Challenges and opportunities for heavy scalar searches in the $t\bar t$ channel at the LHC

TL;DR

This paper investigates the complex interference effects in heavy scalar resonance searches in the top-antitop channel at the LHC, providing analytic tools and exploring new physics contributions to improve search strategies.

Contribution

It offers analytic expressions for interference effects, extends analysis to CP-violation and additional particles, and evaluates the impact on LHC search sensitivities.

Findings

Interference effects significantly alter the signal lineshapes.

Additional particles like stops and vector-like quarks can modify the production process.

Systematic uncertainties and smearing effects are crucial in lineshape searches.

Abstract

Heavy scalar and pseudoscalar resonance searches through the $gg\rightarrow S\rightarrow t\bar t$ process are challenging due to the peculiar behavior of the large interference effects with the standard model $t\bar t$ background. Such effects generate non-trivial lineshapes from additional relative phases between the signal and background amplitudes. We provide the analytic expressions for the differential cross sections to understand the interference effects in the heavy scalar signal lineshapes. We extend our study to the case of CP-violation and further consider the effect of bottom quarks in the production and decay processes. We also evaluate the contributions from additional particles to the gluon fusion production process, such as stops and vector-like quarks, that could lead to significant changes in the behavior of the signal lineshapes. Taking into account the large interference effects, we perform lineshape searches at the LHC and discuss the importance of the systematic uncertainties and smearing effects. We present projected sensitivities for two LHC performance scenarios to probe the $gg\rightarrow S \rightarrow t\bar t$ channel in various models.