ethan@utastro.UUCP (Ethan Vishniac) (08/03/85)
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Thanks to Courtenay for explaining the determination of neutrino
number.
One point I did not quite understand. Are those branching ratios
meant to refer to electrons only or electrons, muons or taus?
It would seem that all three would be allowable on energetic grounds
Is there some other reason why electron decay is preferred?
--
"Don't argue with a fool. Ethan Vishniac
Borrow his money." {charm,ut-sally,ut-ngp,noao}!utastro!ethan
ethan@utastro.UTEXAS.ARPA
Department of Astronomy
University of Texascpf@lasspvax.UUCP (Courtenay Footman) (08/07/85)
> One point I did not quite understand. Are those branching ratios >meant to refer to electrons only or electrons, muons or taus? >It would seem that all three would be allowable on energetic grounds >Is there some other reason why electron decay is preferred? The branching ratios refer to only electrons. The W and Z do decay into muons and taus, but these decays are much harder to detect. The acceptance for detecting electrons is quite high in both UA1 and UA2. UA2 makes no attempt to identify muons, and the acceptance for muons at UA1 is about half that of electrons. (This is my own estimate based on UA1's data.) Taus decay before they get anywhere near the detector, and so present a much harder signal to decipher. Indeed, the UA1 group thinks some of their W->ev signal is actually W-(tau)v->(evv)v, but there is no way to say that that is what happened on any particular event. Update on my previous posting: some analysis of 1984 data has been released. (A person from UA2 gave a seminar here last week.) The new limits, based on both UA1 and UA2 data, are: From the Z width: N(v) < 10, 90% C.L. From the branching ratio ratio: N(v) < 5, 90% C.L. Note that the first limit has gone down, while the second has gone up. -- Courtenay Footman arpa: cpf@lnsvax Newman Lab. of Nuclear Studies usenet: cornell!lnsvax!cpf Cornell University