Search for flavour-changing neutral current top-quark decays t → qZ in proton-proton collisions at $$\sqrt{s}=13 $$ TeV with the ATLAS detector
A search for flavour-changing neutral-current processes in top-quark decays is presented. Data collected with the ATLAS detector from proton-proton collisions at the Large Hadron Collider at a centre-of-mass energy of $$\sqrt{s}=13 $$ TeV, corresponding to an integrated luminosity of 36.1 fb-1, are analysed. The search is performed using top-quark pair events, with one top quark decaying through the t → qZ (q = u, c) flavour-changing neutral-current channel, and the other through the dominant Standard Model mode t → bW. Only Z boson decays into charged leptons and leptonic W boson decays are considered as signal. Consequently, the final-state topology is characterized by the presence of three isolated charged leptons (electrons or muons), at least two jets, one of the jets originating from a b-quark, and missing transverse momentum from the undetected neutrino. Here, the data are consistent with Standard Model background contributions, and at 95% confidence level the search sets observed (expected) upper limits of 1.7 × 10-4 (2.4 × 10-4) on the t → uZ branching ratio and 2.4 × 10-4 (3.2 × 10-4) on the t → cZ branching ratio, constituting the most stringent limits to date.
- Research Organization:
- Harvard Univ., Cambridge, MA (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Univ. of Oregon, Eugene, OR (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), High Energy Physics (HEP); USDOE
- Contributing Organization:
- The ATLAS collaboration
- Grant/Contract Number:
- SC0007881; AC02-76SF00515; SC0017996
- OSTI ID:
- 1735610
- Alternate ID(s):
- OSTI ID: 1475546; OSTI ID: 1605428; OSTI ID: 1769381
- Journal Information:
- Journal of High Energy Physics (Online), Vol. 2018, Issue 7; ISSN 1029-8479
- Publisher:
- Springer BerlinCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Fingerprinting the Top quark FCNC via anomalous $Ztq$ couplings at the LHeC | text | January 2018 |
Fingerprinting the top quark FCNC via anomalous Z t q couplings at the LHeC
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journal | July 2019 |
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