366 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1963 



TT« 



TTO- 



TT«- 



"^ 



Tie- 



^ 



TT^- 



^m- 



■ne- 



Mectron 



y none found 



^ ' (29 expected 

 if only one 

 neutrmo) 



Figure S. — Author and colleagues used this experimental arrangement to detect neutrino 

 interactions. Pions from accelerator target travel 70 feet before striking steel shield; 

 on the way about 10 percent decay to muons and neutrinos. Neutrinos pass through 

 shield to spark chamber where about 1 in 10'^ interact. Lower diagram shows number 

 and types of these interactions: shaded interaction was not observed, indicating that 

 there is more than one kind of neutrino. 



Neutrinos, of course, show no tracks; but their reaction products 

 do. The chamber is triggered whenever a charged particle originates 

 within it. After passing some 10" neutrinos through it, 51 inter- 

 actions were observed. Of these, 29 showed the production of a muon 

 alone and 22 showed the production of a muon along with a pion or 

 something else. If there was only one neutrino, one would have also 

 expected the production of 29 single electrons which would have been 

 easily identified in the chamber. No such electrons were observed, 

 leading to the conclusion that the neutrinos coupled to muons are not 

 the same as those coupled to electrons. 



One of the implications of this discovery is quite clear. It re- 

 moves a major objection to the intermediate boson, and the next 

 neutrino experiments will be designed to search for it directly. This 

 boson, if it does exist and has a mass not much greater than the mass 

 of the proton, can be produced directly along with a muon by 

 presently available energetic neutrinos. Indeed, the Brookhaven 



