Bounds and Prospects for Stable Multiply Charged Particles at the LHC

Abstract

Colored and colorless particles that are stable on collider scales and carry exotic electric charges, so-called multiply-charged heavy stable particles (MCHSPs), exist in extensions of the Standard Model, and can include the top partner(s) in solutions of the hierarchy problem. To obtain bounds on color-triplets and color-singlets of charges up to |Q|=8, we recast searches for signatures of two production channels: the "open" channel - where the particles are pair-produced above threshold, and are detectable in dedicated LHC searches for stable multiply charged leptons, and the "closed" channel - where a particle-antiparticle pair is produced as a bound state, detectable in searches for a diphoton resonance. We recast the open lepton searches by incorporating the relevant strong-interaction effects for color-triplets. In both open and closed production, we provide a careful assessment of photon-induced processes using the accurate LUXqed PDF, resulting in substantially weaker bounds than previously claimed in the literature for the colorless case. Our bounds for colored MCHSPs are shown for the first time, as the LHC experiments have not searched for them directly. Generally, we obtain nearly charge-independent lower mass limits of around 970 GeV (color-triplet scalar), 1200 GeV (color-triplet fermion), and 880 - 900 GeV (color-singlet fermion) from open production, and strongly charge-dependent limits from closed production. In all cases there is a crossover between dominance by open and closed searches at some charge. We provide prospective bounds for $\sqrt{s} = 13$ TeV LHC searches at integrated luminosities of 39.5 fb${}^{-1}$, 100 fb${}^{-1}$, and 300 fb${}^{-1}$. Moreover, we show that a joint observation in the open and the closed channels allows to determine the mass, spin, color, and electric charge of the particle.