Probing Flavor Changing Higgs Interactions at LHC and Future Hadron Colliders

Abstract

In this dissertation, we discuss the prospect of discovering flavor changing neutral Higgs (FCNH) interactions with quarks and leptons at current and future hadron colliders. Particularly, we have looked for $t \to c h^0$ and $\phi^0 \to \tau^{\pm} \mu^{\mp}$, where $\phi^0$ could be a CP-even scalar \bigg[$h^0$ (lighter), $H^0$ (heavier) \bigg ] or a CP-odd pseudo-scalar ($A^0$). A general two Higgs doublet model (gTHDM) is used to simulate $t \to c h^0$ and $\phi^0\to \tau^{\pm} \mu^{\mp} $ decays. The LHC measurements of the light Higgs boson ($h^0$) favor the decoupling limit of gTHDM, in which the couplings of $h^0$ approach Standard Model values. In this limit, FCNH couplings of the light Higgs boson $h^0$ are naturally suppressed by a small mixing parameter $\cos(\beta-\alpha)$, while the FCNH couplings of heavier neutral Higgs bosons $H^0, \mathrm{and} A^0$ are sustained by $\sin(\beta-\alpha) \sim 1$. Promising results are found for the LHC collision energies $\sqrt{s} = 13$ TeV and 14 TeV. In addition, we study the discovery potential of future pp colliders, with $\sqrt{s} = $ 27 TeV and 100 TeV. For $\phi^0 \to \tau^{\pm}\mu^{\mp}$, we evaluate the production rate of physics background from dominant processes ($\tau^+\tau^-, WW, ZZ, Wq, Wg, t\bar{t}$) with realistic acceptance cuts and tagging efficiencies. For $t \to c h^0$, where top is coming from top pair production, we consider $h^0 \to WW^* \to \ell^+ \ell^- + \slashed{E}_T$ and $h^0 \to \tau^+ \tau^- \to \ell^+ \ell^- + \slashed{E}_T$ and another top decaying hadronically to a b quark and two light jets. For this report we have studied $h^0 \to WW^*$ and $h^0 \to \tau^+ \tau^-$ separately. Our analysis suggests a reach of 5$\sigma$ or better, with integrated luminosity $\mathcal{L}$ = 3 $ab^{-1}$ and $\sqrt{s}$ = 13, 14 and 27 TeV for $\lambda_{tc}\leq 0.064$, under the current ATLAS limits for both light Higgs decay mode separately. For $h^0 \to WW^*$ we have also presented the discovery potential at 100 TeV.