Four research groups have proposed the existence of various new particles to explain an anomalous signal picked up by the two largest particle detectors at the Large Hadron Collider at CERN, Europe's particle-physics lab in Geneva, Switzerland.

Physicists with the ATLAS and CMS detectors announced in December 2015 that they had found an excess pair of photons with a combined energy of 750 gigaelectronvolts. Christoffer Petersson at Chalmers University of Technology in Gothenburg, Sweden, and Riccardo Torre at the Swiss Federal Institute of Technology in Lausanne say that the two photons could come from the decay of a boson that is the 'super partner' of a goldstino fermion. Yuichiro Nakai at Harvard University in Cambridge, Massachusetts, and his team suggest that the new particle is made of two exotic quarks held together by a force similar to the strong nuclear force.

Gang Li at Peking University in Beijing and his co-authors propose that the mystery signal is produced by a particle similar to the Higgs boson, but six times more massive. And Won Sang Cho at the Institute for Basic Science in Daejeon, South Korea, and his collaborators propose that the two photons would be only part of the debris produced by a potentially much more massive particle.

More data are needed to confirm whether this is a sign of a new particle or merely a statistical bump.

Phys. Rev. Lett. 116, 151804; 151802; 151803; 151805 (2016)