Twice-Charged Twins on the Hunt express
By the rules of the Standard Model, electric charge is always a multiple of the electron charge — nature deals in whole units. But the equations allow particles with a double charge — bileptons. These 'charged twins' became the collider's quarry: they give themselves away by decaying into four light leptons, much like twins leaving paired footprints. This signal is clean — nothing else produces such a recognizable pattern. A direct hunt is tough: it's easier to ambush exotic quarks — massive relatives of the proton's 'building blocks.' They spit out a bilepton, which instantly breaks apart into a quartet of leptons. Today's collider notices the prey if the quarks are lighter than 1 TeV (a thousand proton masses). After the upgrade (High-Luminosity LHC), the detection range will grow: up to 2.5 TeV for the quarks and up to 2 TeV for the twins themselves. Success would be a scientific bombshell: the law of lepton number conservation, the inviolability of the total count of light particles, would be violated. Nature would allow them to change. And perhaps these particles will help unravel the nature of dark matter.
Original abstract
as written by the authors arXiv:2605.15286
We study the production of pairs of doubly-charged bileptons and assess their discovery potential in light of the integrated luminosities available at the High-Luminosity LHC. The production rates are governed primarily by the bilepton mass, $$(m_Y)$$, and the mass of the exotic heavy quarks, $$(m_D)$$. We consider two complementary production channels: (i) direct bilepton pair production and (ii) bilepton production mediated through heavy-quark decays. Notably, the latter typically yields significantly enhanced cross sections and gives rise to distinctive LHC signatures, even when the bileptons are produced off-shell. The two mechanisms therefore probe complementary regions of parameter space, with direct production being predominantly sensitive to $$m_Y$$, while the heavy-quark-mediated channel depends mainly on $$m_D$$. Owing to the essentially background-free signature of four energetic leptons at the LHC, we show that Run-2 data allow a discovery only for $$m_D \lesssim 1\,\mathrm{TeV}$$, whereas the HL-LHC can achieve a $$5\sigma$$ discovery up to $$m_D \lesssim 2.5\,\mathrm{TeV}$$ (nearly independently of $$m_Y$$) and/or for $$m_Y \lesssim 2\,\mathrm{TeV}$$ (even if $$D$$ is heavy).
The name 'bilepton' comes from Latin bi- (two) and 'lepton': the particle seems to play for two at once in the quantum world. Its discovery would show for the first time that the number of light particles does not have to be conserved, a familiar law of the micro-world would be broken.