Search for flavour-changing neutral current top quark decays $t\to Hq$ in $pp$ collisions at $\sqrt{s}=8$ TeV with the ATLAS detector - Université Clermont Auvergne Accéder directement au contenu
Article Dans Une Revue Journal of High Energy Physics Année : 2015

Search for flavour-changing neutral current top quark decays $t\to Hq$ in $pp$ collisions at $\sqrt{s}=8$ TeV with the ATLAS detector

G. Aad (1) , M.K. Ayoub (2) , A. Bassalat (2) , C. Bécot (2) , S. Binet (2) , C. Bourdarios (2) , D. Delgove (2) , J-B. de Vivie De Regie (2) , L. Duflot (2) , M. Escalier (2) , L. Fayard (2) , D. Fournier (2) , E.L. Gkougkousis (2) , J-F. Grivaz (2) , T. Guillemin (2) , F. Hariri (2) , S. Henrot-Versille (2) , J. Hrivnac (2) , L. Iconomidou-Fayard (2) , M. Kado (2) , A. Lounis (2) , N. Makovec (2) , N. Morange (2) , C. Nellist (2) , P. Petroff (2) , L. Poggioli (2) , P. Puzo (2) , A. Renaud (2) , D. Rousseau (2) , G. Rybkin (2) , A.C. Schaffer (2) , E. Scifo (2) , L. Serin (2) , S. Simion (2) , R. Tanaka (2) , D. Zerwas (2) , Zhongkai Zhang (2) , Y. Zhao (2) , Z. Barnovska (3) , N. Berger (3) , M. Delmastro (3) , L. Di Ciaccio (3) , S. Elles (3) , T. Hryn’ova (3) , S. Jézéquel (3) , I. Koletsou (3) , R. Lafaye (3) , J. Leveque (3) , P. Mastrandrea , G. Sauvage (3) , E. Sauvan (1) , O. Simard (3) , T. Todorov (3) , E. Yatsenko (3) , I. Wingerter-Seez (3) , L. Alio (1) , M. Barbero , Y. Coadou (1) , C. Diaconu (1) , Sara Diglio (1) , F. Djama (1) , O. Duccu (4, 1) , L. Feligioni (1) , J. Gao (1) , G.D. Hallewell (1) , F. Hubaut (1) , S.J. Kahn (1) , E. B. F. G. Knoops (1) , E. Le Guirriec (1) , J. Liu (1) , 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 (1) , 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 (5) , J. Collot (5) , S. Crépé-Renaudin (5) , P.A. Delsart (5) , C. Gabaldon (5) , M.H. Genest (5) , J.Y. Hostachy (5) , F. Ledroit-Guillon (5) , A. Lleres (5) , A. Lucotte (5) , F. Malek (5) , C. Monini (5) , J. Stark (5) , B. Trocmé (5) , M. Wu (5) , D. Boumediene (6) , E. Busato (6) , D. Calvet (6) , S. Calvet (6) , J. Donini (6) , E. Dubreuil (6) , G. Gilles (6) , Ph. Gris (6) , H. Liao (6) , R. Madar (6) , D. Pallin (6) , S.M. Romano Saez (6) , C. Santoni (6) , D. Simon (6) , T. Theveneaux-Pelzer (6) , F. Vazeille (6)
G. Aad
D. Rousseau
N. Berger
T. Hryn’ova
P. Mastrandrea
  • Fonction : Auteur
M. Barbero
  • Fonction : Auteur
Y. Coadou
S. Calvet

Résumé

A search for flavour-changing neutral current decays of a top quark to an up-type quark ($q=u, c$) and the Standard Model Higgs boson, where the Higgs boson decays to $b\bar{b}$, is presented. The analysis searches for top quark pair events in which one top quark decays to $Wb$, with the $W$ boson decaying leptonically, and the other top quark decays to $Hq$. The search is based on $pp$ collisions at $\sqrt{s}=8$ TeV recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider and uses an integrated luminosity of 20.3 fb$^{-1}$. Data are analysed in the lepton-plus-jets final state, characterised by an isolated electron or muon and at least four jets. The search exploits the high multiplicity of $b$-quark jets characteristic of signal events, and employs a likelihood discriminant that uses the kinematic differences between the signal and the background, which is dominated by $t\bar{t} \to WbWb$ decays. No significant excess of events above the background expectation is found, and observed (expected) 95% CL upper limits of 0.56% (0.42%) and 0.61% (0.64%) are derived for the $t\to Hc$ and $t\to Hu$ branching ratios respectively. The combination of this search with other ATLAS searches in the $H \to \gamma\gamma$ and $H\to WW^*, \tau\tau$ decay modes significantly improves the sensitivity, yielding observed (expected) 95% CL upper limits on the $t\to Hc$ and $t\to Hu$ branching ratios of 0.46% (0.25%) and 0.45% (0.29%) respectively. The corresponding combined observed (expected) upper limits on the $|\lambda_{tcH}|$ and $|\lambda_{tuH}|$ couplings are 0.13 (0.10) and 0.13 (0.10) respectively. These are the most restrictive direct bounds on $tqH$ interactions measured so far.

Dates et versions

in2p3-01202985 , version 1 (22-09-2015)

Identifiants

Citer

G. Aad, M.K. Ayoub, A. Bassalat, C. Bécot, S. Binet, et al.. Search for flavour-changing neutral current top quark decays $t\to Hq$ in $pp$ collisions at $\sqrt{s}=8$ TeV with the ATLAS detector. Journal of High Energy Physics, 2015, 12, pp.061. ⟨10.1007/JHEP12(2015)061⟩. ⟨in2p3-01202985⟩
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