Search for single top production using multivariate analyses at CDF

TL;DR

This paper reports on searches for single-top-quark production at CDF using advanced multivariate techniques, setting upper limits and measuring cross sections, and also searches for non-standard model W' boson production.

Contribution

It introduces and compares three multivariate analysis methods for detecting single-top production and sets new limits on W' boson mass.

Findings

Sensitivity ranges from 2.1 to 2.6 sigma for standard model production

Upper limits on cross sections are established at 2.6 pb and 3.7 pb

No evidence found for non-standard W' boson production

Abstract

This article reports on recent searches for single-top-quark production by the CDF collaboration at the Tevatron using a data set that corresponds to an integrated luminosity of 955 fb^-1. Three different analyses techniques are employed, one using likelihood discriminants, one neural networks and one matrix elements. The sensitivity to single-top production at the rate predicted by the standard model ranges from 2.1 to 2.6 sigma. While the first two analyses observe a deficit of single-top like events compared to the expectation, the matrix element method observes an excess corresponding to a background fluctuation of 2.3 sigma. The null results of the likelihood and neural network analyses translate in upper limits on the cross section of 2.6 pb for the t-channel production mode and 3.7 pb for the s-channel mode at the 95% C.L. The matrix element result corresponds to a measurement of 2.7^{+1.5}_{-1.3} pb for the combined t- and s-channel single-top cross section. In addition, CDF has searched for non-standard model production of single-top-quarks via the s-channel exchange of a heavy W' boson. No signal of this process is found resulting in lower mass limits of 760 GeV/c^2 in case the mass of the right-handed neutrino is smaller than the mass of the right-handed W' or 790 GeV/c^2 in the opposite case.