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arXiv · 2305.05386

Exploring lepton flavor violation phenomena of the $Z$ and Higgs bosons at electron-proton colliders

Adil Jueid·Jinheung Kim·Soojin Lee·Jeonghyeon Song·Daohan Wang
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Abstract

We comprehensively study the potential for discovering lepton flavor violation (LFV) phenomena associated with the $Z$ and Higgs bosons at the LHeC and FCC-he. Our meticulous investigation reveals the remarkable suitability of electron-proton colliders for probing these rare new physics signals. This is due to the distinct advantages they offer, including negligible pileups, minimal QCD backgrounds, electron-beam polarization $P_e$, and the capability of distinguishing the charged-current from neutral-current processes. In our pursuit of LFV of the $Z$ boson, we employ an innovative indirect probe, utilizing the $t$-channel mediation of the $Z$ boson in the process $p e^- \to j τ^-$. For LFV in the Higgs sector, we scrutinize direct observations of the on-shell decays of $H\to e^+τ^-$ and $H\to μ^\pmτ^\mp$ through the charged-current production of $H$. Focusing on $H\to e^+τ^-$ proves highly efficient due to the absence of positron-related backgrounds in the charged-current modes at electron-proton colliders. Through a dedicated signal-to-background analysis with the boosted decision tree algorithm, we demonstrate that the LHeC with the total integrated luminosity of $1{\,{\rm ab}^{-1}}$ can put significantly lower $2σ$ bounds than the HL-LHC with $3{\,{\rm ab}^{-1}}$. Specifically, we find ${\rm{Br}}(Z\to eτ)< 2.2 \times 10^{-7}$, ${\rm{Br}}(H\to eτ) <1.7 \times 10^{-4} $, and ${\rm{Br}}(H\to μτ) < 1.0 \times 10^{-4}$. Furthermore, our study uncovers the exceptional precision of the FCC-he in measuring the LFV signatures of the $Z$ and Higgs bosons, which indicates the potential for future discoveries in this captivating field.

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Adil Jueid, Jinheung Kim, Soojin Lee, Jeonghyeon Song, Daohan Wang. 2023-08-09. Exploring lepton flavor violation phenomena of the $Z$ and Higgs bosons at electron-proton colliders. https://arxiv.org/abs/2305.05386

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