c

Nuclear Physics 57 (1964) 479--482; (~) North.Holland Publishing Co., Amsterdam Not to be reproduced by photoprint or microfilm without written permission from the publisher

n o PRODUCTION

IN n - p INTERACTIONS AT 10 GeV/c T. SIEMIARCZUK t

High Energy Laboratory, Institute of Nuclear Research, Warsaw, Poland Received 31 March 1964 Abstract: The average number o f ~ ° per interaction and the mean value Of PT in six and eight prong events are found. The angular and momentum distributions of 7-quanta are analysed and information about those o f ~0 mesons presented.

There is very poor experimental information about n ° production in the GeV region. In this letter are presented results obtained from the study of n ° in 9.9-1-0.5 GeV/c n - p interactions in the 81 cm Saclay HBC with six and eight charged particles in the final state. Scanning and measurements were carried out as described in ref. 1) Results of scanning are presented in table 1. TABLE 1 Prong multiplicity

Number of events

Number of e+e- pairs

6 8

750 100

46 6

Number o f Dalitz pairs 9 2

The scanning efficiency on e+e - pairs was 98%. Dalitz pairs were identified only when the momentum of the slower component of the pair was smaller than (170-180) MeV/c, because only in this region it was possible to distinguish the electron from the n meson by ionization measurements. Fig. 1 shows the laboratory energy distribution of 3'-quanta (in this figure the statistical weights of photons are plotted on the ordinate). The curve is the energy spectrum calculated 2) under the assumption that the laboratory energy distributions of charged and neutral pions are the same. Owing to the fact that the differences between the curve and the experimental distribution are not statistically significant, it was assumed that all 3'-quanta are produced in the decays of n ° mesons generated in rc-p interactions. 52 n - p interactions were accompanied by only one 3,-quantum. For these events the "potential lengths" L~ of v-quanta in the fiducial region were measured and their t Work supported by the Polish State Council for Use o f Nuclear Energy. 479

480

T. SIEMIARCZUK

statistical weight Wz calculated by the f o r m u l a

W,=ll-exp[-L,f,So/-rT/E'cr,(E,,u,)du,]} --I

40(]

20(]

T i 0.2

0.6

1

2

3

Energy (GeV) Fig. 1. Laboratory energy distribution of gammas.

where E i is the energy o f the v-quantum, u~ the ratio o f p o s i t o n to n e g a t o n energy, az the cross section for y m a t e r i a l i z a t i o n . This cross section was calculated t a k i n g into a c c o u n t the effect o f screening a n d the p o s s i b i l i t y o f e+e - c r e a t i o n in a t o m i c electron field s). I n table 2 the t o t a l n u m b e r o f v - q u a n t a in 6 a n d 8 p r o n g events a n d the average n u m b e r o f zc° p e r i n t e r a c t i o n are given. TABLE 2

Prong multiplicity

Total number of F-quanta

Number of n ° per interaction

6 8

1913+290 2524-100

1.28+0.19 1.264-0.50

In six p r o n g events nine D a l i t z pairs w i t h m o m e n t u m smaller t h a n 170-180 M e V / c have been observed. T h e t o t a l n u m b e r o f D a l i t z pairs was f o u n d to be 13 + 4 u n d e r the a s s u m p t i o n t h a t the l a b o r a t o r y energy d i s t r i b u t i o n s o f slower c o m p o n e n t s o f e+e - a n d D a l i t z pairs were identical. The average n u m b e r o f n ° p e r one 6 - p r o n g i n t e r a c t i o n calculated a c c o r d i n g to the b r a n c h i n g r a t i o rc° ~ 2y = 80 ;r o --} 7 + e + e was 1.35__+0.45. This result is in a c c o r d a n c e with the n u m b e r o f no per i n t e r a c t i o n presented in table 2. The average n u m b e r s o f n ° p e r 0 a n d 2 p r o n g interactions t a k e n

~o PRODUCTIONIN ~-p INTERACTIONS

481

from ref. 4,~) are No = 1.5+0.2 and N2 = 1.7__+0.3, but for 4-prong events the maximal and minimal limits amount to 1.0 < N# < 1.8 on the basis ofref. 5). These data exhibit the weak dependence of n ° production on the number of charged particles in the final state. 600~-'~"n

40C

~.

! I I I I |

......

~d"-~

20O

,

10°

i

30°

Gammas rl-

_/__~

i

60°

.

i

~

i

90°

--'k.. . . . "I

120°

150°

Fig. 2. Laboratory angular distribution of gammas and negative pions.

SO0

400

61)0 400

[

200

200 0.2 0.4 0.6 PT (GeV/c) Fig.

3. Transverse m o m e n t u m distribution o f gammas.

011

0'.5

P* (GeV/e~

;

Fig. 4. Centre of mass momentum distribution of gammas.

The laboratory angular distributions of y-quanta and n - mesons are presented in fig. 2. The distributions are identical. It means that the laboratory angular distributions of n ° and n - are almost the same ~). Fig. 3 presents the transverse momentum distribution of photons. The curve gives the expected distribution calculated on the basis of the charged-pion transversemomentum distribution neglecting the v-quanta transverse momentum with regard

482

T. SIEMIARCZUK

to the direction of~ ° motion. The histogram is in good accordance with the calculated curve. The mean transverse momentum and mean energy of n ° are equal: Pz(~ °) m 2PT(V) = 0 . 2 7 + O . 0 2 G e V / c ,

E(7~°) ~ 2E(T) = 1.27_oh2GeV. + o t9

800 [

600

]

-----

Gammas Negative pions

60C

Gammas v,-

.....

400

40(

20(

20C

r -° _.j

.... I .

-0.6

-0.4

-0.2

.

.

0

.

0.2

0.4

0.6

0.8

P~ (aeV/e) Fig. 5. Centre of mass longitudinal momentum distribution of gammas and negative pions.

-0:8

' -0 ' .4

'

6 ' 0.'4 COS 0*

'

0'.8

Fig. 6. Centre of mass angular distribution of gammas and negative pions.

Fig. 4 shows the CMS momentum distribution of photons The CMS longitudinal momentum distribution of T-quanta and n - normalized in region - 0 . 6 < PL ~ 0.8 GeV/c are given in fig. 5. Fig. 6 shows the normalized CMS angular distributions of photons and negative pions. The results of this investigation show that the average number of n ° per interaction in 10 GeV/c n - p interactions is constant within the statistical errors for all multiplicities. There is no significant difference between the angular and momentum distributions of n ° and charged pions, nor between the mean values of Pr and E in 6 and 8-prong events. I am very grateful to the Warsaw Bubble Chamber Group for the possibility of using films from the Saclay HBC and to Dr. R. Sosnowski, Mr. B. Wutach and Mr. L. Michejda for helpful discussions. I also thank Miss E. Janczewska for her help in calcula*~ons.

References 1) M. Bardadin, L. Michejda, S. Otwinowski and R. Sosnowski, Prec. of the Siena International Conference on Elementary Particles 1963 2) A. G. Carlson, J. E. Hoopcr and D. T. King, Phil. Mag. 41 (1950) 701 3) A. I. Ahieser and V. B. Berestetsky, Quantum electrodynamics (Moscow, 1959) 4) D. R. O. Morrison and R. Sosnowski (not published, CERN 1963) 5) N. 1'4. Biswas, I. Derado, N. Schmitz and W. D. Shephard, preprint, January 1964 6) A. A. Tyapkin, JETP 30 (1956) 1150 7) Z. S. Strugalski and T. Siemiarczuk, to be published