In:
Journal of High Energy Physics, Springer Science and Business Media LLC, Vol. 2012, No. 12 ( 2012-12)
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 fb −1 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 σ , 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 $ \mathcal{B}\left( {Z\to 4\ell } \right)=\left( {4.2_{-0.8}^{+0.9}\left( {\mathrm{stat}.} \right)\pm 0.2\left( {\mathrm{syst}.} \right)} \right)\times {10^{-6 }} $ and agrees with the standard model prediction of 4.45 × 10 −6 . The measured cross section times branching fraction is $ \sigma \left( {\mathrm{pp}\to \mathrm{Z}} \right)\mathcal{B}\left( {\mathrm{Z}\to 4\ell } \right)=112_{-20}^{+23}\left( {\mathrm{stat}.} \right)_{-5}^{+7}\left( {\mathrm{syst}.} \right)_{-2}^{+3}\left( {\mathrm{lumi}.} \right) $ fb, also consistent with the standard model prediction of 120 fb. The four-lepton mass peak arising from Z → 4 ℓ decays provides a calibration channel for the Higgs boson search in the H → ZZ → 4 ℓ decay mode.
Type of Medium:
Online Resource
ISSN:
1029-8479
DOI:
10.1007/JHEP12(2012)034
Language:
English
Publisher:
Springer Science and Business Media LLC
Publication Date:
2012
detail.hit.zdb_id:
2027350-2
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