A massive (semi-)stable particle (MSP) would be a new particle that lives long enough that it passes through a detector. A light semi-stable particle is the muon which can travel miles before decaying. Some theories, such as supersymmetry, conjecture that such particles could exist under certain circumstances. They could be charged or uncharged, interacted strongly or not, and have a wide range of lifetimes. MSPs have been searched for in the past; for example in neutral beams lines such as at Fermilab (see PRD37, 3103, 1988). In that case a neutron is long-lived but not massive and one searches for the decays of new, massive particles.
The D0 experiment, which has operated at the Fermilab collider since 1992, also searches for both charged and neutral MSPs. Early studies (such as D0 Notes 390 (D. Green) and 402 (D. Hedin) from 1986) showed that the very good muon coverage would allow charged MSPs to be detected. One triggers on them using the muon detector and then uses the time information from scintillation counters to measure the velocity of the3 particles. all, essentially, have v=c as they are muons; tails are due to the time, and therefor velocity, resolution. Mike Eads, who received his Ph.D. from NIU in 2005, analyzed D0 data looking for charged massive particles. His results are shown below; none were found but it is always worth the effort to look for new phenomena in Nature.
Following his graduation from NIU, Eads has continued analyzing additional D0 data for evidence of charged massive stable particles. He has been joined in this search by colleagues from Brown University. A paper Phys. Rev. Lett. 102, 161802 (2009) was published in 2009.last updated December 2008