- Email: [email protected]
Photoproduction of π+ Mesons from hydrogen at constant momentum transfer
Volume 10, n u m b e r 1
PHYSICS
dependent effects arising from electromagnetic m a s s d i f f e r e n c e s , t h o s e d u e to s i n g l e u O - e x c h a n g e a n d to t h e E + - E - m a s s d i f f e r e n c e , a r e in t h e s a m e d i r e c t i o n , a n d c o n t r i b u t e a b o u t 0.25 M e V to A B A. T h e c o n t r i b u t i o n s to A B A f r o m n u c l e a r s t r u c t u r e e f f e c t s a r e in t h e o p p o s i t e s e n s e a n d a r e e x p e c t e d to b e s i g n i f i c a n t l y s m a l l e r in m a g nitude. The agreement with the experimental v a l u e of A B A d e p e n d s p r i m a r i l y o n t h e s t r e n g t h a n d s i g n of t h e AAu ° c o u p l i n g p a r a m e t e r , w h i c h in t u r n d e p e n d s d o m i n a n t l y on t h e v a l i d i t y of t h e electromagnetic mass formula for the off-diagonal EA e l e m e n t , a n d on t h e c o r r e c t n e s s of t h e s i g n g i v e n f o r gEATr/gNN~r b y u n i t a r y s y m m e t r y . In c o n c l u s i o n , w e a r e h a p p y to r e c o r d o u r i n d e b t e d n e s s t o P r o f e s s o r s B. W. D o w n s a n d S. Glashow for their generous and constructive c r i t i c i s m s of t h e d e t a i l s of t h e a b o v e c a l c u l a t i o n . 1) S. Coleman and S. L. Glashow, P h y s . R e v . L e t t e r s 6 (1961) 423. 2) H. Ticho, The p r e s e n t status of ~ decay, P r o c . Brookhaven Conf. on Weak Interactions (Brookhaven National Laboratory, September, 1963) to be published. 3) L. Jauneau, D . M o r e l l e t , U.Nguyen-Khae. P . P e t i a u , A. Rousset, H. Bingham, D. C. Cundy, W. Koch, B. Ronne, H. Sletten, F.W. Bullock, A.K. Common, M . J . Esten, C . H e n d e r s o n , F . R . S t a n n a r d , J . M . S e a r r , J. Sparrow, A . G . W i l s o n , A. Halsteinslid and R. Mollerud, P h y s i c s L e t t e r s 4 (1963) 49; the m o s t r e c e n t data a r e given in ref. 2. 4) L. Bertanza, V. B r i s s o n , P. L. Connolly, E. L. Hart, I. S. Mittra, G.C. Moneti, R . R . Rau, N . P . Samios, I. O. Skillicorn, S . S . Y a m a m o t o , M. Goldberg, L. Gray, J. L e i t n e r , S. Liehtman and J . W e s t g a r d , P h y s . R e v . L e t t e r s 9 (1962) 229; the m o s t r e c e n t data a r e given in ref. 2.
P H O T O P R O D U C T I O N AT CONSTANT
OF
LETTERS
15 May 1964
5) W. H. B a r k a s , J . N . D y e r and H. H. Heckman, Phys. Rev. L e t t e r s 11 (1963) 26. 6) W. H. B a r k a s and A . H . R o s e n f e l d , Data for p a r t i c l e p h y s i c s , Lawrence Radiation Laboratory Rept. UCRL-8030 R e v . , April, 1963. 7) M . W e l l n e r , P h y s i c s L e t t e r s 7 (1964) 355. 8) R . K r a e m e r , M . N u s s b a u m , L.Madansky and A. P e v s n e r , P r e c . 1962 Int. Conf. on High-Energy P h y s i c s at CERN (CERN, Geneva, 1962), p.273. 9) L. B e r t a n z a , P. L. Connolly, B . B . Culwick, F . R . E i s l e r , T. M o r r i s , R. P a l m e r , A. P r o d e l l and N . P . Samios, P h y s . R e v . L e t t e r s 8 (1962) 332. 10 M. Schwartz, P r o c . 1960 Int. Conf. on High-Energy P h y s i c s (Interseience, New York, 1960), p.685. 11 M. Gell-Mann and A. H. Rosenfeld, Ann. Revs. Nuc l e a r Sci. 7 (1957) 407. 12 S. Okubo and B. Sakita, P h y s . Rev. L e t t e r s 11 (1963) 50. 13 J. J. De Swart and C. K. Iddings, P h y s . Rev. 128 (1962) 2810. 14 A.W. Martin and K. C. Wali, Phys. Rev. 130 (1963) 2455. 15 R. H. Dalitz and B. W. Downs, Phys. Rev. 111 (1958) 967. 16 M. Raymund, The binding energy difference b e tween the Hypernuclides ^He 4 and AH4, Nuovo Cimento, to be published': "" 17) R . G . A m m a r , R. Levi Setti, W. E .Slater, S. Limentani, P . E . S c h l e i n and P . H . S t e i n b e r g , Nuovo C i mento 19 (1961) 20. 18) M. M. Block, L. Lendinara and L. Monari, P r o c . 1962 Int. Conf. on High-Energy P h y s i c s at CERN (CERN, Geneva, 1962), p.371. 19) R . H . D a l i t z , P h y s . R e v . 112 (1958) 605. 2O) H. Collard, R. Hofstadter, A. Johanssen, R. P a r k s , M.Ryneveld, A . W a l k e r , M . R . Y e a r i a n , R . B . D a y and R . T . W a g n e r , P h y s . R e v . L e t t e r s 11 (1963) 132. 21) L. I. Schiff, P h y s . Rev. 133 (1964) B802. 22) J. Schwinger, P h y s . R e v . 78 (1950) 135. 23) R . H . D a l i t z and G . R a j a s e k a r a n , P h y s i c s L e t t e r s 1 (1962) 58.
7r + MESONS M O M E N T U M
FROM TRANSFER
B. H. P A T R I C K , J. M. P A T E R S O N *, J . G. R U T H E R G L E N
H Y D R O G E N
a n d J. G A R V E Y
D e p a r t m e n t of Natural P hylosophy, University o f Glasgow, Scotland
Received 27 April 1964
The differential cross section for the reaction y +p~
rr+ + n
(1)
h a s b e e n m e a s u r e d b e t w e e n E v = 190 a n d 250 M e V a t a n g l e s c o r r e s p o n d i n g t o c o n d i t i o n s of c o n s t a n t
momentum transfer. The results join smoothly on to t h o s e of o t h e r a u t h o r s a b o v e 250 M e V a n d * P r e s e n t address; P h y s i c s Laboratory, C . E . A . , Harvard, Mass., U.S.A.
15'/
Volumel0, number 1
PHYSICS LETTERS
15 May 1964
below 190 MeV and a r e in good a g r e e m e n t with the d i s p e r s i o n r e l a t i o n theory of Chew et al. 1). It was suggested by Baldin 2), that the r e a s o n for the d i s a g r e e m e n t between e x p e r i m e n t and theory for p r o c e s s (1) lies in the c o n t r i b u t i o n f r o m the n o n - p h y s i c a l r e g i o n and he showed that, by m a i n t a i n i n g the m o m e n t u m t r a n s f e r constant and equal to the t h r e s h o l d value, this c o n t r i b u t i o n is made identically zero. In o r d e r to fulfill this condition, the k i n e m a t i c a l v a r i a b l e s have to s a t isfy the equation
k w - kqcosO =0.93 ,
LIQUIO HYDROG£N TARGET
SPECIAL
C.I.
(2)
C.2.
where ~ = c = p = 1, k is the photon e n e r g y , w is the total pion e n e r g y , q is the pion m o m e n t u m and 0 is the production angle of the pion (all quant i t i e s being m e a s u r e d in the c e n t r e of m a s s s y s tem). W a l k e r 3) applied this r e s t r i c t i o n to the available e x p e r i m e n t a l data and found that the r e s u l t s f o r m e d a bump in the c r o s s s e c t i o n at 215 MeV (fig. 2). The p r e s e n t e x p e r i m e n t was p e r f o r m e d to i n vestigate the r e g i o n of the bump. Fig. 1 shows the e x p e r i m e n t a l a r r a n g e m e n t in which a liquid hydrogen t a r g e t , 2~ in. in d i a m e t e r , was i r r a diated by the 290 MeV b r e m s s t r a h l u n g beam f r o m the Glasgow U n i v e r s i t y s y n c h r o t r o n . The pions w e r e detected in a s p a r k c h a m b e r - s c i n t i l l a t i o n c o u n t e r s y s t e m , subtending an angle of 15 ° at the target. The c o u n t e r t e l e s c o p e accepted pions of 30 ± 5 MeV, the s e l e c t i o n being done by dE/dx and range. P i o n s s a t i s f y i n g eq. (2) at Ey = 250 MeV have an energy of 100 MeV at a l a b o r a t o r y angle of 30 ° while at 190 MeV, they have an energy of 30 MeV at 45 °. A s p e c i a l l y shaped copper abs o r b e r was placed in front of the telescope in o r -
C.$,
BEAM
Fig. 1. The experimental arrangement. der to select the pions of the c o r r e c t energy at each angle as r e q u i r e d by eq. (2). The angle of each event was d e t e r m i n e d from the t r a c k in the s p a r k c h a m b e r in front of the a b s o r b e r and the energy from the range. The c o u n t e r s w e r e s u c c e s s i v e l y i n c r e a s e d in a r e a so that the l o s s e s
• • X • A o
P,esent E~peri~an~ Wolke, e~al I~eneventano et ol 5J leissand penne r 8) Knopp et al 9l A d a m o v i c h et o110) Barboro e t al ~1 Al,~oft61 Theo,~ of C , ~ e t o}
2o - ----
i,.i 2
Walker's
Sugge,t~on
i
s
J
*
*
,
i
*
,
i
i
t60
170
180
]90
200
210
220
230
240
250
260
Fig. 2. fT+J 2 against Ey. 158
COPPER
ABSORBER
270
Volume 10, n u m b e r 1
PHYSICS
due to multiple scattering were negligible. T h e e v e n t s w e r e s e l e c t e d by a 1 + 2 + 3 - 4 coinc i d e n c e c i r c u i t (8 n s e c r e s o l v i n g t i m e ) w h i c h m a d e u s e of t h e s p a c e c h a r g e l i m i t e r p r o p e r t i e s of t h e E 1 8 0 F v a l v e , a s d e s c r i b e d by L e p r i 4). T h e i n p u t to e a c h c h a n n e l c o n t a i n e d a v a r i a b l e b i a s and by a d j u s t i n g t h e l e v e l s , t h e m a j o r i t y of e l e c t r o n s were removed from the coincident events. Although some electron events were still accepted, t h e s e w e r e m a i n l y in t h e f o r m of s h o w e r s w h i c h w e r e e a s i l y i d e n t i f i e d in t h e s p a r k c h a m b e r s . T h e m a x i m u m y - r a y e n e r g y w a s r e s t r i c t e d to 290 M e V s o t h a t p r o t o n s f r o m t h e r e a c t i o n 7+p~O+p c o u l d n o t b e d e t e c t e d a n d t h i s m e a n t t h a t t h e only s o u r c e s of p r o t o n s w e r e t h e w a l l s of t h e t a r g e t a s s e m b l y . M o s t of t h e p r o t o n s w e r e r e m o v e d by i n t r o d u c i n g p u l s e s f r o m t h e f i r s t c o u n t e r into a second anticoincidence channel and adjusting the bias level so that the large proton pulses produced an anticoincidence. The remaining protons were r e m o v e d in a b a c k g r o u n d s u b t r a c t i o n w h i c h v a r i e d f r o m 20% at t h e l o w e s t y - r a y e n e r g y to 7% at t h e highest. A b o u t 16 000 ~ + m e s o n s f r o m h y d r o g e n w e r e r e c o r d e d a n d t h e d a t a c o r r e c t e d f o r l o s s e s d u e to d e a d t i m e (3%), d e c a y in f l i g h t (3%) a n d n u c l e a r interactions. The interaction losses were mainly caused by the copper absorber and the first spark c h a m b e r a n d a m o u n t e d to 23% at Ey= 250 M e V f a l l i n g to 2.5% at 190 MeV. T h e y - r a y b e a m w a s monitored by a Cornell ionisation chamber, the c a l i b r a t i o n c o n s t a n t b e i n g t a k e n a s 3.74 × 1018 M e V / c o u l o m b at N . T . P . w i t h a n u n c e r t a i n t y of ± 4%. T h e a v e r a g e v a l u e o f k ~ -kq c o s 0 w a s w i t h i n a b o u t 1% of 0.93 in e a c h m e a s u r e m e n t . T h e t o t a l e r r o r o n e a c h of t h e c r o s s s e c t i o n s i s e s t i m a t e d to b e ± 8%. T h e r e s u l t s h a v e b e e n a n a l y s e d in t h e f o r m 5)
dcr/d~* = W~ T+[ 2 where
LETTERS
15 May 1964 W-
~q [1 + (~tk/M)] 2
a n d a r e s h o w n in fig. 2. A l s o p l o t t e d a r e t h e r e s u l t s of a n e x p e r i m e n t by A l t h o f f 6) at B o n n and t h e o r i g i n a l s u g g e s t i o n of W a l k e r . It is c l e a r t h a t the present experiment together with the results of t h e B o n n g r o u p r u l e out t h e p o s s i b i l i t y of a b u m p a n d it c a n b e s e e n t h a t t h e t h e o r y of C h e w et a l . , w i t h / 2 = 0.081 a n d ¢o~ = 2.08, i s a good fit to t h e d a t a . T h e a u t h o r s w i s h to t h a n k D r . W. M c F a r l a n e and the synchrotron technicians for their coo p e r a t i o n in r u n n i n g t h e m a c h i n e a n d P r o f e s s o r P. I. D e e f o r h i s i n t e r e s t in t h e w o r k . T h e a s s i s t a n c e of M r . I. L. S m i t h d u r i n g t h e d a t a c o l l e c t i o n i s g r a t e f u l l y a c k n o w l e d g e d . O n e of u s ( B . H . P . ) w i s h e s to t h a n k t h e U n i v e r s i t y of G l a s g o w f o r a g r a n t h e l d d u r i n g t h e p e r i o d of t h i s w o r k a n d a n o t h e r (J.G.) w o u l d l i k e t o t h a n k D.S.I.R. f o r a similar maintenance grant.
Rcfc~'cnccs 1) G. F. Chew, M. L. Goldberger, F . E . Low and Y. Nambu, Phys. Rev. 106 (1957) 1345. 2) A.M. Baldin, P r o e . Int. Conf. High Energy P h y s i c s , R o c h e s t e r 1960 (Interscienee P u b l i s h e r s , Inc., New York) p. 325. 3) J. K. Walker, Nuovo Cimente 21 (1961) 577. 4) F. Lepri, Rev. Sci. Instr. 30 (1959) 1049. 5) M. Benevontano, G. B e r n a r d i n i , D. C a r l s o n - L e e , G. Stoppini and L. Tau, Nuovo Cimento 4 (1956) 323. 6) K.Althoff, Z. Physik 175 (1963) 34. 7) J.K. Walker, J . G . Rutherglen, D. B. Miller and J. M. P a t e r s o n , P r o c . Phys. Soc. 81 (1963) 78. 8) J. Leiss and A . S . P e n n e r , Bull. Am. P h y s . Soc. II, 4 (1959) 273. 9) E.Knapp, R . W . K e n n e y and V. P e r e z - M e n d e z , Phys. Rev. 114 (1959) 605. 10) M. I. Adamovich, S. F. Kharlamov, E. G. G o r z h e v s kaya, U.G. Larionova, F . R . Yagudina and V. M. P o pova, r e p o r t e d by Baldin in the P r o c . Int. Conf. High Energy P h y s i c s , R o c h e s t e r 1960 (Interscience P u b l i s h e r s , Inc., New York) p. 26. 11) A. B a r b a r o , E. L. Goldwasser and D. C a r l s o n - L e e , Bull. Am. Phys. Soc. H, 4 (1959) 23.
159
PHYSICS
dependent effects arising from electromagnetic m a s s d i f f e r e n c e s , t h o s e d u e to s i n g l e u O - e x c h a n g e a n d to t h e E + - E - m a s s d i f f e r e n c e , a r e in t h e s a m e d i r e c t i o n , a n d c o n t r i b u t e a b o u t 0.25 M e V to A B A. T h e c o n t r i b u t i o n s to A B A f r o m n u c l e a r s t r u c t u r e e f f e c t s a r e in t h e o p p o s i t e s e n s e a n d a r e e x p e c t e d to b e s i g n i f i c a n t l y s m a l l e r in m a g nitude. The agreement with the experimental v a l u e of A B A d e p e n d s p r i m a r i l y o n t h e s t r e n g t h a n d s i g n of t h e AAu ° c o u p l i n g p a r a m e t e r , w h i c h in t u r n d e p e n d s d o m i n a n t l y on t h e v a l i d i t y of t h e electromagnetic mass formula for the off-diagonal EA e l e m e n t , a n d on t h e c o r r e c t n e s s of t h e s i g n g i v e n f o r gEATr/gNN~r b y u n i t a r y s y m m e t r y . In c o n c l u s i o n , w e a r e h a p p y to r e c o r d o u r i n d e b t e d n e s s t o P r o f e s s o r s B. W. D o w n s a n d S. Glashow for their generous and constructive c r i t i c i s m s of t h e d e t a i l s of t h e a b o v e c a l c u l a t i o n . 1) S. Coleman and S. L. Glashow, P h y s . R e v . L e t t e r s 6 (1961) 423. 2) H. Ticho, The p r e s e n t status of ~ decay, P r o c . Brookhaven Conf. on Weak Interactions (Brookhaven National Laboratory, September, 1963) to be published. 3) L. Jauneau, D . M o r e l l e t , U.Nguyen-Khae. P . P e t i a u , A. Rousset, H. Bingham, D. C. Cundy, W. Koch, B. Ronne, H. Sletten, F.W. Bullock, A.K. Common, M . J . Esten, C . H e n d e r s o n , F . R . S t a n n a r d , J . M . S e a r r , J. Sparrow, A . G . W i l s o n , A. Halsteinslid and R. Mollerud, P h y s i c s L e t t e r s 4 (1963) 49; the m o s t r e c e n t data a r e given in ref. 2. 4) L. Bertanza, V. B r i s s o n , P. L. Connolly, E. L. Hart, I. S. Mittra, G.C. Moneti, R . R . Rau, N . P . Samios, I. O. Skillicorn, S . S . Y a m a m o t o , M. Goldberg, L. Gray, J. L e i t n e r , S. Liehtman and J . W e s t g a r d , P h y s . R e v . L e t t e r s 9 (1962) 229; the m o s t r e c e n t data a r e given in ref. 2.
P H O T O P R O D U C T I O N AT CONSTANT
OF
LETTERS
15 May 1964
5) W. H. B a r k a s , J . N . D y e r and H. H. Heckman, Phys. Rev. L e t t e r s 11 (1963) 26. 6) W. H. B a r k a s and A . H . R o s e n f e l d , Data for p a r t i c l e p h y s i c s , Lawrence Radiation Laboratory Rept. UCRL-8030 R e v . , April, 1963. 7) M . W e l l n e r , P h y s i c s L e t t e r s 7 (1964) 355. 8) R . K r a e m e r , M . N u s s b a u m , L.Madansky and A. P e v s n e r , P r e c . 1962 Int. Conf. on High-Energy P h y s i c s at CERN (CERN, Geneva, 1962), p.273. 9) L. B e r t a n z a , P. L. Connolly, B . B . Culwick, F . R . E i s l e r , T. M o r r i s , R. P a l m e r , A. P r o d e l l and N . P . Samios, P h y s . R e v . L e t t e r s 8 (1962) 332. 10 M. Schwartz, P r o c . 1960 Int. Conf. on High-Energy P h y s i c s (Interseience, New York, 1960), p.685. 11 M. Gell-Mann and A. H. Rosenfeld, Ann. Revs. Nuc l e a r Sci. 7 (1957) 407. 12 S. Okubo and B. Sakita, P h y s . Rev. L e t t e r s 11 (1963) 50. 13 J. J. De Swart and C. K. Iddings, P h y s . Rev. 128 (1962) 2810. 14 A.W. Martin and K. C. Wali, Phys. Rev. 130 (1963) 2455. 15 R. H. Dalitz and B. W. Downs, Phys. Rev. 111 (1958) 967. 16 M. Raymund, The binding energy difference b e tween the Hypernuclides ^He 4 and AH4, Nuovo Cimento, to be published': "" 17) R . G . A m m a r , R. Levi Setti, W. E .Slater, S. Limentani, P . E . S c h l e i n and P . H . S t e i n b e r g , Nuovo C i mento 19 (1961) 20. 18) M. M. Block, L. Lendinara and L. Monari, P r o c . 1962 Int. Conf. on High-Energy P h y s i c s at CERN (CERN, Geneva, 1962), p.371. 19) R . H . D a l i t z , P h y s . R e v . 112 (1958) 605. 2O) H. Collard, R. Hofstadter, A. Johanssen, R. P a r k s , M.Ryneveld, A . W a l k e r , M . R . Y e a r i a n , R . B . D a y and R . T . W a g n e r , P h y s . R e v . L e t t e r s 11 (1963) 132. 21) L. I. Schiff, P h y s . Rev. 133 (1964) B802. 22) J. Schwinger, P h y s . R e v . 78 (1950) 135. 23) R . H . D a l i t z and G . R a j a s e k a r a n , P h y s i c s L e t t e r s 1 (1962) 58.
7r + MESONS M O M E N T U M
FROM TRANSFER
B. H. P A T R I C K , J. M. P A T E R S O N *, J . G. R U T H E R G L E N
H Y D R O G E N
a n d J. G A R V E Y
D e p a r t m e n t of Natural P hylosophy, University o f Glasgow, Scotland
Received 27 April 1964
The differential cross section for the reaction y +p~
rr+ + n
(1)
h a s b e e n m e a s u r e d b e t w e e n E v = 190 a n d 250 M e V a t a n g l e s c o r r e s p o n d i n g t o c o n d i t i o n s of c o n s t a n t
momentum transfer. The results join smoothly on to t h o s e of o t h e r a u t h o r s a b o v e 250 M e V a n d * P r e s e n t address; P h y s i c s Laboratory, C . E . A . , Harvard, Mass., U.S.A.
15'/
Volumel0, number 1
PHYSICS LETTERS
15 May 1964
below 190 MeV and a r e in good a g r e e m e n t with the d i s p e r s i o n r e l a t i o n theory of Chew et al. 1). It was suggested by Baldin 2), that the r e a s o n for the d i s a g r e e m e n t between e x p e r i m e n t and theory for p r o c e s s (1) lies in the c o n t r i b u t i o n f r o m the n o n - p h y s i c a l r e g i o n and he showed that, by m a i n t a i n i n g the m o m e n t u m t r a n s f e r constant and equal to the t h r e s h o l d value, this c o n t r i b u t i o n is made identically zero. In o r d e r to fulfill this condition, the k i n e m a t i c a l v a r i a b l e s have to s a t isfy the equation
k w - kqcosO =0.93 ,
LIQUIO HYDROG£N TARGET
SPECIAL
C.I.
(2)
C.2.
where ~ = c = p = 1, k is the photon e n e r g y , w is the total pion e n e r g y , q is the pion m o m e n t u m and 0 is the production angle of the pion (all quant i t i e s being m e a s u r e d in the c e n t r e of m a s s s y s tem). W a l k e r 3) applied this r e s t r i c t i o n to the available e x p e r i m e n t a l data and found that the r e s u l t s f o r m e d a bump in the c r o s s s e c t i o n at 215 MeV (fig. 2). The p r e s e n t e x p e r i m e n t was p e r f o r m e d to i n vestigate the r e g i o n of the bump. Fig. 1 shows the e x p e r i m e n t a l a r r a n g e m e n t in which a liquid hydrogen t a r g e t , 2~ in. in d i a m e t e r , was i r r a diated by the 290 MeV b r e m s s t r a h l u n g beam f r o m the Glasgow U n i v e r s i t y s y n c h r o t r o n . The pions w e r e detected in a s p a r k c h a m b e r - s c i n t i l l a t i o n c o u n t e r s y s t e m , subtending an angle of 15 ° at the target. The c o u n t e r t e l e s c o p e accepted pions of 30 ± 5 MeV, the s e l e c t i o n being done by dE/dx and range. P i o n s s a t i s f y i n g eq. (2) at Ey = 250 MeV have an energy of 100 MeV at a l a b o r a t o r y angle of 30 ° while at 190 MeV, they have an energy of 30 MeV at 45 °. A s p e c i a l l y shaped copper abs o r b e r was placed in front of the telescope in o r -
C.$,
BEAM
Fig. 1. The experimental arrangement. der to select the pions of the c o r r e c t energy at each angle as r e q u i r e d by eq. (2). The angle of each event was d e t e r m i n e d from the t r a c k in the s p a r k c h a m b e r in front of the a b s o r b e r and the energy from the range. The c o u n t e r s w e r e s u c c e s s i v e l y i n c r e a s e d in a r e a so that the l o s s e s
• • X • A o
P,esent E~peri~an~ Wolke, e~al I~eneventano et ol 5J leissand penne r 8) Knopp et al 9l A d a m o v i c h et o110) Barboro e t al ~1 Al,~oft61 Theo,~ of C , ~ e t o}
2o - ----
i,.i 2
Walker's
Sugge,t~on
i
s
J
*
*
,
i
*
,
i
i
t60
170
180
]90
200
210
220
230
240
250
260
Fig. 2. fT+J 2 against Ey. 158
COPPER
ABSORBER
270
Volume 10, n u m b e r 1
PHYSICS
due to multiple scattering were negligible. T h e e v e n t s w e r e s e l e c t e d by a 1 + 2 + 3 - 4 coinc i d e n c e c i r c u i t (8 n s e c r e s o l v i n g t i m e ) w h i c h m a d e u s e of t h e s p a c e c h a r g e l i m i t e r p r o p e r t i e s of t h e E 1 8 0 F v a l v e , a s d e s c r i b e d by L e p r i 4). T h e i n p u t to e a c h c h a n n e l c o n t a i n e d a v a r i a b l e b i a s and by a d j u s t i n g t h e l e v e l s , t h e m a j o r i t y of e l e c t r o n s were removed from the coincident events. Although some electron events were still accepted, t h e s e w e r e m a i n l y in t h e f o r m of s h o w e r s w h i c h w e r e e a s i l y i d e n t i f i e d in t h e s p a r k c h a m b e r s . T h e m a x i m u m y - r a y e n e r g y w a s r e s t r i c t e d to 290 M e V s o t h a t p r o t o n s f r o m t h e r e a c t i o n 7+p~O+p c o u l d n o t b e d e t e c t e d a n d t h i s m e a n t t h a t t h e only s o u r c e s of p r o t o n s w e r e t h e w a l l s of t h e t a r g e t a s s e m b l y . M o s t of t h e p r o t o n s w e r e r e m o v e d by i n t r o d u c i n g p u l s e s f r o m t h e f i r s t c o u n t e r into a second anticoincidence channel and adjusting the bias level so that the large proton pulses produced an anticoincidence. The remaining protons were r e m o v e d in a b a c k g r o u n d s u b t r a c t i o n w h i c h v a r i e d f r o m 20% at t h e l o w e s t y - r a y e n e r g y to 7% at t h e highest. A b o u t 16 000 ~ + m e s o n s f r o m h y d r o g e n w e r e r e c o r d e d a n d t h e d a t a c o r r e c t e d f o r l o s s e s d u e to d e a d t i m e (3%), d e c a y in f l i g h t (3%) a n d n u c l e a r interactions. The interaction losses were mainly caused by the copper absorber and the first spark c h a m b e r a n d a m o u n t e d to 23% at Ey= 250 M e V f a l l i n g to 2.5% at 190 MeV. T h e y - r a y b e a m w a s monitored by a Cornell ionisation chamber, the c a l i b r a t i o n c o n s t a n t b e i n g t a k e n a s 3.74 × 1018 M e V / c o u l o m b at N . T . P . w i t h a n u n c e r t a i n t y of ± 4%. T h e a v e r a g e v a l u e o f k ~ -kq c o s 0 w a s w i t h i n a b o u t 1% of 0.93 in e a c h m e a s u r e m e n t . T h e t o t a l e r r o r o n e a c h of t h e c r o s s s e c t i o n s i s e s t i m a t e d to b e ± 8%. T h e r e s u l t s h a v e b e e n a n a l y s e d in t h e f o r m 5)
dcr/d~* = W~ T+[ 2 where
LETTERS
15 May 1964 W-
~q [1 + (~tk/M)] 2
a n d a r e s h o w n in fig. 2. A l s o p l o t t e d a r e t h e r e s u l t s of a n e x p e r i m e n t by A l t h o f f 6) at B o n n and t h e o r i g i n a l s u g g e s t i o n of W a l k e r . It is c l e a r t h a t the present experiment together with the results of t h e B o n n g r o u p r u l e out t h e p o s s i b i l i t y of a b u m p a n d it c a n b e s e e n t h a t t h e t h e o r y of C h e w et a l . , w i t h / 2 = 0.081 a n d ¢o~ = 2.08, i s a good fit to t h e d a t a . T h e a u t h o r s w i s h to t h a n k D r . W. M c F a r l a n e and the synchrotron technicians for their coo p e r a t i o n in r u n n i n g t h e m a c h i n e a n d P r o f e s s o r P. I. D e e f o r h i s i n t e r e s t in t h e w o r k . T h e a s s i s t a n c e of M r . I. L. S m i t h d u r i n g t h e d a t a c o l l e c t i o n i s g r a t e f u l l y a c k n o w l e d g e d . O n e of u s ( B . H . P . ) w i s h e s to t h a n k t h e U n i v e r s i t y of G l a s g o w f o r a g r a n t h e l d d u r i n g t h e p e r i o d of t h i s w o r k a n d a n o t h e r (J.G.) w o u l d l i k e t o t h a n k D.S.I.R. f o r a similar maintenance grant.
Rcfc~'cnccs 1) G. F. Chew, M. L. Goldberger, F . E . Low and Y. Nambu, Phys. Rev. 106 (1957) 1345. 2) A.M. Baldin, P r o e . Int. Conf. High Energy P h y s i c s , R o c h e s t e r 1960 (Interscienee P u b l i s h e r s , Inc., New York) p. 325. 3) J. K. Walker, Nuovo Cimente 21 (1961) 577. 4) F. Lepri, Rev. Sci. Instr. 30 (1959) 1049. 5) M. Benevontano, G. B e r n a r d i n i , D. C a r l s o n - L e e , G. Stoppini and L. Tau, Nuovo Cimento 4 (1956) 323. 6) K.Althoff, Z. Physik 175 (1963) 34. 7) J.K. Walker, J . G . Rutherglen, D. B. Miller and J. M. P a t e r s o n , P r o c . Phys. Soc. 81 (1963) 78. 8) J. Leiss and A . S . P e n n e r , Bull. Am. P h y s . Soc. II, 4 (1959) 273. 9) E.Knapp, R . W . K e n n e y and V. P e r e z - M e n d e z , Phys. Rev. 114 (1959) 605. 10) M. I. Adamovich, S. F. Kharlamov, E. G. G o r z h e v s kaya, U.G. Larionova, F . R . Yagudina and V. M. P o pova, r e p o r t e d by Baldin in the P r o c . Int. Conf. High Energy P h y s i c s , R o c h e s t e r 1960 (Interscience P u b l i s h e r s , Inc., New York) p. 26. 11) A. B a r b a r o , E. L. Goldwasser and D. C a r l s o n - L e e , Bull. Am. Phys. Soc. H, 4 (1959) 23.
159