SURVEY OF ππ AND Kπ SCATTERING

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SURVEY OF ππ AND Kπ SCATTERING

G. Laurens

To cite this version:

G. Laurens. SURVEY OF ππ AND Kπ SCATTERING. Journal de Physique Colloques, 1973, 34

(C1), pp.C1-217-C1-219. �10.1051/jphyscol:1973122�. �jpa-00215202�

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SURVEY OF TOt AND K7t SCATTERING CI-217

SURVEY OF rot AND Krc SCATTERING

G. LAURENS D.Ph.P.E., CEN-Saclay

Since the Batavia Conference some interesting works have been done to improve our knowledge of the

rot and Kit phase shifts. They have been widely dis- cussed at the Tallahassee Conference [1] entirely devoted to rat and Kn subjects. It is not the aim here to do a summary of each paper submitted to this ses- sion, nevertheless we can try to estimate the progress done in those last years and make some remarks.

1. nn SCATTERING. - Four experimental analysis of rot phase shifts have been submitted to this Confe- rence.-Villet et al. [2] applying a pure Chew-Low extrapolation procedure (with constraint) to the

o o , . , , o o , ..

reaction it p -> K n n obtain data on the n it channel.

They do an energy independent phase shifts analysis involving simultaneously four channels, on the same spirit as for nN scattering (done by the same group).

- An analysis of Behr et al. [3] of the reaction n p - i r t p jti in heavy liquid bubble chamber.

- Hyams et al. [4] using, the 17 GeV/c it p -* n it n high statistics CERN-Munich experiment, do an analysis of the moments in the physical region (i.e. without extrapolation) with hypotheses which are not too clear in their physical contents, but are partially checked by an overconstrained system of equations.

This analysis is the third one done on the same data [5,6]. The last experiment comes from Losty et al. [7] which study^ with a Chew-Low extrapolation using Diirr-Pilkhun form factors the reaction it p -> (it p)it n to extract 1 = 2 phase shifts.

1.1. SURVEY OF THE PRESENT STATUS OF rot PHASE SHIFTS. - All recent experiments agree on the P.. and D phases up to some l.lGeV. For the S„ and D„ waves,

the general agreement is that they are small and ne- gative. However there is no quantitative agreement on the meaning of "small". In figure 1 are reported the major results and the new points of Losty et al. [7],

For the S wave everybody agrees for a solution smooth in the 500-900 meV region but with a rapid increase of the phase and a strong inelasticity in the KK threshold region. It is also remarkable as

one can see on figures 2 and 3 that different solu- tions issued from different data, agree as well as different analyses of the same experiment [2,4,5, 6,8,91.

Oh

• BATON o WALKER

•z COLTON + BAU81LLIER X * HOOGLAND . i COHEN

• SANDER . TBAKER

•LOSTY OVILLET

0.2 0.4 0.6 0.8 M ^ C G e V / c2)

F i g . l - Experimental S„ phase

160

120

W

tr

a

«f 80

U0

—i 1 1 1 1 1 + OCHS.WAGNER [ < ] ]

o GRAYER [ 6 ] ^CERN.MUNICH

v /EASTABR00K\, MARTIN/ sol.1

J[5]

* *

$ *

tt

400

600

^{800 1000}

x

it it MASS C M e V / c2)

F i g . 2 - S phase from CERN-Munich d a t a only 16

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1973122

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G. LAURENS

o l q I ~ ~ ' " l " ~

200 LOO 600 BOO 1000 1200

n n MA55 <Mev/c2>

Fig.3

-

So phase from d i f f e r e n t experiments 1.2. DISCUSSION OF MORE SPECIFIC POINTS.

-

The agreement between t h e l a s t experimental r e s u l t s

0 0

on t h e low energy n n and K e l e a d t o a v a l u e of a:

4

(a:

=

0.60) s i g n i f i c a n t l y d i f f e r e n t from t h e c u r r e n t a l g e b r a v a l u e (Weinberg a: = 0.17) (Fig. 5).

50

Y)O

; ; i r o o i o o o

.

300

VILLET el-01

a ) Exact behaviour and i n t e r p r e t a t i o n on t h e So phase s h i f t n e a r

Kk

t h r e s h o l d :

So phase s h i f t v a r i e s r a p i d l y n e a r

Kk

t h r e s h o l d b u t Fig.4

-

Argand diagrams of T p f o r t h e m p a r t i a l waves amp1itudes;numbers i n d i c a t e t h e nn energy.

t h e q u a n t i t a t i v e meaning o f t h i s v a r i a t i o n i s n o t y e t Cu,es of Hyams come from energy dependent analysis.

c l a r i f i e d . V i l l e t e t a l . [2] assumes t h a t a resonan- c e o c c u r s a t maximum speed of t h e phase : t h i s l e a d s t o a p o s i t i o n o f t h e p o l e of t h e So c a l l e d S a t

m

975

-

i 5 0 meV, n o t e t h a t 60 > 90' a t t h i s p o i n t which

\

i s l o c a t e d below t h e

Kk

t h r e s h o l d . Hyams e t a l . 141 Protopopescu e t a l . [ 9 ] and d i f f e r e n t o t h e r groups make a K o r M m a t r i x a n a l y s i s ; t h e y o b t a i n d i f f e r e n t answers f o r t h e p o s i t i o n of t h e p o l e , mainly due t o t h e u s e of d i f f e r e n t p a r a m e t r i s a t i o n s , b u t they a l l o b t a i n a narrow resonance. However one may n o t e t h a t t h e r e i s a good agreement between V i l l e t e t a l . 121 and t h e energy independent a n a l y s i s of Hyams e t a l . [4] n e a r t h e Kl? t h r e s h o l d (Fig.4). An i n t e r e s - t i n g c o n t r i b u t i o n has been g i v e n by Binnie e t a1.[10]

0

+ -

who measure t h e r e a c t i o n s rc-p ⁺n + 2 n

,

^Kn.

,

o r

+ -

K K by means of a m i s s i n g mass spectrometer, they

m

0 0

+ -

s e e a n evidence f o r t h e S bumps i n K K

,

ⁿ^K ^and

K

+

K- mass spectrum. The f o l l o w i n g t a b l e summarizes t h e S p o l e p o s i t i o n s r e c e n t l y found

m

:

Protopopescu e t a l . 997 6

-

ⁱ⁽²⁷

+

⁸⁾

Hyams e t a l . 1007

t

10

-

i (15

+

⁵⁾

Estabrooks-Martin 997

-

ⁱ 5

V i l l e t e t a l . 975

-

^i.50

Binnie e t a l . 987

+

6 - i ( 2 4 + 6 ) b) S c a t t e r i n g l e n g t h s .

-

It i s known t h a t they

(.R. BENSIGER

VILLET c t a l

cannot be o b t a i n e d b y e x t r a p o l a t i n g t o t h r e s h o l d pha-

F i g . 5 - Experimental S phase n e a r t h r e s h o l d and s e s h i f t s from h i g h e r r e g i o n (say above 500meV)

1111.

t h e p r e d i e c t e d v a l u e s f o r d i f f e r e n t s c a t t e r i n g l e n g t h s .

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SURVEY OF 7m AND K x SCATTERING C1-219

C) Higher resonances.

-

CERN-Munich analysis[4]

shows a rapid decrease of the Plwave inelasticity parameter followed by a minimum at q z= 0.5 and a drop of the PI phase, they claim that this resonant like behaviour is the evidence of the (m=1590220

r

= 180+50). In the Do wave they do not see the f' meson (1514) but the F wave shows clearly the g meson. In the n0n0 mass range 1200 to 1600 MeV the data of Ape1 et al. [16] are compatible with the CERN-Munich phases [4].

d) Inelasticities.

-

One generally assumes they are negligible below 1 GeV (more precisely below the K ! threshold) but Losty et al. [7] see some inelastic I = 2 contribution just above 800 meV. However an accurate knowledge of inelasticities should be completed by a more careful study including measure- ments of inelastic channels.

1.3. CONCLUSION.

-

Progress in understanding I=0, I =1, nn phase shifts has been achieved owing to some high statistics n-p + n+n-n experiment as well as results on 2 no production experiments. It is quite unfortunate that the I = 2 phases remain unprecise mainly due to the absence of comparable high statis-

+ + - -

tics experiments involving K- no, n n

,

n n channels.

Furthermore, the discrepancies appearing in figure 3, between the different methods for extracting 6

0'

raise the question of the respective advantages of the Chew-Low extrapolation and of the amplitudes ana-

2. KnSCATTERING.

-

Two papers have been presented to this Conference. The first [12] concerns the reactions K-p -, A*

K-n

^{and K-p}⁺A*+anything studied at 14.3 GeV/c in a hydrogen bubble chamber experiment. A classical Chew-Low extrapolation

(without form factors) of the inelastic, and total cross sections leads to values of the total cross section increasing from 3 mb at threshold to about 5.5 mb at 2.6 GeV and an elasticity decreasing down to 0.3

.

The second paper [13] reports the results of an extrapolation applied to the reaction

K n

+

-, K'n-p with form-factors. Corrections being ma- de for effects caused by the use of a deuterium tar-

+ -

get, the K n S112 phase shift is extracted with various hypotheses for the S312 phase. The result in good agreement with previous work [14](Fig.6) shows that the theoretical difficulties, due to the deuterium singularity, that could arise when a Chew- Low extrapolation is applied on reaction involving deuterium 15 do not hold in practice.

lysis. Finally one should probably also try to intro- M t K*K" 1 G ~ V / C ~

duce more efficient smoothing by using dispersion

relations. Fig.6

-

Kn- bL phase (solution down) this solution

is presented Oby Baker.

REFERENCES [I] International Conference on nn and Kn scattering

Tallahassee (Florida), to be published (1973) [2] VILLET (G.) et al., paper no 310

[3] BEHR (L.) et al., paper no 253

[&I

HYAMS (B.) et al., paper no 263

I51 ESTABROOKS(J.P.) and MARTIN (A.D.), CERM TH/1661 (1973)

[6] GRAYER (G.) et al., in "Experimental meson spec- troscopy, 1972" Proc. of the third Int. Conf.

Philadelphia (1972), eds. Kwan-Wu,Lai and A.H. Rosenfeld

171 LOSTY (M.J.) et al., paper no 213

181 BATON (J.P.) et al., Phys. Letters (1970) 525

[9] PROTOPOPESCU (S.D.) et al., Phys. Rev.

a

⁽¹⁹⁷³⁾

1279

[lo] BINNIE et al., paper no 166

[ll] BASDEVANT (J.L.) et al., paper no 73

[12] RUTHERFORD, ECOLE POLYTECHNIQUE, SACLAY colla- boration, paper no 226

[13] BAKER (S.L.) et al., paper no 212

1141 BARBARO-GALTIERI

(A.),

L.R.L. preprint June 1973 1151 FROISSART (M.), Ecole d'Etd des Houches (1965)

16 APEL et al., post deadline paper