z decays collected during the 1996-1998 runs we measure the pole-value of the asymmetry, A 0 LR , to be 0.15056±0.00239 which is equivalent to an effective weak mixing angle of sin 2 θ eff W = 0.23107±0.00030. Our result for the complete 1992-1998 dataset comprising 537 thousand Z decays is sin 2 θ eff W = 0.23097 ± 0.00027. The SLD Collaboration has performed a series of increasingly precise measurements of the left-right cross-section asymmetry in the production of Z bosons by e + e − collisions [1][2][3]. Submitted to Physical Review LettersIn this letter, we present a measurement based upon data recorded during the 1996 and 1997-98 runs of the SLAC Linear Collider (SLC), which represents about three quarters of our total sample and leads to improved statistical precision and reduced systematic uncertainty.The overall average given at the end of this Letter is based upon all the data from the completed SLD experimental program [4].The left-right asymmetry is defined as, where σ L and σ R are the e + e − production cross sections for Z bosons at the Z-pole energy with left-handed and right-handed electrons, respectively. The Standard Model predicts that this quantity depends upon the effective vector (v e ) and axial-vector (a e ) couplings of the Z boson to the electron current,where the effective electroweak mixing parameter is defined [5] as sin 2 θ eff W ≡ (1 − v e /a e )/4. 3The quantity A 0 LR is a sensitive function of sin 2 θ eff W and depends upon virtual electroweak radiative corrections including those which involve the Higgs boson and those arising from new phenomena outside of the scope of the Standard Model (SM). Presently, the most stringent upper bounds on the SM Higgs mass are provided by measurements of sin 2 θ eff W . We measured the left-right asymmetry by counting hadronic and (with low efficiency) τ + τ − final states produced in e + e − collisions near the Z-pole energy for each of the two longitudinal polarization states of the electron beam. The asymmetry formed from these rates, A LR , was then corrected for residual effects arising from pure photon exchange and Z-photon interference to extract A 0 LR . The measurement required knowledge of the absolute beam polarization, but did not require knowledge of the absolute luminosity, detector acceptance, or efficiency [6].The operation of the SLC with a polarized electron beam has been described previously [7]. The maximum luminosity of the collider was approximately 3×10 30 cm −2 sec −1 , and the longitudinal electron polarization at the e + e − collision point was typically ∼75%. Beginning in 1996, two additional detectors were operated in order to assist in the calibration of the primary spectrometer-based polarimeter. Both devices detected Comptonscattere...

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