Problem ofRine+e−annihilation

Abstract

A careful analysis is presented of the most recent data for $R(e^{+}{e}^{-}\to \mathrm{hadrons})$ using improved theoretical techniques. The analysis is based on a generalized method for smoothing $R$. We show why the hadronic cross section is potentially one of the best tests of quantum chromodynamics. The theoretical complications such as unknown parameters and nonperturbative corrections are discussed, and resulting theoretical uncertainties are estimated. Some previously neglected QED corrections are accounted for. We find that for $\sqrt{s}$ near 7 GeV, the data lie about 15-17% above the theory; the experimental uncertainty is ± 10% (dominated by systematics). For $\sqrt{s}$ near 5 GeV, the difference is only 5-8%. This apparent discrepancy may well be due to systematic problems in the experiment. For completeness we consider the possibility that there is a threshold for new particles at $\sqrt{s}\approx 6$ GeV. We consider new quarks, Higgs bosons, color-sextet quarks, integrally charged and even fractionally charged leptons. While most of these hypotheses are not particularly attractive, some cannot be ruled out.