EXCLUSIVE DIFFRACTIVE DISSOCIATION

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EXCLUSIVE DIFFRACTIVE DISSOCIATION

H. Lubatti

To cite this version:

H. Lubatti. EXCLUSIVE DIFFRACTIVE DISSOCIATION. Journal de Physique Colloques, 1973,

34 (C1), pp.C1-277-C1-283. �10.1051/jphyscol:1973133�. �jpa-00215213�

EXCLUSIVE DIFFRACTIVE DISSOCIATION

EXCLUSIVE DIFFRACTIVE DISSOCIATION

V i s u a l Techniques Laboratory

Department o f Physics - U n i v e r s i t y of Washington SEATTLE, WASHINGTON 98195

1.- INTRODUCTION.- Data on e x c l u s i v e d i f f r a c t i v e d i s s o c i a t i o n of hadrons have been accumulating s t e a - d i l y d u r i n g t h e p a s t t e n y e a r s . L e i t h h a s reviewed t h e experimental r e s u l t s a t t h e Batavia Conference and t h e Rencontre de Moriond [ I ] . The s a l i e n t f e a t u - r e s which have emerged i n c l u d e a s h a r p forward peaking of d o / d t which r e f l e c t s t h e s i z e of t h e t a r g e t ; a n i n t e g r a t e d c r o s s - s e c t i o n which i s l a r g e ( s e v e r a l hun- d r e d pb) and approximately energy independent ; par- t i c l e and a n t i p a r t i c l e c r o s s - s e c t i o n s which a r e simi- l a r ; no exchange of i n t e r n a l quantum numbers (C, G, T,

B, o

P ( - 1 ) J

; t h e e x i s t e n c e of t h e c r o s s - o v a e f f e c t ; a n a p p a r e n t non-conservation of s-channel h e l i c i t y f o r c e r t a i n d i f f r a c t i v e l y produced s t a t e s . A l l b u t t h e l a s t i t e m a r e f e a t u r e s of e l a s t i c s c a t t e - r i n g .

Thus t h e d a t a i n d i c a t e t h a t t h e r e i s a m a n i f e s t l y i n e l a s t i c p r o c e s s which h a s most of t h e f e a t u r e s of e l a s t i c s c a t t e r i n g . T h i s l e a d s t o t h e c o n c l u s i o n t h a t d i f f r a c t i v e d i s s o c i a t i o n i s a l s o dominated by Pomeron exchange, which a l l o w s one t o c o n j e c t u r e t h a t f a c t o - r i z a t i o n should a l s o h o l d f o r d i f f r a c t i v e d i s s o c i a - t i o n , and t h i s c o n j e c t u r e can be t e s t e d experimentally.

Most of t h e a v a i l a b l e r e s u l t s on e x c l u s i v e d i f f r a c - t i v e d i s s o c i a t i o n o f hadrons b e f o r e t h i s c o n f e r e n c e were o b t a i n e d from four-body f i n a l s t a t e s i n t h e

energy range 5-20 GeV. These p r o c e s s e s c a n b e summa- r i z e d by t h e f o l l o w i n g r e a c t i o n sequence :

m .

where X 1 s a known resonance which decays i n t o X + ⁿ ; X can be a x ,

o r

and T i s t h e

A.B. . S l ~ a n EoundatSon Research Fellaw

targa' . Thus a hadron p r e f e r e n t i a l l y d i s s o c i a t e s into two p a r t i c l e s , one of which i s always a pion [2].

These r e a c t i o n s have t h e f o l l o w i n g p r o p e r t i e s which areindependent of t h e i n c i d e n t p a r t i c l e

1 ) T h e observed mass d i s t r i b u t i o n peaks n e a r t h e Mx% +

t h r e s h o l d , which i s always w e l l above t h e Xxx t h r e s h o l d (examples a r e t h e Al(prr), ~ ~ ( f ' d , Q (~'(890) x) , L (~'(1420)

, and Arr(1450) enhance- m e n t s ) .

2) The xmn system i s mainly i n a n L=O s t a t e , which i m p l i e s t h a t t h e system

h a s u n n a t u r a l pa- r i t y f o r

n o r

.

3 ) The i n t e r n a l quantum numbers a r e p r e s e r v e d . 4) The i n t e g r a t e d c r o s s - s e c t i o n s a r e l a r g e (e.g.

.o(rrp +Alp) = 100 pb a t 15 GeV/c) and n e a r l y energy independent ( d e c r e a s e l i k e p-0'5) * ^LAB

5) S t u d i e s of t h e

x phase i n t h e A1 and A3 r e g i o n i n d i c a t e t h a t they a r e n o t Breit-Wigner r e s o - nances. The absence o f a l t e r n a t e decay modes and t h e i n a b i l i t y t o produce t h e s e s t a t e s w i t h comparable c r o s s - s e c t i o n s i n charge-exchange o r backward produc- t i o n r e a c t i o n s s u p p o r t t h i s c o n c l u s i o n .

6) The A and

e x h i b i t t h e c r o s s - o v e r phenomena 1

observed i n e l a s t i c s c a t t e r i n g of p i o n s and k a o n s . 7 ) The i n t e r a c t i o n c r o s s - s e c t i o n of t h e system Y o b t a i n e d from c o h e r e n t n u c l e a r p r o d u c t i o n g i v e s

UYN'

om .

8) The d i f f r a c t i v e system Y does n o t conserve s-channel h e l i c i t y i n c o n t r a s t t o e l a s t i c s c a t t e r i n g .

9) d o J d t h a s a n ebt dependence where

m *

b

l/m(X n). For s m a l l X n masses, t h e s l o p e i s

-

- 13-15 GeV , which i s l a r g e r t h a n t h e e l a s t i c va- l u e s .

I

The only e x c e p t i o n i s when

i s a nucleon. I n t h i s c a s e b o t h t h e d i s s o c i a t i o n N-(Ad (1450) and Nd(NdI25q have been observed and have s i m i l a r p r o p e r t i e s . Since t h e r e i s no evidence t h a t t h e s e t h r e s h o l d enhancements a r e d i f f e r e n t from t h e A and

one should r e f r a i n from a s s o c i a t i n g them w i t h t h e ~ ' ( 1 4 7 0 ) (Roper) r e - 1 sonance observed i n phase s h i f t a n a l y s i s . Thus, i n t h i s repott: they a r e r e f e r e d t o a s t h e Arr(1.450) and Nx(1250).

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1973133

C1-278

H . J . LUBA'ITI

The above l i s t summarizes t h e important f e a t u r e s of n e l s . For example, the d i f f r a c t i v e d i s s o c i a t i o n of the d i f f r a c t i v e d i s s o c i a t i o n of hadrons i n t o two par- a pion i n t o f i v e pions has a l s o been observed. I n t i c l e s , one of which decays by pion emission. The ex- t h i s case, the mass spectrum of the f i v e pions peaks perimental information i s summarized i n Table I . These near the ppn threshold ( f a r above the f i v e pion processes a r e by f a r t h e most copious. I n general, threshold), but the cross-section i s approximately very l i t t l e information i s a v a i l a b l e on other chan- an order of magnitude smaller than the A1 cross-

s e c t i o n .

Table I : Typical p r o p e r t i e s of the X m n system produced i n the 5-20 GeV energy range. Parameters a r e ave- rage ones usually taken over t h e whole ~ * n peak. The N (1250) and e l a s t i c s c a t t e r i n g data a r e presented f o r comparison :

Preliminary ( a t t h i s Conference, but data i n e a r l y stages of a n a l y s i s ) .

' =

not known.

A t t h i s conference new r e s u l t s have been presented which confirm and extend the above p a t t e r n . I n par-

t i c u l a r new NAL r e s u l t $ , i n d i c a t e t h a t low m u l t i p l i c i - ty threshold enhancements continue to dominate d i f - f r a c t i v e d i s s o c i a t i o n a t energies above 100 GeV.

2 .-

^{ENERGY RESULTS} .- The r e a c t i o n

- - +

x p

n n n p i s found t o have a c r o s s - s e c t i o n of 530

65 wb a t 205 GeV from an experiment i n the 30 in.HBC, (NAL-Berkeley Collaboration - paper 359).

This i n d i c a t e s t h a t between 20 and 200 GeV t h i s cross-section f a l l s slowly, (see Fig. 9 of

U .

Amaldi's r e p o r t ) and i s perhaps dominated by d i f - f r a c t i v e d i s s o c i a t i o n above 20 GeV. A t 205 GeV these authors find t h a t almost t h e e n t i r e channel i s asso- c i a t e d with e i t h e r a l o w mass 3n(< 3.0 GeV) or

low mass _{prr n} + - _(< 3.5 GeV) s t a t e . Making t h i s c u t they quote

c n - n +

330 * 55.pb and

+ -

u(p-pn n )=180+36 pb. The t h r e e pion mass distributicn i s shown i n Fig. l ( a ) . Although the s t a t i s t i c s a r e small i t seems c l e a r t h a t t h e A1 dominates. The di-pion mass spectrum shown i n F i g , l ( b ) i s domina- ted by t h e p s i g n a l with no i n d i c a t i o n of f or g ,

which agrees with the f a c t t h a t no A3 is seen i n Fig. l ( a ) .

The P n + k mass spectrum gives a few event peak i n the region of 1500 MeV. This channel i s associa- ted with A* and and thus i s c o n s i s t e n t with t h e (An)(1450) threshold enhancements observed a t lower energies.

I n Table 11, t h e cross-section f o r . 8 a ( 3 n ) < 1 . 2 GeV

i s compared with t h e values obtained with t h e

IHEP Boson spectrometer a t 25 and 40 GeV/c (Papers 41

and 42).

EXCLUSIVE DIFFRACT

11 GeV I

IVE DISSOCIATION

F i g . l a . - M ( < ~ : K +

f o r L p

r t - ~ - n + ~ a t 205 GeV.

1b.- M(n n n++) f o r e v e n t s i n F i g . l a (two com- b i n a t i o n s j e v e n t s ) .

GeV/ c

40 153 Jr 5 Papers 41,42

205 160 * ⁴⁰ Paper 359

Table I1 .- C r o s s - s e c t i o n s f o r n

3 n .

Although t h e e r r o r on t h e 205 GeVjc p o i n t a r e large, t h e 25 t o 205 GeV range i s compatible w i t h a c o n s t a n t c r o s s - s e c t i o n .

T h i s same c o l l a b o r a t i o n h a s c o n t r i b u t e d a n o t h e r paper (paper 360) which g i v e s evidence t h a t t h e s e low mass t h r e s h o l d enhancements p e r s i s t a t h i g h e r m u l t i - p l i c i t i e s ; however, t h e r e a r e only a few e v e n t s per- channel and i t i s n o t p o s s i b l e t o make a d e t a i l e d ex- c l u s i v e s t u d y .

The USSR-USA c o l l a b o r a t i o n h a s observed t h e produc- t i o n o f low mass s t a t e s i n p+p

Y + p [ 3 ] . The ex- periment u s e s t h e i n t e r n a l gas j e t t a r g e t a t NAL and observes t h e slow r e c o i l p r o t o n . The p r e l i m i n a r y r e - s u l t s o b t a i n e d a t s e v e r a l momenta between 175 and 400 GeV/c cover It 1<.05 ( ~ e ~ / c ) ~ . The m i s s i n g mass spectrum g i v e s a peak a t 1 . 3 5 GeV w i t h d o / d t -

d o l d t i s approximatly c o n s t a n t over t h e i r energy range. Presumably t h i s peak i s a mixture of t h e N ~ ( 1 2 5 0 ) and An(1450) which could account f o r t h e observed v a l u e o f 1.35 GeV. T h i s r e s u l t , w h i l e s t i l l p r e l i m i n a r y , a l s o i n d i c a t e s t h a t t h e behavior of d i f - f r a c t i v e d i s s o c i a t i o n a t NAL e n e r g i e s i s s i m i l a r t o

t h a t observed i n t h e 5-20 GeV r a n g e .

3.- NUCLEAR TARGETS.- S e v e r a l new r e s u l t s have been r e p o r t e d u s i n g n u c l e a r t a r g e t s , which have t h e advan- t a g e of s u p p r e s s i n g n o n - d i f f r a c t i v e p r o d u c t i o n mecha- nisms provided t h a t t h e nucleus i s n o t broken up i n t h e i n t e r a c t i o n [2 1.

A new d i f f r a c t i v e enhancement h a s been observed by t h e S e a t t l e - B e r k e l e y c o l l a b o r a t i o n (Paper 376) i n t h e

- - +

r e a c t i o n n d

n n n d a t 15 GeVlc. The t h r e e p i o n mass spectrum shown i n F i g . 10. Amaldi's r e p o r t i s dominated by t h e Al(pn) . There i s a c l e a r A3(fn) s i g n a l a t 1.65 GeV and i n a d d i t i o n a t h r e e s t a n d a r d d e v i a t i o n enhancement i s observed a t 1.96 GeV. T h i s new enhancement, c a l l e d t h e A4 , i s a s s o c i a t e d w i t h g n f i n a l s t a t e s

however, a n i n s u f f i c i e n t number o f g ' s a r e observed t o account f o r t h e e n t i r e enhance- ment. It i s tempting t o assume t h a t one i s o b s e r v i n g d i f f r a c t i v e d i s s o c i a t i o n of a n i n t o gn f i n a l s t a t e s , which, i n view of t h e l a r g e d i s s o c i a t i o n of n i n t o pn and f n , i s n o t unexpected. N e v e r t h e l e s s , a s t h e s t a t i s t i c s a r e l i m i t e d , t h i s r e s u l t r e q u i r e s c o n f i r m a t i o n .

P r e l i m i n a r y - r e s u l t s from t h e r e a c t i o n

(z ^{) + A}

(z ^{) 71-2 + A ,} where A r e p r e s e n t s nu- c l e a r t a r g e t : ranging from Be t o

were p r e s e n t e d by t h e Northwestern-Rochester-Carnegie Mellon (NRCM) c o l l a b o r a t i o n (Paper 390). The experiment was p e r f o r - med a t BNL u s i n g t h e Lindenbaum-Osaki s p e c t r o m e t e r . An i n t e r e s t i n g f e a t u r e i s t h a t a Cherenkov c o u n t e r hodoscope followed t h e s p e c t r o m e t e r s o t h a t t h e pro- ton could be i d e n t i f i e d and an o p t i c a l , s t e e l p l a t e s p a r k chamber was i n c l u d e d f o r measurement of y ' s from no decay. T y p i c a l l y 25x10 e v e n t s / n u c l e u s 3 were o b t a i n e d , and i t i s n o t p o s s i b l e i n t h i s r e p o r t

t o do j u s t i c e t o t h i s v a s t amount of d a t a . The 371 s t a t e s c o n t a i n mainly A l ( ~ n ) . ^For

m(3n)>1.5 GeV t h e r e i s a n f s i g n a l which i s a s s o - c i a t e d w i t h t h e A3 r e g i o n .

T h i s experiment g i v e s , a v e r y good

s t a t i s t i c s f o r t h e d i f f r a c t i v e d i s s o c i a t i o n

+ N n n . + -

The p n n i n v a r i a n t mass spectrum from i n t e r a c - t i o n s on carbon i s shown i n F i g . 2 a . Enhancements a r e observed a t 1.45 and 1.7 GeV. The t h r e s h o l d enhance- ment c o n s i s t s mainly of Ax f i n a l s t a t e s a s can be seen i n F i g s . 2 b , c .

The p$ i n v a r i a n t mass spectrum o b t a i n e d from

~ + A P

p$ + A 8 a s shown i n F i g . 3 does n o t g i v e any

s i g n i f i c a n t i n d i c a t i o n of

f o r m a t i o n i n t h e

1.7 GeV r e g i o n . The a c c e p t a n c e f o r p$ i s approxi-

H . J .

LUBATTI

CARBON 1500

I-

z

c ll

W t b >

P r+

*

,

< C >

P n-

1.00 1.15 130 1.4 1.60

Fig. 2 .- I n v a r i a n t mass s p e c t r a from p+C * p n + < + ~ ( a l l spectra corrected f o r acceptance, which i s determined from phase space Monte

Carlo).

2a.- I n v a r i a n t mass spectrum of pn+n- from co- herent production op farbon a t 23 GeV/c.

2b.- $l(pn+) p 1.4cM(pn n )<1.6 GeV t'c.04 (GeVlc)

2c.- M(pn

.

Fig. 3 .- ^{~ ( ~} from p+AP ^{2 )}

p n O + ~ P (corrected f o r acceptance which i s determined from phase space Monte Carlo).

3a.- A l l e v e n t s .

3b.- t'c.04 ( G ~ V I C ) ~ .

mately constant between 1.3 and 1.8 GeV. The usual Nn threshold enhancement i s c l e a r l y present. A simi-

l a r r e s u l t was obtained by M.J. Longo e t a l . [4] i n t h e reaction n+A

p n - + ~ .

I t

i s d i f f i c u l t t o understand how the #(1700) can be observed i n the N m channel and not i n the Nn channel s i n c e i n t h i s mass region the 8 ' s a r e 40 t o 60 % e l a s t i c . Perhaps one is observing an N m ( 1 5 0 0 ) ~ threshold e f f e c t ? This i s c e r t a i n l y one puzzle which i s becomming very i n t e r e s t i n g .

Preliminary r e s u l t s were presented by the Clermont Ferrand-Lyon-Strasbourg-CERN c o l l a b o r a t i o n (Paper 451, p+ He 4

+ ^{4 ~ e} a t 24 GeV/c) and t h e Saclay- Caen-Frascati c o l l a b o r a t i o n (Paper 120, d+p

d+Y a t 2.95 and 3.4 GeV/c). Both experiments observe a low mass threshold enhancement i n the missing mass r e c o i l i n g a g a i n s t t h e nucleus. Since t h e f i n a l s t a t e nucleus i s i d e n t i f i e d the enhancements have i s o t o p i c spin 112. The 4 ~ e experiment a l s o observes an en- hancement i n the region of 1.7 GeV. Further a n a l y s i s of these data should provide much u s e f u l information.

4.- ABSORPTION

NUCLEI.- Coherent production on nuclei allows one t o determine the absorption cross- s e c t i o n of the produced s t a t e i n nuclear matter. Se- v e r a l r e s u l t s were presented a t t h i s conference.

The NRCM collaboration (Paper 390) has made a pre- liminary comparison of the 1 . 4 c ~ ( ~ n + r t - ) < l . b GeV co- herent production cross-section a s a function of atomic number with the c a l c u l a t i o n s of Margclis. The conclusion i s t h a t the absorption cross-section f o r the An threshold enhancement i s

urn , ^which

agrees with the p a t t e r n observed f o r the A1 and

enhancements.

The CERN-ETH-MILAN0 c o l l a b o r a t i o n has made two

contributions to t h i s subject. They have presented

t h e i r f i n a l r e s u l t s f o r t h e

(Paper 216) and find

uQN

22. * ^{2 mb} f o r l.O<m(Knn)<l.4 GeV, s l i g h t l y

l a r g e r than uKN , but s t i l l considerably smaller

than urn + ^ud . They have a l s o reanalyzed the

absorption cross-section f o r the three pions system

produced on n u c l e i . They find a s before t h a t f o r

l.O<m(3n)<1.2 GeV t h e absorption cross-section i s

23

1.5 mb. This r e s u l t has been known f o r some

time [5]. A t t h i s conference they r e p o r t the r e s u l t

of a s p i n p a r i t y a n a l y s i s which f i n d s predominently

1 + (px) and small ( c 10 %) amounts of 0-(75 % en and

25 % pn). Must astonishing i s t h a t they find

54: :; mb f o r the absorption cross-section of t h i s

0 - . Because the

i s only a small f r a c t i o n of

EXCLUSIVE DIFFRACTIVE DISSOCIATION C1-28

t h e s i g n a l they have been o b l i g e d t o a v e r a g e over nu- c l e i i n o r d e r t o e x t r a c t t h e a b s o r p t i o n c r o s s - s e c t i o n . I f v e r i f i e d , t h i s r e s u l t w i l l modify many of t h e ex- p l a n a t i o n s which have been proposed t o i n t e r p r e t t h e v a l u e of' t h e uyN c r o s s - s e c t i o n s . The NRCM c o l l a b o -

r a t i o n h a s more d a t a t h a n t h e CERN experiment and should be a b l e t o improve t h e confidence l e v e l of t h i s c o n c l u s i o n .

5.- CROSS-OVER PHENOMENON.- New r e s u l t s were pre- s e n t e d i n which c r o s s - o v e r was observed i n Q-, Q+

d i f f e r e n t i a l c r o s s - s e c t i o n s . The Saclay-Ecole Poly*

technique-Rutherford c o l l a b o r a t i o n (Paper 218) com- b i n e t h e i r K-p d a t a a t 14.3 GeV/c w i t h t h e Berkeley K+p r e s u l t s a t 12 GeV/c and o b t a i n a c r o s s - over a t t=0.17 + .05 (GeV/c) 2 f o r l.O<m(Km)<l.5 GeV.

- ²

The s l o p e d i f f e r e n c e i s Ab _Q

1.7

0.3 (GeV/c) .

The SLAC s p e c t r o m e t e r group [ 6 ] a t 13 GeV/c have b o t h

+ +

K-

-tQ- and e l a s t i c s c a t t e r i n g . T h e i r p r e l i m i n a r y r e s u l t i s Ab

1.1 + .35 (GeV/c) -2 and

Q 2

=

1.6 * 0 . 1 (GeV/c) .

6.- ISOSPIN DECOMPOSITION.- Unlike n u c l e a r t a r g e t s , p r o d u c t i o n on f r e e nucleons a l l o w s i s o s p i n exchange.

Thus s e v e r a l i s o s p i n s t a t e s a r e a v a i l a b l e t o t h e pro- duced system. For d i f f r a c t i v e p r o c e s s e s one i s i n t e - r e s t e d i n t h e $ a m p l i t u d e , where t h e s u b s c r i p t and s u p e r s c r i p t r e f e r t o t h e i s o s p i n of t h e t-channel exchange and produced system r e s p e c t i v e l y .

The Saclay-Ecole Polytechnique-Rutherford c o l l a b o - r a t i o n (Paper 218) have determined t h e 1 ~ : ~ ~ I / 1 ~ : ' ~ 1

r a t i o f o r

( F x x ) ~ . They f i n d t h a t t h e T = l exchanges become important f o r rn(Knx),l.4 GeV . ^{T h i s}

i s n o t s u r p r i s i n g s i n c e they observe some ~ ~ ( 1 4 2 0 ) i n t h e Knx system. Table I11 g i v e s t h e v a l u e s ob- t a i n e d . C l e a r l y T=O exchanges dominate i n t h e Q r e g i o n , which i s expected f o r a d i f f r a c t i v e p r o c e s s . T h i s i s q u i t e c o n s i s t e n t w i t h t h e energy dependence o f t h e c r o s s - s e c t i o n (shown i n Table I I I ) , which i n - d i c a t e s t h a t f o r M(Kn7t)tl.k GeV t h e c r o s s - s e c t i o n h a s only a s l i g h t d e c r e a s e w i t h i n c r e a s i n g energy.

I ^{(from 9-} l i p n )

I s o s p i n a n a l y s e s of t h e r e a c t i o n XN - X(Nx) were r e p o r t e d f o r

x a t 8 and 16 GeV by t h e Aachen- Berlin-Bonn-CERN-Notre Dame-Pennsylvania-Tohoku c o l l a b o r a t i o n (Paper 237), and f o r

a t 12 and 24 GeV by t h e Bonn-Hamburg-MGnchen c o l l a b o r a t i o n

(Paper 267) and t h e Weizmann-Technion c o l l a b o r a t i o n (Paper 326). The r e s u l t s a r e t h a t t h e T=1/2 (Nx) mass spectrum due t o T=O exchange g i v e s a n almost energy-independent, broad enhancement which f o r s m a l l

peaks a t approximatly 1.3 GeV. The energy depen- dence of ~ t / ~ (T=O exchange, T=1/2 Nx system) f o r s e v e r a l m(Nx) r e g i o n s i s g i v e n i n Table

Table

Energy dependence of T=1/2 Nx system produced by T=O exchange i n KN

n ( N d a t 8 and 16 GeV/c (Paper 237).

M a s s - i n t e r v a l ( G e V ) 1.08 - 1.32 1.32 - ^1.56

1.56 - ^1.80

1.80 - ^2.04

2.04 - ^2.28

A l l masses

The e s s e n t i a l l y c o n s t a n t c r o s s - s e c t i o n f o r s m a l l m(Nx) s u g g e s t s t h a t t h e (Ndh250) t h r e s h o l d enhan- cement may behave d i f f e r e n t l y from t h e remainder of t h e T=1/2 Nrr: spectrum. I n any c a s e t h e s m a l l energy dependence s t r o n g l y s u g g e s t s t h a t t h e d i f f r a c t i v e component i s i s o l a t e d .

The momentum t r a n s f e r d i s t r i b u t i o n can be parame- Exponent n ( f r o m u ~ l l p n )

0.03 + 0.20 0.09 2 0.13 0.32 + ^0.15

0.26 + ^{0 . 2 1}

0.70

0.29 0.17

0.18

b

t r i z e d by e and b - ^l/m(Nx) a s i s shown i n F i g . 4.

T h i s i n v e r s e r e l a t i o n s h i p between t h e s l o p e and t h e mass of t h e d i f f r a c t i v e system o c c u r s f o r Al and

p r o d u c t i o n ( s e e p a p e r s 41, 42, 218, 418) where t h e same r a n g e of b o c c u r s . The i m p l i c a t i o n s of t h i s r e s u l t a r e d i s c u s s e d by

Zalewski.

From t h e above d a t a i t i s p o s s i b l e t o t e s t f a c t o r i - z a t i o n . Table V p r e p a r e d by

Biickmann t e l l s u s t h a t f a c t o r i z a t i o n seems t o be remarkably good. The only p o i n t which i s s l i g h t l y o f f i s t h e 24 GeV/c p o i n t , i n t h i s c a s e T = l exchange c o n t r i b u t i o n s t o t h e

T=1/2 NIT system could n o t be removed s i n c e pn d a t a a t 24 GeV/c were n o t a v a i l a b l e .

T a b l e 111.- C o n t r i b u t i o n of i s o s p i n 1 exchances i n

Q p r o d u c t i o n .

H.J.

8.- DOUBLE DIFFRACTIVE DISSOCIATION.- I f f a c t o r i z a - t i o n h o l d s t h i s p r o c e s s i s expected t o be a few per-

F i g . 4.- Dependence of t h f , f l o p e parameter on t h e mass of t h e ( N d O system (from paper 237).

0 :

'

[Xp

X (Nn) ] (

2

% ) I ^R(X'

^{qt xp} - ^xp

T a b l e V . - T e s t of f a c t o r i z a t i o n f o r t h e T=1/2 Nn system produced by T=O exchance i n t h e r e a c t i o n

X(Nn) .

Contains T=l exchange a l s o because pn d a t a n o t a v a i l a b l e a t t h i s energy.

7 . - PARTIALWAVE.- P a r t i a l wave a n a l y s e s have been submitted t o t h i s c o n f e r e n c e f o r t h e A1 and A3 (Papers 41, 42) and t h e Q (Paper 306).

These a r e d i s c u s s e d i n t h e r e p o r t s of I . Butterworth and G . O t t e r and only a b r i e f summary i s g i v e n h e r e . F o r t h e KnK system - ^{70 %} of t h e ~ * ( 8 9 0 ) n i n t h e Q r e g i o n i s I+, w h i l e i n t h e L-region t h e KX(1420)n

system i s mainly 2 . The CERN-IHEP a n a l y s i s concluded t h a t t h e A1 and Aj cannot be d e s c r i b e d by a B r e i t - Wigner a m p l i t u d e . An a n a l y s i s o f - 33x10 e v e n t s of 3

+ + + -

n p

x n x p a t 1 3 GeV/c by t h e Purdue group c l a i m s t o d e t e c t a phase change i n t h e f n s-wave ampli- t u d e [8 1. Thus, p r o v i d i n g t h i s r e s u l t h o l d s up, one must q u e s t i o n t h e non-resonant i n t e r p r e t a t i o n of t h e A3

c e n t of s i n g l e d i f f r a c t i v e d i s s o c i a t i o n , s i n c e s i n g l e

i s a few p e r c e n t of t h e e l a s t i c c r o s s - s e c t i o n . Because i t i s s m a l l and because

i n v o l v e s a s s o c i a - t i n g more t h a n one p a r t i c l e w i t h each v e r t e x it i s e x p e r i m e n t a l l y d i f f i c u l t t o o b t a i n c l e a n samples which y i e l d q u a n t i t a t i v e r e s u l t s . The ABBCH-collabo- r a t i o n (Paper 199) h a s p r e s e n t e d evidence f o r double d i f f r a c t i v e d i s s o c i a t i o n i n t h e channels

+ + + - 0

+ +

x-p

r t x n x p and fPm-$rt-n+n . Candidates f o r t h e d i f f r a c t i v e d i s s o c i a t i o n r e a c t i o n x p -f

(379' ( N d f a r e r e q u i r e d t o have a l l - t h r e e p i o n s w i t h l o n g i t u d i - n a l momentum (PL) > 0 and b o t h t h e N and remai- n i n g x,PL < 0 . F u r t h e r t h e (3n) system must con- t a i n a p and be produced w i t h

1<.75 (GeV/c) 2 .

T h i s g i v e s a sample of e v e n t s which c a n be compared

+ ^{k +} -I-

n-p

(3n) p and n-p -, n ( ~ r t ) ' o b t a i n e d i n t h e same experiment. The m(3n) and m(Nn) s p e c t r a compare f a - v o r a b l y , e s p e c i a l l y i n t h e Al and Nn(1250) r e g i o n s .

+ + +

The n p

A ; ( N ~ ) c r o s s - s e c t i o n i s - 15 pb. A moment a n a l y s i s i s made. The r a t i o o f t h e moment which p i c k s o u t p r e f e r e n t i a l l y t h e 1 pn s t a t e s i n d i c a t e s t h a t +

+ + + +

[n-p

A; (Nn)+]/ [rt-p

A i ^{N ]}

^.11 * ^.04

( c f . Table V) which i n d i c a t e s t h a t f a c t o r i z a t i o n h o l d s . C l e a r l y , t h e a n a l y s i s i s n o t s t r a i g h t f o r w a r d . ^The

Saclay-Rutherford-Ecole Polytechnique c o l l a b o r a t i o n (Paper 230) have observed K-p

Q- [An(1450) ] w i t h a c r o s s - s e c t i o n of approximatly 7 pb., c o n s i s t e n t w i t h f a c t o r i z a t i o n .

9.- DIFFRACTIVE DISSOCIATION OF

.- A t h r e s h o l d enhancement h a s been observed f o r t h e f i r s t time i n t h e r e a c t i o n f + Nucleus

AR- + Anything a t 24.6 GeV/c [ 9 ] . The Art- i n v a r i a n t mass spectrum i s shown i n F i g . 5a. The absence of Z-(1385) which h a s

P +

J =3/2 (a c 70 pb w i t h 90 % confidence) a g r e e s w i t h SLT3 p r e d i c t i o n s ( a s s u m i n g a u n i t a r y s i n g l e t P ex- change) and a l s o w i t h t h e Gribov-Morrison c o n j e c t u r e . No evidence of a n e v e n t u a l SU(3) analogue of t h e Roper i s observed. Note t h a t , t h e a c c e p t a n c e beyond 1 . 5 GeV i s only a few p e r c e n t .

T h i s o b s e r v a t i o n s u g g e s t s how important t h e s e t h r e s -

h o l d d i f f r a c t i v e enhancements a r e . Hardly a n y t h i n g

h a s been measured w i t h Z beams, b u t t h e f i r s t i n e -

l a s t i c r e a c t i o n observed i s d i f f r a c t i v e d i s s o c i a t i o n

i n t o a t h r e s h o l d AR s t a t e . Since v e r y l i k e l y t h i s

begins a new c h a p t e r i n t h e d i f f r a c t i v e d i s s o c i a t i o n

saga

i s a good p l a c e t o s t o p and w a i t f o r t h e n e x t

conference.

EXCLUSIVE DIFFRACTIVE DISSOCIATION

I

ACKNOWLEDGEMENTS

The a u t h o r w i s h e s t o thank t h e o r g a n i z e r s of t h e Conference and t h e s e c r e t a r i a l s t a f f f o r t h e i r h e l p . He i s i n d e b t e d t o R. Barloutaud, H. Bingham,

W. Beusch,

~ s c k m a n n , B. Gobbi, R. P h i l l i p s and

Zalewski.

F i g . 5.- M(AR-) from t h e r e a c t i o n f p

^{An-p a t}

24.6 GeV/c. The c u r v e i s a Monte C a r l o c a l - c u l a t i o n o f t h e Deck diagram i n F i g . 4b. The a c c e p t a n c e o f t h e a p p a r a t u s h a s been i n c l u - ded i n t h e Deck c a l c u l a t i o n .

[I] LEITH (D.W.G.S.); " D i f f r a c t i o n D i s s o c i a t i o n " , Proceedings o f XVI I n t & r n a t i o n a l Conference on High Energy P h y s i c s , B a t a v i a , I l l . , S e p t . 1972 VIIIRenconrre de Moriond ed.J. T r a n Tan Van.

[2 1 LUBATTI (H. J . ) , Acta Physica P o l o n i c a (1972 j 721.

[3] BARTENEV (B.) e t a l . , To b e p u b l i s h e d - Also p r i - v a t e communication fromK.Goulianas and E. Malamud.

[4] LONG0 (M.J.) e t a l . , P h y s i c s L e t t e r s 36B (1972) 560.

BEMPORAD (C.) e t a l . , Nuc. Phys. B33 (1971) 627

B42 (1972) 627.

CARNEGIE (R.) e t a l . , P r i v a t e communication.

GRAESSLER

Nuc. Phys. (1972) 43.

THOMPSON (G.)

a l . , P r e p r i n t Purdue P h y s i c s Dept.

[9 ] HUNGERBUEHLER (V.) e t a l . , Y a l e U n i v e r s i t y Pre-

p r i n t .