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

Aad, Georges; Abbott, Brad; Abdallah, Jalal; Abdinov, Ovsat; Aben, Rosemarie; Abolins, Maris; AbouZeid, Ossama; Abramowicz, Halina; Abreu, Henso; Abreu, Ricardo

doi:10.1007/JHEP12(2015)061

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

ATLAS

Collaboration

Sep 20, 2015

61 pages

Published in:

JHEP 12 (2015) 061

Published: Dec 10, 2015

e-Print:

1509.06047 [hep-ex]

DOI:

10.1007/JHEP12(2015)061

PDG:

{{\mathit t}}

\rightarrow

{{\mathit H}}{{\mathit u}}

Report number:

CERN-PH-EP-2015-229

Experiments:

CERN-LHC-ATLAS

View in:

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Abstract: (Springer)

A search for flavour-changing neutral current decays of a top quark to an uptype quark (q = u, c) and the Standard Model Higgs boson, where the Higgs boson decays to

b\overline{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\overline{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 → Hc and t → Hu branching ratios respectively. The combination of this search with other ATLAS searches in the H → γγ and H → WW

^{*}

, ττ decay modes significantly improves the sensitivity, yielding observed (expected) 95% CL upper limits on the t → Hc and t → Hu branching ratios of 0.46% (0.25%) and 0.45% (0.29%) respectively. The corresponding combined observed (expected) upper limits on the |λ

_{tcH}

| and |λ

_{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.

Note:

44 pages + author list + cover pages (61 pages total), 14 figures, 5 tables, submitted to JHEP. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2014-14/

Hadron-Hadron Scattering
Top Physics
Higgs Physics
FCNC Interactions
p p: scattering
p p: colliding beams
top: rare decay
neutral current: flavor changing
Higgs particle: hadronic decay
jet: bottom

References(104)

Figures(34)

[1]

Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC

ATLAS

Collaboration

•

Georges Aad
(
- Freiburg U.
)

et al.

- Phys.Lett.B 716 (2012) 1-29
•
e-Print:
- 1207.7214
•
DOI:
- 10.1016/j.physletb.2012.08.020

[2]

Observation of a New Boson at a Mass of 125 GeV with the CMS Experiment at the LHC

CMS

Collaboration

•

Serguei Chatrchyan
(
- Yerevan Phys. Inst.
)

et al.

- Phys.Lett.B 716 (2012) 30-61
•
e-Print:
- 1207.7235
•
DOI:
- 10.1016/j.physletb.2012.08.021

[3]

Combined Measurement of the Higgs Boson Mass in $pp$ Collisions at $\sqrt{s}=7$ and 8 TeV with the ATLAS and CMS Experiments

ATLAS and
CMS

Collaborations

•

Georges Aad
(
- Marseille, CPPM
)

et al.

- Phys.Rev.Lett. 114 (2015) 191803
•
e-Print:
- 1503.07589
•
DOI:
- 10.1103/PhysRevLett.114.191803

[4]

Weak Interactions with Lepton-Hadron Symmetry

- Phys.Rev.D 2 (1970) 1285-1292,
- Also in *Lai, C. H. (ed.): Gauge Theory Of Weak and Electromagnetic Interactions*, 203-210,
- In *Rosner, J.L. (ed.): New Particles*, 18-25,
- In *Lichtenberg, D. B. (Ed.), Rosen, S. P. (Ed.): Developments In The Quark Theory Of Hadrons, Vol. 1*, 193-200.,
- In *Bologna 1984, Proceedings, Fifty Years of Weak-Interaction Physics* 687-694
•
DOI:
- 10.1103/PhysRevD.2.1285