Researchers have proposed a new search strategy for long-lived doubly charged scalar particles at the High-Luminosity Large Hadron Collider (HL-LHC). These particles, predicted by some extensions of the Standard Model, could have an intermediate lifetime where current searches lose sensitivity. The study focuses on a proper decay length range, $c\tau$, between approximately $0.1~\mathrm{mm}$ and $100~\mathrm{mm}$, a regime not effectively covered by prompt particle searches or heavy stable charged particle (HSCP) searches.

The work explores two main scenarios for the doubly charged scalar ($H^{\pm\pm}$): one where it interacts with leptons via a $\Delta L=2$ Yukawa coupling (associated with an $SU(2)_L$ complex triplet), and a "fermiophobic" one where this coupling is absent. In the first case, the particle can only be long-lived for masses between $100$ and $150~\mathrm{GeV}$. However, in the fermiophobic scenario, the mass range extends up to the TeV scale, significantly broadening the discovery potential.

The proposed strategy relies on searching for displaced vertices, i.e., points where the $H^{\pm\pm}$ particle decays far from the initial interaction point. The researchers demonstrate that a cut on the invariant mass of the displaced vertex, reconstructed from the tracks of the daughter particles, can strongly suppress Standard Model backgrounds. They have presented projected limits for the Drell-Yan pair-production cross-section of these scalars at a collision energy of $\sqrt{s}=14~\mathrm{TeV}$ and an integrated luminosity of $3000~\mathrm{fb}^{-1}$. This new methodology would allow probing a region of the parameter space complementary to those explored by existing searches.