ON THE ZENITH ANGLE AND MOMENTUM SPECTRUM OF MUONS AT SEA LEVEL

80 Pages·02.64 MB·English

by  ZAR, JACOB L

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Xerox University Microfilms
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LD3907
.07 Zar, Jacob L., 1917-
1951 On the zonltn ^ngle and momentum
7Z3 spectrum of mu-mesons at sea lev el.
61p. diagrs*
Thesis (Ph.jL?.) - Gradutte
School, 1951*
BiDliography: p .59-61.
COI88I4.
l.fc'esotrons. 2 .J is s e rta tic n 3, Aca­
demic - ii.Y.U. - 19i>l» I .T itle : Zenith
angle and momentum spectrum of pax-
mesons at sea vel. I I .T itle :Momentum
spectrum of mu-mesons at sea leveX
III .T itle : iu-mesons* W.-j;; l,,:
Xerox University Microfilms, Ann Arbor, Michigan 48106
THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED.
ON THE ZENITH ANGLE AND MOMENTUM SPECTRUM OP
MU-MESONS AT SEA LEVEL.
by
Jacob L. Zar
-Jtou— 16-. .I9§a
'T ^ s’ l
A dissertatio n in the department of Physics
submitted in p a rtia l fulfillm ent of the require­
ments fo r the degree of Doctor of Philosophy at
New York U niversity.
TABLE OP CONTENTS
ABSTRACT ...................................................................................... 1
I INTRODUCTION
A. General Introduction ............................................. 2
B. H istorical Introduction ...................................... 6
II APPARATUS
A. Telescope ......................................................................... 18
B. Counters ............................................................................ 19
C. C ircuits ...............................................................................20
D. Mean Angular Resolution of Telescope ... 2 3
III EXPERIMENTAL PROCEDURE
A. Selection of Zenith Angles .............................. 2k
B. Selection of Momentum Values ......................... 25
C . Rotation of Observations ......................................28
IV MEASUREMENTS OF ZENITHA NGLE SPECTRA
A. Integral Spectrum ..................................................... 31
B. D ifferen tial Spectrum fo r Penetrating
P articles ..................................................................... 33
C. D ifferen tial Spectrum for Mesons ............... 36
D. Comparison with Other Work .................................^0
V LIFETIME OP THE MU-MESON ................................................k2
APPENDIX I. CIRCUITS ................................................... 50
APPENDIX II. MEAN ANGULAR RESOLUTION OP
TELESCOPE................................................................................. 53
2 o 4 < b U
APPENDIX III . THE NUMBER OF MESONS DECAYING
DURING THE FIRST MICROSECOND...................................... 55
APPENDIX IV. CORRECTION FOR DELAYS GREATER
THAN NINE MICROSECONDS...................................................... 57
ACKNOWLEDGMENT............................................................................... 58
BIBLIOGRAPHY.................................................................................... 59
ABSTRACT
The zenith angle dependence of the u-meson in-tensity
at sea-level has been measured for several values of
momentum. Results were obtained by three methods, the
coincidence, anti-coincidence and delayed coincidence
methods; and i t has been found that the shape of the
zenith spectrum depends on which technique was used for
its determ ination. The delayed coincidence method was
capable of determining meson in te n sitie s in the presence
of other types of penetrating p articles and is therefore
the most accurate.
The lifetim e of the meson was also computed from its
anomalous absorption in the atmosphere. Its value was
found to be 2.2 ± .3 microseconds.
I . INTRODUCTION
A. GENERAL INTRODUCTION
This paper reports some recent measurements of the
inten sity of sea-level mesons in several zenith directions
and in several momentum in terv als. Sim ilar measurements
were made a number of times in the past, but the present
work differs from those in the respect that a relatively
new procedure has been used which has made the id en tifica­
tion of mesons much more certain . A summary of the ea rlie r
measurements w ill be found in the section entitled "H istor­
ical Introduction.” Before th is, however, a criticism of
the various experimental techniques w ill be presented.
It is customary to divide the ionizing part of the
cosmic radiation into two components according to the ease
of absorption in lead. The soft component is that part
which is absorbed by a ten to fifte e n cm thick lead f ilte r ;
consequently i t is composed of electrons, photons and those
of the heavier p a rtic le s that have low energy. The charged
particles that can penetrate this layer of lead make up the
hard component. At sea level they are almost a ll ja-mesons
(mass - 110 Mev/c ; proper lifetim e - 2 . 2 microseconds).
3 .
In the past i t had been thought that besides mesons, the
number of other p a rtic le s in the hard component was negligibly
small. For example, Rossi in an a rtic le in 1948, reviewing
the contemporaneous sta te of knowledge of cosmic radiation
stated:'1’ " It is estim ated that less than 1 percent of the
O
penetrating p a rtic le s with momenta larger than 7 x 10 ev/c
are protons." Hence, in nearly a ll the e a rlie r measurements
of the zenith and momentum spectrum of the hard component i t
was customary to make a sim plifying assumption, namely, that
the in te n sitie s measured with counters and absorbers could
be en tirely a ttrib u te d to mesons. In recent years doubt has
been cast on th is assumption. It has been found or suggested
by various authors that:
a. A considerable number of protons are found in the
low energy region of the hard component. It follows
from the work of Leprince Ringuet that among the par-
2
t i d e s which penetrate one hundred g/cm of lead and
2 2
stop per g/cm , 10 percent are protons. More r e ­
cent measurements by Conversi give l 6 percent for
3
th is quantity.
b. A sig n ifican t number of electrons and photons has
been found by Reynolds to be able to penetrate ten
B. Rossi, Rev. Mod. Phys. 20, 537 (1948).
2
L. Leprince Ringuet, Comptes Rend. 221, 4o6 (19^5)*
^ M. Conversi, Phys. Rev. 76, pp. 444, 849, 851 (1949)*
cm of lead. These may be counted in the hard com­
ponent .
c . An overestim ation of the number of mesons that stop
in the apparatus may resu lt from scattering of par­
tic le s out of the beam defined by counters. Kraushaar
and Rusk have shown that th is facto r led to errors in
5, 6
some of the e a rlie r measurements.
It is quite lik ely that the discrepancies that have
appeared in some of the preceding work may be due to the
id en tificatio n of the hard component with mesons. Two p rin ­
cipal types of discrepancies may be found: (1) The zenith
angle variation of meson in ten sity is not the same when ob­
tained from coincidence and from anticoincidence experiments.
(2) The lifetim e of the meson, as deduced from its in sta b ility
in the atmosphere, has varied considerably in d ifferent exper­
iments. It was usually found to be longer than the 2.2 micro­
seconds that was determined by Nereson and Rossi from a direct
7
measurement of the radioactive decay.
Because of these disagreements and the uncertain compo­
sitio n of the hard component, the zenith and momentum spectrum
of mesons was chosen fo r investigation by the method of delayed
^ G. T. Reynolds, Rev. Mod. Phys. 21, 122 (1949).
c
W. L. Kraushaar, Phys. Rev. 76, 1045 (1949)*
/T
R. D. Rusk and A. Rosenbaum, Phys. Rev. 76, 1166 (1949).
7
N. Nereson and B. Rossi, Phys. Rev. 76, 199 (1943)-
5.
coincidences. In th is method the mesons are recognized
through the detection of the decay electrons that are emitted
a fte r they stop in a suitable absorber. Counters and elec ­
tronic c irc u its are employed to determine the time in terv al
between two related events, v iz ., the stopping of a p a rtic le
in an absorber followed by the emission of a secondary par­
tic le . If I t is found that the time delays observed in a
number of these occurrences are d istributed according to a
decreasing exponential function with a decay constant equal
to the mean life of the meson, there is l i t t l e doubt that one
is observing the absorption of ^i-mesons and th e ir subsequent
decay. Thus, th is method unambigously yields the relativ e
in te n sitie s of mesons that stop in an absorber. It was f ir s t
used fo r the id en tificatio n of mesons by Rossi, Sands, and
Sard In th e ir measurement of the slow meson in ten sity as a
ft
function of a ltitu d e . Shortly afterw ard Shamos and Levy
published re su lts on the positive excess of mesons appraised
q
In this way. Recently i t was employed by Kraushaar, by
5, 3
Conversi, and by others.
Notwithstanding the usefulness of th is technique, i t has
not been universally adopted in investigations involving mesons
because of two experimental d iffic u ltie s . (1) Somewhat more
complicated electronic c irc u its are required fo r measuring
delayed coincidences that fo r simple coincidences or a n ti-
8 B. Rossi, M. Sands, and R. P. Sard, Phys. Rev. 72, 120 (19^7).
^ M. H. Shamos and M. G. Levy, Phys. Rev. 75, 1396 (19^8).