SLAC-PUB-6169 July 1993 (T/E) FIRST MEASUREMENT OF THE LEFT-RIGHT ASYMMETRY IN Z-BOSON PRODUCTION THE SLD COLLABOFtATION’ represented by ROBERT ELIA Stanford Linear Accelerator Center, Stanford University, Stanford, CA 94309, USA We review the first measurement of the left-right cross section asymmetry (ALR) in Z-boson production observed at the SLAC Linear Collider. In 1992 the SLD detector recorded 10,224 Z events produced by the collision of longitudinally polarized electrons with an unpolarized positron beam at a center-of-mass energy of 91.55 GeV. The average $ectron beam polarization during the run was (22.4 f O.S)%. We measure ALR to be 0.100 f 0.044 (stat.) f 0.004 (syst.), which determines the effective weak mixing angle to be sin’@ = 0.2378 f 0.0056 (stat.) f 0.0005 (syst.). . .-, -_ _ 1. Introduction In this article we review the first measurement’ of the left-right cross section asym- metry (ALR) in Z-boson production by efe- collisions. The left-right asymmetry is defined as2 &R 5 CL -CR uL+flR ' (1) where UL and UR are the e+e- production cross sections for Z bosons at the Z pole with left-handed and right-handed electrons. The tree-level Standard Model calculation of this quantity yields ALR= 2we 2[1- 4sin2Bg] - = 1+ [l - 4si&?$]2 ’ u,2+ u: (2) where ue and ae are the vector and axial-vector couplings of the electron current to the Z and sin20$ E (1 - ue/ae)/4 is the effective electroweak mixing parameter.3 *Work supported by Department of Energy contract DE-AC03-76SF00515. Submitted to Modern Physics Letters A