A team interprets the massive four-jet excesses observed by CMS in RUN2 and RUN3 data as possible signs of Kaluza-Klein excitations. Under their proposal, two heavy Kaluza-Klein gluons, with masses of 3.6 TeV and 8.6 TeV, would decay into pairs of Kaluza-Klein quarks of 1 TeV and 2.1 TeV. The work builds on a previous paper by the same group, in which they already presented evidence for a sequence of Kaluza-Klein gravitons.

The proposal conflicts with current experimental limits for a 3.6 TeV Kaluza-Klein gluon, which appear to exclude that mass. The authors argue, however, that those limits assume a dominant decay into top-quark pairs, a hypothesis they consider questionable, as they already noted in their earlier study of Kaluza-Klein graviton decays. For the 8.6 TeV gluon, the predicted cross section would require a branching ratio into pairs of 2.1 TeV Kaluza-Klein quarks of order 10%, a value the authors describe as plausible.

The work is a reinterpretation of data already published by CMS, not a new direct measurement. Kaluza-Klein excitations are massive states that arise in theories with extra spatial dimensions, where Standard Model fields propagate in the higher-dimensional spacetime and appear in four dimensions as towers of particles with increasing masses.

The authors note that prospects for reaching local evidence at the 6 standard deviation level with RUN3 data are promising for three channels. If confirmed, the signal would support the existence of extra dimensions and offer a common explanation for several excesses observed in CMS.