QED

Non-discoveries are also important in particle physics

 
Published: Monday 31 August 1998

Splitting particles: scientist (Credit: CERN Photo)PARTICLE physics is a peculiar field. The theoretical consistency of various models predicts the existence of several particles which have to exist to make the theory work. Some of them can be seen, but some remain elusive. Magnetic monopoles (a single electric charge having a spherically symmetrical field) belong to the latter. They have been predicted by almost all reasonable theories of particle physics but have never been seen. Now, we have another report from Fermilab, USA, reporting the non-discovery of monopoles. This is important as it puts new limits on the mass which the monopole may have.

Electric charges come in two varieties, positive and negative, which can exist separately. But magnetic charges always come in pairs: north and south pole. One cannot separate the two by any means. However, under certain conditions a single magnetic charge may exist. This was first proposed by the English physicist Dirac, but was soon forgotten as it was never seen. Renewed interest in the matter was sparked by the discovery that certain unified theories of physics, which purport to unify all the interactions, can only be consistent if magnetic monopoles exist. What is more, if they exist, then they could help explain some of the deepest mysteries, such as why electric charges always come in multiples of the charge of the electron.

These objects are believed to be created in the Big Bang and hence one should be seeing the relic monopoles in the Universe. Scientists have been looking for monopoles in many different places. From cosmic ray collisions, to their tracks in geological deposits, the search has been wide. But never has a monopole or its trace been reported. The theory also predicts that they can be created in high energy collisions in accelerators.

This is precisely where Greg Landsberg of Fermilab looked. He studied the data from the collisions of protons and anti-protons in the Tevatron, the world's largest accelerator. The millions of collisions that were analysed failed to show any traces of monopoles. Disappointing that the result is, there is a silver lining. The search puts a new limit on the monopole mass, which should be 1,600 times more than the mass of the proton. Researchers may get lucky when the next generation collider at Geneva is operational in 2007. Till then, monopoles will remain a theoretical curiosity.

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