Search for flavour-changing neutral current top quark decays t -> Hq in pp collisions at root s=8 TeV with the ATLAS detector

G. Aad; B. Abbott; J. Abdallah; O. Abdinov; R. Aben; M. Abolins; O.S. AbouZeid; H. Abramowicz; H. Abreu; R. Abreu; Mogens Dam; Jørn Dines Hansen; Jørgen Beck Hansen; Stefania Xella; Peter Henrik Hansen; Troels Christian Petersen; Lotte Ansgaard Thomsen; Sascha Mehlhase; Morten Dam Jørgensen; Almut Maria Pingel; Ask Emil Løvschall-Jensen; Alejandro Alonso Diaz; James William Monk; Lars Egholm Pedersen; Graig Wiglesworth; Gorm Aske Gram Krohn Galster

doi:10.1007/JHEP12(2015)061

Search for flavour-changing neutral current top quark decays t -> Hq in pp collisions at root s=8 TeV with the ATLAS detector

G. Aad, B. Abbott, J. Abdallah, O. Abdinov, R. Aben, M. Abolins, O.S. AbouZeid, H. Abramowicz, H. Abreu, R. Abreu, Mogens Dam, Jørn Dines Hansen, Jørgen Beck Hansen, Stefania Xella, Peter Henrik Hansen, Troels Christian Petersen, Lotte Ansgaard Thomsen, Sascha Mehlhase, Morten Dam Jørgensen, Almut Maria PingelAsk Emil Løvschall-Jensen, Alejandro Alonso Diaz, James William Monk, Lars Egholm Pedersen, Graig Wiglesworth, Gorm Aske Gram Krohn Galster

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Abstract

Abstract: 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(Formula Presented.), 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 (Formula Presented.) 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 (Formula Presented.) 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.[Figure not available: see fulltext.]

Originalsprog	Engelsk
Artikelnummer	061
Tidsskrift	Journal of High Energy Physics (Online)
Vol/bind	2015
Udgave nummer	12
ISSN	1126-6708
DOI	https://doi.org/10.1007/JHEP12(2015)061
Status	Udgivet - 1 dec. 2015

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10.1007/JHEP12(2015)061

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Aad, G., Abbott, B., Abdallah, J., Abdinov, O., Aben, R., Abolins, M., AbouZeid, O. S., Abramowicz, H., Abreu, H., Abreu, R., Dam, M., Hansen, J. D., Hansen, J. B., Xella, S., Hansen, P. H., Petersen, T. C., Thomsen, L. A., Mehlhase, S., Jørgensen, M. D., ... Galster, G. A. G. K. (2015). Search for flavour-changing neutral current top quark decays t -> Hq in pp collisions at root s=8 TeV with the ATLAS detector. Journal of High Energy Physics (Online), 2015(12), Artikel 061. https://doi.org/10.1007/JHEP12(2015)061

Aad, G, Abbott, B, Abdallah, J, Abdinov, O, Aben, R, Abolins, M, AbouZeid, OS, Abramowicz, H, Abreu, H, Abreu, R, Dam, M , Hansen, JD , Hansen, JB , Xella, S , Hansen, PH , Petersen, TC, Thomsen, LA, Mehlhase, S, Jørgensen, MD, Pingel, AM, Løvschall-Jensen, AE, Alonso Diaz, A, Monk, JW, Pedersen, LE, Wiglesworth, G & Galster, GAGK 2015, 'Search for flavour-changing neutral current top quark decays t -> Hq in pp collisions at root s=8 TeV with the ATLAS detector', Journal of High Energy Physics (Online), bind 2015, nr. 12, 061. https://doi.org/10.1007/JHEP12(2015)061

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title = "Search for flavour-changing neutral current top quark decays t -> Hq in pp collisions at root s=8 TeV with the ATLAS detector",

abstract = "Abstract: 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(Formula Presented.), 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 (Formula Presented.) 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 (Formula Presented.) 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 |λtcH| and |λtuH| 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.[Figure not available: see fulltext.]",

author = "G. Aad and B. Abbott and J. Abdallah and O. Abdinov and R. Aben and M. Abolins and O.S. AbouZeid and H. Abramowicz and H. Abreu and R. Abreu and Mogens Dam and Hansen, {J{\o}rn Dines} and Hansen, {J{\o}rgen Beck} and Stefania Xella and Hansen, {Peter Henrik} and Petersen, {Troels Christian} and Thomsen, {Lotte Ansgaard} and Sascha Mehlhase and J{\o}rgensen, {Morten Dam} and Pingel, {Almut Maria} and L{\o}vschall-Jensen, {Ask Emil} and {Alonso Diaz}, Alejandro and Monk, {James William} and Pedersen, {Lars Egholm} and Graig Wiglesworth and Galster, {Gorm Aske Gram Krohn}",

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T1 - Search for flavour-changing neutral current top quark decays t -> Hq in pp collisions at root s=8 TeV with the ATLAS detector

AU - Aad, G.

AU - Abbott, B.

AU - Abdallah, J.

AU - Abdinov, O.

AU - Aben, R.

AU - Abolins, M.

AU - AbouZeid, O.S.

AU - Abramowicz, H.

AU - Abreu, H.

AU - Abreu, R.

AU - Dam, Mogens

AU - Hansen, Jørn Dines

AU - Hansen, Jørgen Beck

AU - Xella, Stefania

AU - Hansen, Peter Henrik

AU - Petersen, Troels Christian

AU - Thomsen, Lotte Ansgaard

AU - Mehlhase, Sascha

AU - Jørgensen, Morten Dam

AU - Pingel, Almut Maria

AU - Løvschall-Jensen, Ask Emil

AU - Alonso Diaz, Alejandro

AU - Monk, James William

AU - Pedersen, Lars Egholm

AU - Wiglesworth, Graig

AU - Galster, Gorm Aske Gram Krohn

PY - 2015/12/1

Y1 - 2015/12/1

N2 - Abstract: 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(Formula Presented.), 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 (Formula Presented.) 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 (Formula Presented.) 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 |λtcH| and |λtuH| 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.[Figure not available: see fulltext.]

AB - Abstract: 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(Formula Presented.), 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 (Formula Presented.) 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 (Formula Presented.) 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 |λtcH| and |λtuH| 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.[Figure not available: see fulltext.]

U2 - 10.1007/JHEP12(2015)061

DO - 10.1007/JHEP12(2015)061

M3 - Journal article

SN - 1126-6708

VL - 2015

JO - Journal of High Energy Physics (Online)

JF - Journal of High Energy Physics (Online)

IS - 12

M1 - 061

ER -

Search for flavour-changing neutral current top quark decays t -> Hq in pp collisions at root s=8 TeV with the ATLAS detector

Abstract

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