LIMITING TRENDS VISIBLE AT LOWER ENERGIES

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LIMITING TRENDS VISIBLE AT LOWER ENERGIES

Horst Wahl

To cite this version:

Horst Wahl. LIMITING TRENDS VISIBLE AT LOWER ENERGIES. Journal de Physique Colloques, 1973, 34 (C1), pp.C1-373-C1-378. �10.1051/jphyscol:1973151�. �jpa-00215231�

LIMITING TRENDS VISIBLE AT LOWER ENERGIES

LIMITING TRENDS VISIBLE AT LOWER ENERGIES Horst WAHL

CERN

1.- INTRODUCTION : APOLOGIES AND JUSTIFICATION. -

This report deals with the results on many body reac- tions obtained in the momentum range up to 30 GeV/c.

Due to the high number of papers submitted, not all of them could be considered, and I apologize for all the omissions I made.

Although the asymptotic region may not even start at ISR energies, I nevertheless believe that there is justification for studying many body reactions below 30 GeV/c incident energy. The main reasons are the following :

c Also atSOGeV/c,many body reactions represent a large fraction of the cross section. Therefore, the knowledge of these reactions is necessary to complete one's picture of hadron reactions at low energies.

A lot of data has been accummulared and is ready to be used for physics analysis. These data can be used not only to study these reactionsbut also to develop methods for the study of many body reactions.

a The knowledge of these reactions at low energies is also useful to find trends in the energy beha- viour. Also it has been pointed out by Van Horn [I]

that two of the characteristic features of inclusive reactiorsat high energies, namely the existence of a diffractive and a pionization component, was already evident in studies of exclusive four-body reactions between 10 and 20 GeV/c.

2.- ORIGIN OF THE DATA. - Most of the data pre- sented here originate from bubble chamber experi- ments done by large collaborations.

Table I Collaboration

...

Bonn-Hamburg-Munchen

Aachen-Berlin-Bonn-CERN-Cracow- Heidelberg-Warsaw

Aachen-Berlin-CERN-London-Vienna Athens-Democritas-Liverpool-Vienna Notre-Dame

-

CERN-Bruxelles Vanderbilt-Yale Scandinavian

3.- SINGLE PARTICLE PRODUCTION.

3.1. - KO, A AND

a

gitudinal distributions is summarized in Table 2.

Init.

state

---

PP rtfp n p K - ~ K - ~ K-P K+P pp PP

Beam GeV/c

---

12,24 8,16,23

16 10,16 8 I : :

; 5,8,16

21.5 19

Table 2 Initial

state

---

PP

K-P K+P PP K-P K+P

'~'p

I

I

1

Particle observed

---

KO

-

KO

KO

A A A

-

Momentum range

_---__

12-205

3.9-16 5- 16 12-205 3-16 8- 16

--- a rise

(factor41

-

rises slowly rises like ,-I12 decreases rises

Shape of F (x)

---

-'Onst.

changes

? changes changes changes changes

References

(nb. of papers at this Conference

- _ _ _ _ - - _ _ _ _ - - _ _ _ _ _ _ - - -

369

303 2 papers with contradicting 82

)

3 92 369 3 03 401

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1973151

C1-374 H. WAHL

The energy behaviour of K-p + A + x ^{and K-p + KO+} x

i s shown i n f i g u r e 1.

K-p total cross section

1

F i g . 1

-

Lab

The p o l a r i z a t i o n of t h e A i s found t o be compati- b l e w i t h z e r o when t h e A i s produced i n K+p o r pp i n t e r a c t i o n s , w h i l e i t i s n e g a t i v e f o r forward A's produced i n K - ~ r e a c t i o n s [ 2 ]

.

T h e r e f o r e t h i s e f f e c t seems t o be a s s o c i a t e d w i t h baryon exchange.

3.2. - ^x0 PRODUCTION. - The p r o d u c t i o n of n e u t r a l p i o n s h a s been s t u d i e d i n t h e p a p e r s 198, 220, 288, 369, 379 and 384. I t i s by now a w e l l e s t a b l i s h e d f a c t t h a t (n .) i s roughly l i n e a r l y dependent

x "-

on n-

.

3.3. - RESONANCE PRODUCTION.

-

3.9 mb 2 0.4 mb f o r t h e r e a c t i o n pp + POX a t 24GeV/c, v i a v e c t o r meson dominance t h e a u t h o r s o b t a i n a n

Fig.2

-

.

e s t i m a t e f o r l e p t o n p a i r p r o d u c t i o n i n pp i n t e r a c - more, assuming DselI-Yan s c a l i n g e0 - F( - 1 Q2

t i o n s : ^{2 dQ2} - Qe s

t o h o l b o n t h e average i n t h e Q r e g i o n dominated

-32 2 by v e c t o r mesons, they o b t a i n

4 . 5 ~ 1 0 cm G ~ v - ' f o r M e e = 1 GeV

dC/dMee ¹

6. ~ X I O - ~ ~ C ~ ~ G ~ v - ' f o r Me, = 2 CeV

.

s = 2770 Gev2 ,

These v a l u e s a g r e e w i t h t h e r e s u l t s of t h e Columbia-

which a g r e e s with t h e 90% C.L. upper l i m i t of t h e Brookhaven experiment a t 29.5 GeV/c [ 4 1

.

LIMITING TRENDS VISIBLE AT LOWER ENERGIES ^C1-375

4.- CHARGE DISTRIBUTIONS AND CHARGE EXCHANGE.

-

4.1.- CHARGE DISTRIBUTIOXS. - The d i s t r i b u t i o n of c h a r g e i n r a p i d i t y i s g i v e n by

where t h e sum i s t a k e n o v e r a l l c h a r g e d p a r t i c l e s c and qc d e n o t e s t h e c h a r g e o f p a r t i c l e c , I f t h e s i n g l e p a r t i c l e d i s t r i b u t i o n s dcc/dy have a p l a - t e a u i n t h e c e n t e r , we e x p e c t t h e c h a r g e d i s t r i b u - t i o n s a l s o t o have s u c h a p l a t e a u , w i t h a h e i g h t which d e c r e a s e s l i k e ( e n s ) -I.

T h e a u t h o r s of p a p e r 1 4 3 u s e t h e c h a r g e d i s t r i b u t i o n s from R +- p i n t e r a c t i o n s a t 16 GeV/c [ 6 ] t o e x t r a c t t h a t p a r t o f t h e c h a r g e d i s t r i b u t i o n coming from p r o t o n f r a g q e n t a t i o n . From t h i s , t h e y r e c o n s t r u c t t h e c h a r g e d i s t r i h u t i o n e x p e c t e d f o r pp i n t e r a c - t i o n s . A s c a n be s e e n i n f i g u r e 3 , t h e agreement

Ycm

F i g . 3 - Comparison o f + t h e c h a r g e d i s t r i b u t i o n as, r e c o n s t r u c t e d from X-p d a t a w i t h t h e e x p r i m e n t a l one. F i g u r e from p a p e r 143,

between e x p e r i m e n t a l and r e c o n s t r u c t e d d ' i s t r i b u t i o n i s q u i t e good. T h i s c a n be c o n s i d e r e d a s a n o t h e r p i e c e o f e v i d e n c e f o r f a c t o r i z a t i o n .

4 . 2 . - CHARGE EXCHANGE.

-

F o r y = ⁰ , we o b t a i n t h e o r d i n a r y charge-change i n one hemisphere a s d e f i n e d i n LPS-analyses o f ex- c l u s i v e r e a c t i o n s . The f r a c t i o n s o f t h e t o t a l i n e - l a s t i c c r o s s s e c t i o n c o n t r i b u t i n g t o d i f f e r e n t v a l u e s o f c h a r g e exchange have been d e t e r m i n e d i n K-p and pp i n t e r a c t i o n s [7]. I t i s found t h a t : ( a ) AQ = 0 and ~ A Q 1 z 1 a r e e q u a l l y i m p o r t a n t , ( b ) AQ = 0 dominates t h e low m u l t i p l i c i t i e s . When one p l o t s

-

.

K - ~ and pp d a t a c o i n c i d e and a r e e n e r g y indepen- d e n t between 1 0 and 205 GeV/c ( s e e f i g u r e 4)[8].

F i g . 4

-

-

/As) f o r t h e r e a c t i o n s i n d i c a t e d ( d a t a from p a p e r s 8 1 , 1 4 3 and p r i v a t e communication). 1 0 GeV/c K-0 y = 0 , + 12 GeV/c pp y = -1, - . 5 , 0 , 16 GeV/c K-p y = ^{0 , 0} 24 GeV/c pp y = -1, - . 5 , 0 , 7 102 GeV/c pp y = 0 , A 205 GeV/c pp y = 0

.

From c l . u s t e r models [91 one e x p e t s t h e s q u a r e of t h e d i s p e r s i o n o f t h e c h a r g e exchange, D' = ((LQ)')

-

.

A i s t h e w i d t h of t h e c l u s t e r i n r a p i d i t y , P t h e p a r t i c l e d e n s i t y and t h e p r o p o r t i o n a l i t y f a c t o r a depends on t h e d e t a i l s o f t h e model. F i g u r e 5 shows D 2 ( y ) a n d P ( y ) f o r K-p i n t e r a c t i o n s a t 16 GeV/c.

As c a n be s e e n , t h e a g r e e r e n t i s v e r y good, t h u s

-

- , -

RAPIDITY OF REFERENCE FRAME WITH RESPECT TO C.M FRAME

F i g . 5

-

g i v i n g support t o t h i s kind o f models. Assuming t h e model of Quigg ano Thomas, one o b t a i n s a c l u s t e r width of A = 1.20 0.01. A s i m i l a r v a l u e i s o b t a i - ned i n pp i n t e r a c t i o n s .

5.

-

-

The r e s u l t s f o r aD , ^(n),, and t h e methods used f o r s e p a r a t i o n a r e summarized i n t a b l e 3. As c a n be s e e n from t h e t a b l e , a slow i n c r e a s e of both cD and (n)D w i t h energy i s observed. The v a l u e s a r e i n agreement w i t h e a r l i e r r e s u l t s o b t a i n e d by f i t t i n g two component models t o m u l t i p l i c i t y d i s t r i b u t i o n s .

6.

-

-

- -

Table 3

r e a c t i o n s : non e x o t i c ) . The a u t h o r s of paper 392 f i n d e a r l y

Paper

}

]

- - - 220

pp + pX a t l a and 24 GeV/c paper 402 N [ .

(n> D

3.13

+

3.41

+

+

( n total )

5.9

+

K-p + pX a t 14.3 GeV/c paper 349

7L+p + A++X a t 8,16,23 GeV/c paper 389

.

uD mb

4.9 5.4

2.68 + .04 2.99 + ^.04

3.31 .18

2.4

+

s c a l i n g i n r e a c t i o n s ( 1 ) , ( 2 ) , ( 6 ) , ( s e e fig.. 6 )

.

( I t h i n k i t would be e a s i e r t o draw c o n c l u s i o n s i f method

}

S e p a r a t i o n of "boundary"

from " c e n t r a l " r e g i o n i n a n Xf v s X,p p l o t (LPS), where if i s t h e reduced l o n g i t u d i n a l c.m. momentum of t h e f a s t e s t beamlike p i o n

f i t of a two-component model t o measured channel c r o s s s e c t i o n s Reaction

s t u d i e d

PP + PX

+

n-p + r t ~ pX

K - ~ + E n

+

t h e r a t i o of c r o s s s e c t i o n were shown). Furthermore, i t i s found t h a t r e a c t i o n s (1) and ( 2 ) f a c t o r i z e

7st

-

w i t h p 4 ^71' and p ^-% w i t h i n 2070. Facto- Beam

momentum GeV/c

:z

8 16 23

10

The o v e ' r a l l c o n c l u s i o n i s t h a t t h e t r i p l e Regge f o r - r i z a t i o n i s a l s o observed i n r e a c t i o n s (9) and (10) mula p r o v i d e s a good phenomenological d e s c r i p t i o n ( s e e f i g . 7 ) 131

.

of t h e d a t a even a t t h e s e low e n e r g i e s . A l l t h e s e o b s e r v a t i o n s seem t o support the i d e a t h a t a b z e x o t i c i m p l i e s absence of meson c o n t r i - 7.

-

wllth t h e i r " e x o t i c i t y p r o p e r t i e s " (E = e x o t i c , N z T h e r e f o r e , t h e s c a l t n e of ~ e a e t i o n s C.1) i. (2 ), (6

LIMITING TRENDS VISIBLE AT MWER ENERGIES

Table 4 number

1

2 3 4

5 6 7

8 9 10

Fig.6

-

c o u l d be a coincidence. Thus t h e c o n c l u s i o n i s t h a t t h e s i t u a t i o n i s r a t h e r u n c l e a r , a l t h o u g h t h e Chan- c o n d i t i o n seems t o work i n many cases.

There a r e two p i e c e s of evidence t h a t c o n s i d e r a t i o n o f p l a n a r d u a l i t y diagrams f o r 3 body s c a t t e r i n g c a n l e a d t o p r e d i c t i o n s about t h e energy dependence of f r a g m e n t a t i o n processes. I n t h e r e a c t i o n s p + ~ O K+

and p --9 x- A + p i o n s b e s i d e s t h e Poneron diagram o n l y one w i t h a XX p a i r exchange is allowed. Thus one e x p e c t s a n energy dependence l i k e s -1 , c o r r e s -

Fig.7 - D i s t r i b u t i o n of t h e missing mass t o t h e A++ i n r e a c t i o n s ( 9 ) and ( l o ) , n r a l i z e d w i t h t h e t o t a l c r o s s s e c t i o n , f o r 0 . 3 <

It7

.

b a - + c

P + * K + +

-

P + K K + p 5 ^x-

K+ q ^rc-

K + J R +

p: A

+

P %

r

p % A+;F+

P

f

ponding t o cp - exchange. Experimentally, one f i n d s

-0.8 K+

f o r p + KO

.

a;

N N N N E N N E N N

8. - CONCLUSIONS. - I n c o n c l u s i o n , I want t o s t a t e t h a t t h e s t u d y of many body r e a c t i o n s a l s o a t ener- g i e s below 30 GeV i s i n t e r e s t i n g and should n o t be completely f o r g o t t e n o v e r t h e excitement about new a b c

E N N E E E E E E

a b

E E N N E E E E N N

bc

N E E N N N E N E E

momenta

11.8,16 8 , l l . 8,16 10,16 10,16 8,16 8,16 8,12.7,16

8,16 16 16

H. WAHL

Fig.8 - Longitudinal lab-momentum d i s t r i b u t i o n of X- from t h e r e a c t i o n p K - , ' K - a t 1 0 and 16 GeV/c. F i - g u r e from r e f .

r

.

r e s u l t s from ISR, NAL and Serpukhov. Of c o u r s e , good i d e a s i n t h e a n a l y s i s of t h e d a t a a r e i n d i s - pensable i f one r e a l l y wants t o l e a r n something new.

D e t a i l e d s t u d i e s of r e a c t i o n mechanisms c o n t r i b u t i n g t o e x c l u s i v e many body r e a c t i o n s , i n a l l v a r i a b l e s , may t u r n o u t t o be u s e f u l i n d i s c o v e r i n g new f a c t s and trends.

Fig.9

-

' K - P + n + x , A P P + n + r c : , @ k + A + x .

REFERENCES

[1 ] VAN HOVE (L. ), P a v i a Conference 1973 [2 ] P a p e r 303 submitted t o t h i s Conference and

BARTSCH (J.) e t a l . , Nucl. Phys. B40 (1972) 103 [ 3 ] ABECCHLW c o l l a b o r a t i o n , p r i v a t e communication

from BARNHAM (K.W.J.)

[ 4 1 CHRISTENSON (J.H.) et a l . , Phys. Rev. L e t t e r s 25 (1970) 1523

[5] B~~SSER (F.W.) et a l . , C o n t r i b u t i o n t o t h e Van- d e r b i l t meeting, N a s h v i l l e (1973)

[6] ABBCCHW C o l l a b o r a t i o n , i n D.R.0 MORRISON'S review t a l k a t Oxford (1972)

[ 7 ] P a p e r 81 and 143 submitted t o t h i s Conference, and preliminary r e s u l t s from NAL d a t a ( s e e t h e mini-report by FERBEL (T.) given a t t h i s Conference)

[8 1 I am g r a t e f u l t o Dr. BREITENLOHNER (P. ) ( ~ G n c h e n ) f o r supplying one w i t h t h i s f i g u r e .

E9I QUIW (C.) and THOMAS (G.H.), Charge t r a n s f e r i n a m u l t i p e r i p h e r a l p i c t u r e , NAL/THY-96, (1972);

FIA&KOWSKI (K.), C o n t r i b u t i o n t o t h e P a v i a Conference, (1973)

[lo] See, e. g. M. JACOB'S ,review i n t h e Proc. of t h e XVI I n t e r n . Conf. on High Energy P h y s i c s , Chicago 1972, and a l s o CHAN HONG-MO, r e p o r t g i v e n a t t h i s Conference.

[ l l 1 ABCLV C o l l a b o r a t i o n , p r i v a t e communication from R. STROYNOWSKI

[12 1 Compilation by INAMI (T. and MIETTINEN (H. 1, p r i v a t e communication.