The Standard Model of particle physics is currently our best description of nature, but it is well known that it cannot be complete. BSM (Beyond the Standard Model) theories often attempt to solve this problem by including new particles—most famously, supersymmetric versions of existing particles. This question will resolve as yes if, by December 31, 2025, a new, BSM particle has been discovered according to broad scientific consensus.

Note: only elementary particles will count for the purposes of this question. E.g. if a new, exotic bound state of quarks is discovered, this will not count as a new, BSM particle, even if theoretical calculations involve modifications of existing theory, in this case QCD; however, if said measurement implies the existence of a BSM particle to a stastically significant degree (5 sigma or better) and there is consensus about the status of this particle, then the question will resolve as yes.