Electroweak and Higgs Measurements Using Tau Final States with the LHCb Detector

Spin correlations for tau lepton decays are included in the Pythia 8 event generation software and the spin correlations for the decays of tau leptons produced from electroweak and Higgs bosons are calculated. Decays of the tau lepton using sophisticated resonance models are included in Pythia 8 for all channels with experimentally observed branching fractions greater than 0.04%. The mass distributions for the decay products of these channels are validated and the technical implementation of these decays is described. A measurement of the inclusive Z to di-tau cross-section using 1.0 inverse fb of data from pp collisions at sqrt(s) = 7 TeV collected with the LHCb detector is presented. Reconstructed final states containing two muons, a muon and an electron, a muon and a charged hadron, or an electron and a charged hadron are selected as candidates. The cross-section for Z bosons with a mass between 60 and 120 GeV decaying into tau leptons with pseudo-rapidities between 2.0 and 4.5 and transverse momenta greater than 20 GeV is measured to be 72.3 +- 3.5 +- 2.9 +- 2.5 pb. The first uncertainty is statistical, the second uncertainty is systematic, and the third is to due the integrated luminosity uncertainty. Limits on the production of neutral Higgs bosons decaying into tau lepton pairs with pseudo-rapidities between 2.0 and 4.5 are set at a 95% confidence level using the same LHCb dataset. A model independent upper limit on the production of neutral Higgs bosons decaying into tau leptons is set and ranges between 8.6 pb for a Higgs boson mass of 90 GeV to 0.7 pb for a Higgs boson mass of 250 GeV. An upper limit on tan-beta in the CP-odd Higgs mass and tan-beta plane is set for the mh-max scenario of the minimal supersymmetric model and varies from 34 for a CP-odd Higgs boson mass of 90 GeV to 70 for a CP-odd Higgs boson mass of 140 GeV.

Limits on neutral Higgs boson production in the forward region in $pp$ collisions at $sqrt{s} = 7$ TeV

Limits on the cross-section times branching fraction for neutral Higgs bosons, produced in $pp$ collisions at $sqrt{s} = 7$ TeV, and decaying to two tau leptons with pseudorapidities between 2.0 and 4.5, are presented. The result is based on a dataset, corresponding to an integrated luminosity of 1.0 $mathrm{fb}^{-1}$, collected with the LHCb detector. Candidates are identified by reconstructing final states with two muons, a muon and an electron, a muon and a hadron, or an electron and a hadron. A model independent upper limit at the 95% confidence level is set on a neutral Higgs boson cross-section times branching fraction. It varies from 8.6 pb for a Higgs boson mass of 90 GeV to 0.7 pb for a Higgs boson mass of 250 GeV, and is compared to the Standard Model expectation. An upper limit on $tanbeta$ in the Minimal Supersymmetric Model is set in the $m_{h^0}^mathrm{max}$ scenario. It ranges from 34 for a CP-odd Higgs boson mass of 90 GeV to 70 for a pseudo-scalar Higgs boson mass of 140 GeV.

$Z to tautau$ and $W to tau u_tau$ Cross-Sections at the LHC

Measurements of the $Z to tautau$ and $W to tau u_tau$ cross-sections at the LHC with data taken at $sqrt{s} = 7$ TeV are reported for the ATLAS, CMS, and LHCb experiments. All results are found to agree with the Standard Model.

Tau Decays in Pythia 8

As of version 8.150 of Pythia, the isotropic decay model of tau-leptons has been replaced with sophisticated tau-lepton decay machinery. The decays and spin correlations for tau-leptons in Pythia 8 are described, including the spin correlation algorithm, the available tau-lepton production processes, the tau-lepton decay models, the user interface, and the implementation.

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

A measurement of the inclusive $Z to tautau$ 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 $Z to tautau$ 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 $sigma_{pp to Z to tautau} = 71.4 pm 3.5 pm 2.8 pm 2.5$ 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 $Z to tautau$ to $Z to mumu$ 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.