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Observations of Σ hyperonic atoms
Volume 33B, n u m b e r 3
PHYSICS
LETTERS
12 October 1970
O B S E R V A T I O N S OF E H Y P E R O N I C ATOMS G. B A C K E N S T O S S , T. B U N A C I U , S. C H A R A L A M B U S , J. E G G E R * a n d H. KOCH Institut f ~ r Experirnentelte Kernphysik der Universittit und des Kernforschungszentrums, Earlsruhe , Germany and CERN, Geneva, Switzerland and A. B A M B E R G E R , U. L Y N E N , H . G . R I T T E R a n d H. S C H M I T T Max-Planck-Institut f'dr Kernphysik, Heidelberg, Germany Received 28 August 1970 Clear evidence for the o b s e r v a t i o n of E - atoms is presented, b a s e d on a s e r i e s of E atomic X - r a y lines in three t a r g e t elements• X - r a y e n e r g i e s and the n u m b e r of E atoms produced p e r stopped Km e s o n agree with expectations.
In t h e X - r a y s p e c t r a of t h e K m e s o n i c S, C1 and Zn atoms, several lines were found which could be unambiguously identified as X-ray transit i o n s of t h e c o r r e s p o n d i n g E a t o m s . In r e c e n t l y p u b l i s h e d K m e s o n i c s p e c t r a , a l r e a d y two ~ - l i n e s w e r e s u s p e c t e d to b e E h y p e r o n i c l i n e s , t h e E 6 --* 5 t r a n s i t i o n i n p o t a s s i u m [1] a n d t h e E 6 --* 5 t r a n s i t i o n i n s u l p h u r [2]. B u t a p r o o f on t h e b a s i s of o n l y a s i n g l e l i n e i s w e a k , b e c a u s e of t h e p o s s i b l e p r e s e n c e of n u c l e a r ~ - r a y s i n t h e K m e s o n i c s p e c t r a . T h e e v i d e n c e f o r Y. a t o m s i s d e r i v e d h e r e f r o m t h e m e a s u r e m e n t of a s e r i e s of X - r a y t r a n s i t i o n s of t h e t y p e ( n - ~ n - 1), ( n - 1 ~ n 2) •.. in E atoms, which are compared with calculated values for three different nuclei. The E- hyperons are produced by stopped Kmesons which are captured by the target nuclei. T h e p r e d o m i n a n t r e a c t i o n s w h i c h g i v e r i s e to a E - a r e [3] K - + p--* E
+~+
(1)
K- + n-~ E- + ~ °
(2)
K- + p + n
(3)
~ E- +p.
T h e E h y p e r o n s p r o d u c e d i n r e a c t i o n s (1) a n d (2) h a v e e n e r g i e s c e n t r e d a r o u n d 20 M e V . S i n c e t h e l i f e t i m e of t h e E - h y p e r o n s i s c o m p a r a b l e w i t h t h e i r s l o w i n g d o w n t i m e , a p a r t of t h e m d e c a y s before they can form a E hyperonic atoms. React i o n (3) y i e l d s l e s s t h a n 3 0 % of t h e p r o d u c e d E h y p e r o n s [3]. S i n c e t h e s e E - h y p e r o n s h a v e * V i s i t o r f r o m the ETH, ZUrich. 230
h i g h e r e n e r g i e s , m o s t of t h e m d e c a y b e f o r e t h e y are captured. Therefore the E- hyperons which g i v e r i s e to E a t o m s o r i g i n a t e m a i n l y f r o m r e a c t i o n s (I) and (2). The capture of the E- hyperons take place in atomic levels with high main quantum number n, and is followed by a cascade of the E hyperons towards the atomic ground state. In the upper part of the cascade, a E transition is accompanied by the emission of an Auger-electron, and in the lower part by the emission of an X-ray. The typical pattern of the E hyperonic X-rays is determined by the fact that the E - hyperon, similar to the ~- and K- mesons, is a strongly interacting particle. Therefore, nuclear absorption takes place from a certain orbit leading to a disappearance of the X-ray cascade. The function R = Fx/(F a + Fx) of the radiative electric dipole width Fx and the nuclear absorption width F a is a measure for the yield of a transition. F a was calculated assuming a purely imaginary E-nucleus potential V ~ i ImAp(r) where Im A was taken tobe equal to I fm and p(r) equal to the charge distribution J;. In this way the values of col. 1 of table 1 were calculated. The energies of the X-ray transitions have been calculated for the pure electromagnetic interaction, including vacuum polarization, and are displayed in col. 2 of table 1. The low energetic K- mesons were produced at the CERN PS using a specially designed beam We appreciate the help of Dr. M.KrelI. who adapted his p r o g r a m for pionic atoms [4] to E atoms.
V o l u m e 33B
number 3
PHYSICS
LETTERS
12 O c t o b e r 1970
Table 1 E2
E trans.
Rtheory
Eealc"
Emeas"
(%)
(keV)
(keV)
1 16 S
17C1
30 Zn
(%) 4
5
86 3
96.52 177.92
96.70 • 0.30 -
5.6 ± 1.0 -
5~ 4
7 --*6 6 ~ 5 5~4
99 74 2
65.87 109.38
66.18 ± 0.50 109.40 ± 0.20 -
4.3 ± 1.1 6.5 ± 1.2 -
5~ 4 5~ 4
100 100 100 99 45 1
49.03 66.32 92.79 135.46 208.94 345.68
~ 10 ~9 ~ 8 ~ 7 ~ 6 -~ 5
[5]. A b o u t 1 0 0 0 K 1 / b u r s t c o u l d b e s t o p p e d i n a t a r g e t of 8 g / c m 2 t h i c k n e s s . S i n c e t h e t i m e e l a p s i n g b e t w e e n a K - s t o p a n d t h e c a s c a d e of t h e secondary E 1 is very short compared with the r e s o l u t i o n t i m e of t h e s y s t e m , X l r a y s f r o m atoms appear simultaneously with the K mesonic X-rays. Therefore, the experimental technique i s e x a c t l y t h a t d e s c r i b e d i n r e f . [2]. I n a d d i t i o n , also pionic X-rays are seen which originate from pions produced by the K 1 1 nucleus interaction. T h e s p e c t r a of C1 (LiC1) a n d Z n a r e s h o w n i n
3
ref. t r a n s . (K)
6 ~5 5 ~ 4
11 10 9 8 7 6
2
IF/I K
•
49.33 ± 0.40 Coincides with K 1 0 ~ 8 and ~" 7 ~ 5 92.33 ± 0.50 3.7 ± 0.9 6~ 5 134.99 ± 0.50 4.0 ± 1.0 6~ 5 Coincides with K 10 ~ 6
f i g s . 1 a n d 2. T h e s u l p h u r s p e c t r u m w a s a l r e a d y p u b l i s h e d [2]. T h e e f f i c i e n c y of t h e d e t e c t i o n system at low energies allowed an observation of t r a n s i t i o n s o n l y f o r e n e r g i e s l a r g e r t h a n 5 0 60 k e V . T h e m e a s u r e d t r a n s i t i o n e n e r g i e s a r e g i v e n i n c o l . 3 of t a b l e 1. I n t h e s u l p h u r s p e c trum , only the 6 ~ 5 tra ns ition at 96.7 keV is v i s i b l e . T h e n e x t t r a n s i t i o n (5 -* 4) a t 177 k e V is not s e e n . We c o u l d not e x p e c t to s e e t h i s line w i t h t h e l o w y i e l d s h o w n i n c o l . 1 o n t a b l e 1. T h e C1 s p e c t r u m (fig. 1) s h o w s t w o E l i n e s . T h e
K-(z-~zn t48x 106 K-stops
o
A
x
A
E
l
I ,:
150
l
200
250
300
bey
Fig. 2. X - r a y lines f r o m K, E and rr a t o m s obtained f r o m s t o p p i n g K- m e s o n s in 30Zn. The E t r a n s i t i o n s in b r a c k e t s [ ] indicate only the e x p e c t e d p o s i t i o n of a ~ line that is o b s c u r e d by o t h e r lines. 231
PHYSICS
Volume 33B, number 3
7~ .., ,
7
6
~'~
~
_
4
~'
¢
,,~
~I
~ 86xI0~ k- stops
•
150 Fig. 1. X - r a y lines from K, ~ and ?r atoms obtained from stopping K- mesons in a LiCl target. 7 -, 6 (66 keV) a n d t h e 6 -~ 5 (109 k e V ) t r a n s i t i o n s a r e c l e a r l y v i s i b l e . T h e 5 --* 4 (200 k e V ) t r a n s i t i o n i s not o b s e r v e d , w h i c h i s i n a g r e e m e n t w i t h t h e 2 % y i e l d g i v e n in col. 1. In t h e Zn spectrum, three ~ lines could be observed: t h e 11 ~ 10, 9 ~ 8, a n d 8--* 7 t r a n s i t i o n s a t 49, 92, a n d 135 keV, r e s p e c t i v e l y . T h e 9 ~ 8 t r a n s i t i o n a p p e a r s a s a s h o u l d e r of t h e K 9 ~ 7 t r a n s i t i o n . H o w e v e r , a d e t a i l e d a n a l y s i s of t h i s structure using the calcaulated energy difference gives the intensities and the expected energies of t h e two l i n e s . T h e m i s s i n g t r a n s i t i o n s , 10--" 9 (66 k e V ) a n d 7 --* 6 (209 k e V ) , t h e i n t e n s i t i e s of w h i c h a r e not s m a l l , c o u l d not b e s e e n . T h e y c o i n c i d e w i t h t h e K 10 --* 8 a n d ~ 7 ~ 5 t r a n s i t i o n s , a n d w i t h t h e K 10 -~ 6 t r a n s i t i o n , r e s p e c t i v e l y . T h e 6 -~ 5 (346 keV) t r a n s i t i o n h a s a g a i n a y i e l d t h a t i s too low to b e o b s e r v e d . C o m p a r i s o n b e t w e e n c o l s . 2 a n d 3 s h o w s full agreement between measured and calculated energies within the experimental errors. This c a n b e e x p e c t e d f r o m e s t i m a t i o n s [6] of t h e i n f l u e n c e of t h e s t r o n g i n t e r a c t i o n b e t w e e n t h e hyperon and the nucleus. Level shifts and broadenings should play an important role only in the l o w e r t r a n s i t i o n s , w h i c h c o u l d not b e o b s e r v e d in t h e s e f i r s t m e a s u r e m e n t s b e c a u s e of t h e i r low y i e l d . A l l E t r a n s i t i o n s w h i c h , a c c o r d i n g to col. 1 of t a b l e 1, a r e e x p e c t e d to h a v e h i g h
232
2OO
LETTERS
12 October 1970
yields, have been observed, except those which are superimposed by other identified and expected lines. Further information is contained in the rel a t i v e i n t e n s i t i e s b e t w e e n K a n d ~ X - r a y s . In col. 4 t a b l e 1 t h e i n t e n s i t y r a t i o b e t w e e n t h e l i n e a n d a k a o n i c l i n e of t h e s a m e s p e c t r u m i s given. It is corrected for absorption effects in t h e t a r g e t a n d d i f f e r e n t Ge d e t e c t o r e f f i c i e n c i e s . T h e K a t o m i c r e f e r e n c e t r a n s i t i o n l i s t e d i n col. 5 w a s a l w a y s c h o s e n not t o b e a t t e n u a t e d b y n u c l e a r a b s o r p t i o n . If o n e c o r r e c t s t h e v a l u e s of col. 4 f o r t h e e s t i m a t e d y i e l d of t h e ~ l i n e (col. 1), one obtains the ratio between K and ~ atoms formed in the target, where uncertainties in the p o p u l a t i o n of t h e i n i t i a l s t a t e s of t h e c o m p a r e d t r a n s i t i o n s a n d t h e s m a l l n u m b e r of ~ h y p e r o n s escaping from the target are neglected. In o r d e r t o c o m p a r e t h i s r a t i o w i t h t h e 8 % ~ hyperons produced per stopping K meson as obs e r v e d i n e m u l s i o n s [3], o u r d a t a m u s t b e c o r rected for ~ - hyperons decaying before they are s t o p p e d . T h i s c o r r e c t i o n i s e s t i m a t e d to b e 36, 34, a n d 13 p e r c e n t f o r S, LiC1, a n d Zn, r e s p e c t i v e l y , i n c r e a s i n g t h e v a l u e s of col. 4 c o r r e s p o n d ingly. The agreement between the present and t h e e m u l s i o n d a t a a p p e a r s , t h e r e f o r e , to b e s a t i s f a c t o r y . T h e p r e s e n t d a t a , h o w e v e r , a r e not y e t s u f f i c i e n t to e x h i b i t c l e a r l y a d e p e n d e n c e of t h e ~ y i e l d on t h e n u c l e a r m a s s . It can be concluded that both the energy and int e n s i t y of t h e o b s e r v e d X - r a y t r a n s i t i o n s a r e c o n sistent with them being identified as originating i n t h e c a s c a d e p r o c e s s of a ~ a t o m . It i s a p l e a s u r e to t h a n k D r s . T. E. O. E r i c s o n a n d M. K r e l l f o r m a n y d i s c u s s i o n s . T h e h e l p of M r . R. B a u e r d u r i n g t h e e v a l u a t i o n of t h e d a t a i s appreciated.
References [1] C. E. Wiegand, Phys. Rev. L e t t e r s 22 {1969) 1235. [2] G. Backenstoss. A. B a m b e r g e r . J. Egger, W.D. Hamilton, H. Koch, U. Lynen, H.G. Ritter and H. Schmitt, Phys. L e t t e r s 32B {1970) 399. [3] European K- collaboration, Nuovo Cimento 14 {1959) 315. [4] M. Kreli and T. E. O. Ericson, Nuclear Phys. B l l (1969) 521. [5] U. Lynen et ai.. to be published. [6] M. Krei[ and T. E. O. E r i c s o n , private communication.
PHYSICS
LETTERS
12 October 1970
O B S E R V A T I O N S OF E H Y P E R O N I C ATOMS G. B A C K E N S T O S S , T. B U N A C I U , S. C H A R A L A M B U S , J. E G G E R * a n d H. KOCH Institut f ~ r Experirnentelte Kernphysik der Universittit und des Kernforschungszentrums, Earlsruhe , Germany and CERN, Geneva, Switzerland and A. B A M B E R G E R , U. L Y N E N , H . G . R I T T E R a n d H. S C H M I T T Max-Planck-Institut f'dr Kernphysik, Heidelberg, Germany Received 28 August 1970 Clear evidence for the o b s e r v a t i o n of E - atoms is presented, b a s e d on a s e r i e s of E atomic X - r a y lines in three t a r g e t elements• X - r a y e n e r g i e s and the n u m b e r of E atoms produced p e r stopped Km e s o n agree with expectations.
In t h e X - r a y s p e c t r a of t h e K m e s o n i c S, C1 and Zn atoms, several lines were found which could be unambiguously identified as X-ray transit i o n s of t h e c o r r e s p o n d i n g E a t o m s . In r e c e n t l y p u b l i s h e d K m e s o n i c s p e c t r a , a l r e a d y two ~ - l i n e s w e r e s u s p e c t e d to b e E h y p e r o n i c l i n e s , t h e E 6 --* 5 t r a n s i t i o n i n p o t a s s i u m [1] a n d t h e E 6 --* 5 t r a n s i t i o n i n s u l p h u r [2]. B u t a p r o o f on t h e b a s i s of o n l y a s i n g l e l i n e i s w e a k , b e c a u s e of t h e p o s s i b l e p r e s e n c e of n u c l e a r ~ - r a y s i n t h e K m e s o n i c s p e c t r a . T h e e v i d e n c e f o r Y. a t o m s i s d e r i v e d h e r e f r o m t h e m e a s u r e m e n t of a s e r i e s of X - r a y t r a n s i t i o n s of t h e t y p e ( n - ~ n - 1), ( n - 1 ~ n 2) •.. in E atoms, which are compared with calculated values for three different nuclei. The E- hyperons are produced by stopped Kmesons which are captured by the target nuclei. T h e p r e d o m i n a n t r e a c t i o n s w h i c h g i v e r i s e to a E - a r e [3] K - + p--* E
+~+
(1)
K- + n-~ E- + ~ °
(2)
K- + p + n
(3)
~ E- +p.
T h e E h y p e r o n s p r o d u c e d i n r e a c t i o n s (1) a n d (2) h a v e e n e r g i e s c e n t r e d a r o u n d 20 M e V . S i n c e t h e l i f e t i m e of t h e E - h y p e r o n s i s c o m p a r a b l e w i t h t h e i r s l o w i n g d o w n t i m e , a p a r t of t h e m d e c a y s before they can form a E hyperonic atoms. React i o n (3) y i e l d s l e s s t h a n 3 0 % of t h e p r o d u c e d E h y p e r o n s [3]. S i n c e t h e s e E - h y p e r o n s h a v e * V i s i t o r f r o m the ETH, ZUrich. 230
h i g h e r e n e r g i e s , m o s t of t h e m d e c a y b e f o r e t h e y are captured. Therefore the E- hyperons which g i v e r i s e to E a t o m s o r i g i n a t e m a i n l y f r o m r e a c t i o n s (I) and (2). The capture of the E- hyperons take place in atomic levels with high main quantum number n, and is followed by a cascade of the E hyperons towards the atomic ground state. In the upper part of the cascade, a E transition is accompanied by the emission of an Auger-electron, and in the lower part by the emission of an X-ray. The typical pattern of the E hyperonic X-rays is determined by the fact that the E - hyperon, similar to the ~- and K- mesons, is a strongly interacting particle. Therefore, nuclear absorption takes place from a certain orbit leading to a disappearance of the X-ray cascade. The function R = Fx/(F a + Fx) of the radiative electric dipole width Fx and the nuclear absorption width F a is a measure for the yield of a transition. F a was calculated assuming a purely imaginary E-nucleus potential V ~ i ImAp(r) where Im A was taken tobe equal to I fm and p(r) equal to the charge distribution J;. In this way the values of col. 1 of table 1 were calculated. The energies of the X-ray transitions have been calculated for the pure electromagnetic interaction, including vacuum polarization, and are displayed in col. 2 of table 1. The low energetic K- mesons were produced at the CERN PS using a specially designed beam We appreciate the help of Dr. M.KrelI. who adapted his p r o g r a m for pionic atoms [4] to E atoms.
V o l u m e 33B
number 3
PHYSICS
LETTERS
12 O c t o b e r 1970
Table 1 E2
E trans.
Rtheory
Eealc"
Emeas"
(%)
(keV)
(keV)
1 16 S
17C1
30 Zn
(%) 4
5
86 3
96.52 177.92
96.70 • 0.30 -
5.6 ± 1.0 -
5~ 4
7 --*6 6 ~ 5 5~4
99 74 2
65.87 109.38
66.18 ± 0.50 109.40 ± 0.20 -
4.3 ± 1.1 6.5 ± 1.2 -
5~ 4 5~ 4
100 100 100 99 45 1
49.03 66.32 92.79 135.46 208.94 345.68
~ 10 ~9 ~ 8 ~ 7 ~ 6 -~ 5
[5]. A b o u t 1 0 0 0 K 1 / b u r s t c o u l d b e s t o p p e d i n a t a r g e t of 8 g / c m 2 t h i c k n e s s . S i n c e t h e t i m e e l a p s i n g b e t w e e n a K - s t o p a n d t h e c a s c a d e of t h e secondary E 1 is very short compared with the r e s o l u t i o n t i m e of t h e s y s t e m , X l r a y s f r o m atoms appear simultaneously with the K mesonic X-rays. Therefore, the experimental technique i s e x a c t l y t h a t d e s c r i b e d i n r e f . [2]. I n a d d i t i o n , also pionic X-rays are seen which originate from pions produced by the K 1 1 nucleus interaction. T h e s p e c t r a of C1 (LiC1) a n d Z n a r e s h o w n i n
3
ref. t r a n s . (K)
6 ~5 5 ~ 4
11 10 9 8 7 6
2
IF/I K
•
49.33 ± 0.40 Coincides with K 1 0 ~ 8 and ~" 7 ~ 5 92.33 ± 0.50 3.7 ± 0.9 6~ 5 134.99 ± 0.50 4.0 ± 1.0 6~ 5 Coincides with K 10 ~ 6
f i g s . 1 a n d 2. T h e s u l p h u r s p e c t r u m w a s a l r e a d y p u b l i s h e d [2]. T h e e f f i c i e n c y of t h e d e t e c t i o n system at low energies allowed an observation of t r a n s i t i o n s o n l y f o r e n e r g i e s l a r g e r t h a n 5 0 60 k e V . T h e m e a s u r e d t r a n s i t i o n e n e r g i e s a r e g i v e n i n c o l . 3 of t a b l e 1. I n t h e s u l p h u r s p e c trum , only the 6 ~ 5 tra ns ition at 96.7 keV is v i s i b l e . T h e n e x t t r a n s i t i o n (5 -* 4) a t 177 k e V is not s e e n . We c o u l d not e x p e c t to s e e t h i s line w i t h t h e l o w y i e l d s h o w n i n c o l . 1 o n t a b l e 1. T h e C1 s p e c t r u m (fig. 1) s h o w s t w o E l i n e s . T h e
K-(z-~zn t48x 106 K-stops
o
A
x
A
E
l
I ,:
150
l
200
250
300
bey
Fig. 2. X - r a y lines f r o m K, E and rr a t o m s obtained f r o m s t o p p i n g K- m e s o n s in 30Zn. The E t r a n s i t i o n s in b r a c k e t s [ ] indicate only the e x p e c t e d p o s i t i o n of a ~ line that is o b s c u r e d by o t h e r lines. 231
PHYSICS
Volume 33B, number 3
7~ .., ,
7
6
~'~
~
_
4
~'
¢
,,~
~I
~ 86xI0~ k- stops
•
150 Fig. 1. X - r a y lines from K, ~ and ?r atoms obtained from stopping K- mesons in a LiCl target. 7 -, 6 (66 keV) a n d t h e 6 -~ 5 (109 k e V ) t r a n s i t i o n s a r e c l e a r l y v i s i b l e . T h e 5 --* 4 (200 k e V ) t r a n s i t i o n i s not o b s e r v e d , w h i c h i s i n a g r e e m e n t w i t h t h e 2 % y i e l d g i v e n in col. 1. In t h e Zn spectrum, three ~ lines could be observed: t h e 11 ~ 10, 9 ~ 8, a n d 8--* 7 t r a n s i t i o n s a t 49, 92, a n d 135 keV, r e s p e c t i v e l y . T h e 9 ~ 8 t r a n s i t i o n a p p e a r s a s a s h o u l d e r of t h e K 9 ~ 7 t r a n s i t i o n . H o w e v e r , a d e t a i l e d a n a l y s i s of t h i s structure using the calcaulated energy difference gives the intensities and the expected energies of t h e two l i n e s . T h e m i s s i n g t r a n s i t i o n s , 10--" 9 (66 k e V ) a n d 7 --* 6 (209 k e V ) , t h e i n t e n s i t i e s of w h i c h a r e not s m a l l , c o u l d not b e s e e n . T h e y c o i n c i d e w i t h t h e K 10 --* 8 a n d ~ 7 ~ 5 t r a n s i t i o n s , a n d w i t h t h e K 10 -~ 6 t r a n s i t i o n , r e s p e c t i v e l y . T h e 6 -~ 5 (346 keV) t r a n s i t i o n h a s a g a i n a y i e l d t h a t i s too low to b e o b s e r v e d . C o m p a r i s o n b e t w e e n c o l s . 2 a n d 3 s h o w s full agreement between measured and calculated energies within the experimental errors. This c a n b e e x p e c t e d f r o m e s t i m a t i o n s [6] of t h e i n f l u e n c e of t h e s t r o n g i n t e r a c t i o n b e t w e e n t h e hyperon and the nucleus. Level shifts and broadenings should play an important role only in the l o w e r t r a n s i t i o n s , w h i c h c o u l d not b e o b s e r v e d in t h e s e f i r s t m e a s u r e m e n t s b e c a u s e of t h e i r low y i e l d . A l l E t r a n s i t i o n s w h i c h , a c c o r d i n g to col. 1 of t a b l e 1, a r e e x p e c t e d to h a v e h i g h
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yields, have been observed, except those which are superimposed by other identified and expected lines. Further information is contained in the rel a t i v e i n t e n s i t i e s b e t w e e n K a n d ~ X - r a y s . In col. 4 t a b l e 1 t h e i n t e n s i t y r a t i o b e t w e e n t h e l i n e a n d a k a o n i c l i n e of t h e s a m e s p e c t r u m i s given. It is corrected for absorption effects in t h e t a r g e t a n d d i f f e r e n t Ge d e t e c t o r e f f i c i e n c i e s . T h e K a t o m i c r e f e r e n c e t r a n s i t i o n l i s t e d i n col. 5 w a s a l w a y s c h o s e n not t o b e a t t e n u a t e d b y n u c l e a r a b s o r p t i o n . If o n e c o r r e c t s t h e v a l u e s of col. 4 f o r t h e e s t i m a t e d y i e l d of t h e ~ l i n e (col. 1), one obtains the ratio between K and ~ atoms formed in the target, where uncertainties in the p o p u l a t i o n of t h e i n i t i a l s t a t e s of t h e c o m p a r e d t r a n s i t i o n s a n d t h e s m a l l n u m b e r of ~ h y p e r o n s escaping from the target are neglected. In o r d e r t o c o m p a r e t h i s r a t i o w i t h t h e 8 % ~ hyperons produced per stopping K meson as obs e r v e d i n e m u l s i o n s [3], o u r d a t a m u s t b e c o r rected for ~ - hyperons decaying before they are s t o p p e d . T h i s c o r r e c t i o n i s e s t i m a t e d to b e 36, 34, a n d 13 p e r c e n t f o r S, LiC1, a n d Zn, r e s p e c t i v e l y , i n c r e a s i n g t h e v a l u e s of col. 4 c o r r e s p o n d ingly. The agreement between the present and t h e e m u l s i o n d a t a a p p e a r s , t h e r e f o r e , to b e s a t i s f a c t o r y . T h e p r e s e n t d a t a , h o w e v e r , a r e not y e t s u f f i c i e n t to e x h i b i t c l e a r l y a d e p e n d e n c e of t h e ~ y i e l d on t h e n u c l e a r m a s s . It can be concluded that both the energy and int e n s i t y of t h e o b s e r v e d X - r a y t r a n s i t i o n s a r e c o n sistent with them being identified as originating i n t h e c a s c a d e p r o c e s s of a ~ a t o m . It i s a p l e a s u r e to t h a n k D r s . T. E. O. E r i c s o n a n d M. K r e l l f o r m a n y d i s c u s s i o n s . T h e h e l p of M r . R. B a u e r d u r i n g t h e e v a l u a t i o n of t h e d a t a i s appreciated.
References [1] C. E. Wiegand, Phys. Rev. L e t t e r s 22 {1969) 1235. [2] G. Backenstoss. A. B a m b e r g e r . J. Egger, W.D. Hamilton, H. Koch, U. Lynen, H.G. Ritter and H. Schmitt, Phys. L e t t e r s 32B {1970) 399. [3] European K- collaboration, Nuovo Cimento 14 {1959) 315. [4] M. Kreli and T. E. O. Ericson, Nuclear Phys. B l l (1969) 521. [5] U. Lynen et ai.. to be published. [6] M. Krei[ and T. E. O. E r i c s o n , private communication.