Download On the Star Production by Cosmic

2.H
Letters to the Editor
On the Star Production by CosmicRay Underground
S. Miura and S. Ogawa
in<t-it'ute 0/ Thearet£cal Phydc~,
Nagoya University
February 14, 1951
Previously, we have analyzed the star
production by the cosmic-ray underground. l )
Then, we have intended that the charged
star agent is 7t-meson produced by only rrays in equilibrium with the ,a-meson component underground, since the additive
interaction of ,a-meson with matter should
cause considerable modifications in the absorption spectrum of the cosmic-ray underground. This idea, however, is insufficient,
because charged ,a-mesons are able to produce
7t-meson by .its own electromagnetic field in
the collision 'with nucleons.2 ) According to
Williams-Weizsacker method, the suggested
r-7t cross section in (A) gives too large ,a-7t
cross section (a factor,.....,,10). Thus we must
give some additions and modifications in
our previous idea on the star production.
I) Charged star agel),ts include not only
7t-meson but also ,u-meson and in small
fraction, protons. In the collision with
nucleus by Coulomb interaction, ,a-meson
gives some fraction of its kinetic energy to
nucleus, causing the nuclear evaporation.
Recent experiment .shows that high energy
r-ray makes nuclear evaporation with cross
section 10-~8 cm 2Jnucleon. 3) Thus ,a-meson's
cross section for star formation becomes, in
Williams-Weizsaker method,
,.....,,(e2Jlic) log (EJ,a) .10- 28 cm 2 Jnucleon
_10- 29 cm 2Jnucleon.
The value is consistent with the experiment,
This process may belong to 1p in Evans'
notation.
II) The stars accompanied with several
fast secondaries are thought to be more
preferably caused by 7t-meson than by ,ameson. Because we cannot accept reasonably
that such a weak interaction as electromagnetic effect of ,a-meson may give multiple
7t-produc.tion. On the other hand, if it is
confirmed that ,a. meson itself produces 7tmesons multiply,4) it indicates an interesting
feature of 7t-production,-suggesting "multiple" (not "plural") production. Because,
due to its weak interaction, ,a-meson may
not be able to collide several times with
nucleons in "one" nucleus.
III) 7t-mesons and nucleon components
can be produced in the following process.
a) ,a-mesons produce ,,-meson by its
own electromagnetic field in the collision
with nucleon in nucleus. The cross section
is,O)
U=(g2JIi.c)(e 2 Jlic)2(1iJ,acJ2(M/,a) log (EJ~lf)
~0.7x10-29
(g2Jlic).log(EJM);
cm 2/ nucleon.
Taking into account that the average energy
of ,a-meson at the depth,.....,,50 m R,O underground is ,.....,,14 Bev, and that (g2Jlic),.....,,1
from r-7t eTect, U becomes ,.....,,3.10- 29
cm 2 /nucleon in consistent with the experiment:
This eJfect responds to 2p and 3p (if recoil
proton of high energy is included).
b) r-rays in equilibrium with ,a-meson
component 7t-meson. If we take u.. _.. ~10-2s
cm 2Jnucleon, the contribution is of magnitude
10% compared with the interactian (a). This
becomes clear from the fact that the value
of u.. _.. is small by a factor 10 compared
with Ua_ .. taken in (A).
c) In the above process, recoil nucleons
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Leiters to the Editor
may be ejected with considerable energy.
Stars are also accompanied with such occasions.
IV) On stars are caused by neutrons
emitted in the above process. These phenomena belong to relatively low energy process.
In such energy region, charged particle loses
its energy more by ionization than by nuclear
collision. This implication is consistent with
the fact that 0" is more frequent than 01"
Small fraction (-10%) of 0" may be caused
by r-ray.
01' stars are caused by the capture of
low energy 1t-meson and by the nuclear
collision of the low energy protons.
Further the /A-1t interaction mentioned
in III, a), is accompanied with the corresponding energy loss of /A-meson. It would
result in the considerable modifications of
the depth-intensity spectrum of the /A-meson
component underground. Wataghin61 suggested that 1t-meson of high energy may
diminish its nuclear interaction, from the
analysis of the depth-intensity curve- based
on a definite spectrum of the /A-meson.
spectrum at sea level. His idea, however,
is premature. Because the meson spectrum
in high energy region at sea level is known
not so precisely that the spectrum at sea
level must be checked by another analysis,
for instance, by the detailed size~frequency
curve of the /A-meson bursts in high energy.
On this point, some analysis may be reported
in near future.
In conclusion, we should like to express
our deep gratitude to Prof. S. Sakata, and
we are much indebted to Mr. Hayakawa for
his valuable discussions.
1)
2)
3)
4)
S. Ogawa and S. Miura, Prcg. Theor. Phys.
5 (1950), 897, cited as (A).
S. Hayakawa, private communication and
ref. 5.
S. Kikuchi, Phys. Rev. 80 (1950), 492.
J. Evans, private communication. We thank
his kindness to send us his recent ex·
perimental results.
5)
E. Strick and D. Hear, Phys. Rev. 78 (1950),
6)
C. M. Garelli and G. Wataghin, Phys. Rev.
79 (1950), 718.
68.