Long-lived neutral particles provide a challenge in the construction of particle detectors, because they do not interact electromagnetically, except possibly through their magnetic moments.
This means that they do not leave tracks of ionized particles or curve in magnetic fields.
Examples of such particles include photons,[PDG 1] neutrons,[PDG 2] and neutrinos.
[PDG 3] Other neutral particles are very short-lived and decay before they could be detected even if they were charged.
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