The analysis of experimental data on hadron-nucleus collisions at energies from about 2 up to about 400 GeV was performed in order to discover a physical meaning of the multiplicity of emitted nucleons. Simple relations between the multiplicities and the thickness of the nuclear matter layer involved in collisions were obtained

Strugalski, Z.

English

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108
PHYSICAL MEANING OP THE MULTIPLICITIES OF EMITTED NUCLEONS
IN HADRON-NUCLEUS COLLISIONS
Strugalski Z.
Institute of Physics of the Warsaw Technical University
ul. Koszykowa 75
00-662 Warsaw, Poland
and
Joint Institute for Nuclear Research, High Energy Lab.
Dubna, USSR
ABSTRACT
The analysis of experimental data on hadron-nucleus
collisions at energies from about 2 up to about 400
GeV was performed in order to discover a physical
meaning of the multiplicity of emitted nucleons. Sim
ple relations between the multiplicities and the
thickness of the nuclear matter layer involved in
collisions were obtained. -
I. Introduction
It is commonly known thatwhen atomic nuclei are bom-
bardedby high energy hadrons, with energies higher than
the pion production threshold, the emission of nucleons f-
rom the target nucleus, the particle production, and the
evaporation of nuclear fragments take place. The presence
of events in which intensive emission of nucleons and frag
ment evaporation appear without particle production leads
to the conolusion that the nucleon emission process can
proceed independently of the particle production, Strugal-
ski Z., Pluta J. (1974), Strugalski Z., Pawlak T., Pluta
(1982); the emitted nuclei are with kinetic energies from
about 20 up to about 400 MeV, in the emulsion technique the
nuclei are known as the so called g-track leaving partic -
klos.
In considerations about the nucleon emission, the
emission process can be treated separately, because the in
fluence on it by the particle production process is negli-
gible, Strugalski Z.(1984 a,b), and the fragment evapora -
tion is due to the target nucleus destruction in the nucle-
on emission process, Strugalski Z. (1984 c).
But, the emitted nucleons are constituents of the tar
get nucleus, and it is reasonable to expect that characte-
ristics of these nucleons should be connected with the pa
rameters of the target - with itssize and nucleon density
distribution in it. When the connections will be found, sim
ple physical meaning of the multiplicities of the emitted
nucleons, of the protons in particular, may be achieved.
https://ntrs.nasa.gov/search.jsp?R=19850027564 2020-03-20T17:21:43+00:00Z
_ 1.3-5
109
The subject matter in this paper is to present results
of our investigations in question.
2. _ethqd
The method of experimental investigations is based on
two facts: a) It is possible now to realize experiments, u-
sing heavy liquid chambers as 41>1 geometry detectors, in
which emitted protons aud produced pions of any electric
charge including zero are registered with the efficiency ne
ar to 100 %; additional suplementary information about the
target nuclei fragmentation can be obtained from emulsion
experiments. Characteristics of the outcomes in hadron-nuc-
leus collisions, such as multiplicities of produced or emit
ted particles, and momentum and angular spectra can be ob -
tained fully as well. This way, experimental data obtained
now are of such a sort as data which one can expect to ob -
tain in a total experiment, b) Now many aspects about the
nuclear matter distribution in atomic nuclei are so firmly
established that it has been possible to use them in order
to investigate other physical quantities, Elton LRB (1961).
It is possible, therefore, to estimate the number of nucle-
ons, or protons only, contained within any cylindrical volu
me centered on the hadron course in an atomic nucleus.
The method of investigation of the physical meaning of
the multiplicities of the emitted nucleons, or of the emit-
ted protons in particular, consists in comparison of the da
ta on nucleon multiplicity distribution, obtained in inves-
tigations of collisions of definite hadrons with definite
target nucleus, with data on distributions of the nucleon
numbers contained within some cylindrical volumes centered
on various possible hadron courses in the target nucleus$
the distributions are determined from the information about
the target nucleus size and nucleon density distribution in
it.
_. Experiment
In our investigations we have used the 26 and 180 lit-
re xenon bubble chambers, Kanarek T.I. et al. (1959), Kuz -
netsov E.V. et al. (1970). The first one was exposed to
2.34 GeV/c, 5 GeV/c, 9 GeV/c momentum pions from the synch-
rophasotron of the Joint Institute for Nuclear Research at
Dubma. The second one was exposed to 3.5 GeV/c negatively
charged pions from the accelerator of the Institute of Ex -
perimental and Theoretical Physics in Moscow. Abou_ 20 000
" pion-xenon nucleus collision events were analysed, Strugal-
ski Z. et al. (1982, 1983). Additionally, compilations of
corresponding data obtained in emulsion experiments were
used, Andersson B. et al. (1978), Babecki J. and Nowak G.
(1978), Busza W. (1977), Gurtu A. et al. (1974), Otterlund
I. et al. (1978), Tsai-Cha et al. (1977).
110 iIE 1.3-5
$. Results
It was found that the thicknesses of nuclear matter la
yers involved in had_on-nucleus collisions should be natura
lly and conveniently expressed in number of nucleons per so
me area S = _D_ _ 10 fm_, where D O is the diameter of
the nucleon; they can be expressed as well in protons/S, or
in neutrons/S. We use these units only later on.
The analysis of the experimental data, in the light of
the data on the target nuclei, leads to conclusions that:
I. The number n_ of protons ( or of the g-track leaving
particles ) emitted in a collision is a measure of the thic
kness _ in protons/S of the nuclear matter layer invol -
ved in the collision:
(I)
2. The mean number <n_ > of protons emitted in a sample
of the hadron-nucleus c_llisions equals the mean thickness
_ >in protcns/S of the nuclear matter layer involved in
the collisions:
3. At the incident hadron energy larger than a few GeV,
the mean number of protons ( np _ emitted in hadrcn-nuc-leus collisions is:
<Z>S ( I - exp(-(_>/<_t >) ) ( 3 )<np_=
where <_t _ in protons/S is the mean free path for in
teraction of the incident hadro_ with a nucleon in nucle
ar matter, _ = I/ _t_ , and _. _ is the cross-se
ction for the _adron-nucl_ any-type _lisicn.
More _information can be found in my previous works ,
Strugalski Z. (1984 a - c).
_. Remarks
From formula ( I ) it follows that the nucleon emis-
sion proceeds monotonically. But, this formula is accura-
te when the multiplicity of the emitted protons n is
not larger than DS, where D is in prctons/s the diameter
of the target nucleus. In some small number of collision
events, in no more than about 10 %, np > DS. The ap-
pearance of such values of n > DS is due to the pertur
bations in nucleon emission p_ocess, Strugalski Z. (1984b_
Formulas ( 1 ) - ( 3 ) were tested experimentally
within the incident hadron energy interval up to about
2000 GeV, where the nucleon emission intensities were un-
der studies. Nevertheless, we hope that the formulas are
valid through the total region of the projectile energies
above the pion production threshold.
We have investigated mainly the proton emission only,
but additional analysis, Strugalski Z. (1984), provided be
sults which incline us to think that formulas ( I ) - ( 3 )
are valid for both the nucleons together, and for the neu-
trons only, as well.
References
Andersson B. et al., 1978, Physics Letters, B73, 343.
Babecki J. And Nowak G., 1978, Acta Physica Polonica,
Bg, 401.
Busza W., 1977, Acta Physica Polonica, B8, 333.
Gurtu A.mt al., 1974, Pramana, _, 311.
Elton L.R.B., 1961, Nuclear Sizes, Oxford University
Press, Oxford.
Kanarek T.I. et al., 1959, Proc. Intern. Conf. on Hi-
gh Energy Accelerators and Instrumemtation,
CERN, p. 508.
Kuznetsov Eo V. et al., 1970, Sov. Journ. PTE,
vol. 2, p. 56.
Otterlund I. et al., 1978, Nuclear Physics, BI_,
445.
Strugalski Z., Pluta J., 1974, Soy. Journ for Nuclear
Physics, 27, 504.
Strugalski Z., Pawlak T., Pluta J._ 1982, Communica-
tions JINR, Dubna: EI-82-718, EI-82-719, EI-82-
841.
Strugalski Z., 1984 a, Communications JINR, Dubna
EI-84-268.
Strugalski Z., 1984 b, Communications JINE, Dubna
EI-84-854.
Strugalski Z., 1984 c, Communications JINR, Dubna
EI-84-195.
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Physical meaning of the multiplicities of emitted nucleons in hadron-nucleus collisions

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