A study of the $Z$ production cross-section in $pp$ collisions at $\sqrt{s}=7$ TeV using tau final states

Abstract

A measurement of the inclusive $Z\to \ddot{I}„\ddot{I}„$ cross-section in $pp$ collisions at $\sqrt{s}=7$ TeV is presented based on a dataset of 1.0 fb${}^{-1}$ collected by the LHCb detector. Candidates for $Z\to \ddot{I}„\ddot{I}„$ decays are identified through reconstructed final states with two muons, a muon and an electron, a muon and a hadron, or an electron and a hadron. The production cross-section for $Z$ bosons, with invariant mass between 60 and 120 GeV/$c^2$, which decay to $\ddot{I}„$ leptons with transverse momenta greater than 20 GeV/$c$ and pseudorapidities between 2.0 and 4.5, is measured to be $\ddot{I}{ƒ}_{pp\to Z\to \ddot{I}„\ddot{I}„}=71.4\pm 3.5\pm 2.8\pm 2.5$ pb; the first uncertainty is statistical, the second uncertainty is systematic, and the third is due to the uncertainty on the integrated luminosity. The ratio of the cross-sections for $Z\to \ddot{I}„\ddot{I}„$ to $Z\to \hat{I}¼\hat{I}¼$ is determined to be $0.93\pm 0.09$, where the uncertainty is the combination of statistical, systematic, and luminosity uncertainties of the two measurements.

15 pages, 2 figures, 2 tables