Finding them, however, is easier said than done. Higgsinos would not appear as pure particles; instead, they would mix with other supersymmetric particles to produce physical states called neutralinos and charginos, whose masses can vary widely. Although extremely rare and difficult to detect, LHC experiments have been on the hunt for these particles for many years.<\/p>\n
When the mass difference \u2013 or \u201cmass splitting\u201d \u2013 between charginos and neutralinos is small, the resulting experimental signatures become even harder to identify. Explorations of this \u201ccompressed mass spectrum\u201d have long been limited by challenges in particle reconstruction and identification.<\/p>\n
Equipped with new machine-learning techniques, the ATLAS Collaboration has met the challenge, setting new constraints on compressed higgsinos in regions last explored by the LEP experiments<\/a>. The new result examines the full LHC Run-2 dataset, with targeted searches for the lightest higgsino-like states \u2013 namely, a chargino (\u03c7\u0303\u00b11) and two neutralinos (\u03c7\u030301 and \u03c7\u030302) \u2013 which are pair-produced. The mass splitting of these states strongly affects how they would appear in the ATLAS experiment. Researchers therefore conducted two distinct searches targeting different mass-splitting regimes.<\/p>\n The ATLAS Collaboration has now established constraints across the full range of higgsino mass splittings, closing gaps left by previous LHC results.<\/p>\n
![\"Physics,ATLAS\"](\"https:\/\/www.newsbeep.com\/il\/wp-content\/uploads\/2026\/03\/file.png\"\/)
<\/a>Figure 1: Observed and expected limits at 95% confidence CL for the higgsino model from 1L1T (purple) and displaced track (red) searches. The limits are shown in the \u0394m(\u03c7\u0303\u00b11, \u03c7\u030301) vs. m(\u03c7\u0303\u00b11) plane, along with previous limits from the LEP2 experiments (grey) and the ATLAS experiment (blue, light green, and yellow). (Image: ATLAS Collaboration\/CERN)<\/p>\n