Search for single production of vector-like quarks decaying into Wb in pp collisions at s
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Springer
Received: December 20, Revised: April 15, Accepted: May 6, Published: May 27,
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The ATLAS collaboration E-mail: [email protected] Abstract: A search for singly produced vector-like quarks Q, where Q can be either a T quark with charge +2/3 or a Y quark with charge −4/3, is performed in proton– proton collision data at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 36.1 fb−1 , recorded with the ATLAS detector at the LHC in 2015 and 2016. The analysis targets Q → W b decays where the W boson decays leptonically. No significant deviation from the expected Standard Model background is observed. Upper limits are set on the QW b coupling strength and the mixing between the Standard Model sector and a singlet T quark or a Y quark from a (B, Y ) doublet or a (T, B, Y ) triplet, taking into account the interference effects with the Standard Model background. The upper limits set on the mixing angle are as small as | sin θL | = 0.18 for a singlet T quark of mass 800 GeV, | sin θR | = 0.17 for a Y quark of mass 800 GeV in a (B, Y ) doublet model and | sin θL | = 0.16 for a Y quark of mass 800 GeV in a (T, B, Y ) triplet model. Within a (B, Y ) doublet model, the limits set on the mixing parameter | sin θR | are comparable with the exclusion limits from electroweak precision observables in the mass range between about 900 GeV and 1250 GeV. Keywords: Exotics, Hadron-Hadron scattering (experiments) ArXiv ePrint: 1812.07343
Open Access, Copyright CERN, for the benefit of the ATLAS Collaboration. Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP05(2019)164
JHEP05(2019)164
Search for single production of vector-like quarks √ decaying into W b in pp collisions at s = 13 TeV with the ATLAS detector
Contents 1 Introduction
1
2 ATLAS detector
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3 Physics object reconstruction
5 8 8 10
5 Event selection and background estimation 5.1 Signal and control regions definition 5.2 Estimation of non-prompt and fake lepton backgrounds 5.3 Signal candidate mass reconstruction
14 14 15 15
6 Systematic uncertainties 6.1 Experimental uncertainties 6.2 Theoretical modelling uncertainties
17 17 20
7 Results 7.1 Statistical interpretation 7.2 Fit results 7.3 Limits on the VLQ production
21 21 22 23
8 Conclusion
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The ATLAS collaboration
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1
Introduction
Vector-like quarks (VLQs) are hypothetical spin-1/2 coloured particles with left-handed and right-handed components that transform in the same way under the Standard Model (SM) gauge group. Therefore, their masses are not generated by a Yukawa coupling to the Higgs boson [1]. While the discovery of the Higgs boson (H) at the Large Hadron Collider (LHC) [2, 3] excludes a perturbative, fourth generation of chiral quarks [4], since their contribution to loop-mediated Higgs boson couplings would significantly alter the production cross-section and the decay rates of the Higgs boson, the effects on Higgs boson production and decay rates from loop diagrams including VLQs are much smaller than the uncertainty
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