Abstract

This Letter reports on a search for narrow high-mass resonances decaying into dilepton final states. The data were recorded by the ATLAS experiment in pp collisions at sqrt(s) = 7 TeV at the LHC and correspond to a total integrated luminosity of 1.08/fb (1.21/fb) in the ee (mumu) channel. No statistically significant excess above the Standard Model expectation is observed and upper limits are set at the 95% C.L. on the cross section times branching ratio of Z' resonances and Randall-Sundrum gravitons decaying into dileptons as a function of the resonance mass. A lower mass limit of 1.83 TeV on the Sequential Standard Model Z' boson is set. A Randall-Sundrum graviton with coupling k/M_Pl=0.1 is excluded at 95% C.L. for masses below 1.63 TeV.

Highlights

  • DimuonsNormalization parton distribution functions (PDFs)= S QCD K factor Weak K factor Trigger/reconstruction Total5% Not applicable Not applicable Not applicable Negligible 5%week ending 30 DECEMBER 2011 diboson and W þ jets backgrounds from Monte Carlo simulation are scaled according to their respective cross sections and added to the QCD background

  • The scaling factor is within 1% of unity

  • The advantage of this approach is that the uncertainty on the luminosity

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Summary

85 Æ 5 150 Æ 26 191 Æ 75 6128 Æ 200

The Z= Ã cross section is calculated at next-to-next-toleading order (NNLO) using PHOZPR [36] with MSTW2008 PDFs [37]. The ratio of this cross section to the leadingorder cross section is used to determine a mass-dependent QCD K factor which is applied to the results of the leadingorder simulations. In the reversed electron identification technique, data with both electron candidates failing some identification criteria (chosen not to affect kinematic distributions) are used to determine the QCD background distribution versus mee This method is used for the central estimate and the others which bracket it, to assign a systematic uncertainty.

Background
Z0 models
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