Probing anomalous tqh couplings via single top production in associated with the Higgs boson at the HE-LHC and FCC-hh
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Regular Article - Theoretical Physics
Probing anomalous tqh couplings via single top production in associated with the Higgs boson at the HE-LHC and FCC-hh Yan-Ju Zhanga , Jie-Fen Shenb School of Biomedical Engineering, Xinxiang Medical University, Xinxiang 453003, People’s Republic of China
Received: 28 June 2020 / Accepted: 17 August 2020 © The Author(s) 2020
Abstract We investigate the prospects for discovering the Flavour Changing Neutral Current (FCNC) tqh couplings via the process pp → th at the proposed High Energy Large Hadron Collider (HE-LHC) and Future Circular Collider in hadron-hadron mode (FCC-hh) including the realistic detector effects. The relevant SM backgrounds are considered in the cut based analysis to obtain the limits on the the branching ratios of t → qh (q = u, c), followed by the leptonic decay channel of the top quark and diphoton decay channel of the Higgs boson. The upper limits on the FCNC branching ratios at 95% confidence level (CL) and the 5σ discovery reach for the different integrated luminosities are obtained. It is shown that at the 27 TeV HE-LHC with an integrated luminosity of 15 ab−1 and at the 100 TeV FCC-hh with an integrated luminosity of 30 ab−1 , the BR(t → uh) (BR(t → ch)) can be probed, respectively, to 4.4 (6.4)×10−5 and 1.3 (1.6)×10−5 at the 95% CL.
1 Introduction The discovery of the Higgs boson by the Large Hadron Collider (LHC) [1,2] experiments has opened up a new era of the direct searches for new physics (NP) beyond the Standard Model (SM). One of the possible anomalous interactions is the flavour-changing neutral currents (FCNC) process mediated by the Higgs boson, and such processes are forbidden in SM at tree level and are strongly suppressed at loop-level due to the Glashow-Iliopoulos-Maiani (GIM) mechanism [3,4]. Being the most massive elementary particle in the SM, the top quark is an excellent probe not only to search the dynamics of electroweak symmetry breaking, but also to test SM and NP beyond the SM. The flavor-violating Higgs couplings involving a top quark in the SM, i.e., the vertex tqh (q = u, c), a e-mail:
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b e-mail:
[email protected] (corresponding author)
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are out of range for current LHC experimental sensitivities. While in some NP scenarios such as supersymmetry [5–7], two-Higgs-doublet model [8–12], 3-3-1 model [13], and other NP models by extending the Higgs sector [14,15], the branching ratios of top quark FCNC decays t → qh are predicted promisingly at the order of 10−6 − 10−3 . Thus searches for such FCNC processes are very important and could be considered as a clear signal for NP beyond the SM [16–18]. By searching for pp → t t¯ process with one top decaying to W b and the other assumed to decay to hq, the ATLAS and CMS collaborations have given the upper limits on the top quark FCNC branching ratios at 95% Confidence Level √ (CL) at s = 13 TeV [19–22]. For example, the combination of these searches with ATLAS yields observed limits [21]: Br (t → uh) ≤ 1.2 × 10−3 , and Br (t → ch) ≤
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