A PARTICLE accelerator in Germany has witnessed three strange events that no one can explain. One speculative suggestion is that so-called 鈥渟upersymmetric鈥� particles from a hidden world have popped into existence.
In the HERA particle accelerator at the German Electron-Synchrotron near Hamburg, anti-electrons (or positrons) collide with protons. An experiment called H1 has pinpointed three unusual collisions between 1994 and 1997. Each time, a positron appeared to turn into a muon, something that defies theorists鈥� expectations. And some of the momentum of the positron and proton appeared to vanish, indicating that an undetectable particle 鈥� perhaps a neutrino 鈥� carried off some momentum without being seen.
One conventional explanation is that a quark in the proton spat out a particle that carries the weak force called a W boson, which decayed into a muon and a neutrino. But the trajectories of the muons didn鈥檛 fit that explanation. 鈥淚t鈥檚 still possible that a W is involved, but it鈥檚 not very likely,鈥� says John Dainton of the University of Liverpool, the H1 experiment team leader.
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Alternatively, the three events might involve supersymmetric matter. Supersymmetry theory attempts to show that the building blocks of matter 鈥� quarks and leptons 鈥� and the force-carrying particles that glue them together are just different faces of the same coin. Some physicists believe this would help them develop an elegant theory showing how all the known forces acted as one force in the early Universe.
Glennys Farrar, a particle physicist at New York University, speculates that one possibility is that each of three collisions produced a 鈥渟top quark鈥�, the supersymmetric partner of a top quark. This would then have decayed into a 鈥渟bottom quark鈥� and a W boson, which in turn decayed into a muon and a neutrino.
But previous events which researchers thought might be sightings of supersymmetric particles have never been confirmed (New 杏吧原创, Science, 27 April 1996, p 18). 鈥淓xperience suggests the most likely explanation is a `cocktail鈥� of ordinary effects like statistical fluctuation in the characteristics of W production, possible misidentification, and so on,鈥� says Farrar.
The resolution of the puzzle will have to await an upgrade of the HERA accelerator to give higher collision rates, according to Dainton. 鈥淏y 2001 or 2002, we should know exactly what we have got,鈥� he says. His team has submitted the results to European Physics Journal C.
