Search for the associated production of the Higgs boson with a top quark pair in multilepton final states with the ATLAS detector

G. Aad (1) , Z. Barnovska (2) , N. Berger (2) , M. Delmastro (2) , L. Di Ciaccio (2) , S. Elles (2) , T. Hryn’ova (2) , S. Jézéquel (2) , I. Koletsou (2) , R. Lafaye (2) , J. Leveque (2) , N. Massol (2) , G. Sauvage (2) , E. Sauvan (2) , O. Simard (2) , T. Todorov (2) , I. Wingerter-Seez (2) , E. Yatsenko (2) , G . Rahal (3) , M.K. Ayoub (4) , A. Bassalat (4) , C. Becot (4) , S. Binet (4) , C. Bourdarios (4) , J.B. de Vivie De Regie (4) , D. Delgove (4) , L. Duflot (4) , M. Escalier (4) , L. Fayard (4) , D. Fournier (4) , E.L. Gkougkousis (4) , J.-F. Grivaz (4) , T. Guillemin (4) , F. Hariri (4) , S. Henrot-Versillé (4) , J. Hrivnac (4) , L. Iconomidou-Fayard (4) , M. Kado (4) , A. Lounis (4) , N. Makovec (4) , N. Morange (4) , C. Nellist (4) , L. Poggioli (4) , P. Puzo (4) , A. Renaud (4) , D. Rousseau (4) , G. Rybkin (4) , A.C. Schaffer (4) , E. Scifo (4) , L. Serin (4) , S. Simion (4) , R. Tanaka (4) , H.L. Tran (4) , D. Zerwas (4) , Z. Zhang (4) , Y. Zhao (4) , D. Boumediene (5) , Emmanuel Busato (5) , D. Calvet (5) , S. Calvet (5) , J. Donini (5) , E. Dubreuil (5) , G. Gilles (5) , Ph. Gris (5) , H. Liao (5) , R. Madar (5) , D. Pallin (5) , S.M. Romano Saez (5) , C. Santoni (5) , D. Simon (5) , Timothée Theveneaux-Pelzer (5) , F. Vazeille (5) , L. Alio (1) , M. Barbero (1) , Y. Coadou (1) , C. Diaconu (1) , Sara Diglio (1) , F. Djama (1) , O. Duccu (1, 6) , L. Feligioni (1) , J. Gao (7) , G.D. Hallewell (1) , F. Hubaut (1) , S.J. Kahn (1) , E. B. F. G. Knoops (1) , E. Le Guirriec (1) , J. Liu , K. Liu (1) , D. Madaffari (1) , K. Mochizuki (1) , E. Monnier (1) , S. Muanza (1) , Y. Nagai (1) , E. Nagy (1) , P. Pralavorio (1) , A. Rozanov , T. Serre (1) , M. Talby (1) , R.E. Ticse Torres (1) , E. Tiouchichine (1) , S. Tisserant (1) , J. Toth (1) , F. Touchard (1) , L. Vacavant (1) , S. Albrand (8) , J. Brown (8) , J. Collot (8) , S. Crépé-Renaudin (8) , P.A. Delsart (8) , C. Gabaldon (8) , M.H. Genest (8) , J.Y. Hostachy (8) , F. Ledroit-Guillon (8) , A. Lleres (8) , A. Lucotte (8) , F. Malek (8) , C. Monini (8) , J. Stark (8) , B. Trocmé (8) , M. Wu (8)

1 CPPM - Centre de Physique des Particules de Marseille
2 LAPP - Laboratoire d'Annecy de Physique des Particules
3 CC-IN2P3 - Centre de Calcul de l'IN2P3
4 LAL - Laboratoire de l'Accélérateur Linéaire
5 LPC - Laboratoire de Physique Corpusculaire - Clermont-Ferrand
6 NIPNE - Horia Hulubei National Institute of Physics and Nuclear Engineering
7 MSE - Department of Materials Science and Engineering [Blacksburg]
8 LPSC - Laboratoire de Physique Subatomique et de Cosmologie

A search for the associated production of the Higgs boson with a top quark pair is performed in multilepton final states using 20.3 fb$^{-1}$ of proton-proton collision data recorded by the ATLAS experiment at $\sqrt{s}=8$ TeV at the Large Hadron Collider. Five final states, targeting the decays $H\to WW^*$, $\tau\tau$, and $ZZ^*$, are examined for the presence of the Standard Model (SM) Higgs boson: two same-charge light leptons ($e$ or $\mu$) without a hadronically decaying $\tau$ lepton; three light leptons; two same-charge light leptons with a hadronically decaying $\tau$ lepton; four light leptons; and one light lepton and two hadronically decaying $\tau$ leptons. No significant excess of events is observed above the background expectation. The best fit for the $t\bar t H$ production cross section, assuming a Higgs boson mass of 125 GeV, is $2.1 ^{+1.4}_{-1.2}$ times the SM expectation, and the observed (expected) upper limit at the 95% confidence level is 4.7 (2.4) times the SM rate. The $p$-value for compatibility with the background-only hypothesis is $1.8\sigma$; the expectation in the presence of a Standard Model signal is $0.9\sigma$.

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

G. Aad, Z. Barnovska, N. Berger, M. Delmastro, L. Di Ciaccio, et al.. Search for the associated production of the Higgs boson with a top quark pair in multilepton final states with the ATLAS detector. Physics Letters B, 2015, 749, pp.519-541. ⟨10.1016/j.physletb.2015.07.079⟩. ⟨in2p3-01166348⟩