|
Fractionally charged particles |
Where does the charge quantisation the electric come from?
Holdom showed that by adding a second, unobserved photon ("shadow photon") one can construct in a natural way grand unified models with a small electric charge.
Diagram for a second unobserved photon
This stimulated new
experimental results, the most recent search was performed at SLAC in 2000.
Mass-charge parameter space, where e is the fraction of the electron charge (Davidson, Hannelstadt, Raffelt, JHEP 05 (2000) 003)
If fractionally charged particles exist, o-Ps could decay apparently invisibly, since such particles would mostly penetrate any type of calorimeter without any interaction.
Tokyo results on Br(o-Ps &rarr invisible) < 2.8 ppm set a limit for e<10-4 for m<me
Our goal is to go down to Br(o-Ps &rarr invisible) < 10-8, which will result in e<10-5 for m<me
BACK TO POSITRONIUM AS A PROBE FOR NEW PHYSICS...