Observation of Z decays to four leptons with the CMS detector at the LHC
CMS Collaboration (ukupan broj autora: 2191)
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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 fb(-1) at root 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 LT m(4l) LT 100 GeV, where m(4l) is the invariant mass of the four leptons, and m(ll) GT 4 GeV for all pairs of leptons, where m(ll) is the two-lepton invariant mass. The measured branching fraction is B(Z - GT 4(l)) = 4.2(-0.8)(+0.9)(stat.) +/- 0.2(syst.)) x 10(-6) and agrees with the standard model prediction of 4.45 x 10(-6). The measured cross section times branching fracti...on is sigma(pp - GT Z) B (Z - GT 4l) = 112(-20)(+23)(stat.) +/-(+7)(-5)(syst.)(-2)(+3) (lumi.) fb, also consistent with the standard model prediction of 120 fb. The four-lepton mass peak arising from Z - GT 4l decays provides a calibration channel for the Higgs boson search in the H - GT ZZ - GT 4l decay mode.
Source:Journal of High Energy Physics, 2012, 12
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