Interactions of 400 GeV protons with different target nuclei in emulsion

Radiat. Phys. Chem.Vol.48, No. 4, pp. 427-431, 1996 Pergamon

0969-806X(95)00169-7

Copyright© 1996ElsevierScienceLtd Printed in Great Britain.All rights reserved 0969-806X/96 $15.00+ 0.00

INTERACTIONS OF 400 GeV PROTONS WITH D I F F E R E N T TARGET NUCLEI IN EMULSIONI" M. EL-NADI, l S. M. ABDEL HALIM, 2 M. N. YASIN 3 and M. S. E L - N A G D Y 4 ~Physics Department, Faculty of Science, Cairo University, Cairo, Egypt, 2physics Department, Faculty of Science, Zagazig University, Bertha Branch, Benha, Egypt, 3physics Department, Faculty of Education, Cairo University, Fayoum Branch, Fayoum, Egypt and 4Basic Science Department, Faculty of Petroleum Engineering, Suez Canal University, Suez, Egypt

(Received 30 May 1995) Abstract--The interaction characteristics of 400 GeV protons with emulsion nuclei were studied and discussed. The multiplicity distributions of secondary charged particles have been measured for 480 inelastic events and are compared with the results obtained in p-emulsion (P-Em) collisions at different energies. The integral distribution of the number of disintegrated particles from the target nuclei Nh is used to separate the number of the inelastic interactions of proton with light (CNO) and heavy (AgBr) nuclei in the emulsion. The interaction characteristics of protons (400 GeV) with different groups of target nuclei have been investigated. Copyright © 1996 Elsevier Science Ltd

1. INTRODUCTION The investigation of proton-nucleus (P-A) interactions at very high energy is fundamental for understanding the nature of the interaction process, as new accelerator beams become available. One of the most attractive features to study at high energies is the mechanism of multiparticle production. Several models have been proposed to explain this phenomenon, one of the most widely accepted is the cluster model (Quigg et al., 1975). The reason for its general acceptance has been the observation of correlations among the secondary particles in hadronhadron and hadron-nucleus interactions at high energies. The present work is devoted to study of a number of basic experimental characteristics of inelastic interactions of protons at 400 GeV in nuclear photographic emulsion. Also we separated the number of the events due to the interaction with the different groups of the emulsion nuclei, i.e. H, CNO and AgBr. 2. EXPERIMENTAL MATERIAL

A stack of Ilford G5 emulsion pellicles of dimensions 10 x 8 x 0.06cm 3 was exposed to a proton beam of energy 400 GeV at Fermi lab. The beam flux was 2 x 104 particles/cm2. Along the track double scanning was carried out by using a binocular Wild microscope with magnification 100 x . The one prong events, with an emission angle of secondary particle 0 < 5° and no visible tracks from excitation tPaper presented at the Second Radiation Physics Conference, Menoufia, Egypt, 20-24 November, 1994.

or disintegration of target nucleus, were excluded as they were considered to be due to the elastic scattering. The total length of the scanned tracks equals .~ 100.32 m; 280 inelastic interactions were picked up yielding an experimental mean free path of 35.83 + 1.1 crn. A sample of 200 events collected by area scanning was carefully taken with the events collected by along the track-method. We found that the average values of secondaries, i.e. (N~), (Ng), ( N b ) and (Nh), produced in both scanning methods are similar. Secondary tracks emerging from each interaction are classified according to the emulsion experiment terminology based upon their appearance in the microscope. These tracks are shower "N~", grey "Ns" and black "Nb". The shower tracks (fl = v/c t> 0.7) correspond to singly charged relativistic particles, whereas grey has (0.3 ~< fl < 0.7) and range of track in emulsion R/> 3 ram. The true range of a straight track is determined by measuring its projected length on the surface of the emulsion and the dip angle. If P is the projected range of a track, fl is the dip angle, then the true range of the track is R = P/cos ft. Grey tracks are mostly recoil protons. The black (fl ~<0.3) tracks are produced by comparatively slower particles emitted from the target nucleus. Grey and black tracks taken together are referred to as the heavy tracks, N h ( = N s + Nb).

3. RESULTS AND DISCUSSION

Table 1 includes the mean value of shower particles ( N , ) , the dispersion D {D = ( ( N ~ ) - ( N ~ ) 2 ) I/2} of the multiplicity distributions, the derived ratios D / ( N , ) and the normafized multiplicity R = (N~)/(Nch ) is a useful parameter called multiplicity 427

M. E1-Nadi et al.

428

Table 1. Multiplicity data for shower particles [the data taken from Abdouzhamilov et al. (1985), Badawy (1976) and present data*]

Proton energy (GeV)



67 200 300 400 400* 800

9.35 + 13.84 ± 16.00 ± 16.42 ± 15.97 ± 20.02 ±

D

0.16 0.16 1.50 0.17 0.78 0.29

5.62 + 8.15 ± 8.50 ± 10.03 ± 8.74 ± I 1.98 ±

O/
0.60 ± 0.59 ± 0.53 ± 0.61 ± 0.55 ± 0.60 ±

R

0.03 0.02 0.02 0.01 0.02 0.02

1.45 ± 1.64 ± -1.66 ± 1.83 ± 1.75 ±

0.03 0.02 0.02 0.02 0.03

Table 2. The average multiplicities of target fragments at different energies

Proton energy (GeV)



67 200 300 400 400 800

2.74 + 2.60 ± 2.60 ± 2.79 ± 1.98 ± 1.64 ±

0.10 0.06 0.10 0.06 0.10 0.10


0.14 0.10 0.10 0.08 0.28 0.15

ratio between the mean number of shower particles stemming from proton-nucleus collisions and the mean number of charged secondaries (Nch > from P - P collisions in a hydrogen bubble chamber at similar energy (Alner et al., 1985). It is clear that (Ns) is strongly dependent on energy, it increases rapidly with the incident energy. The dispersion increases with energy. The D/(N~> values do not depend on the primary proton energy. I(a)

Ref.

0.22 0.15 0.20 0.13 0.37 0.24

Babacki et al. (1978) Azimov et al. (1977) Abdelhalim (1980) Boos et al. (1978) Present work Abdouzhamilov et al. (1987)

The behaviour of D/(N,> suggests that there are positive long-range correlations between the particles in inclusive spectra which may be due to the superposition of the different mechanisms of particle production. R increases slowly with energy over the full energy range investigated. The value of R signifies nuclear transparency at very high energy. The multiplicity distribution of shower particles emitted from P-Era interactions at 400GeV is

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32

Interactions of protons and target nuclei

429

Table 3. The characteristicsof the interactionsof proton (400GeV) with differentgroups of

nuclei and interactionpercentageaccordingto Nn-integrationcurve Interaction

percentage 7.29 25.00 67.71

Target

H CNO AgBr

(Ns) 9.19 + 0.93 12.22 _ i. 10 18.17 + 1.01

depicted in Fig. 1(a) compared with data at 200 and 800GeV (Abdelhalim, 1980). It is clear that the multiplicity distribution at 400GeV is shifted; towards higher values compared to that at 200 G-eV and lower values compared to that at 800 GeV. There is also a lower production of low Ns events in the interactions of P (800 GeV) than the other interactions (400, 200 G-eV). This is expected since the shower-particle multiplicity shows a logarithmic dependence upon the primary energy. In Fig. l(b, c and d) we present the multiplicity distributions of grey, black and heavy-tracks for proton emulsion interactions at 400 GeV compared with that of P (200 GeV) and P (800 GeV). The mean values of these distributions are given in Table 2. Our results confirm the observations at lower and higher energies that the distributions of heavily ionizing particles do not depend on the energy of the incoming particle, provided the same projectile is considered. It has been suggested that the number of heavily ionizing

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Fig. 2. The integral distribution of the number of events as a function of Nh in P-Em.

(Ns) 0.10 + 0.01 0.40 + 0.04 2.62 _ 0.15

(Nb) (Nh) 0.32 + 0.03 0.42 + 0.04 2.33 + 0.21 2.73 _ 0.25 7.48 + 0.45 10.06+ 0.60

particles measures the impact parameter of the collision and consequently is related to the number of nucleon-nucleon collisions inside the target nucleus (Anderson et al., 1978; Hegab and H/ifner, 1981; Babecki, 1978).

Target separation and the corresponding multiplicities The nuclear emulsion used contains mainly two groups of nuclei, leaving free hydrogen apart. These two groups are light (CNO) and heavy (AgBr) nuclei of average atomic weights 14 and 94, respectively. The problem of separating the events due to the interactions with (CNO) and (AgBr) groups is quite formidable and in general unambiguous separation is difficult to achieve. The number of heavily ionizing particles Nh emitted in an interaction is an important parameter and greatly helps in that interactions having Nh > 8 almost definitely belong to the heavy group (AgBr), while the interactions with Nh ~<8 belong to both (CNO) and (AgBr) groups. So, a reasonable criterion is needed to separate the events due to (CNO) and (AgBr) groups having Nh ~< 8. A large number of selection criteria (Friedlander, 1959; Lohrmann and Teucher, 1962; Florain et al., 1973; Jakobsson and Kulberg, 1975) have been proposed to separate these two types of events. In the present investigations, we used the Florian et al. (1973) method. In this method, they assumed that the interaction cross-sections are proportional to A 2/3 (A is the mass number of the target nucleus). Knowing the emulsion composition used, the number of events belonging to H, light and heavy groups can be determined. To separate the number of events due to the heavy group and having Nh < 8 they draw the differential Nh distribution for events with all values of Nh and then extrapolate the distribution for events with Nh > 8 smoothly in the region of Nh < 8 such that a number of events exactly equals the difference between the total number of events due to the interaction with the heavy group and the number of events with Nh > 8 are contained in the extrapolated region. Consequently, the number of events due to the (CNO) group for each value of Nh can be determined. The integral frequency distribution for events in the present work as a function of the number of heavy tracks Nh is shown in Fig. 2, where N/> Nh is the number of events containing more than or equal to Nh ranges. The plotted points fall along four straight-line segments with distinctive breaks at Nh= 0, 7, 17 and 25. The difference in slopes of these four straight-line segments can be interpreted as indication of the presence of different dynamic

430

M. EI-Nadi et al. 24

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Fig. 3. The N i distributions for the interaction of proton with the different components of the emulsion.

situations. Where the first and second segments, i.e. Nh = 0 and 7, correspond to interactions with light target nuclei H, CNO. The first segment, N h = 0-1, may be interpreted as being due to interactions with hydrogen, while the second segment, Nh = 7, may be due to interactions with CNO and perpherality of heavy group AgBr. The other segments Nh(7-17) and Nh(18-25) and N h > 2 5 are due to interactions with heavy target nuclei AgBr for different impact parameters, i.e. differentiating between peripheral and central collisions with heavy target nuclei. From the fitting we can separate the number of events belonging to the interactions of the projectile with different emulsion groups of nuclei (H, CNO and AgBr). The percentages of the interactions with these groups of target nuclei are listed in Table 3. It

is noticed that as the target mass number increases the average values of shower () and heavy tracks ((N>) increase. The multiplicity distributions of shower (Ns), grey (Ng), black (Nb), and heavy (Nh) tracks in the interactions of P (400 GeV) with (CNO) and (AgBr) groups are presented in Fig. 3(a, b, c and d), respectively. It is noticed that the distributions for P-(AgBr) are broader than those for P - C N O interactions. This may reflect the effect of the target mass number on the number of collisions of P with the target nuclei. It would be interesting to study the correlation between produced from inelastic interactions of protons with a certain target A (i.e. of atomic number A, emulsion, CNO, AgBr and/or proton or nucleon) and the corresponding values when p - p is interacted

22

Interactions of protons and target nuclei at similar energy even in a hydrogen bubble chamber, abbreviated by (Nch), or in emulsion as selected events due to interactions with hydrogen, abbreviated by ( N s ) ~ or (N,)pN. Such a study can be done by using multiplicity ratio RE = (Ns)r~m~io~ (Ns >pp or

431

charged secondaries produced on a nuclear target at energies E l and E2 (where E l , E2 ~>GeV) is constant in nuclear emulsion as a function of Nh and this value is the same as for P - P interactions. In our data we have found that: R e ( P A ) ~ = 1.05&RE(PP)~ = 1.04

and

RE(PA)~ = 1.24&Re(PP)24°°o0o= 1.02

~SO (N,>:no =

p,

and so on. The importance of this study is useful for understanding mechanisms of nucleon-nucleus and nucleon-nucleon collisions at the same or different energies and the same or different targets. Jain et aL (1975) have found that ( N , ) grows slowly with the atomic weight, A, of the target. The rise is primarily in the target fragmentation region, while in the projectile region, the multiplicity is the same for heavy nuclei targets as for hydrogen. For nucleonnucleus interactions Ra = ( N s)PA/(N, )pp ~---A ~t where is a constant. Jain has found that • = 0.13, from which P~m = 1.74, RCNO= 1.41, RA~r = 1.8, a very weak dependence on mass number A. These relations are independent o f energy at E > 100 GeV. In the present work, it was found experimentaly that R ~ = 1.74, RcNo = 1.33, RASBr= 1.98 which is in good agreement with that calculated by Jain with =0.13. For protons (800GeV) (Shivpuri and Kotha, 1987) the value of R for the (CNO) and (AgBr) groups of nuclei is found to equal 1.45 _+ 0.14 and 2.04 + 0.17, respectively. The value of R for the light group of nuclei shows that the proton interactions with such nuclei behave like proton nucleon interactions. The larger value of R for the (AgBr) group of nuclei shows that there is some contribution to the multiplicity from more than one nucleon during the collision process. However, the low value of R even for the heavy group of target nuclei precludes the formation of an intranuclear cascade in our interaction. Jain et al. (1975) have also found that the ratio R e = ( N s ) e l / ( N s )e2 of the mean multiplicities of fast

which is in agreement with that given by Jain. We can say that for p-nucleus interactions, the increase in multiplicity comes only in the fragmentation region of the target. Acknowledgements--We are very grateful to Professor P. L.

Jain, State University of New York at Buffalo for supplying the emulsion plates of Proton-400 GeV. REFERENCF~

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