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An Extensive Survey of the Characteristics of Pseudorapidity Distributions in Hadron-Nucleus Collisions at High and Ultra High Energies.

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Annalen der Physik. 7. Folge, Band 37, Heft 3, 1980, S. 183-188
J. A. Barth, Leipzig
An Extensive Survey of the Characteristics of Pseudorapidity
Distributions in Hadron-Nucleus Collisions
at High and Ultra High Energies
By DIPAKG m s i I
High Energy Physics Division, Department of Physics, Jadavpur University, Calcutta (India)
Abstract. This paper presents an extensive study of the nature of the pseudorapidity distribution i n hadron-nucleus collision in emulsion from accelerator energy t o super high cosmic ray energies
(36GeV/c to 4 TeV). The energy and the target dependence of the distributions and their possible
significance are also discussed.
Ausfuhrliche ubersicht der Charaktoristika yon Pseudorapidity-Verteilungenbei HadronKern-Reaktionen fur hohe und ultrshohe Energien
Inhaltsubersicht. Diese Arbeit ist eine ausf~ihrlicheUntersucliung der Eigenschaften von
Pseudorapidity-Verteilungenbei Hadron-Kern-Reaktionen in Emulsionen, angefangen von Beschleuniger-Energien his hin zu ultrahohen Energien der kosmischen Strahlung (24 GeVjc bis 4 TeV).
Die Abhkngigkeit der Vertcilungen von der Energie und vom Target sowie die mogliche Bedeutung
diesrr Verteilungen werden diskutiert.
Introduction
I n recent years the study of hadron-nucleus collisions at high and ultra high energies
has been a subject of increasing interest both from the theoretical and experimental
point of view [I-51. This is due to the fact that the nucleus is the only tool available
for studying many intriguing factors such as space-time development of particle production, the interaction of resonance with nucleus and even the interactions of almost
free quarks. Many interesting features have been observed experimentally and also
on the threoretical side considerable progress has been made in understanding the
qualitative features of hadron nucleus collision in terms of niodels of hadron-hadron
interaction although no clear picture has so far been emerged. However, all intrinsically
different theoretical ideas, such as hydrodynamics [5 - G I , cumulative effects [71,
partons [S] and niultiperipheral model [9] suggest that hadron nucleus collisions might
provide a better understanding of hadrons and their interactions.
The most striking features of multi-particle production in a hadron nucleus collision
is its weak A dependence. Evidence of the building up of an intra-nuclear cascade
is not strong (if any). This weak A dependence and the characteristic dependence of
pseudorapidity distributions on nuclear size have stimulated theoretical work on
hadron nucleus collisions with the hope that these features in experimental data would
provide strong tests of theoretical models. Although many classes of models qualitatively predict these results the only definite conclusion that can be drawn is that
in a hndron-hadron interaction the only asymptotic final state is not produced instan-
184
D. GEOSH
taneously. It is, therefore, necessary t o study the experimental data in greater details
in particular, among others, the energy and target dependence of the pseudorapidity
distribution and t o see whether the A dependent region of pseudorapidity expands
with energy (indicative of some long range order). Although a few works a t accelerrator
energies have been published no such study has been reported a t high and ultra-high
cosmic ray energies. Further there is still controversy over the detailed A dependence
in the forward few units of pseudorapidity distribution and no definite conclusion
could be arrived at. It is instructive for these sort of study to use target nuclei differing
greatly in their atomic weights. Nuclear emulsions have gained wide acceptance in this
respect since they contain a light group ( A w 14) and a heavy group ( A = 84) of
nuclei.
I n this paper we have presented a n extensive study of the nature of pseudorapidity
distribution in hadron-nucleus collision from accelerator to super-high cosmic ray
energies (24 GeV-4 TeV) using emulsion data. The parameter Ni, (the number of
observed nuclear fragment) has been used as a criterion for separating the target
nuclei in emulsion into two groups, a light group (CNO) for which 2 5 Nh 6 and a
heavy group (AgBr) for which Nh > 6 .
Experimental Data
Tn this investigation data have been taken from our emulsion analysis (24 and
70 GeV), from the works of Hebert et al. (200-300 GeV) [lo] and I.C.E.F.data sheet
[11] (300 GeV to 4 TeV).
I n case of I.C.E.F. [Ill data from different events having almost the same primary
energy are chosen and grouped together namely (300 GeV, 400 GeV, 500 GeV, 600 GeV,
750 GeV, 1TeV, 2 TeV and 4 TeV). At each primary energy (both accelerator and
cosinic ray) events were classified into two groups according to the criteria 2 5 Nh 5 6
and Nh > G to indicate (p-CNO) collision and (p-AgBr) collision respectively. The
values of pseudorapidity have been calculated from the emission angle 0, using the
relation 17 = - In tan Or,/2. We now illustrate in graphical form the features of these
data.
Resiilts and Discussions
Fig. 1 (a-d) shows the pseudorapidity distribution a t different accelerator energy
namely (24, 70, 200 and 300 GeV) for p C N O and pa-AgBrcollision. Fig. 2 (a-f) is a
similar plot for different cosmic ray energies namely (300 GeV-4 TeV).
It is evident from Fig. 1that the distribution in the projectile fragmentation region
is independent of target size. I n the case of heavier targets the excess of particles
appears a t larger angle and the centre of the distribution is shifted towards smaller
values of r. Further it appears that a t all energies it is only the most forward few
units of the pseudorapidity distribution that are approximately A dependent.
I n the case of cosmic ray data (Fig. 2) the same conclusion can be drawn regarding
the appearance of excess particles a t large angle for heavier target and the corresponding shift of the centre of the distribution. Also there is evidence a t all energies that the
forward few units show target independence although no positive conclusion can be
drawn about the extent of the A dependent region.
A comparison between the observed rapidity distribution and the predictions of
various theoretical models of multiparticle production requires more experimental
data covering a greater number of different target elements. However, some important
remarks can be made. There is some indication (at least in accelerator energies) that
the target dependent region of pseudorapidity moves out in q with the increase of
185
Pseudorapidity Distributions in Hadron-NucleusCollisions
'IAg 6r
CNO
d
;--.-,
I
1
1
:
I
I-5
,-.J
L-.
"'2
L-1
I
.-1
r-I
!
3 0 0 GeV
I
I
---- Ag 0r
1.c
I
0 ,8
1'6 2 4
3 2 4 0 48 5'6 6 4 7 2
0
l
'8
l
1
I
l
l
I
l
l
1-6 2.4 3'2 6'0 4 8 5 6 6'4 7 2
Fig. 1 (a-d) Pseudorapidity distribution at accelerator energy for p-CNO and p-AgBr Collision
D. GHOSH
186
1
I
I
I
I
I
I
I
I-r
Fig. 2a-d
7
187
Pseudorapidity Distributions in Hadron-Nucleus Collisions
energy. This is far from the predictions of all models which have only short, range
order [12]. Further, the A dependent region moves out in q with energy a t a faster
rate than that predicted by the EFC model [13].
Thus we can conclude that the results of this extensive analysis will present some
restrictions on the possible mechanism of multiparticle production in hadron-nucleus
collision a t high and ultra-high energies and stimulate further theoretical works on
hadron-nucleus collision.
r i
I I
I L
4
h
1 1
[
I
188
D. GHOSH
The author is greatly indebted to Prof. A. Z. HERZof CERN and Prof. K. D. TOLSSERPUKHOV for kindly supplying the exposed emulsion plates.
TOV of
References
[l]A. SUBRAMANITJM,Proceedings of the Seminar on Interaction of Elementary Particles with
Nuclei, Santiniketan, March 1976.
[ Z ] S. A. Amrov et al., Proceedings of the Meeting on Nuclear Production at Very High Energies.
Triesta, June 1976.
[3] W. BUSZA,Proceedings of the VIth International Conference on High Energy Phpim and
Nuclear Structure, Santa Fe Los Alamos 1975.
[4] K. GOTTFRIED,
Proceedings of the Vth International Conference on High Energy Phpics and
Nuclear Structure, Uppsala 1973.
Proceedis of the VIIth International Colloquium on Multiparticle Reactions,
[5] B. ANDERSON,
Tutzing, June 1976.
[GI N. MASNDAand R. M. WE-,
University of Lenven preprints July and Sept. 1976 and earlier
references there.
[7] A. DAR, S. A. Azmov, et al., Proceedings of the Meeting on Nuclear Production at Very High
Energies, Trieste, June 1976.
A. Z. PATASHINSICII,
JEW Lett. 19, 338 (1974).
S. FREDR~SSON,
Stockholm KTH preprints 1976.
Y. AFEKet al., Technion preprints Ph-TP-48.
[8] G. R. FARRER,
Phys. Lett. B 66, 185 (1975).
8. KRYZWICKI,
ibid and Orsay preprint LPTPE-76/1.
N. N. NXEOLACV,
IVth International Seminar on Problems of High Energy Physics, Dubna
1976.
[9] G. A. WINBOWet al., Rutgers preprint RU-76-03.
J. KOPLIB:
and A. H. MUELLER,Phys. Rev. D 12, 3638 (1976).
L. CANESCEUand A. SCHE-ER, CERN Preprint Th 2051, 1976.
[lo] J. HEBERT,
Phys. Rev. D 16,1867 (1977).
[ll]I. C. E. F. data, Nuovo Cim. Suppl. 1, 1963.
[12] A. CAPELLA and A. KREZYWICKI,
Phys. Lett. B 67, 88 (1977).
[13] K. GOTTFRIED,
Phys. Rev. Lett. 82, 957 (1974).
Bei der Redaktion eingegangen am 30. August 1979.
Anschr. d. Verf. : Dr. DIPAE GHOSH
High Energy Physics Division
Department of Physics
Jadavpur University
Ca.lcutta - 700032 (India)
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