Hadrons with kinetic energies higher than the pion production threshold lose their kinetic energies monotonically in traversing atomic nuclei, due to the strong interactions in nuclear matter. This phenomenon is a crude analogy to the energy loss of charged particles in their passage through materials. Experimental evidence is presented

Strugalski, Z.

English

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118
EXPERIMENTAL EVIDENCE OF THE DECREASE OF KINETIC ENERGY OF
HADRONS IN PASSING THROUGH ATOMIC NUCLEI
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
Hadrons with kinetic energies higher than the
pion production threshold lose their kinetic
energies monotonically in traversing atomic
nuclei, due to the strong interactions in nuc
lear matter. This phenomenon is a crude analo
gy to the energy loss of charged particles in
their passage throughmaterials. Experimental
evidence is presented.
I. Introduction
We have observed, in the 26 and 180 litre xenon bubble
chambers that GeV pions can be deflected or absorbed in nuc
lei without causing particle production, without causing pi
on production in particular, when are falling on layers of
nuclear matter thick enough, Strugalski Z. and Pluta J.
(1974), Strugalski Z., Pawlak T., and Pluta J. (1982); the
deflection or absorption is always accompanied by intensive
emission of nucleons with kinetic energies from about 20 to
about 400 MeV.
The energy and angular distributions of the protons in
such deflected and stopped events are the same, and they a-
re identical with the distributions of protons in collisio-
ns with particle production as well. It is remarkable and
leads to the opinion that it is reasonable to think that ha
drons lose their kinetic energies, in traversing nuclear
matter, by causing nucleon emission.
The subject matter in this paper is to present short -
ly our results of experimental investigations of degradati-
on of hadron energy through nuclei.
2. E_perimental Evidence
We found experimentally that the number n_T of emit -
ted nucleons which accompany_ the passage of a h_dron thro -
ugh a nucleus along a path _ fm equals the number of nuc-
https://ntrs.nasa.gov/search.jsp?R=19850027567 2020-03-20T17:21:54+00:00Z
119
loons contained within the volume v = _D 2 _ fm3 centered
on _ in the target nucleus:
where < _ > nucleons/f_ 3 is mean density of nucleons in the
target nucleus along _ , Do is approximately as large as
the nucleon diameter, Strugalski Z. (1978,1979), Pluta J.
and Strugalski Z. (1985).
Relation ( I ) may be rewritten i a more convenient
form:
/-hs (2)
if the path length _ is expressed in nucleons per the area
S, and S = _Do; the number np of the emitted protons is:
Z *Afs ( 3 )
where _" is in protons per S, Z and A are the charge and
mass numbers of the target nucleus.
The simplest observable effects which provide crucial
evidence and support for formulas ( I ) - ( 3 ) are: a) At
! energies high enough, higher than a few GeV, the mean num -
ber < n > of emitted protons in the deflected events is con
stant a_d almost equals<A > S, where _ > is the mes_; thi
ckness of the target nucleus in protons/S, b) At some pro -
jectile energy, definite for a given incident hadron and a
given target nucleus, the distribution of multiplicities of
protons emitted in the stopped events is symmetrical and
its maximum lies at the multiplicity n as large as D S,
where D is the diameter of the target n_cleus in protons/_.
c) The probability of an appearance of the stopped events,
in collisions of a given hadron with a given nucleus, decre
ases with the increase of the incident hadron energy; at e-
nergies high enough, the stopped events do not appear at
all, only the deflected events present themselves in some
portion of the collision events, Struga&ski Z., Pawlak T. ,
Pluta J. (1984).
An analysis in details of the experimental facts led
to the conclusion that: A hadron of kinetic energy E_ lar-
- ger than the pion production threshold loses its kinetic e-
nergy in passing through nuclear matter; the fraction A Eh
of the energy lost on the path length _ nucleons/s is:
* nEh = 6h "'_ ( 4 )
where 6_ _eV/(nucleon/S) is the measurable coefficient
which dSpends on the hadron identity - for pions _ = _
_180 MeV/(nucleon/S), for protons _, = 6 _ 360 '_
MeV/(nucleon/S), Strugalski Z. (19_3).n P
_E 1.3-8
In support for this conclusion, some additional experi
mental facts of the crucial value may be adduced: a) The me
an number <n _ of emitted protons in the stopped events is
quantitativel_ predictable by simple relation
np =(Eh/ Eh), S ( 5 )
which is valid for such values of E. when (E_/6_) S _< DS
where D in nucleons/S is the targetnnucleus d_am@ter times
Z/A, Strugalski Z. (1983). b) The mean multiplicity<n > of
emitted protons is energy-dependent at the incident barren
energies E_ _< D E_, and the energy-dependence is predictab
le quantita$ively _f formulas ( 3 ) and ( 4 ) are used for
a given target nucleus and for a given incident hadron, St-
rugalski Z. (1984). c) Indirectly, the degradation of the
incident hadron energy manifests itself in observed degra -
dation of the kinetic energy and of the momenta of produced
pions with the increase of the nuclear mstter layer thick -
hess n_ = _ 3 the incident hadron of a given kinetic ene
rgy in_racted with, as it is shown in Pig..
Pig. Mean kinetic energy
_+ '** 1 <E_o> , mean longitudinal
<E_ _ _'_,'+,_,_ momentum < PT v o> , mean4_ , transverse m_ntum < P_r__
c 1 and mean cosine of the _zon'
+._ .............._ emission angle _ cos @_. o>o _ '0_ of neutral pions produced
,_ _ -***,**,**. in pion-xenon nucleus colli
-.. _9 sions at 3.5 GeV/c momen-
o.............5 ,o._. o 5 ,o ._p tum, in dependence on the
' ' ....... j multiplicity n of emitted
I_;_i+_ 1 _+*" _/° protons; the m_itiplicityn is connected with the
,o-_ n_clear matter layer thick-
, i..........'..... neSs _ the incident hadron
+ _ interacted with as: n ="A S,
_ where S = _'D_ _ 10 f_2 and
++ o ++ DO is the diameter of the
_0_ _+ _ ._ nucleon. D/< > are the nor-
_ malized dispersions of cor-
_,_.' responding quantities.
,_ .+_ o.o.... _.... ,o_
.....""i ....'-I
o _...._ ...,0_ $ 3. Conclusions
o............... , o ...",_,',_..... that, in sudying hadron-nuc .
o _ ,0_ o _ ,o_ leus collisions, we have m-
et a phenomenon which may
be regarded as a crude analogy to the phenomenon_ consisting
in the energy loss of a charged particle in materials; simi
HE 1 3-8
121
larly, hadrons lose their energies in traversing nuclear
matter. But, the newly observed energy loss of hadrons is
due to the strong interactions of had_ ons with nuclear mat
ter.
In many cases, when particle-produclng reactions oc -
cur, the nucleon emission and therefore the incident had -
ton energy loss, due to this emission, is going in advance
of the particle-producing reaction; the incident hadron co
vers firstly some path in the target nucleus without parti
cle-producing reaction and then it causes this reaction in
the nucleus; in many cases it may happen on,the end of the
hadron path in the target nucleus.
The effects caused by the hadron energy loss are ob -
served clearly when the incident hadron energy is not lar-
ger than 6_ D, where E h is in GeV/(nucleons/S) and D in
nucleons/S _s the target nucleus diameter.
Reference s •_
Pluta J. and Strugalskl Z., 1985, to be published in
Communications JINR, Dubna.
Strugalski Z. and Pluta J., 1974, Sov. Journ. of Nucl.
Physics, 20, 504.
Strugalski Z., P-awlak T., Pluta J., 1982, Communicati-
ons JINR, Dubna: EI-82-718, EI-82-719, EI-82-841.
Strugalski Z., Pawlak T., Pluta J., 1984, Communicati-
ons JINR, Dubna, EI-84-855.
Strugalski Z., 1978, Communications JINR, Dubna,
EI-I 1976.
Strugalski Z., 1979, Communications JINR, Dubna,
El-I2086.
Strugalski Z., 1983, Communications JINR, Dubna,
EI-83-850.
Strugalski Z., 1984, Communications JINR, Dubna,
E1-84-268.


Experimental evidence of the decrease of kinetic energy of hadrons in passing through atomic nuclei

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