ENGINEERING LIBRARY
Obgerº long-lived ºutral V. Particles”
K. Lande, E. T. Booth, J. Impeduglia and L. M. Lederman
E} TECHNICAL REPORTs an ,s,
Columbia University
and
W. Chinowsky
Brookhaven National Laboratory
The application of rigorous charge conjugation invariance to
strange particle interactions has led to the prediction of rather
startling properties for the e°-meson state”. Some of these are:
(1) the existence of a second neutral particle, e3, for which two
pion decay is prohibited; (II) the consequent existence of a second
lifetime, considerably longer than that for two pion decay of the
e? (~ 1 x 10° sec); (III) a complicated time dependence for the
nuclear interaction properties". The only additional assumption in
this "particle mixture" theory is the non-identity of 9° and its
anti-particle.
These theoretical consideratiens have stimulated ue to under-
take a search for long lived neutral particles. To this end, the
Columbia 56" magnet cloud chamber was exposed to the neutral radiation
emitted from a copper target at an angle of 68° to the 3 Bev external
proton beam of the ** Cosmotron”. The 6 meter flight path
from target to chamber represents - 100 mean lifes for the well
* 2 º is ºvſ
IIII
9015 08645 4140

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known /\º and 9° particles which are produced at this energy". To
date twenty-six w" events have been observed. All of these events
have anomalous Q-values for two pion decay, all but one are noti-
coplanar with the line of flight and all but one demand at least one
neutral secondary to balance transverse momentum.
A plan view of the experimental arrangement is shown in Fig. l.
charged particles are eliminated by the combination of the 4' long
Pb collimator and the l; x 10° gauss-inch sweeping magnet. The cloud
chamber operates at a pressure of 0.91 atm of He and 0.10 atta of
Argon. The only additional matter in the direct path of the neutral
radiation is the l cm thick lucite chamber wall. A 1.5 in. thick lead
filter was placed at the entrance to the collimator to reduce the
V ray flux reaching the chamber. The aperture (5 in. x 1.5 in.) defined
a solid angle of 0.002 steradians at 68° to the incident protons. The
arrangement yielded readable photographs at a beam intensity of ~ 10°
protons per pulse, although the flux through the chamber was estimated
to be ~10° neutrons. The latter fact points up the virtue of the
technique employed.
The relevant primary data on 25 measured wº events, found in a
run of 1200 pictures, are listed in Table I. We have considered various
background effects which could possibly simulate wº events:
(1) Production of meson paire in the gas by neutrons or photons,
the nuclear recoil track being too short to observe. However, the
number of neutrons above meson production threshold energy at 68° was
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expected to be quite small. This was verified experimentally by the
fact that no negative prongs (i.e., x- mesons) were observed to
emerge from 1218 neutron induced stars in the gāt; a
(2) Decay of n° mesons, produced in the gas without recoil,
into the alternate mode e” e." Y . This is ruled out kinematicelly
for 16 of the events. The argument in (l) also spplies.
(5) Production of large angle electron pairs in the gas by
photons.
(k) Bremsstrahlung or scattering of backward moving particles
with consequent large angle deflections.
These possibilities lead to the prediction of thousands of smaller
angle events and to the necessity for large fluxes of backward moving
particles. Meither of these are observed. These arguments will be
detailed in a more complete report. They lead to the conclusion that
the events listed in Table I are indeed examples of the disintegration
of a long-lived neutral particle.
A preliminary analysis of the data yields some information on the
properties of the new particle.
(1) All but three of the forty-six secondaries are determined to be
lighter in mags than the K-meson • Mone can be protons. We have
agsumed that all are pions, muons or electrons. The identification of
several of the decay products as pions or electrong is indicated in
the table,
• * -
(2) We have considered various three body decay schemes motivated
by the observed charged K meson modee. In Fig. 2, we plot for assumed
decay products x* e” Vo and for r" tº 12 " , the variation of the
average computed mass (15 events were available) of the incoming primary
as a function of its aggºrmed velocity. Permutations of the relevant
combinations of r's, u's, e's and L' 's yield similar results. For
example n° u" V , u” (“ ” , g” e- r" snd at e- ** are climost coinci-
dent. These graphs snºphasize the conclusion thet the resultant incoming
velocity distribution is kinematically sensible only for prizary masses
near the X-mass of 500 Mevº. One may elso infer that, for a K-mass
primary, we v secondaries are more frequent than tº 12 or, say, per .
(5) All but two of the events are kinematically inconsistent with a
./\º-mass particle decaying into u" et N or e” et n. *
(k) Fig. 3 illustrates the detection sensitivity as a function of life-
time for a K-mass particle. Although the production cross section for
K* mesong" has a large uncertainty, comparison with the observed yield
serves to limit the lifetime to the range 10° sec > t > 3 x 10^9 sec.
The observed uniform distribution of events in the chamber, together
with Fig. 2 also sets a lower limit: t > 1 x 10° sec. If the life-
time is on the short side of the above intervel , then it is likely that
many of the Briogaloºzg vº's observed in cosmic rays are examples of this
particle, and not simply alternate decay modes of the *.*
At the present stage of the invastigation one mey only conclude that
Table I, Fig. 2 and Q.” plots are consistent with a K"-type particle
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** three body decay. In this case the mode wep is probably
prominent”, the mode ruv' and perhaps other combinations may exist
but are more difficult to establish and r* r * is relatively rare.
Although the Gell-Mºm-Pais predictions (I} and (II) have been con-
firmed, long lifetime and "enomalous" decay mode are not sufficient to
identify the observed particle with e; . In particular, a neutral 7,
meson, if three pion decay has a small branching ratio, may have these
properties. A much stronger test of particle mixtureg must await the
observation of nuclear interactions or of the gtriking interference effects
which are also predicted.***** **
The authors are indebted to Prof. A. Pais whose - ---------~ elucidation
of the theory directly stimulated this research. The effectiveness of
Cosmotron staff collaboration is evidenced by the successful coincident
operation of six magnets and the Cosmotron with the cloud chamber.
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Table I • cont’d
& § b & C
; Pt. 1- P I- tº . Q fºg Conrºent
r_Mov/c. -à- Mev/c _____. New -čić:
167 a 3 < 2 lik a 3 < 2 65.5° lºo a 2
lºº & 5 < 2 120 * 24 < 2 112.5° 79 & 8
283 - 10 <2 222 - 10 < 2 50.1° 72 + 6 Coplanar, P = 59 a 50 Meye
89 + 1 < 2 272 + 9 < 5 128.5° 13', a lo not tº
Notes:
a. This is a visual estimate of the ionization, in
C e
d.
units of minimum ionization as determined from nearby
light tracks of P × 50 Mev/c.
Angle errors have not been computed. An average error
of 5° has been used.
yº: ©
©. for a normal 9° is 211, Mev.
tº is defined as –2 w" + x" + x° and is excluded
by Q-value or transverse momentum.
l-
2.
5.
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Figure Cagticº
Experimental arrangement for production and detection of long-lived
w° particles.
Average calculated primary mass vs. velocity of primary particle
for assumed decay schemes tº e V* and r" u" V e. The arrow
indicates the peak of the phase space spectra (ref. 5). The vertical
bars are average deviations.
Jetection sensitivity for K-mesons as function of lifetime. The
composite curve is obtained with the spectra of reforence 5. The
point indicates the observed yield with a production cross-section
of ~ 20 ºbn/ster.
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References
* Supported by the AEC and the AEC-CNR Joint Program.
* M. Gell-Mann and A. Pais, Phys. Rev. 97, 1587 (1955).
* Further discussion of particle mixtures have been given by
a) A. Pais and o. Piccioni, Phys. Rev. 100, 932 (1955).
b) G. Snow
c) 8. Treiman and R. G. Bachs in press
d) K. Case
* See Piccioni, Clark, Cool, Friedlander and Kassner, Rev. Sci. Instr.
26, 252 (1955).
The ejected been is focused by a quadrupole magnet peir to a 5" diameter
circle. Two bending magnets were used to steer the beam catc the
1.5" x k" x 5" long target.
* Blumenfeld, Booth, Lederman and Chinowsky, Phys. Rev. 102, 1184 (1956).
* We are grateful to R. Sternheimer for computing the energy spectrum
of K mesons emitted at 68° under various assumptions as to the
collision mechanism. These calculations yield similar spectra, all
of which peak near 100 Mev. See Block, Harth and 8ternheimer, Phys. Rev.
100, 32; (1956).
* For example, one member of a -/\* parity doublet may have a long
lifetime. Bee T. D. Lee and C. N. Yang, Phys. Rev. 102, 290 (1956).
" G. Collins, v. Fitch and R. Sternheimer, Private communication.
• 8 -
References - cont'd
* Kadyk, trilling, Leighton end Anderson, Bull. Am. Phys. Soc. 1, 251
(1956). For a recent summary see Ballam, Grisaru and Treiman,
Phys. Rev. 101, lº& (1956).
º Examples of this decay rºode have been reported by 81aughter, Block
and Harth, Bull. Am. Phys. Soc. i., 186 (1956). A particularly
clear event has been observed by the Ecole Polytechnique group.
We are indebted to J. Tinlot and B. Gregory for this data and for
helpful discussions on anomalous vº"e.
10 R. Serber, private communication.