Z boson pair production in e+e- collisions at sqrt(s) = 183 and 189 GeV

TL;DR

This paper reports measurements of Z boson pair production at energies near 183 and 189 GeV in e+e- collisions, confirming Standard Model predictions and setting limits on anomalous couplings.

Contribution

First precise measurement of Z pair production cross sections at these energies, including separation of decay channels and limits on anomalous couplings.

Findings

Measured cross section at 189 GeV: 0.80 pb with uncertainties.

Upper limit at 183 GeV: 0.55 pb (95% CL).

Set limits on anomalous ZZgamma and ZZZ couplings.

Abstract

A study of Z boson pair production in e+e- annihilation at center-of-mass energies near 183 GeV and 189 GeV is reported. Final states containing only leptons, (l+l-l+l- and l+l-nu nubar), quark and lepton pairs, (q qbar l+l-, q qbar nu nubar) and the all-hadronic final state (q qbar q qbar) are considered. In all states with at least one Z boson decaying hadronically, q qbar and b bbar final states are considered separately using lifetime and event-shape tags, thereby improving the cross-section measurement. At sqrt(s) = 189 GeV the Z-pair cross section was measured to be 0.80 (+0.14-0.13, stat.) (+0.06-0.05, syst.) pb, consistent with the Standard Model prediction. At sqrt(s) = 183 GeV the 95% C.L. upper limit is 0.55 pb. Limits on anomalous ZZgamma and ZZZ couplings are derived.