S-Matrix Approach to the $Z$ Line Shape

Abstract

We analyze the $Z$ line shape assuming the existence of an analytic, unitary S-matrix. As an example, from hadron production at LEP we determine $M_Z=91.134\pm 0.020\pm 0.020(\mathrm{LEP})$ GeV, ${\Gamma }_Z=2.506\pm 0.018$ GeV. This is in accordance with earlier results after performing a shift of the $Z$ mass value of about $\frac{1}{2}{\Gamma }_Z^2/M_Z=34$ MeV. The cross section and related observables may be described by a small number of additional degrees of freedom without relying on a specific field-theoretic model.

Comments: 9 pages, LaTex, 1 table, a uuencoded file containing the latex file is available at ftp://ftp.ifh.de/pub/preprint/desy91-111.uu Note: paper published in Phys. Lett. B273 (1991) 513