Z cross-section measurement at √s=7 TeV using the channel Z→ττ

The preprint is available here.

J. High Energy Phys. 01 (2013) 111

arXiv:1210.6289

More detailed information: ANA note 2012-056

Abstract

A measurement of the inclusive $Z \to \tau\tau$ 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 $Z \to \tau\tau$ 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 $\tau$ leptons with transverse momenta greater than 20 GeV$/c$ and pseudorapidities between 2.0 and 4.5, is measured to be $\sigma_{pp \to Z \to \tau\tau} = 71.4 \pm 3.5 \pm 2.8 \pm 2.5$ 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 $Z \to \tau\tau$ to $Z \to \mu\mu$ 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.

Figures

Caption Figure
(Fig.1a.eps, Fig.1a.pdf, Fig.1a.png) Invariant mass distributions for the \begin{displaymath}\tau_\mu\tau_\mu\end{displaymath}, $\tau_\mu\tau_e$, $\tau_e\tau_\mu$, $\tau_\mu\tau_h$, and $\tau_e\tau_h$ candidates with the excluded mass range indicated for $\tau_\mu\tau_\mu$. The $Z \to \tau\tau$ simulation (solid red) is normalised to the number of signal events. The QCD (horizontal green), electroweak (vertical blue), and $Z$ (solid cyan) backgrounds are estimated from data. The $t\bar{t}$ (vertical orange) and $WW$ (horizontal magenta) backgrounds are estimated from simulation and generally not visible. Fig.1a.png
(Fig.1b.eps, Fig.1b.pdf, Fig.1b.png) Invariant mass distributions for the $\tau_\mu\tau_\mu$, \begin{displaymath}\tau_\mu\tau_e\end{displaymath}, $\tau_e\tau_\mu$, $\tau_\mu\tau_h$, and $\tau_e\tau_h$ candidates with the excluded mass range indicated for $\tau_\mu\tau_\mu$. The $Z \to \tau\tau$ simulation (solid red) is normalised to the number of signal events. The QCD (horizontal green), electroweak (vertical blue), and $Z$ (solid cyan) backgrounds are estimated from data. The $t\bar{t}$ (vertical orange) and $WW$ (horizontal magenta) backgrounds are estimated from simulation and generally not visible. Fig.1b.png
(Fig.1c.eps, Fig.1c.pdf, Fig.1c.png) Invariant mass distributions for the $\tau_\mu\tau_\mu$, $\tau_\mu\tau_e$, \begin{displaymath}\tau_e\tau_\mu\end{displaymath}, $\tau_\mu\tau_h$, and $\tau_e\tau_h$ candidates with the excluded mass range indicated for $\tau_\mu\tau_\mu$. The $Z \to \tau\tau$ simulation (solid red) is normalised to the number of signal events. The QCD (horizontal green), electroweak (vertical blue), and $Z$ (solid cyan) backgrounds are estimated from data. The $t\bar{t}$ (vertical orange) and $WW$ (horizontal magenta) backgrounds are estimated from simulation and generally not visible. Fig.1c.png
(Fig.1d.eps, Fig.1d.pdf, Fig.1d.png) Invariant mass distributions for the $\tau_\mu\tau_\mu$, $\tau_\mu\tau_e$, $\tau_e\tau_\mu$, \begin{displaymath}\tau_\mu\tau_h\end{displaymath}, and $\tau_e\tau_h$ candidates with the excluded mass range indicated for $\tau_\mu\tau_\mu$. The $Z \to \tau\tau$ simulation (solid red) is normalised to the number of signal events. The QCD (horizontal green), electroweak (vertical blue), and $Z$ (solid cyan) backgrounds are estimated from data. The $t\bar{t}$ (vertical orange) and $WW$ (horizontal magenta) backgrounds are estimated from simulation and generally not visible. Fig.1d.png
(Fig.1e.eps, Fig.1e.pdf, Fig.1e.png) Invariant mass distributions for the $\tau_\mu\tau_\mu$, $\tau_\mu\tau_e$, $\tau_e\tau_\mu$, $\tau_\mu\tau_h$, and \begin{displaymath}\tau_e\tau_h\end{displaymath} candidates with the excluded mass range indicated for $\tau_\mu\tau_\mu$. The $Z \to \tau\tau$ simulation (solid red) is normalised to the number of signal events. The QCD (horizontal green), electroweak (vertical blue), and $Z$ (solid cyan) backgrounds are estimated from data. The $t\bar{t}$ (vertical orange) and $WW$ (horizontal magenta) backgrounds are estimated from simulation and generally not visible. Fig.1e.png
(Fig.2.eps, Fig.2.pdf, Fig.2.png) Measured cross-sections for the $Z$ decaying to the final states $\tau_\mu\tau_\mu$, $\tau_\mu\tau_e$, $\tau_e\tau_\mu$, $\tau_\mu\tau_h$, and $\tau_e\tau_h$ (open points) compared with theory (yellow band) and the combined $Z \to \tau\tau$ and LHCB $Z \to \mu\mu$ measurements (closed points) where $p_\mathrm{T}$ and $\eta$ are the transverse momentum and pseudorapidity of the leptons, and $M$ is the di-lepton invariant mass. The inner error bars represent combined statistical, systematic, and luminosity uncertainties. The central theory value is given by the light yellow line while the associated uncertainty by the orange band. Fig.2.png
Topic attachments
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PDFpdf Fig.1a.pdf r1 manage 69.7 K 2012-10-30 - 14:23 PhilipIlten  
PNGpng Fig.1a.png r1 manage 76.4 K 2012-10-30 - 14:23 PhilipIlten  
Unknown file formateps Fig.1b.eps r1 manage 203.4 K 2012-10-30 - 14:24 PhilipIlten  
PDFpdf Fig.1b.pdf r1 manage 70.0 K 2012-10-30 - 14:24 PhilipIlten  
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PNGpng Fig.1c.png r1 manage 52.6 K 2012-10-30 - 14:24 PhilipIlten  
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PDFpdf Fig.1d.pdf r1 manage 67.4 K 2012-10-30 - 14:25 PhilipIlten  
PNGpng Fig.1d.png r1 manage 58.6 K 2012-10-30 - 14:25 PhilipIlten  
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PDFpdf Fig.1e.pdf r1 manage 67.6 K 2012-10-30 - 14:25 PhilipIlten  
PNGpng Fig.1e.png r1 manage 54.7 K 2012-10-30 - 14:25 PhilipIlten  
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