A new analysis has revised the exclusion limits for doubly charged Higgs bosons (H±±), hypothetical particles that would extend the Standard Model. This work re-examines a search conducted by the ATLAS collaboration at CERN's Large Hadron Collider (LHC), utilizing the full Run 2 dataset at a collision energy of 13 TeV. The original ATLAS search, published in Eur. Phys. J. C 83 (2023) 605, set the strongest limits to date on the mass of these doubly charged scalars, largely driven by an essentially background-free four-lepton channel.

The current study identifies a discrepancy in the four-lepton signal efficiency reported by ATLAS. The authors demonstrate that the implied efficiency from the original analysis exceeds a strict, mass-independent upper bound derived from key assumptions such as equal branching ratios, leptonic tau (τ) branching fractions, and ATLAS lepton reconstruction efficiencies. This discrepancy cannot be explained by hadronic τ or jet misidentification without invoking unrealistically high fake rates.

To correct this inconsistency, the researchers independently regenerated the signal and recomputed the exclusion limits. They used the corrected signal yields, ATLAS background predictions and uncertainties, and the same CLs procedure (modified frequentist confidence limit) implemented in pyhf. The results indicate that the expected lower mass bound shifts from 1065 GeV to approximately 950 GeV for the left-right symmetric type-II seesaw model, and from 880 GeV to about 770 GeV for the Zee-Babu model. These new limits are systematically higher than the ATLAS expected limits by a factor of two or more, implying that the excluded mass region is smaller than initially thought.