Nuclear fragmentation at 4.5 a GeV/c in 28Si with emulsion interactions

doi:10.4236/ns.2011.35055

Paper Menu >>

Journal Menu >>

Vol.3, No.5, 408-413 (2011) Natural Science

http://dx.doi.org/10.4236/ns.2011.35055

Nuclear fragmentation at 4.5 A GeV/c in 28Si with

emulsion interactions

A. Abd El-Daiem1*, A. Abdel-Hafiez2, M. A. Khalifa3

1Physics Department, Faculty of Science, Sohag University, Sohag, Egypt; *Corresponding Author: [email protected]

2Experimental Nuclear Physics Department, Nuclear Research Center, Cairo, Egypt

3Mathematical Deparment, Faculty of Science, Tanta University, Tanta, Egypt

Received 11 February 2011; revised 13 March 2011; accepted 27 March 2011.

ABSTRACT

The experimental results of complete charge

distribution of projectile fragments (PFS) and

the total charge of the projectile fragments (PFS )

are presented. Also the multiplicity distributions

of (PFS) and the rapidity distribution of shower

tracks produced from events with nh = 0 from

28Si with emulsion at 4.5 A GeV/c are obtained.

Keywords: Multiplicity Distribution;

Total Chare and Rapidity Distribution

1. INTRODUCTION

Nuclear fragmentation and its possible connection

with a critical phenomenon of a phase transition has

been the subject intensive theoretical and experimental

investigation in the interaction of relativistic heavy nu-

clei nucleus collision [1,2] the overlapping region of

nuclear volumes is called the participant region, where

multiple productions of new particles occurs and the

matter breaks up into nucleons. An estimate the degree

of centrality of a collision of the nuclei can be made if

we determine the total charge Q of the non interacting

nucleons or fragments of the projectile nucleus, to which

we assign the relativistic particles emitted at an angel θ <

3˚ [3,4]. Then the number of interacting nucleons of the

projectile nucleus is on the average nint =28 − 2Q [5]. In

the collision of two nuclei, the elementary interaction is

more amplified than in the case of hadrons-nucleus in-

teraction. At such high energy (4.5 A GeV/c) the rapidity

gap between the projectile target fragmentation regions

is quite wide, which provides us with a good possibility

for testing the limiting fragmentation hypothesis [6,7] in

playing that no correlations exist between the projectile

and target fragments.

These results were obtained from the study of single

partied inclusive experiments where the degree of target

fragmentation can take any value. It is interesting to

compare these results with those of projectile fragments

angular distribution from the special class of events nh =

0, where there is no target fragmentation but only a pro-

jectile fragmentation.

2. EXPERIMENTS

In our experiments, the layers of photo emulsions

NIKFI-BR2, with dimensions of 20 cm × 10 cm × 600

µm were irradiated by the 28Si beam from the syncho-

phastron in the high energy laboratory of JINR, at Dubna

with an average beam momentum of 4.5 A GeV/c. Along

the track double scanning was carried out, fast in the

forward direction and slow in the backward direction.

The scanned beam tracks were further examined by

measuring the delta electron density on each of them to

exclude the tracks having the secondary particles is clas-

sified as follows:

1) Black particle tracks (nb) having a range L < 3 mm

in emulsion which corresponds to a proton kinetic en-

ergy of 26 MeV.

2) Grey particle tracks (ng) relative ionization I* (=

I/I0) < 1.4 and L > 3 mm which correspond to a proton

kinetic energy of 26 - 400 MeV, where I is the particle

track ionization and I0 is the ionization of a shower track

in the narrow forward cone of an opening angel of θ < 3˚

(the b and g particle tracks are called heavy ionization

particle tracks (nh)).

3) Shower particle (ns) having I* < 1.4 (tracks of such

type with an emission angel of θ < 3 were further sub-

jected to rigorous multiple scattering measurement for

moment determination and consequently, for separating

the produced pions and singly charged projectile frag-

ments (protons, deuterons, tritons).

A total of 1000 interactions of 28Si with the nuclei of

the emulsion were observed by following a primary

track length of 78.12 meters, which led to a mean free

path of λ = 8.71 ± 0.30 cm. In each event, the charge Z ≥

A. A. El-Daiem et al. / Natural Science 3 (2011) 408-413

409

2 of individual projectile fragments were determined by

the combination of several methods, which include grain

and delta ray densities. More details on the charge de-

terminations of projectile fragments are given in Refer-

ence [8]. Projectile fragments essentially travel with the

same speed as that if the parent beam nucleus, so the

energy of the produced projectile fragments as high

enough to distinguish them easily from the target frag-

ments.

3. THE TOTAL CHARGE OF THE

PROJECTILE FRAGMENTS (PFS)

In the Table 1 we have given the data obtained on the

average multiplicities of h and s particles as functions of

nint. It can be seen that the number of thin prongs in a

disintegration increases linearly with increase of nint, and

within experimental error this occurs in a completely

identical way for the light and heavy emulsion compo-

nents. This dependence of < ns > on Q is consistent with

the model of independent interactions and indicates a

decisive roll of the first interaction. In collisions of light

nuclei the values of < nh > do not depend on nint, while

for heavy nuclei they rise almost linearly.

In Figures 1(a) and (b) we have shown the distribution in

Q for events in standard emulsion, and also the distribu-

tions obtained by the different methods for three differ-

ent groups of nuclei, normalized to the corresponding

probability of inelastic interaction. It is evident that the

distributions in Q depend substantially on the type of

target nucleus. The average total charge for disintegra-

tion of an incident 28Si nucleus in hydrogen, light and

heavy emulsion nuclei were respectively 11.71 to 0.17,

9.62 ± 0.11 and 4.68 ± 0.16. Note that in Figures 1(a) and

(b) in the light emulsion nuclei (H,C,O) there are practi-

cally no central interactions (Q = 0), collisions with the

heavy component are characterized by a wide set of A

values. Study of the dependence of the total charge of

the spectator fragments on the impact parameter for

events produced in heavy emulsion nuclei. Figures 1(a)

and (b) show that for large impact parameters (nh  7)

this distribution is practically the same as the distribution

in Q for hydrogen of the emulsion and for 8 nh 15 it is

close the distribution for events in nuclei (C,N,O). For

large nh a dominance of central interactions is observed.

In order to see the dependence of the number of inter-

acting nucleons on the collision geometry, we have

shown in Figure 2 nint as a function of nh. This figure

indicate that even in collisions where no, or very little

Table 1. Experimental dependence of average multiplicities <nh> and <ns> on the number of interacting nucleon and the pa-

rameter Q.

target nucleus

AgBr CNO

nint

1.0 ± 0.0 6.2 ± 0.6 1.0 ± 1.4 1.3 ± 1.9 0 14

3.0 ± 0.8 8.3 ± 0.5 2.5 ± 1.8 2.3 ± 2.2 2 13

5.8 ± 3.0 12.3 ± 3.9 3.4 ± 2.4 3.1 ± 2.4 4 12

5.6 ± 2.1 14.1 ± 4.7 4.1 ± 3.0 2.9 ± 2.4 6 11

6.4 ± 2.6 14.4 ± 4.8 5.9 ± 3.2 3.5 ± 2.4 8 10

8.8 ± 4.0 16.5 ± 6.7 6.4 ± 3.0 3.3 ± 2.3 10 9

10.4 ± 4.1 16.2 ± 6.7 8.2 ± 2.6 3.8 ± 2.2 12 8

13.3 ± 4.7 16.6 ± 7.4 10.0 ± 2.8 4.6 ± 1.9 14 7

13.8 ± 5.1 16.5 ± 7.4 12.3 ± 4.7 4.5 ± 1.8 16 6

16.5 ± 5.2 22.7 ± 8.8 12.6 ± 4.5 4.1 ± 2.1 18 5

19.7 ± 6.8 25.3 ± 9.2 11.4 ± 5.2 4.4 ± 1.5 20 4

22.0 ± 6.8 24.5 ± 9.4 17.7 ± 2.1 5.3 ± 1.3 22 3

22.7 ± 7.2 26.3 ± 9.7 17.6 ± 1.6 5.6 ± 1.0 24 2

26.6 ± 6.5 31.0 ± 6.9 26 1

32.2 ± 6.8 33.4 ± 7.6 28 0

A. A. El-Daiem et al. / Natural Science 3 (2011) 408-413

410

(a) (b)

Figure 1. Distribution in total charge Q of fragments of the incident 28Si nucleus with the groups of emulsion nuclei (a) and

distribution in Q for events in nuclei (a) and distribution in Q for events in heavy nuclei (AgBr) with different numbers of h-

particles (b). The dot. Dash histogram shows interactions in H, and the solid histogram in (CNO). The dashed histogram is in

(AgBr) nuclei, and the doted histogram is for center emulsion.

A. A. El-Daiem et al. / Natural Science 3 (2011) 408-413

411

Figure 2. Variation of <nint> with nh.

excitation of the target occurs (i.e. nh = 0 and 1).

Some of the nucleons of the projectile take part in the

interactions. We also observe that the mean number of

interacting projectile nucleons increases quickly as the

value of nh increases, as expected, but attains amore or

less constant value for extreme central collisions.

4. MULTIPLICITY DISTRIBUTIONS OF

PROJECTILE FRAGMENTS

In this part 950 28Si inelastic interactions emulsion

were measured, 856 events were observed to have emit-

ted projectile fragments, 90% o the total events represent

peripheral and quasi peripheral collisions. This percent-

age is about two times larger than the corresponding one

in interaction of a- particle with emulsion 9(9) at the

same energy per nucleon.The multiplicity distributions

of the emitted charge projectile fragments are shown in

Figures 3(a), (b) for a class of events without target

fragmentation as well as sample. It can be seen that there

is no great difference between these distributions.

5. ANGULAR DISTRIBUTIONS OF

PROJECTILE FRAGMENTS

Figure 4 represent the angular distribution of Z = 1,2

and Y3 projectil fragments, in terms of cosθ where θ is

the space angle between the emitted projectile fragments

and the beam direction. It can be seen clearly that the

angular distribution becomes narrow with increase of

fragment charge Z, in all these distributions there are

pronounced peaks cos θ = 1.

6. SOME FEATURES OF EVENTS WITH

PROJECTILE FRAGMENTATION

ONLY (nh = 0)

In the 94 events satisfying the criteria nh = 0 from our

sample of 950 inelastic interactions, the projectile frag-

ments are divided into Z = 1, 2, 3, ···, 14. We explicitly in

(a)

(b)

Figure 3. The multiplicity distribution of charged projectile frag-

ments z = 1, z = 2 and z = 3, (a) Total sample; (b) nh = 0.

Figure 4. The angular distribution of z = 1, z = 2 , z = 3 for a

class of events with nh = 0.

all the reaction produced observed in these 94 events

which are ordered according to the value of Z*, the total

A. A. El-Daiem et al. / Natural Science 3 (2011) 408-413

412

charge the emitted projectile fragments. The production

frequency of event s in 28Si with emulsion interactions as

a function of Zmax, the highest charged projectile frag-

ment emitted in the interactions, is shown in Figure 5. It

should be noted that the fragmentation probability is

higher for events with Zmax = 2, 6 and 8. This is inter-

preted as due to the structure of 28Si nucleus, which is an

even-even nucleus of total spin I = 0. This means that the

nuclear structure of the projectile may play an important

role in the fragmentation process. Figure 6 represent the

frequency distribution of Z*, the total charge of the

emitted projectile fragments in an interaction for our

sample of nh =0 events the distribution is smooth and the

frequency increases with Value of Z*.

The average value of Z* equals (11.9 ± 2.1) and the

average number of produced pions charged in these

Figure 5. The production frequency of nh = 0 events as a func-

tion of Zmax the highest charge of projectile fragments in an

event.

Figure 6. The production frequency of nh = 0 events as a func-

tion of Z* the highest charge of projectile fragments in an

event.

events equals (2.2 ± 1.2). Figure 7 illustrates the rapidity

(η = − ln tanθ/2) distribution for all shower tracks emer-

ged from stars of nh = 0 in comparison with correspond-

ing distributions of shower tracks from central event, i.e.

events with Z* = 0. A pronounced rapidity gap is ob-

served between the two distributions. The distribution of

central events extends from the target fragmentation

region to the projectile fragmentation region due to the

absence of the spectator and the complete dominance of

actors. The distribution from nh = 0 events is dominated

by the projectile spectators, thus it is mainly concen-

trated in the projectile fragmentation region.

7. CONCLUSIONS

From the investigation of particles emitted from 28Si

with emulsion collisions, we can make the following

conclusions:

1) We notice that the distribution in Q depend sub-

stantially on the type of nucleus and the average total

charge for this integration of an incident 28Si nucleus in

hydrogen, light and heavy emulsion nuclei were respec-

tively 11.71 ± 0.17, 9.62 ± 0.11 and 4.68 ± 0.16.

2) We observe that the mean number of interacting

projectile nucleons increases quickly as the value of nh

increases, as expected but attains a more or less constant

value for extreme central collisions.

3) The fragmentation probability is higher for events

with Zmax = 2, 6 and 8. This interpreted as due to the

structure of 28Si nucleus, which is an even – even nu-

cleus of total spin1 = 0.

4) The rapidity distribution of shower tracks from nh =

0 events has its peak the high rapidity region, i.e. the

projectile fragmentation region, it is separated by a

Figure 7. The rabidity (η = −ln tan θ/2) distribution of shower

tracks produced from events with nh = 0 and from central

events Z* = 0.

A. A. El-Daiem et al. / Natural Science 3 (2011) 408-413

413

measurable rapidity gap from the target fragmentation

region.

REFERENCES

[1] Goldhaber, A.S. (1974) Statistical models of fragmenta-

tion processes. Physics Letters, 47, 306.

[2] Goldhaber, A.S. and Heckman, H.H. Ann. (1978)

High-energy interactions of nuclei. Review of Nuclear

and Particle Science, 28, 161.

[3] Adamovish, M.I. et al. (1977) JINR Report El-10838

Dubna.

[4] Lindstrom, P.J., et al. (1976) Cross sections for produc-

tion of stable and long-lived nuclides by high energy

spallation of iron; cosmic ray implications. Preprint LBL,

3650.

[5] Fu, H. (2002) Target fragmentation in oxygen-emulsion

collisions at dubna and SPS energies. Chinese Journal of

Physics, 40, 159-167.

[6] El–Nagy, A. (1981) Fvosccti report. NF. 81/3, submitted

to IL Nuvo Cimento.

[7] Bucharest, D. and Kosice, L. (1974) Collaboration:

Dubna preprints. JINR, PI. 687.

[8] Adamovish, M.I. M.M., AygarwaI, Y.A., et al. (1999)

(EMu – 01 collaboration), Fragmentation and multifrag-

mentation of 10.6A GeV gold nuclei. European Physics

Journal A, 5, 429.

[9] Chernov, G.M., Gulamov, K.G., Gulyamov, U.G. and

Svechnikova, L.N. (1977) Multiplicity and angular dis-

tributions of charged particles in interactions of 56Fe in

emulsion at 2.5A GeV/c. Physics. A, 280, 478.

doi:10.1016/0375-9474(77)90616-9