Observation of Z decays to four leptons with the CMS detector at the LHC

Abstract : The first observation of the Z boson decaying to four leptons in proton-proton collisions is presented. The analyzed data set corresponds to an integrated luminosity of 5.02 inverse femtobarns at sqrt(s) = 7 TeV collected by the CMS detector at the Large Hadron Collider. A pronounced resonance peak, with a statistical significance of 9.7 sigma, is observed in the distribution of the invariant mass of four leptons (electrons and/or muons) with mass and width consistent with expectations for Z boson decays. The branching fraction and cross section reported here are defined by phase space restrictions on the leptons, namely, 80 < m[4l] < 100 GeV, where m[4l] is the invariant mass of the four leptons, and m[ll] > 4 GeV for all pairs of leptons, where m[ll] is the two-lepton invariant mass. The measured branching fraction is B(Z to 4l) = (4.2/+0.9/-0.8 (stat.) +/- 0.2 (syst.)) 10E-6 and agrees with the standard model prediction of 4.45 10E-6. The measured cross section times branching fraction is sigma(pp to Z) B(Z to 4 l) = 112+23/-20 (stat.) +7/-5 (syst.) +3/-2 (lumi.) fb, also consistent with the standard model prediction of 120 fb. The four-lepton mass peak arising from Z to 4 l decays provides a calibration channel for the Higgs boson search in the H to ZZ to 4 l decay mode.
Document type :
Journal articles
Journal of High Energy Physics, Springer, 2012, 12, pp.034. <10.1007/JHEP12(2012)034>

http://hal.in2p3.fr/in2p3-00742132
Contributor : Sylvie Flores <>
Submitted on : Tuesday, October 16, 2012 - 8:04:39 AM
Last modification on : Thursday, April 23, 2015 - 2:16:18 PM

Citation

S. Chatrchyan, M. Besançon, S. Choudhury, M. Dejardin, D. Denegri, et al.. Observation of Z decays to four leptons with the CMS detector at the LHC. Journal of High Energy Physics, Springer, 2012, 12, pp.034. <10.1007/JHEP12(2012)034>. <in2p3-00742132>

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