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.

Chatrchyan, S., Khachatryan, V., Sirunyan, A., Tumasyan, A., Adam, W., Bergauer, T., et al. (2012). Observation of Z decays to four leptons with the CMS detector at the LHC. JOURNAL OF HIGH ENERGY PHYSICS, 2012(12) [10.1007/JHEP12(2012)034].

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

BENAGLIA, ANDREA DAVIDE;DE GUIO, FEDERICO;DI MATTEO, LEONARDO;FIORENDI, SARA;GHEZZI, ALESSIO;MANZONI, RICCARDO ANDREA;MARTELLI, ARABELLA;MASSIRONI, ANDREA;MORONI, LUIGI;PAGANONI, MARCO;RAGAZZI, STEFANO;TABARELLI DE FATIS, TOMMASO
Penultimo
;
Branca, A;GOVONI, PIETRO;DINARDO, MAURO EMANUELE;
2012

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.
Articolo in rivista - Articolo scientifico
high energy collider; LHC; CMS; physics beyond the Standard Model
English
2012
2012
12
none
Chatrchyan, S., Khachatryan, V., Sirunyan, A., Tumasyan, A., Adam, W., Bergauer, T., et al. (2012). Observation of Z decays to four leptons with the CMS detector at the LHC. JOURNAL OF HIGH ENERGY PHYSICS, 2012(12) [10.1007/JHEP12(2012)034].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/46404
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