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Some aspects of 400 GeV proton interactions in nuclear emulsions
NUCLEAR
INSTRUMENTS
AND METHODS
147 ( 1 9 7 7 )
255-257
;t~ NORTH-HOLLAND
PUBLISHING
CO.
SOME ASPECTS OF 400 GeV P R O T O N INTERACTIONS IN NUCLEAR EMULSIONS* P. S. YOUNG
Mississipi State University, Mississippi 39762, U.S.A. K. FUKUI t
Air Force Geophysics Laboratory, Bedford Mass. 01731, U.S.A. and Y . V . RAO
Dublin Institute for Advanced Studies, Dublin, Ireland
llford G5 nuclear emulsions were exposed to 300 GeV and 400 GeV proton beams at the National Accelerator Laboratory. A total of 350 interactions were found and analyzed. The study was concentrated on non-white stars because of insufficient scanning efficiency for white stars. The mean free path for 300 GeV proton is 36.9___2.6 cm which is in good agreement with other authors. A linear relation is observed between the charge shower particle multiplicity and the star size indicating that the number of shower particles is independent of the target nuclei. Black prongs for smaller stars seems to show higher value of forward-backward ratio suggesting larger motion of nucleus after collisions.
1. Introduction In order to study interactions between high energy protons and complex target nuclei in emulsion, stacks of nuclear emulsion were exposed to proton beams of highest energy available today at the National Accelerator Laboratory, Batavia. Studies of interest cover star size distribution, charged shower multiplicity, the ratio of black and gray tracks as well as the ratio of forwardly ejected tracks against backwardly ejected tracks from the stars as a function of the entrance proton energy. 2. Exposure, processing and scanning Several stacks of Ilford G 5 nuclear emulsions, 600/zm thick, were exposed to 300GeV proton beams at the Fermi National Accelerator Laboratory, Batavia, Illinois, in October 1973. The flux of the proton beam was in the order of l0 s per cm 2. Other stacks were exposed to 400GeV proton beam at the same laboratory in November 1975, and the flux was in the order of 104 per cm 2. The emulsions exposed to the 300 GeV beam were unmounted pellicles. They were processed in full strength. But those exposed to the 400 GeV * This paper was read at the 9th International Conference on Solid State Nuclear Track Detectors, Neuherberg/Mtinchen, September 30 - October 6, 1976. The complete Proceedings will be published by Pergamon Press, Oxford and New York. t NCR-AFSC Resident Research Associate.
beams were glass mounted plates, and they were processed in slightly weaker strength in order to avoid heavy background. The development without glass plates seems more uniform and it is easy to observe shower particles of low grain density; however some distortion of emulsion plates may be unavoidable. In this work only area scanning with a 150× magnification was used. To avoid stars created by secondary interactions, only those stars due to entrance proton beam with less than 1 degree from the original beam direction were taken. Also the scanning was limited to the area close to the entrance edge of the plates. Namely for the 300 GeV plates the area between 4 mm and 22 mm, and for the 400GeV plates the area between 10 and 29 mm from the entrance edge were used. This method limits the contamination by secondaries to less than 5%. The study on white stars without heavy prongs, and semi-white stars with one heavy prong are of importance for the analysis of p-p collisions. However, this scanning was not aimed to find substantial amount of white stars. Higher magnifications and the following track method should be applied for systematic study of white stars. In this preliminary report only the study on stars with definite prongs was carried out. Total numbers of stars identified as interactions due to primary protons and target nuclei in emulX. A P P L I C A T I O N S
IN N U C L E A R
PHYSICS
256
P . s . YOUNG et al. 25
x
x
20
~, 30 0
f
15
1
,0
I
I0
I I ~I
l
=
I1
20
Nh Fig. ]. Histogram of the combined N h distribution from 300 GeV and 400 GeV plates.
sion from above scanning are 154 for the 400 GeV plates and 196 for the 300 GeV plates.
I
I
I
5
I0
15
| 20
Nh Fig. 2. Charged shower particle multiplicity (n s) vs the star size N h. • 400 GeV plates and ~ 300 GeV plates of this work. © Paris, × L u n d , • Ottawa, [] Bucharest, all from 200 GeV protons j ).
3. Analysis 3.1. THE STARSIZE DISTRIBUTION AND THE INELASTIC MEAN FREE PATH
The star size distribution obtained from the 300 GeV and 400 GeV plates is shown in fig. 1. Nh indicates the number of total prongs including both black and gray tracks. In this distribution, the percentage of events for N 4 8 is about 50% of the total event. It is estimated that about half of these events as well as all the larger stars are due to Ag or Br stars. Most of the remaining half of N 4 8 stars are due to N, C, O stars and only a small percentage of these stars is due to p-p collisions. From the theoretical consideration, it is believed that only 4% of the interactions should take place in hydrogen, thus the amount of small stars not included in this distribution is in the order of not more than 8% of the entire events. The inelastic mean free path was calculated. The value obtained for the 300 GeV plates is (36.9_2.6) cm, and this is slightly higher than the value given by Hebert et al.l). If we consider the amount of loss mentioned above, this value may be lowered to 34.0cm, and becomes in good agreement with the other authors. Thus there is no significant difference in the mean free path for 300 GeV and 200 GeV protons.
3.2. CHARGE SHOWER PARTICLE MULTIPLICITY AS A FUNCTION OF STAR SIZE
The charge shower particle multiplicity (ns) as a function of star size N, is plotted in fig. 2 together with the values of other works. Agreement with other works is within the statistical error and no drastic change due to the energy of incident proton beams is observed. We observe a similar tendency for this work and for the work by others. Namely relationship between two .factors seems a linear increase. This fact indicates that the number o f shower particles is not depending on the target nuclei, but it rather depends on the process of braking up targets. The amount of shower particles is apparently decided by the complex process of creating black and gray prongs inside the target nuclei after collision. Table 1 shows a comparison of the results of the average black tracks, gray tracks and shower tracks associated with stars obtained for 300 GeV and 400 GeV together with other works of lower energies. The (Nb) and (Ng) of this work are in good agreement with the work of lower energies, but somewhat different from the values by 200 GeV. On the other hand (Ns) for this work seems to agree better with the 200 GeV result. Even con-
400 GeV PROTON
257
INTERACTIONS
TABLE |
TABLE 2
Composition of events.
The ratio of forward and backward tracks, a
E(GeV)
(N~
(Ng)
(N s)
6.2 a 22.5 a 200 b 300 400
5.68_+0.21 5.22_+0.29 7.0 _ + 0 . 1 5.42_+0.19 5.32_+0.17
3.58_+0.11 3.38_+0.14 2.79_+0.15 3.92_+0.16 3.93_+0.14
2.21_+0.04 5.08_+0.12 12.9 _+0.15 12.99_+0.29 12.03_+0.25
(F/B~ 300 GeV 400 GeV Nh~<8 Nh~>9
(F/B~
1.22_+0.08 1.18_+0.08
1.19_+0.09 1.22_+0.11
1.32--0.11 1.15--+0.06
1.18_+0.12 1.21_+0.08
(F/B~ 1.21 _+0.06 1.19_+0.06
a Winzeler. b Hebert et al., after ref. 1.
a b, g, h stand for black, gray tracks and total track respectively.
sidering value of incident apparent results.
4. Conclusion There is no fundamental difference between the interactions of this work and other works by lower energy protons. Only the significant difference appears to be the increase of (N) for higher energy protons. However, the number of gray and black tracks should be carefully examined with higher statistics. The ratio of forward and backward tracks should be checked with the result of plastic detectors whose components consist of only C, N, O and H. Such data may be available at this conference. Further study and scanning of the events including white stars should be continued.
the loss of white stars in this work the (Ns) seems to increase as the energy of protons increases. There is however no difference between the 300 and 400 GeV
3.3. RATIO OF FORWARDAND BACKWARDTRACKS Table 2 shows the ratio of forwardly ejected prongs and backwardly ejected prongs for black tracks, gray tracks and the total. The black tracks are due to the evaporation process of the residual nucleus. Evaporation particles are believed to be ejected after the target nuclei are set in motion as a result of interaction. The motion for heavier nuclei such as Ag or Br should thus be smaller and this ratio should also be smaller than the ratio for smaller nuclei such as C, N, O. If stars Nh>~9 are mostly by Ag or Br and stars Nh~<8 are admixture of different nuclei, it should be observed that this ratio is larger for smaller stars such as Nh~<8. This is demonstrated in the second part of table 2. Namely the ratio is about 15% larger for black tracks of small stars.
The authors thank Dr. Voyvodic of the National Accelerator Laboratory for the exposure of the emulsions.
Reference 1) j. Hebert et al., AlP Conf. Proceed. no. 12 (1973) p.131.
X. A P P L I C A T I O N S
IN N U C L E A R
PHYSICS
INSTRUMENTS
AND METHODS
147 ( 1 9 7 7 )
255-257
;t~ NORTH-HOLLAND
PUBLISHING
CO.
SOME ASPECTS OF 400 GeV P R O T O N INTERACTIONS IN NUCLEAR EMULSIONS* P. S. YOUNG
Mississipi State University, Mississippi 39762, U.S.A. K. FUKUI t
Air Force Geophysics Laboratory, Bedford Mass. 01731, U.S.A. and Y . V . RAO
Dublin Institute for Advanced Studies, Dublin, Ireland
llford G5 nuclear emulsions were exposed to 300 GeV and 400 GeV proton beams at the National Accelerator Laboratory. A total of 350 interactions were found and analyzed. The study was concentrated on non-white stars because of insufficient scanning efficiency for white stars. The mean free path for 300 GeV proton is 36.9___2.6 cm which is in good agreement with other authors. A linear relation is observed between the charge shower particle multiplicity and the star size indicating that the number of shower particles is independent of the target nuclei. Black prongs for smaller stars seems to show higher value of forward-backward ratio suggesting larger motion of nucleus after collisions.
1. Introduction In order to study interactions between high energy protons and complex target nuclei in emulsion, stacks of nuclear emulsion were exposed to proton beams of highest energy available today at the National Accelerator Laboratory, Batavia. Studies of interest cover star size distribution, charged shower multiplicity, the ratio of black and gray tracks as well as the ratio of forwardly ejected tracks against backwardly ejected tracks from the stars as a function of the entrance proton energy. 2. Exposure, processing and scanning Several stacks of Ilford G 5 nuclear emulsions, 600/zm thick, were exposed to 300GeV proton beams at the Fermi National Accelerator Laboratory, Batavia, Illinois, in October 1973. The flux of the proton beam was in the order of l0 s per cm 2. Other stacks were exposed to 400GeV proton beam at the same laboratory in November 1975, and the flux was in the order of 104 per cm 2. The emulsions exposed to the 300 GeV beam were unmounted pellicles. They were processed in full strength. But those exposed to the 400 GeV * This paper was read at the 9th International Conference on Solid State Nuclear Track Detectors, Neuherberg/Mtinchen, September 30 - October 6, 1976. The complete Proceedings will be published by Pergamon Press, Oxford and New York. t NCR-AFSC Resident Research Associate.
beams were glass mounted plates, and they were processed in slightly weaker strength in order to avoid heavy background. The development without glass plates seems more uniform and it is easy to observe shower particles of low grain density; however some distortion of emulsion plates may be unavoidable. In this work only area scanning with a 150× magnification was used. To avoid stars created by secondary interactions, only those stars due to entrance proton beam with less than 1 degree from the original beam direction were taken. Also the scanning was limited to the area close to the entrance edge of the plates. Namely for the 300 GeV plates the area between 4 mm and 22 mm, and for the 400GeV plates the area between 10 and 29 mm from the entrance edge were used. This method limits the contamination by secondaries to less than 5%. The study on white stars without heavy prongs, and semi-white stars with one heavy prong are of importance for the analysis of p-p collisions. However, this scanning was not aimed to find substantial amount of white stars. Higher magnifications and the following track method should be applied for systematic study of white stars. In this preliminary report only the study on stars with definite prongs was carried out. Total numbers of stars identified as interactions due to primary protons and target nuclei in emulX. A P P L I C A T I O N S
IN N U C L E A R
PHYSICS
256
P . s . YOUNG et al. 25
x
x
20
~, 30 0
f
15
1
,0
I
I0
I I ~I
l
=
I1
20
Nh Fig. ]. Histogram of the combined N h distribution from 300 GeV and 400 GeV plates.
sion from above scanning are 154 for the 400 GeV plates and 196 for the 300 GeV plates.
I
I
I
5
I0
15
| 20
Nh Fig. 2. Charged shower particle multiplicity (n s) vs the star size N h. • 400 GeV plates and ~ 300 GeV plates of this work. © Paris, × L u n d , • Ottawa, [] Bucharest, all from 200 GeV protons j ).
3. Analysis 3.1. THE STARSIZE DISTRIBUTION AND THE INELASTIC MEAN FREE PATH
The star size distribution obtained from the 300 GeV and 400 GeV plates is shown in fig. 1. Nh indicates the number of total prongs including both black and gray tracks. In this distribution, the percentage of events for N 4 8 is about 50% of the total event. It is estimated that about half of these events as well as all the larger stars are due to Ag or Br stars. Most of the remaining half of N 4 8 stars are due to N, C, O stars and only a small percentage of these stars is due to p-p collisions. From the theoretical consideration, it is believed that only 4% of the interactions should take place in hydrogen, thus the amount of small stars not included in this distribution is in the order of not more than 8% of the entire events. The inelastic mean free path was calculated. The value obtained for the 300 GeV plates is (36.9_2.6) cm, and this is slightly higher than the value given by Hebert et al.l). If we consider the amount of loss mentioned above, this value may be lowered to 34.0cm, and becomes in good agreement with the other authors. Thus there is no significant difference in the mean free path for 300 GeV and 200 GeV protons.
3.2. CHARGE SHOWER PARTICLE MULTIPLICITY AS A FUNCTION OF STAR SIZE
The charge shower particle multiplicity (ns) as a function of star size N, is plotted in fig. 2 together with the values of other works. Agreement with other works is within the statistical error and no drastic change due to the energy of incident proton beams is observed. We observe a similar tendency for this work and for the work by others. Namely relationship between two .factors seems a linear increase. This fact indicates that the number o f shower particles is not depending on the target nuclei, but it rather depends on the process of braking up targets. The amount of shower particles is apparently decided by the complex process of creating black and gray prongs inside the target nuclei after collision. Table 1 shows a comparison of the results of the average black tracks, gray tracks and shower tracks associated with stars obtained for 300 GeV and 400 GeV together with other works of lower energies. The (Nb) and (Ng) of this work are in good agreement with the work of lower energies, but somewhat different from the values by 200 GeV. On the other hand (Ns) for this work seems to agree better with the 200 GeV result. Even con-
400 GeV PROTON
257
INTERACTIONS
TABLE |
TABLE 2
Composition of events.
The ratio of forward and backward tracks, a
E(GeV)
(N~
(Ng)
(N s)
6.2 a 22.5 a 200 b 300 400
5.68_+0.21 5.22_+0.29 7.0 _ + 0 . 1 5.42_+0.19 5.32_+0.17
3.58_+0.11 3.38_+0.14 2.79_+0.15 3.92_+0.16 3.93_+0.14
2.21_+0.04 5.08_+0.12 12.9 _+0.15 12.99_+0.29 12.03_+0.25
(F/B~ 300 GeV 400 GeV Nh~<8 Nh~>9
(F/B~
1.22_+0.08 1.18_+0.08
1.19_+0.09 1.22_+0.11
1.32--0.11 1.15--+0.06
1.18_+0.12 1.21_+0.08
(F/B~ 1.21 _+0.06 1.19_+0.06
a Winzeler. b Hebert et al., after ref. 1.
a b, g, h stand for black, gray tracks and total track respectively.
sidering value of incident apparent results.
4. Conclusion There is no fundamental difference between the interactions of this work and other works by lower energy protons. Only the significant difference appears to be the increase of (N) for higher energy protons. However, the number of gray and black tracks should be carefully examined with higher statistics. The ratio of forward and backward tracks should be checked with the result of plastic detectors whose components consist of only C, N, O and H. Such data may be available at this conference. Further study and scanning of the events including white stars should be continued.
the loss of white stars in this work the (Ns) seems to increase as the energy of protons increases. There is however no difference between the 300 and 400 GeV
3.3. RATIO OF FORWARDAND BACKWARDTRACKS Table 2 shows the ratio of forwardly ejected prongs and backwardly ejected prongs for black tracks, gray tracks and the total. The black tracks are due to the evaporation process of the residual nucleus. Evaporation particles are believed to be ejected after the target nuclei are set in motion as a result of interaction. The motion for heavier nuclei such as Ag or Br should thus be smaller and this ratio should also be smaller than the ratio for smaller nuclei such as C, N, O. If stars Nh>~9 are mostly by Ag or Br and stars Nh~<8 are admixture of different nuclei, it should be observed that this ratio is larger for smaller stars such as Nh~<8. This is demonstrated in the second part of table 2. Namely the ratio is about 15% larger for black tracks of small stars.
The authors thank Dr. Voyvodic of the National Accelerator Laboratory for the exposure of the emulsions.
Reference 1) j. Hebert et al., AlP Conf. Proceed. no. 12 (1973) p.131.
X. A P P L I C A T I O N S
IN N U C L E A R
PHYSICS