ethan@utastro.UUCP (Ethan Vishniac) (07/31/85)
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A week ago I passed along a rumor based on an article in New Scientist.
Since it looks interesting and because of the large popular demand
(actually I got one mail message that I couldn't seem to send a reply
to) I have decided to post it. I do not have the permission of the
New Scientist to do so, and if I'm sued I expect you all to come
testify to my good character.
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CERN neutrinos on cue
Experiments in the beams of the UA1 and UA2 colliders at CERN have
confirmed a cosmological "prediction" of the number of types of neutrino
in the Universe. Cosmologists, delving back (theoretically) to the
conditions of the big bang, in which hydrogen formed and about 25% of it
was cooked into helium, recently decided that there must be no more than
four types of neutrino in the Universe. The argument is that more families
of these particles would have caused the cooking to proceed slightly
differently, resulting in a Universe with a different amount of helium today.
The argument is rather exotic, but fits in neatly with the known
existence of just three types of lepton, the electron, muon, and tau
particle, each with an associated neutrino. But while particle physicists
had indeed found only three types of neutrino, until a few weeks ago they
had no direct evidence for or against the existence of moe varieties.
At a recent meeting in Rome, however, Abdus Salaam, of the International
Centre for Theoretical Physics in Trieste, reported tat he had just heard from
CERN that the same experiments that detected the W and Z particles have
now set limits on the possible numbers of neutrino families and these fall
exactly in line with the cosmological calculations. This rare example
of perfect agreement between the theory of the Universe at large and experiments
on the very small caused a flurry of excitement in Rome; full details from
CERN are eagerly awaited.
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I tried asking a particle physicist (S. Weinberg) about this and he
said he knew nothing about it and was under the impression that the
CERN group didn't anticipate setting these kinds of limits for another
few years. This squares with the last I had heard which was that the
upper limit was of order 20 and dropping slowly.
--
"Don't argue with a fool. Ethan Vishniac
Borrow his money." {charm,ut-sally,ut-ngp,noao}!utastro!ethan
Department of Astronomy
University of Texas