OBSERVATIONS ON THE DISCOVERY OF THE
STRANGE PARTICLES
G. Rochester
To cite this version:
G. Rochester.
OBSERVATIONS ON THE DISCOVERY OF THE STRANGE
PARTICLES. Journal de Physique Colloques, 1982, 43 (C8), pp.C8-169-C8-175.
<10.1051/jphyscol:1982807>. <jpa-00222367>
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JOURNAL DE PHYSIQUE
Colloque
C8, supplément
au n° 12, Tome 43,
décembre
1982
page C8-169
OBSERVATIONS ON THE DISCOVERY OF THE STRANGE PARTICLES
G.D. R o c h e s t e r
Department
of Physios,
Durham University,
South
Road, Durham, DH1 ZLE,
U.K.
Résumé. - Quelques réflexions concernant l'origine de l'histoire de la
découverte des particules étranges, commencée en 1940 grâce à l'ouverage
de L. Janossy et de ses collègues sur les gerbes de particules pénétrantes et
en concluant avec les travaux de C D . Anderson et de son groupe de Pasadena
qui, en 1950, confirmait les découvertes faites à Manchester. Nous
soulignons l'importance du rôle de P.M.S. Blackett.
Abstract. - Observations on the early history of the discovery of the strange
particles, starting in 1940 with the work of L. Janossy and his collaborators
on showers of penetrating particles and ending with the confirmation of the
Manchester discoveries by C D . Anderson and his group in Pasadena in 1950.
The r6le of P.M.S. Blackett is emphasised.
1. Pre-war Manchester. - My connection with Cosmic Rays stems from the appointment
of P.M.S. Blackett to the Langworthy Chair of Physics at Manchester University in
1937 in direct succession to three great physicists, Schuster, Rutherford and
Bragg, and in a building, the Schuster Laboratory, hallowed by the brilliant
discoveries of the Rutherford School. To Manchester in 1938 Blackett brought
J.G. Wilson and L. Janossy and a very important piece of equipment, an 11-ton
electromagnet and cloud chamber, which was destined to be used later by Clifford
Butler and myself on our V-particle work.
Bernard Lovell and I were already in Manchester working in other fields but we were
soon switched to cosmic Rays. Round Bruno Rossi and this group Blackett built
the Manchester School and by the end of 1938 a large programme of research was
under way. But the School was short-lived for the shadow of war was spreading
across Europe and indeed in the summer of 1939 the British members were sent to
man a secret Radar Station on the east coast. However, the Manpower Commission
decided, after the outbreak of war, that Manchester must continue to train
physicists, and so I was sent back to the University where, in addition to teaching
physics, I had to run a small fire brigade and help with Civil Defence. In
consequence I spent many hours in the University and there I came into close
contact with Lajos Janossy who was also in Civil Defence.
2. Janossy and penetrating showers. - As air raids were very infrequent Janossy
and I spent many hours discussing the major problems of Cosmic Rays and we rapidly
came to the conclusion that the experiment which he and Ingleby had started
in 1939 could be a key one. The set up is shown in Fig. 1. The arrangement is a
five-fold set of counters (123 AB) in a large mass of lead such that no particle
can trigger the set without penetrating at least 50 cm lead. The counters H
are hodoscoped. Fig. 2 is a picture of the equipment. With this equipment Janossy
showed there were showers, of rate about 40 per hundred hours, which could
penetrate great thicknesses of lead. Electro-magnetic cascades were completely
excluded as an electron shower would require an energy in excess of 10 seV and
these were very rare. Wataghin et al. \_2\ also found penetrating showers with a
rather simpler arrangement than Janossy's. Thus it seemed that if the showers were
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982807
JOURNAL DE PHYSIQUE
F i g . 1 - The Jsnossy-Ingleby
P e n e t r a t i n g Shower Set-up
[l]. T i s t h e producing
layer.
lead
Iron
12224rDzl
F i g . 2 - The ~ b n o s s y - I n g l e b y
P e n e t r a t i n g Shower s e t .
groups of p e n e t r a t i n g p a r t i c l e s , t h e equipment could be used f o r s t u d y i n g t h e i r
c r e a t i o n and p r o p e r t i e s . T h i s p o i n t was p u t t o B l a c k e t t i n 1940 and h e agreed t o
l e t u s c o n t i n u e r e s e a r c h i n a modest way. Thus I teamed up with J h o s s y and we
f i r s t addressed o u r s e l v e s t o t h e f o l l o w i n g two q u e s t i o n s :
1. c o u l d we show by c l o u d chamber s t u d i e s t h a t charged p e n e t r a t i n g p a r t i c l e s
(pp) were p r e s e n t i n p e n e t r a t i n g showers ( p s ) ?
2.
What was t h e n a t u r e of t h e p r i m a r i e s o f ps?
The f i r s t q u e s t i o n was answered i n t h e a f f i r m a t i v e by our g e t t i n g one of t h e many
cloud chambers i n t h e l a b o r a t o r y running.,triggered by a p s s e t . Examples of t h e
Other
f i r s t and l a t e r photographs a r e shown i n F i g s . 3 and 4 , L3] and L4].
workers i n t h e U.S.A.
and France o b t a i n e d s i m i l a r photographs.
N a t u r a l l y , we
t h o u g h t we were o b s e r v i n g cosmic r a y mesons, i e muons and of c o u r s e , we Were
wrong, a s t h e b r i l l i a n t I t a l i a n work showed l a t e r .
The second q u e s t i o n was answered by b u i l d i n g a more complex p i e c e of equipment a s
With
shown i n Fig. 5. by which t h e n a t u r e of t h e p r i m a r i e s could b e s t u d i e d [s].
t h i s equipment, which was designed t o study both charged and n e u t r a l p r i m a r i e s ,
we showed t h a t t h e a t t e n u a t i o n l e n g t h s o f both types were enormously longer t h a n
i f p s had been produced by t h e s o f t component, i n f a c t , of t h e order o f 300 g cmd2
of lead. J6nossyts previous i d e a was shown t o be wrong. The new r e s u l t s
suggested nucleons and were i n accord with t h e l a t e s t r e s u l t s of Schein and h i s
co-workers and t h e E-W e f f e c t discovered by Johnson.
An i n t e r e s t i n g by-product o f t h i s work was t h e abandonment o f much of t h e f o l k l o r e
surrounding t h e c o n s t r u c t i o n of G-M counters i n t h a t we showed t h a t none of t h e
complicated p r e p a r a t i o n of t h e copper f o i l , introduced, I b e l i e v e , by Max
Cosyns, was necessary. With polished copper s h e a t h s s t r a i g h t from t h e g l a s s
blower t h e anti-coincidence counters had e f f i c i e n c i e s of more than 99.9%. When
I t o l d t h i s s t o r y t o Bruno Rossi r e c e n t l y , he capped it with a s i m i l a r s t o r y
about t h e f o l k l o r e surrounding t h e n a t u r e of the wire.
JOURNAL DE PHYSIQUE
Fig. 5 - Ps s e t of ~ s n o s s y
and Rochester t o study t h e
n a t u r e of t h e p r i m a r i e s . The
anti-coincidence s h i e l d round
t h e producing l a y e r , T ,
allowed n e u t r a l p r i m a r i e s t o
be s t u d i e d .
3 . T h e o r e t i c a l s p e c u l a t i o n . - Because of t h e war we were t o t a l l y o u t of touch
with t h e o r e t i c a l p h y s i c i s t s and knew nothing Of t h e work of t h e Japanese o r
Americans. We knew two-meson t h e o r i e s were much i n vogue, h u t knew only of t h e
work of Hamilton, H e i t l e r and Peng who had suggested t h a t mesons a r e produced i n
r e a c t i o n s o f t h e type: -
-
P + P + ~ + P + Y
where t h e y ' s a r e Yukawa p a r t i c l e s w i t h t h e following p r o p e r t i e s :
1.
pseudoscalar mesons, T = 10-=s,s p i n 0, decaying t o e l e c t r o n s .
2.
v e c t o r mesons, T = 10-'s,
s p i n 1, a l s o decaying t o e l e c t r o n s .
Mesons of type 1 were i d e n t i f i e d with t h e o r d i n a r y CR mesons. Vector mesons were
thought r e s p o n s i b l e f o r t h e s o f t component. T h i s theory p r e d i c t e d s i n g l e production
~
t h a t successive s i n g l e production
and t h i s was obviously wrong, b u t ~ d n o s sshowed
i n a heavy nucleus, l i k e l e a d , would simulate showers.
4. Post-war work. The V-particles.- B l a c k e t t r e t u r n e d t o Manchester immediately
a f t e r t h e war and he quickly b u i l t up a s t r o n g School a g a i n and a department i n
which t h e l e v e l of s c i e n t i f i c c r i t i c i s m and t e c h n i c a l s k i l l was v e r y high. He was
very impressed with t h e work on ps and agreed t h a t t h e s e showers should be i n v e s t i gated with t h e b e s t equipment we had. We a l s o showed him a number o f c a s e s i n which
we had seen sudden l a r g e d e f l e c t i o n s of t r a c k s i n t h e g a s of t h e cloud chamber and
pointed o u t t h a t o t h e r s , e.g. Daudin i n France, had seen t h e same. I t was
impossible t o do much with t h e s e a t t h e time because o f t h e absence of magnetic
f i e l d s . Also t h e r e had been suggestions of h e a v i e r p - w t i c l e s e s p e c i a l l y t h e
I was t h e r e f o r e given a
unusual p a r t i c l e o f ~ e p r i n c e - R i n g u e t and L h e r i t i e r [6A.
brxght young colleague, C.C. B u t l e r , and t o g e t h e r we completely modernised t h e
B l a c k e t t magnet cloud chamber. New flash-tube l i g h t i n g was i n s t a l l e d , s p e c i a l
l e n s e s were obtained and f a s t Kodak f i l m used. Two types o f ps s e t , a s shown i n
Fig. 6 , were used and with t h e f i r s t t h e v o - p a r t i c l e was obtained on 1 5 t h October
F2ZZZZA
-1
00_
u
I
-
Fig. 6 - Various p s s e t s used with
magnet cloud chambers.
The two
on t h e l e f t a r e t h o s e used by
Rochester & B u t l e r while t h e
f i r s t on t h e r i g h t i s t h e
P i c du Midi Manchester s e t up.
The second on t h e r i g h t i s t h a t
of Thompson e t a l . a t Indiana.
- 0
O&O
CHS
CUS
1946 and with t h e second t h e f i r s t article on 24th May 1947. B l a c k e t t was
very e x c i t e d with t h e V-photographs and c o n s t a n t l y worked on t h e VO a s we d i d
a l s o , indeed, we a l l a r r i v e d a t t h e same answer simultaneously.
C r i t i c i s m and
argument from o t h e r c o l l e a g u e s i n t h e l a b o r a t o r y and i n t h e t h e o r e t i c a l s e c t i o n
was very h e l p f u l .
E s p e c i a l l y important was t h e key argument a r r i v e d a t by
B l a c k e t t which convinced everyone t h a t t h e ' e v e n t s ' r e p r e s e n t e d decays and not
interactions.
The c a s e was enormously s t r e n g t h e n e d i n my view by t h e d i s c o v e r y
t h e mass from t h e well-determined
of t h e V+ because t h i s gave an i n d i c a t i o n of
Apart from Manchester, I f i r s t t a l k e d a b o u t t h e new p a r t i c l e s i n
v a l u e of p*.
Dublin on 3rd December 1947 w i t h de Valera i n t h e audience.
It i s i n t e r e s t i n g
t o n o t e t h a t t h e e s s e n t i a l r e l a t i o n of n- and p- mesons was f i r s t a r r i v e d a t i n
d i s c u s s i o n s i n Dublin e a r l i e r i n t h e same y e a r , namely J u l y , 1947. The d i s c o v e r y
of t h e V - o a r t i c l e s was p u b l i s h e d on 20th December 1947 [7].
5. The ~au-meson. - The two y e a r s following 1947 were t a n t a l i z i n g and embarrassing
because no more V - p a r t i c l e s were found i n t h i s p e r i o d and, i n f a c t , t h e n e x t
important d i s c o v e r y of a p a r t i c l e of mass about 1,000 m, was made a t B r i s t o l i n
1949 by Brown e t a l . [8] who found i t i n one of t h e f i r s t e l e c t r o n - s e n s i t i v e
emulsions, t h e Kodak NT4, over exposed. The exposure took p l a c e a t t h e
Jungfraujoch t h e p l a t e s being under a c o n s i d e r a b l e t h i c k n e s s o f l e a d . This was
a n o t h e r key discovery because t h e form of t h e decay was completely determined and
hence t h e f i r s t p r e c i s e value of t h e mass of a K-meson was determined.
6. V - p a r t i c l e s 1948-50. - S i n c e t h e V - p a r t i c l e s occurred i n p s which were produced
by nucleons i t was Soon r e a l i s e d t h a t t o improve t h e y i e l d i t was e s s e n t i a l t o move
t h e equipment on t o a mountain and t o g e t dense m a t e r i a l c l o s e r t o t h e chamber.
B l a c k e t t d e c i d e d , t h e r e f o r e , t o s e t up a new team w i t h C l i f f o r d B u t l e r a s l e a d e r
w i t h a view t o e x p l o r i n g p o s s i b l e s i t e s and implementing any d e c i s i o n s r e moving
A s you w i l l h e a r t h e P i c du Midi was chosen l a r g e l y on t h e
from Manchester.
advice of O c c h i a l i n i and Cosyns and t h e c h o i c e proved i d e a l .
News of t h e new p a r t i c l e s discovered i n England i n 1947 s p r e a d r a p i d l y i n 1948 and
was undoubtedly a c c e l e r a t e d by l e c t u r e s a t t h e Symposium on Cosmic Rays i n honour
A l l t h e l e a d i n g cosmic r a y
of M i l l i k a n ' s 8 0 t h Birthday h e l d a t Cal. Tech. i n June.
s p e c i a l i s t s were t h e r e and t h e V - p a r t i c l e work i n p a r t i c u l a r r e c e i v e d good
A s a r e s u l t many cosmic r a y p h y s i c i s t s , notably C.D. Anderson,switched
publicity.
t h e i r cloud chambers t o p s work. The inOSt e x c i t i n g consequence f o r us was a l e t t e r
s e n t t o B l a c k e t t and myself i n Manchester on 28th November 1949 from Anderson
s t a t i n g t h a t he had completely confirmed t h e V - p a r t i c l e d i s c o v e r i e s . T h i s work was
p u b l i s h e d i n 1950 under t h e names of S e r i f f , Leighton, Hsiao, Cowan and Anderson
[9] and r e p o r t e d 6vofound i n Pasadena and 24 Vo and 4 ~ +
found a t White Mountain.
Good evidence f o r two-body decays, f o r l i g h t p a r t i c l e s of mass 200-400 me, and of
heavy p a r t i c l e s , l i k e p r o t o n s , was o b t a i n e d . Anderson never published photographs
of h i s V - p a r t i c l e s because of d i s t o r t i o n i n the g a s of t h e chamber b u t he k i n d l y
allowed J . G . Wilson and myself t o i n c l u d e s e v e r a l i n our book C b U d C h b a
Two examples a r e shown i n F i g s . 7 and 8.
P h o t ~ g h a p h n 0 6 thc? Co4m.k ic~ediaa%n [lo].
C8- 174
JOURNAL DE PHYSIQUE
7. Comment. - Since t h i s i s a h i s t o r y conference, it i s perhaps i n p l a c e t o make
some observations on the V-particle d i s c o v e r i e s .
I t seems t o me it i s f a i r t o
conclude t h a t t h e s e d i s c o v e r i e s followed a f a m i l i a r p a t t e r n i n t h a t they were t h e
Fig. 7 - An example o f a vo-decay
by S e r i f f e t a l . [9].
This would
appear t o b e s i m i l a r t o t h e o r i g i n
VO ( s e e [lo])
-
Fig. 8 - An example of a vo-decay
by S e r i f f e t a l . [g] i n which b o t h
products a r e h e a v i l y i o n i z i n g . This
would seem t o be a c a s e o f V -decay
with a proton and a l i g h t meson.
(see [LO]).
r e s u l t of good f o r t u n e , good s c i e n c e and t h e r i g h t technique.
The good f o r t u n e was
t o b e i n B l a c k e t t ' s Laboratory and have a counter-controlled magnet cloud chamber
working a t t h e r i g h t time, and of roughly t h e c o r r e c t p h y s i c a l dimensions t o have
a reasonably high p r o b a b i l i t y of s e e i n g t h e decays of r e l a t i v i s t i c p a r t i c l e s with
I t was good s c i e n c e t o use p s s e l e c t i o n
l i f e t i m e s i n t h e range 10-'s t o 10-1°s.
with a heavy m a t e r i a l l i k e l e a d c l o s e t o t h e chamber. A v i t a l t e c h n i c a l p o i n t of
g r e a t importance i n t h e discovery of t h e v o - p a r t i c l e was t h e f a c t t h a t counter
c o n t r o l provided t h e e s s e n t i a l requirement of time a s s o c i a t i o n .
Undoubtedly t h e
not being discovered
lack of time a s s o c i a t i o n was t h e main reason f o r
f i r s t i n emulsions.
articles
I have stressed h o w t h e V - p a r t i c l e w o r k g r e w n a t u r a l l y f r o m the w o r k on ps and t o
u n d e r l i n e t h i s p o i n t I w i l l c o n c l u d e w i t h s o m e c o m m e n t s m a d e by C a r l A n d e r s o n i n a
f a s c i n a t i n g h i s t o r i c a l paper [ll] presented t o t h e I n t e r n a t i o n a l S y m p o s i u m o n
P a r t i c l e P h y s i c s i n 1980. I n t h i s paper he gives an a c c o u n t of h i s p o s t - w a r w o r k
a n d of h o w he and h i s group f i t t e d o u t a B-29 i n 1 9 4 6 w i t h h i s m a g n e t cloud c h a m b e r
a n d m a d e 3 5 f l i g h t s each of 5 h o u r s d u r a t i o n a t a l t i t u d e s of b e t w e e n 30 - 4 0 , 0 0 0 f t .
T h e r e s u l t s w e r e i n t e r e s t i n g b u t he c o m m e n t s :
...
arguing about c o s m i c rays
" H a d w e f o r g o t t e n t h e B-29 and spent a w e e k
and p h y s i c s , w e could h a v e d o n e b e t t e r . A l l t h e clues w e r e p r e s e n t and
p u b l i s h e d , o n e of the m o s t i m p o r t a n t being the e x p e r i m e n t s of Jsnossy
i n w h i c h h e selected nuclear c o l l i s i o n s of high e n e r g y . We needed o n l y
a n d triple c o i n c i d e n c e s .
T h i s w o u l d have selected n u c l e a r
2 0 c m lead
e v e n t s a n d u n d o u b t e d l y w o u l d have g i v e n u s hundreds of the u n s t a b l e
particles
s u b s e q u e n t l y discovered by R o c h e s t e r and B u t l e r " .
...
...
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