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Register a new userConstraining $t to u$ flavor changing neutral Higgs coupling at the LHC
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We study the constraints on $tto u$ flavor changing neutral Higgs (FCNH) coupling, and how it may be explored further at the Large Hadron Collider (LHC). In the general two Higgs doublet model, such transitions can be induced by a nonzero $rho_{tu}$ Yukawa coupling. We show that such couplings can be constrained by existing searches at the LHC for $m_H$, $m_A$ and, $m_{H^+}$ in the sub-TeV range, where $H$, $A$ and $H^+$ are the exotic $CP$-even, $CP$-odd and charged scalars. We find that a dedicated $ugto t H/tA to t t bar u$ search can probe the available parameter space of $rho_{tu}$ down to a few percent level for $200,mbox{GeV} lesssim m_H,,m_A lesssim 600$ GeV, with discovery possible at high luminosity. Effects of how other extra top Yukawa couplings, such as $rho_{tc}$ and $rho_{tt}$, dilute the sensitivity of the $rho_{tu}$ probe are discussed.
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We investigate the prospects for discovering a top quark decaying into one light Higgs boson along with a charm quark in top quark pair production at the CERN Large Hadron Collider (LHC). A general two Higgs doublet model is adopted to study the signature of flavor changing neutral Higgs decay $t to cphi^0$, %or $bar{t} to bar{c}phi^0$ where $phi^0$ could be CP-even ($H^0$) or CP-odd ($A^0$). The dominant physics background is evaluated with realistic acceptance cuts as well as tagging and mistagging efficiencies. For a reasonably large top-charm-Higgs coupling ($lambda_{tc}/lambda_{t} agt 0.09$), the abundance of signal events and the %that our acceptance cuts reduction in physics background allow us to establish a $5sigma$ signal for $M_phi sim 125$ GeV at the LHC with a center of mass energy ($sqrt{s}$) of 8 TeV and an integrated luminosity of 20 fb$^{-1}$. The discovery potential will be greatly enhanced with the full energy of $sqrt{s} = 14$ TeV.
A general two Higgs doublet model (2HDM) is adopted to study the signature of flavor changing neutral Higgs (FCNH) decay $phi^0 to tbar{c}+bar{t}c$, where $phi^0$ could be a CP-even scalar ($H^0$) or a CP-odd pseudoscalar ($A^0$). Measurement of the light 125 GeV neutral Higgs boson ($h^0$) couplings at the Large Hadron Collider (LHC) favor the decoupling limit or the alignment limit of a 2HDM, in which gauge boson and diagonal fermion couplings of $h^0$ approach Standard Model values. In such limit, FCNH couplings of $h^0$ are naturally suppressed by a small mixing parameter $cos(beta-alpha)$, while the off-diagonal couplings of heavier neutral scalars $phi^0$ are sustained by $sin(beta-alpha) sim 1$. We study physics background from dominant processes with realistic acceptance cuts and tagging efficiencies. Promising results are found for the LHC running at 13 or 14 TeV collision energies.
Despite the discovery of the Higgs boson decay in five separate channels many parameters of the Higgs boson remain largely unconstrained. In this paper, we present a new approach to constraining the Higgs total width by requiring the Higgs to be resolved as a single high p$_T$ jet and measuring the inclusive Higgs boson cross section. To measure the inclusive Higgs boson cross section, we rely on new approaches from machine learning and a modified jet reconstruction. This approach is found to be complementary to the existing off-shell width measurement and, with the full HL-LHC luminosity, is capable of yielding similar sensitivity to the off-shell projections. We outline the theoretical and experimental limitations and present a path towards making this approach a truly model-independent measurement of the Higgs boson total width.
The $h(125)$ boson, discovered only in 2012, is lower than the top quark in mass, hence $t to ch$ search commenced immediately thereafter, with current limits at the per mille level and improving. As the $t to ch$ rate vanishes with the $h$-$H$ mixing angle $cosgamma to 0$, we briefly review the collider probes of the top changing $tcH/tcA$ coupling $rho_{tc}$ of the exotic $CP$-even/odd Higgs bosons $H/A$. Together with an extra top conserving $ttH/ttA$ coupling $rho_{tt}$, one has an enhanced $cbH^+$ coupling alongside the familiar $tbH^+$ coupling, where $H^+$ is the charged Higgs boson. The main processes we advocate are $cg to tH/A to ttbar c,; ttbar t$ (same-sign top and triple-top), and $cg to bH^+ to btbar b$. We also discuss some related processes such as $cg to thh$, $tZH$ that depend on $cosgamma$ being nonzero, comment briefly on $gg to H/A to tbar t, tbar c$ resonant production, and touch upon the $rho_{tu}$ coupling.
We investigate the prospects of discovering the top quark decay into a charm quark and a Higgs boson ($t to c h^0$) in top quark pair production at the CERN Large Hadron Collider (LHC). A general two Higgs doublet model is adopted to study flavor changing neutral Higgs (FCNH) interactions. We perform a parton level analysis as well as Monte Carlo simulations using textsc{Pythia}~8 and textsc{Delphes} to study the flavor changing top quark decay $t to c h^0$, followed by the Higgs decaying into $tau^+ tau^-$, with the other top quark decaying to a bottom quark ($b$) and two light jets ($tto bWto bjj$). To reduce the physics background to the Higgs signal, only the leptonic decays of tau leptons are used, $tau^+tau^- to e^pmmu^mp +slashed{E}_T$, where $slashed{E}_T$ represents the missing transverse energy from the neutrinos. In order to reconstruct the Higgs boson and top quark masses as well as to effectively remove the physics background, the collinear approximation for the highly boosted tau decays is employed. Our analysis suggests that a high energy LHC at $sqrt{s} = 27$ TeV will be able to discover this FCNH signal with an integrated luminosity $mathcal{L} = 3$ ab$^{-1}$ for a branching fraction ${cal B}(t to ch^0) agt 1.4 times 10^{-4}$ that corresponds to a FCNH coupling $|lambda_{tch}| agt 0.023$. This FCNH coupling is significantly below the current ATLAS combined upper limit of $|lambda_{tch}| = 0.064$.
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