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PRESENT AND FUTURE OF HIGH ENERGY PHYSICS
M. Veltman
To cite this version:
M. Veltman. PRESENT AND FUTURE OF HIGH ENERGY PHYSICS. Journal de Physique Col-
loques, 1980, 41 (C3), pp.C3-115-C3-123. �10.1051/jphyscol:1980315�. �jpa-00219834�
PRESENT AND FUTURE OF H I G H ENERGY ? H Y S I C S
Veltman, I I .
I n s t i t u t f o r T h e o r e t i c a l P h y s i c s , U t r e c h t U n i v e r s i t y , T h e Netherlands.
RESUME particles with m a ~ s ' ~ r o v i d e d that all L16tat actuel de la physique des couplin~s and particle multiplets obey hautes enerqies, et en particulier notre
connaissance actuelle des particules fonda- some symmetry. Differently stated : the mentales sont examids afin dl&valuer les
possibilit6s de yrogrss futur ainsi aue le Lagrangian of the theory must be symmetric r61e
a
jouer par les futurs Grands AccGlB-rateurs Europsens. under some transformations, and these
ABSTRACT transformations transform particles into
The present status of high-enerqy each other. If these requirements are not physics, and in particular our present
knowledge on fundamental particles and fulfilled then the theory is non-renormali- their interactions, are critically examined
in order to assess what proqress can be zable, which simply means that going beyond expected in the future and the role to be
played by future European Accelerators. the lowest order approximation one obtains infinity for all kinds of perfectly
sensible quantities.
Now it was already known for a long time that weak interactions are of a vector In recent years spectacular develop-
ments have taken place in elementary par- ticle physics. Both theory and experiment have met with great success in the past 3 years. We will try to give an outline of what happened, what are the current in- sights, and what is foreseen for the future Some of it will be known, but we will tell it all to sketch a coherent tableau.
The "new physics", as it is sometimes called,started in 1971 with the proof of renormalizatility of a class of theories, called gauge theories. In simpler,words it meant this: it is possible to construct theoretically a consistent quantum theory for systems also containing vector
nature, that is they behave as if a very massive vector particle is exchanged (Fig. 1)
Neutron decay N + p + e V + v e
Muon decay l~
-
+ v + e - + v e l~Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980315
JOURNAL DE PHYSIQUE
l e f t handed e l e c t r o n , n e u t r i n o
r i g h t handed e l e c t r o n
N e u t r i n o p r o c e s s v + N + u
-
+ P!J
A t low e n e r g i e s t h e W i s n o t e x p l i - c i t l y o b s e r v e d , t h e whole l o o k s l i k e a 4-fermion i n t e r a c t i o n . One sees t h e s p i n 1, t h e v e c t o r n a t u r e o f what i s exchanqed, b u t
l e f t handed meson, n e u t r i n o
r i g h t handed meson
F i g . 2
no a c t u a l p r o p a g a t i o n , and t h e mass h a s n o t For i n s t a n c e t h e c o u p l i n g W
+
(e-ve) i m p l i e sbeen measured. a c o u p l i n g WO (%ve) : n e u t r a l c u r r e n t s a r e
Up t o 1 9 7 1 no t h e o r y e x i s t e d f o r t h i s p r e d i c t e d . P i c t o r i a l l y t h i s law c a n b e k i n d of p r o c e s s ; everyone t r i e d t h i s model r e p r e s e n t e d a s a r a c e - t r a c k . T h i s t r a c k o r t h a t , and t h e r e e x i s t e d many more o r must b e c l o s e d ( F i g . 3 ) .
l e s s phenomenoloqical models. A f t e r 1971 g w -
we knew what t h e t h e o r y s h o u l d b e , and we knew what models were t h e b e s t o n e s from a
d quantum f i e l d t h e o r y p o i n t o f view. These
models a r e nowadays known a s t h e Weinberg model, and t h e G . I . M . (Glashow-Iliopoulos- Maiani) mechanism. We w i l l v e r y b r i e f l y d e s c r i b e t h e s e models.
I n t h e Weinberg model t h e symmetry i s SU2, and p a r t i c l e s a r e grouped i n s i n g l e t s and doub1,ets ( f i g . 2 )
.
There a r e f o u r+ -
v e c t o r - l i k e ' p a r t i c l e s , namely W
,
W,
WOand photon y. Under SU2 t h e p a r t i c l e s o f a m u l t i p l e t t r a n s f o r m i n t o e a c h o t h e r , and a l s o t h e v e c t o r p a r t i c l e s t r a n s f o r m i n t o e a c h o t h e r . A s a consequence i n v a r i a n c e under t h e g r o u p i m p l i e s t h a t one s o r t o f c o u p l i n g g e n e r a t e s o t h e r s .
The r e a c t i o n s e-+ ve+ W and e-+w+
imply t h e e x i s t e n c e o f e-+e-+ e WO and ve+ve+ wO. S i m i l a r l y f o r t h e p-v
1-1 system.
F i g . 3
The s o - p r e d i c t e d n e u t r a l c o u p l i n g s imply t h e e x i s t e n c e o f t h e r e a c t i o n :
v
+
e -+ v + e ( F i g . 4 )lJ lJ
F i g . 4
T h i s r e a c t i o n (and o t h e r s i m i l a r r e a c t i o n s have meanwhile been o b s e r v e d (Gargamelle, CERN). T h i s v e r y i m p o r t a n t e x p e r i m e n t a l
o f t h e model. t h e o r y i s t h e Cabbibo t h e o r y o f weak i n t e r - But now comes t h e q u e s t i o n o f c o u p l i n g a c t i o n s .
t o hadrons. Nowadays most h i g h e n e r g y p h y s i c i s t s b e l i e v e i n q u a r k s , and i n any c a s e it i s a n e f f e c t i v e d e s c r i p t i o n . A t t h a t t i m e t h r e e q u a r k s were needed t o e x p l a i n t h e t h e n known p a r t i c l e s . These q u a r k s were c a l l e d t h e up, down and s t r a n g e q u a r k r e s p e c t i v e l y , w i t h c h a r g e s 2/3, -1/3
and -1/3. Each o f t h e s e q u a r k s comes i n Cabbibo model o f weak i n t e r a c t i o n s t h r e e v a r i e t i e s , and t h i s i s d e n o t e d by a o f hadrons
c o l o r code.Thus t h e r e a r e t h r e e up-quarks F i g . 6
c a l l e d up-red, up-blue and up-green.
Most o f t h e knqwn hadrons a r e made up from t h r e e q u a r k s w i t h t h r e e d i f f e r e n t
c o l o r s ( t h u s making w h i t e a l t o g e t h e r ) o r s + U + W -
a quark and an a n t i q u a r k from t h e same U -t s + w +
c o l o r ( o r r a t h e r c o l o r and t h e complemen- I f gauge t h e o r y a p p l i e s t h e n t h e r e must be t a r y c o l o r , t h u s a g a i n making w h i t e ) . t r a n s i t i o n s such t h a t t h e r a c e - t r a c k c l o s e s Examples ( t h e b a r d e n o t e s t h e a n t i p a r t i c l e ) : T h i s i m p l i e s n e u t r a l c o u p l i n g s , such a s
udd
+
Neutron .rr
~a
P r o t o n uud K+ uE
Lambda uds
Neutron decay i s t h o u g h t t o b e due t o d-U-W- c o u p l i n g ( F i q . 5 )
N -t P
+
e-+ ve F i g . 5u + u
+ wO,
b u t a l s o t h e c o u p l i n g s + d+
WOd + s
+
WO ( F i g . 7 ).
However, t h i s c o u p l i n gNew c o u p l i n g s needed t o e n l a r g e Cabbibo t h e o r y i n t o gauge t h e o r y .
F i g . 7
i s e x p e r i m e n t a l l y e x c l u d e d b e c a u s e it would l e a d t o t h e decay:
A(uds) -t N(udd) + e+
-
e - ( F i g . 8 ) . And t h i s r e a c t i o n h a s n o t been s e e n .The r e a c t i o n t h e n known c o u l d a l l b e u n d e r s t o o d a s b e i n g due t o t h e v a r i o u s
JOURNAL DE PHYSIQUE
The decay A
-
N +e-+e following from+
the coupling s + d+wO Fig. 8
The cure to this problem is the G.1.M mechanism. A new quark and an alternative route are introduced (Fig.9):
A new quark of charge 2/3 is introduced in the G.I.M. scheme
Fig. 9
Supposedly this new quark, called charmed quark, was rather heavy, thus ncjL expeii- mentally discovered.
In a famous paper M.Gaillard,B.Lee and Rossner analyzed the situation and pointed out that this quark shohld not be heavier than 3 GeV.
In 1974 a new particle was discovered with a mass of about 3 . 1 GeV and called the J/$. Soon the hypothesis was put forward that this J/$ particle was a bound state of a charm and an anti-charm quark, which would imply that the charmed quark has a mass of about 1.5 GeV. Since then many experiments have confirmed this idea, and
we have learned that this G.I.M. idea is correct. Thus there exists a fourth quark, and in the past few years a whole spectrum of new particles, all in the 2-3 GeV region has been established. They are understood again as three-quark and quark-anti-quark bound states, but now with one or more of these quarks being the new heavy charm quark-Needless to say that all this was a tremendous boost to the gauge idea.
Meanwhile, as usual in physics, the picture has changed again, and many
question marks have appeared. Let us first discuss a very fundamental problem.
One of the very outstanding and intriguing problems is this: why is elec- tric charge quantized ? Why have proton and electron so precisely opposite charge ?
This feature finds some explanation in gauge theories. There is a class of gauge theories where the electric charges of all particles are related to each other.
In these theories the sum of the electric charges of all the elementary particles must be zero. Let us make up the balance
including the new charm quark and also taking into account that every quark occurs in three color types
leptons quarks
Indeed, the sum total is zero ! This is
l i t t l e a b o u t t h e u n d e r l y i n g t h e o r y . However, t h e e x p e r i m e n t a l i s t s from SLAC had a n o t h e r s u r p r i s e coming: t h e y d i s c o v e r e d y e t a n o t h e r l e p t o n , t h e T w i t h i t s own n e u t r i n o . T h i s r p a r t i c l e behaves r e a l l y p r e c i s e l y a s a n e l e c t r o n , e x c e p t t h a t it i s much h e a v i e r . I t h a s t h e same c h a r g e a s t h e e l e c t r o n , it seems t o be c o u p l e d i n weak i n t e r a c t i o n s p r e c i s e l y l i k e t h e e l e c t r o n , and f u r t h e r m o r e , l i k e t h e e l e c t r o n , it i g n o r e s t h e s t r o n g i n t e r a c t i o n And f i n a l l y , l i k e t h e e l e c t r o n , it h a s i t s own n e u t r i n o , a s was s u b s e q u e n t l y d i s c o - v e r e d . T h i s e x g e r i m a n t a l d i s c o v e r y , unasked f o r by t h e o r i s t s had o n e u n d e s i r e d conse- quence : t h e T - l e p t o n u p s e t s o u r e l e c t r i c b a l a n c e .
How t o c u r e t h i s e l e c t r i c u n b a l a n c e ? I f we t r y t o c u r e t h i s w i t h q u a r k s we need a n o t h e r two q u a r k s , t ( t o p , c h a r g e 2/3) and b (bottom, c h a r g e - 1 / 3 ) , each a g a i n i n t h r e e c o l o r v a r i e t i e s . Then, by j u s t d u p l i - c a t i n g t h e c o n f i g u r a t i o n s e e n w i t h e l e c t r o n and muon t h e e l e c t r i c b a l a n c e c a n b e r e s - t o r e d . Of c o u r s e , t h e r e a r e o t h e r r e s p o n s i - b i l i t e s , b u t i n t h e p r e s e n t t h e o r e t i c a l scheme t h a t was t h e s i m p l e s t p o s s i b l e e x t e n s i o n .
Another m i r a c l e o c c u r e d . Very r e c e n t l y Lederman e t a l . , d i s c o v e r e d a n o t h e r new p a r t i c l e t h a t looked v e r y much l i k e t h e f i r s t symptom o f a bottom q u a r k w i t h a mass o f a b o u t 5 GeV. I n f a c t , t h e y d i s c o v e r e d t h e u p s i l o n , w i t h a mass o f a b o u t 9.5 G e V , and t h i s u p s i l o n was s p e c u l a t e d t o a bottom-anti-bottom q u a r k bound s t a t e . I f t h i s i s t r u e t h e n we must e x p e c t a n o t h e r
Meanwhile DESY i n Hamburg h a s confirmed and aucpented t h i s d i s c o v e r y . And v e r y soon PETRA, t h e new e l e c t r o n machine i n Hamburg, w i l l h o p e f u l l y g i v e u s a l l t h e d e t a i l s .
Aside from t h e bottom q u a r k we s r i l l need a n o t h e r q u a r k , t h e t o p quark. By now most h i g h e n e r g y p h y s i c i s t s a r e p r e p a r e d t o b e l i e v e t h a t it e x i s t s , and we w i l l a l s o assume t h a t it w i l l be d i s c o v e r e d i n d u e t i m e . But now o n e g e t s t h e uneasy f e e l i n g t h a t l e p t o n s and q u a r k s a r e l i k e r a b b i t s , m u l t i p l y i n g i n an u n c o n t r o l l e d way. Is t h e r e a l i m i t t o t h i s game ? W i l l more and more l e p t o n s and q u a r k s t u r n up a s we go t o h i g h e r and h i g h e r e n e r g i e s ? Is t h e r e a l i m i t ? What do we know ?
L e t u s make a n i n v e n t o r y o f t h i n g s d i s c o v e r e d s o f a r . A p i c t u r e r e s e m b l i n g t h r e e f l a g p o l e s emerges ( F i g . 1 0 )
The t h r e e f l a g p o l e s F i g . 10
F o r c e s between t h o s e p a r t i c l e s a r e due t o g l u o n s t h a t m e d i a t e s t r o n g i n t e r a c t i o n s and c o u p l e o n l y t o q u a r k s , and t h e weak f o r c e s a r e due t o t h r e e v e r y heavy v e c t o r bosons W
+ ,
W- and wO, w i t h a mass o f 80- 90 GeV. These v e c t o r bosons c o u p l e . t o-
q u a r k s and 1eptons.The e l e c t r o m a g n e t i c f o r c e s a r e mediated by photons t h a t c o u p l e t o c h a r g e d p a r t i c l e s . There i s a n o t h e r
.
-c3-120 JOURNAL DE PHYSIQUE
f o r c e and o t h e r p a r t i c l e s r e q u i r e d by t h e t h e o r y , b u t we w i l l d i s c u s s t h a t l a t e r .
The f i r s t q u e s t i o n t h a t comes t o mind i s : a r e t h e r e s t i l l more l e p t o n s and q u a r k s ? Is t h e r e p r e h a p s a n i n f i n i t e sequence of f l a g p o l e s ?
Concerning t h i s t h e r e i s an argument coming from a s t r o p h y s i c s , from a n i d e a due t o Shrartsman. The argument was c a r r i e d f u r t h e r by Steigman e t a l . , and f i n a l l y by Hut ( P h y s . L e t . E ( l 9 7 7 ) 8 5 ) . The i d e a i s t h a t t h e t h e r m a l e q u i l i b r i u m a t t h e t i m e o f t h e b i g bang depends on what p a r t i c l e s t a k e p a r t i n t h e p a r t i t i o n . And a f t e r t h e
" f r e e z e i n " t h i s r e f l e c t s i t s e l f i n t h e n e u t r o n / p r o t o n r a t i o , which i n t u r n c a n be o b s e r v e d from Helium abundance i n t h e Universe. And s e c o n d l y , i f it comes t o weakly i n t e r a c t i n g n e u t r a l p a r t i c l e s such a s m a s s - l e s s n e u t r i n o ' s t h e n t h e r e c a n n o t b e t o o many k i n d s o f them, b e c a u s e , b e i n g s t a b l e , t h e y would s t i l l be around and add t o t h e 'energy c o n t e n t o f t h e Universe. T h a t however can b e t o l e r a t e d o n l y up t o some e x t e n d .
The c o n c l u s i o n from t h e s e arguments i s t h a t t h e r e a r e a t most 8 d e g r e e s of freedom a v a i l a b l e f o r s t a b l e m a s s i v e n e u t r a l
l e p t o n s . As f o r m a s s - l e s s n e u t r i n o ' s t h e r e i s s t i l l room f o r 2 o f t h e s e . Thus i f new f l a g p o l e s c o n t a i n a l s o m a s s - l e s s n e u t r i n o ' s t h e n we c a n t o l e r a t e a t most two new
f l a g p o l e s . I n any c a s e , t h e number i s l i m i t e d , and t h e r e c a n b e no i n f i n i t e s e r i e s o f f l a g p o l e s w i t h m a s s - l e s s n e u t r i - n o ' s .
The above argument depends o n cosmo- l o g y , and f u r t h e r m o r e t h e new n e u t r i n o ' s
c o u l d have mass, be u n s t a b l e , and s o e s c a p e t h i s argument. I f however t h e s e n e u t r i n o ' s a r e p a r t o f a f l a g p o l e , w i t h c e r t a i n mass d i f f e r e n c e s between t h e p a r t i c l e s o f such a f l a q p o l e , t h e n a n o t h e r argument a p p l i e s . I t h a s been shown t h a t t h e sum o f t h e mass d i f f e r e n c e s c a n n o t exceed a c e r t a i n number, and t o be s p e c i f i c , i f t h e r e i s o n l y one new f l a g p o l e t h e n t h e mass d i f f e r e n c e must be l e s s t h a n 5 0 0 GeV. While t h i s number i s l a r g e , it i s n e v e r t h e l e s s n o t i n f i n i t e , and a g a i n we c o n c l u d e t h a t t h e number o f f l a g - p o l e s i s l i m i t e d . I n f a c t , i n c l u d i n g a l s o some o t h e r , much vaguer c o n s i d e r a t i o n s , o n e g e t s t h e f e e l i n g t h a t t h e r e i s maybe o n e , o r p e r h a p s two new f l a g p o l e s , b u t no more.
So t h i s i s a s f a r a s t h i n g s have come t o d a y . The v e r y e x c i t i n g p a s t 8 y e a r s have b r o u g h t u s gauge t h e o r i e s , a s w e l l a s a massive amount of e x p e r i m e n t a l d a t a showing t h a t t h e s e i d e a s a p p l y t o weak, e . m . and s t r o n g i n t e r a c t i o n s . And g r a d u a l l y we have come t o a new s i t u a t i o n , w i t h new q u e s t i o n s and new p e r s p e c t i v e s . Again n a t u r e p u t s new p y s t e r i e s i n f r o n t o f u s , and a g a i n p l a n s a r e made t o probe e x p e r i m e n t a l l y f o r f u r t h e r i n f o r m a t i o n .
A l t o g e t h e r what we know t o e x i s t , o r b e l i e v e t o e x i s t , c a n b e t a k e n a l t o g e t h e r i n a v e r y s i m p l e t h r e e f l a g p o l e p i c t u r e . These t h r e e f l a g p o l e s c o n t a i n f e r m i o n s , t h a t , i s q u a r k s and l e p t o n s , o f s p i n 1 / 2 o n l y . F u r t h e r t h e r e a r e f o r c e s between t h e s e p a r t i c l e s , and a s s o c i a t e d w i t h t h e s e f o r c e s t h e r e a r e a d d i t i o n a l p a r t i c l e s ,
namely :
W
' ,w-, wO, intermediating weak interactions, 8 gluons, intermediating strong interactions.
The t h e o r y p r e d i c t s masses o f 80 and 9 0 GeV f o r W
t
and W0 r e s p e c t i v e l y . A l l t h e s e p a r t i - c l e s have s p i n 1.A symmetry i s a s s o c i a t e d w i t h e a c h i n t e r a c t i o n , namely U (1)
,
SU ( 2 ) and SU ( 3 ) r e s p e c t i v e l y .I n a d d i t i o n t o a l l t h i s t h e t h e o r y r e q u i r e s t h e e x i s t e n c e o f a t l e a s t one more p a r t i c l e , of s p i n 0 and o f a s a s y e t unde- t e r m i n e d mass. T h i s p a r t i c l e i s c a l l e d t h e Higgs p a r t i c l e and i n t h e t h e o r y t h i s p a r t i c l e i s t h e r e t o m e d i a t e a new f o r c e . T h i s f o r c e i s i n t r o d u c e d a s a means t o g i v e masses t o a l l p a r t i c l e s , f e r m i o n s and v e c t o r b o s o n s . A s a consequence t h i s Higgs p a r t i c l e i s c o u p l e d t o a l l m a s s i v e p a r t i - c l e s , w i t h a s t r e n g t h p r o p o r t i o n a l t o t h e masses o f t h e s e p a r t i c l e s .
Looking a t a l l t h i s many q u e s t i o n s a r i s e . F i r s t of a l l , b e l i e v i n g e v e r y t h i n g s t a t e d s o f a r , t h e r e a r e s t i l l g e n e r a l un- u n d e r s t o o d f a c e t s o f t h e t h e o r y . For
i n s t a n c e , we do n o t u n d e r s t a n d y e t comple- t e l y q u a r k confinement. I t seems a n e x p e r i - m e n t a l f a c t , t h e t h e o r y a l s o c o n t a i n s some
s t r o n g s u g g e s t i o n s i n t h i s s e n s e , b u t u p t o now n o t h i n g h a s been proven.
Secondly, t h e r e a r e some f a c t s p r e d i c - t e d by t h e t h e o r y t h a t have n o t y e t been t e s t e d e x p e r i m e n t a l l y . For i n s t a n c e , t h e W-bosons o f weak i n t e r a c t i o n s h a v e , n o t y e t , been shown t o e x i s t . And a b s o l u t e l y n o t h i n g i s known f o r s u r e a b o u t t h i s new f o r c e a s s o c i a t e d w i t h t h e e q u a l l y h y p o t h e t i c a l
Higgs p a r t i c l e .
which we have no e x p l a n a t i o n . To be p r e c i s e t h e y a r e n o t i n c o n f l i c t w i t h t h e t h e o r y , b u t on t h e o t h e r hand t h e y a r e n o t needed e i t h e r . L e t u s c o n c e n t r a t e f o r a moment on t h e s e e x t r a f e a t u r e s .
The f i r s t q u e s t i o n is: why a r e t h e r e t h r e e f l a g p o l e s ( o r maybe f o u r o r f i v e ) ? I s t h e r e a d e e p e r s t r u c t u r e u n d e r l y i n g t h i s ? F o r i n s t a n c e , t h e p e r i o d i c system of atoms i s a t h i n g t h a t we now u n d e r s t a n d a s b e i n g L d u e t o t h e f a c t t h a t t h e atoms a r e b u i l d u p from p r o t o n s , n e u t r o n s and e l e c - t r o n s . P e r h a p s t h e f l a g p o l e s a r e due t o some f u r t h e r i n t e r n a l s t r u c t u r e o f t h e p a r t i c l e s . I f t h i s i s s o , t o what e n e r g y must we go b e f o r e t h i s s t r u c t u r e shows up ? For example, i f hydrogen atoms c o l l i d e w i t h an e n e r g y o f a few eV t h e n t h e y b r e a k up
( i o n i s e ) , and we s e e t h e c o n s t i t u e n t s ( p r o t o n and e l e c t r o n ) . Can we e x p e c t some- t h i n g s i m i l a r f o r e l e c t r o n s o r q u a r k s , b u t a t much h i g h e r e n e r g y ?
Another g r e a t mystery shows i n t h e masses o f t h e v a r i o u s p a r t i c l e s . The q u a r k masses a r e n o t w e l l known (due t o t h e f a c t t h a t no f r e e q u a r k s have been o b s e r v e d ) , b u t w e have some i d e a s . The f o l l o w i n g r e s u l t s o b t a i n f o r t h e t h r e e f l a g p o l e s (we i g n o r e t h e c o m p l i c a t i o n s due t o ~ a b b i b o m i x i n g ) .
It must b e s t a t e d t h a t we do n o t know which
C3-122 JOURNAL DE PHYSIQUE
l e p t o n p a i r g o e s w i t h what a u a r k p a i r , b u t we have a r r a n g e d them i n o r d e r o f i n c r e a - s i n g mass.
Concerning now t h e s e masses we r e a l l y have no i d e a where t h e y come from. I n t h e t h e o r y t h e y c o r r e s p o n d t o f r e e p a r a m e t e r s and it i s r e a l l y t h i s f e a t u r e t h a t i s d i s - t u r b i n g . The t h e o r y h a s t o o many f r e e p a r a m e t e r s . I t seems i m p o s s i b l e t o e s c a p e t h e i d e a t h a t t h e r e must b e a d e e p e r s t r u c - t u r e , which t h e n n a t u r a l l y g i v e s r i s e t o t h i s l a r g e number o f t h i n g s .
I f we a c c e p t t h i s view t h e n t h e v e r y fundamental q u e s t i o n o f t h i s moment i s : a t what energy w i l l t h i s d e e p e r s t r u c t u r e show up ?
Very l i t t l e c a n be s a i d on t h i s m a t t e r . The Only c l u e d i s c o v e r e d s o f a r i s i n t h e Higgs system. Now t h i s system i s r e s p o n - s i b l e f o r t h e p a r t i c l e masses, and it seems n a t u r a l t o suppose t h a t t h i s i s t h e segment o f t h e t h e o r y t h a t i s t h e most i n t e r e s t i n g from t h e above p o i n t o f view.
Here t h e f o l l o w i n g f a c t h a s been d i s c o v e r e d i f t h e Higgs p a r t i c l e i s h e a v i e r t h a n 1000 G e V t h e n t h e Higgs f o r c e s become v e r y
a n e n e r g y o f a b o u t 300 GeV. R i g h t now c o n s t r u c t i o n i s underway t o p u l l a n t i - p r o t o n s of t h e same e n e r g y i n t o t h e same r i n g , t u r n i n g however i n t h e o p p o s i t e s e n s . I n t h i s way c o l l i s i o n s i n v o l v i n g hundreds o f GeV w i l l be p o s s i b l e by t h e end o f 1981.
However, t h e p r o t o n (and t h e a n t i - p r o t o n ) i s n o t a n e l e m e n t a r y p a r t i c l e , b u t i s made up from t h r e e q u a r k s and a c l o u d o f g l u o n s . And e a c h o f t h e s e q u a r k s c a r r i e s o n l y a p a r t o f t h e e n e r g y . The c o l l i s i o n s w i l l t h e r e f o r e be complex r e a c t i o n s ,
i n v o l v i n g c o l l i d i n g q u a r k s , and q u a r k s p a s s i n g o n , and masses o f g l u o n s exchanged and e m i t t e d ( i n t h e form o f p i o n s , u l t i - m a t e l y ) . A l t o g e t h e r we e x p e c t a complex s i t u a t i o n , and it w i l l b e v e r y d i f f i c u l t t o o b s e r v e t h e e f f e c t s t h a t we a r e i n t e - r e s t e d i n .
I t i s f o r t h e s e r e a s o n s t h a t h i g h e n e r g y p h y s i c i s t s have t u r n e d t o e l e c t r o n machines, i n f a c t t o e l e c t r o n - p o s i t r o n c o l l i d i n g beams. I n European c o n t e x t a p r o p o s a l f o r a l a r g e e l e c t r o n - p o s i t r o n machine (LEP) i s b e i n g p r e p a r e d , and we s t r o n g f o r c e s t h a t c o u l d w e l l g i v e r i s e t o hope t h a t t h i s machine w i l l g i v e u s some bound s t a t e s and composite systems. T h i s i s answers t o t h e fundamental i s s u e s . The t h e n t h e humber s u g g e s t e d by t h e t h e o r y : e n e r g y w i l l p r o b a b l y n o t b e beyond 300 G e V something i n t h e r a n g e o f 1000 GeV. We i n t o t a l , b u t t h i s i s enough t o e x p l o r e e x p e c t t h a t a t a n e n e r g y below, o r n o t much f o r f u r t h e r f l a g p o l e s , and t o e s t a b l i s h above t h i s v a l u e t h i n g w i l l c r a c k up, w e t h e e x i s t e n c e o f t h e v e c t o r bosons.
w i l l s e e a new s t r u c t u r e , and heaven knows Moreover, we may r e s o n a b l y hope t o g e t more
what it w i l l be. i n s i g h t i n t h e Higgs f o r c e s , b e c a u s e such
What c a n b e done from a n e x p e r i m e n t a l a machine would b e c a p a b l e o f t h e produc- p o i n t o f view ? An e n e r g y o f 1000 GeV i s by t i o n o f a p a i r o f v e c t o r bosons, and s i n c e i t s e l f not'beyond t e c h n i c a l p o s s i b i l i t i e s . t h e s e p a r t i c l e s a r e s o heavy a l s o t h e Higgs
I
A t CERN,Geneva, p r o t o n s a r e a c c e l e r a t e d t o f o r c e between them i s a p p r e c i a b l e and
The machine mentioned i s r e a l l y v e r y b i g , v e r y d i f f i c u l t t o c o n s t r u c t and expen- s i v e i n e x p l o i t a t i o n . To g i v e n a n i d e a o f t h e problems it i s p e r h a p s i n s t r u c t i v e t o d i s c u s s some f e a t u r e s o f t h i s machlne.
The v e r s i o n p r e s e n t l y under s t u d y a t CERN c o n s i s t s of a l a r g e r i n g w i t h a d i a - m e t e r o f 10 kms. I n t h i s r i n g t h e r e c i r - c u l a t e two beams i n t h e o p p o s i t e s e n s . Each beam i s made up from 4 bunches. The e l e c - t r o n s and p o s i t r o n s have an energy o f
----
85 GeV implying a f3 ( = l / K v 2 / c 2 ) o f 17 ' x
l o 8 .
Each beam c o n t a i n s a b o u t 5 x 10 12 p a r t i c l e s .I n i t s e l f from a macroscopic p o i n t o f view, t h e energy r e s i d i n g i n e a c h beam i s n o t v e r y l a r g e , namely a b o u t 2.2 x 1 0 - ~ k w h . The t r o u b l e i s t h a t e l e c t r o n s g o i n g around l o s e e n e r g y t h r o u g h s y n c h r o t r o n r a d i a t i o n and t h i s l o s s i s b i g b e c a u s e f3 i s s o l a r g e I n f a c t , w i t h t h e r a d i u s g i v e n t h e l o s s i s a b o u t 1 . 5 % p e r t u r n , which means t h a t p e r t u r n 3 x 1 0 - ~ kwh must b e p r o v i d e d . Now t h e e l e c t r o n s t u r n 10.000 t i m e s p e r second, t h a t i s 3.6 x
l o 7
t u r n s p e r h o u r , and we s o f i n d an e n e r g y l o s s o f 10.8 x10 kwh= 3 11 Mw.S i n c e t h e r e a r e two beams we have a l o s s of 22 Mw, which must b e p r o v i d e d c o n t i n u o u s l y . T h i s s e t s t h e s c a l e o f ' t h i n g s . The power must be p r o v i d e d t h r o u g h c a v i t i e s t h a t a r e
f e d by k l y s t r o n s , o s c i l l a t i n g a t a f r e - quency o f 353 Mhz. Of c o u r s e , l o s s e s a l s o o c c u r h e r e , and f u r t h e r m o r e t h e r e i s energy consumption a l s o i n t h e bending magnets.
A l l t o g e t h e r t h e machine w i l l need more t h a n 100 Mw t o g e n e r a t e , i n t h e end ( g o i n g t o h i g h e r e n e r g y ) p e r h a p s a s much a s 300 Mw
energy consumption ( a b o u t 10-30 % o f t h e o u t p u t o f an e l e c t r i c i t y c e n t r a l ) may w e l l be an o b s t a c l e . I n any c a s e , we a r e c l e a r l y coming t o t h e l i m i t s of t h e p o s s i b l e . I f e v e r we want t o go t o h i g h e r e n e r g i e s we w i l l need o t h e r p r i n c i p l e s . A p o s s i b i l i t y
i s c o l l i d i n g l i n e a r a c c e l e r a t o r s ; t h i s w i l l b e p o s s i b l e p r o v i d e d low t e m p e r a t u r e p h y s i c i s t s succeed i n b u i l d i n g good s u p e r - c o n d u c t i o n c a v i t i e s ( s e e U.Amaldi,Physics Let.61B(1976) - 3 1 3 ) .
The machine e n v i s a g e d , c o s t i n g a b o u t 10' Swfr. can be p a i d o u t o f t h e c u r r e n t CERN budget o v e r a p e r i o d o f a b o u t 8 y e a r s . The p l a n i s n o t t o a s k f o r more money, b u t t o do i t w i t h t h e p r e s e n t means. Whether t h i s i s r e a l l y p o s s i b l e , and whether governments w i l l a g r e e w i t h t h i s w i l l become c l e a r w i t h i n t h e n e x t two y e a r s . And t h e n p e r h a p s around 1988 e x p e r i m e n t s w i l l s t a r t p r o b i n g f u r t h e r i n t o t h o s e v e r y , v e r y deep m y s t e r i e s o f n a t u r e .
