Probing baryon number with missing energy

TL;DR

This paper investigates baryon number violation via quark portal interactions involving a light fermion, analyzing constraints from collider data, rare decays, and implications for models like mesogenesis and future experiments.

Contribution

It provides new constraints on baryon number violating interactions, explores displaced vertex signatures, and discusses implications for mesogenesis models and rare decay searches.

Findings

LHC data constrains scales up to 11 TeV for certain MET signatures.

Displaced vertex signatures become prominent at higher masses or larger couplings.

Rare decays like $ ext{Lambda}_c$ to meson plus invisible are significant for future flavor experiments.

Abstract

Quark portal interactions $qqqN$ with a light singlet fermion $N$ make baryon number testable through missing transverse energy (MET). We find that present LHC data constrain scales up to 10 TeV (MET plus jet), 8 TeV (MET plus top) and 11 TeV (MET plus bjet). With increasing mass, or larger portal couplings, $N$ becomes less long-lived, and gives clean displaced vertex signatures, which encourage dedicated searches. We also narrow down viable mesogenesis models with color triplet scalars to a mass range $\sim y \,\cdot 3 \, \text{TeV}$ (with charm) and $\sim y \, \cdot 5 \, \text{TeV}$ (charmless) couplings $y$ to $b$ and lighter quarks, a window that can be scrutinized by HL-LHC. Interactions also induce rare decays of type baryon (meson) to meson (baryon) plus invisible, which complement high-$p_T$ searches and can prove baryon number violation. We explore charm decays $\Lambda_c \to (\pi,K) + \mathrm{invisible}$. Their branching ratios are subject to sizable hadronic uncertainties and require high luminosity flavor facilities such as a Tera-Z facility (FCC-ee, CEPC). Branching ratios of top quarks into one or two $b$-jets plus $N$ can reach few$\times 10^{-6}$.