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

S. Chatrchyan , M. Besançon (1) , S. Choudhury (1) , M. Dejardin (1) , D. Denegri (1) , B. Fabbro (1) , J.L. Faure (1) , F. Ferri (1) , S. Ganjour (1) , A. Givernaud (1) , P. Gras (1) , G. Hamel de Monchenault (1) , P. Jarry (1) , E. Locci (1) , J. Malcles (1) , L. Millischer (1) , A. Nayak (1) , J. Rander (1) , A. Rosowsky (1) , I. Shreyber (1) , M. Titov (1) , S. Baffioni (2) , F. Beaudette (2) , L. Benhabib (2) , L. Bianchini (2) , M. Bluj (2) , C. Broutin (2) , Pierre Busson (2) , C. Charlot (2) , N. Daci (2) , T. Dahms (2) , L. Dobrzynski (2) , R. Granier de Cassagnac (2) , M. Haguenauer (2) , P. Mine (2) , C. Mironov (2) , M. Nguyen (2) , C. Ochando (2) , P. Paganini (2) , D. Sabes (2) , R. Salerno (2) , Y. Sirois (2) , C. Veelken (2) , A. Zabi (2) , J.-L. Agram (3) , J. Andrea (3) , D. Bloch (3) , D. Bodin (3) , J.-M. Brom (3) , M. Cardaci (3) , E.C. Chabert (3) , C. Collard (3) , E. Conte (3) , F. Drouhin (3) , C. Ferro (3) , J.-C. Fontaine (3) , D. Gele (3) , U. Goerlach (3) , P. Juillot (3) , A.-C. Le Bihan (3) , P. van Hove (3) , F. Fassi (4) , D. Mercier (4) , S. Beauceron (5) , N. Beaupere (5) , O. Bondu (5) , G. Boudoul (5) , J. Chasserat (5) , R. Chierici (5) , D. Contardo (5) , P. Depasse (5) , H. El Mamouni (5) , J. Fay (5) , S. Gascon (5) , M. Gouzevitch (5) , B. Ille (5) , T. Kurca (5) , M. Lethuillier (5) , L. Mirabito (5) , S. Perries (5) , V. Sordini (5) , S. Tosi (5) , Y. Tschudi (5) , P. Verdier (5) , S. Viret (5)

1 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers
2 LLR - Laboratoire Leprince-Ringuet
3 DRS-IPHC - Département Recherches Subatomiques
4 CC-IN2P3 - Centre de Calcul de l'IN2P3
5 IPNL - Institut de Physique Nucléaire de Lyon

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.

Domaines: Physique des Hautes Energies - Expérience [hep-ex]

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, 2012, 12, pp.034. ⟨10.1007/JHEP12(2012)034⟩. ⟨in2p3-00742132⟩