Air showers containing delayed sub-showers which may be produced by a long-lived massive particle have been investigated by using twelve detectors. Ten events have been selected out as the candidates. However, a definite conclusion cannot be reached at the present time

Inoue, N.

Kawamoto, M.

Manabe, O.

Misaki, Y.

Takeuchi, T.

Toyoda, Y.

English

NASA Technical Reports Server

HE 6, 2-10
287
SEARCH FOR LONG-LIVED MASSIVE PARTICLES IN EXTENSIVE AIR SHOWERS
M. Kawamoto and N. Inoue
The Graduate School of Science and Technology, Kobe University,
Kobe 657, Japan
Y. Misaki, O. Manabe, T. Takeuchi and Y. Toyoda
Department of Physics, Kobe University, Kobe 657, Japan
Abstract
Air showers containing delayed sub-showers which
may be produced by a long-lived massive particle
have been investigated by using twelve detectors.
Ten events have been selected out as the candidates.
However, a definite conclusion cannot be got at the
present time.
i. Introduction
In our previous experiment, some effort to seek long-lived massive-
particles which may be produced in extensive air showers (EAS) was at-
tempted (i) (2). Double-peaked coincidence pulses from plural detectors
set at separate places in EAS array were investigated to observe these
particles. This method is based on the following idea. If a long-lived
massive particle is produced by a hlgh-energy interaction in the upper
atmosphere and it decays to some particles after long flight, the second-
ary products from them will arrive at ground as delayed sub-showers
relative to main EAS particles. Four events were reported as candidates
for the massive particles, and furthermore, three events were added by
an observation after that time. This observation, however, was carried
out by using a few detectors, and accordingly the information on the size
. of delayed sub-showers could not be obtained. A newextended experiment
has been carried out by using twelve detectors in the Akeno EAS array to
get more information. Some preliminary results are reported in this
paper.
2. Experimental
Twelve scintillation counters for measuring the arrival-tlme distri-
bution of EAS particles were set in the Akeno array (S2 station). The
arrangement of detectors is shown in Fig. i. In the figure, D1 and D2
detectors were piled up inserting iron sheets with total thickness of
i0 cm between them. The signals from detectors AI_A3 were transmitted
to a storage oscilloscop_ (I00 MHz, lwatsu TS-8123) through co-axlal
cables with different length, respectively, and accordingly three sig-
nals were displayed on the same sweep of the oscilloscope. Detectors
BlaB3 and CI_C3 were also operated by the same system. Signals displayed
on each oscilloscope were send to a mlcro-computer (NEC PC-9801)
through A/D converters and the pulse profiles were stored in a floppy
disk. The pulses from detectors DIED3 were displayed on a normal storage
oscilloscope (I00 MHz, Tektronix 466), and recorded by an autocamera.
Each oscilloscope was triggered by the coincidence pulses from the
three detectors shown in the figure_ and events accompanied by air shower
master pulses from the Akeno array were recorded.
https://ntrs.nasa.gov/search.jsp?R=19850027833 2020-03-20T17:09:43+00:00Z
288 HE 6. 2-10
3. Results
Pulses of 6300 showers were
N
analyzed in detail. The core
distances of 95% of analyzed
showers are less than 75 m. In
[] these showers, we found about
[] D3 70 events whose pulses from
B3
B2 three or more detectors showed
[] double peaks and one or more of
• these delayed second pulses con-Sl
m tained at least five particles.
AI
[] D1,D2 DC2 _,..
A3 D
A2 •C1 B4/o_s_ 15:29 20ns
i "_ _ ' i i i " i i _' i 1
c3O .
5m '
[] lm2 Scinti. C_nter
• Trig. Counter !/_v'
c_ _j._-,._
Fig. i Arrangement of _/ .
detectors D _ •
However, 32 of these events show the
second pulses with the same time [] []
delay (the time interval between the
_m
first peak and the second peak), e_
considering the difference of the " = "
time response of each detector
(4 ns). Further, only ten of these _. _.
events show the double pulses from |_ _ " = .
adjacent three detectors arranged
in a regular triangular form. An
example of these showers is given [] , o = []
in Fig. 2. In most of these cases,
delayed pulses do not distri_u_
over these triangular areas. We
have selected out these ten events Fig. 2 An example of
as candidates containing the delayed candidates containing
sub-showers, and investigated various delayed sub-showers
characters of these showers : shower
age, incident angle and muon size The EAS size is 3.0x106
et al. These showers show normal and the core distance
character in various points, of the sub-shower is
35 m. The closed squares
show the detectors with
the second pulses and the figuers are the delay
times and particle numbers of the second pulses.
HE 6. 2-10
289
4. Discussion
When the number of incident particles to a detector is small, spu-
rious double pulses are produced due to the statistical fluctuation of
the arrival-time distribution of main EAS particles. Using the average
arrival-time distribution (HE 4, 7-2)(3) and the density distribution
obtained by 0ur experiment for various core distances, this effect was
investigated by Monte Carlo simulation. An example of the results is
given in Fig. 3. In the figure,
observed integral numbers of
double-peaked pulses, curve _a),
are shown as a function of the "
1OOO_' I ' I ' I ' I ' ' I '= time delay, and curve (b) is a
_ result of the simulation. As
• •j seen in the figure, the observed
-\ numbers are much more than the
•. calculated value. The origin
\ _ of the difference is not clear.1oo
_ _ Any useful calculation about the
z " \4 fluctuation of the arrival-time> distribution of electromagnetic
w shower particles or nuclear
O_ 10 a) cascade particles is not obtained
O ! I (i_!i_= at the present time.
Z - The spreads of detectable de-
layed particles are of the order
of 5 m from the present experiment
I i I , , and then we could not get the
O 50 70 detailed information about the
DELAY TiME [ns] structure of delayed sub-shower
from our arrangement of detectors.
A preliminary observation has
, been carried out by the compact
Fig. 3 Integral number arrangement which consists of 9
spectrum of double- detectors within a regular tri-
, peaked pulses angle of i0 m sides. We havefound three events which contain
five or more pulses showing double
peaked structure with the same
time delay. Finally, to arrive at the conclusion about the long-lived
massive particle, a more elaborate experiment is necessary,
references
(i) Yoshida, M. et al. : 18th ICRC at Bangalore, I_i, 371, (1983)
" (2) Yoshida, M., Toyoda, Y. and Maeda, T. : J. Phy. Soc. Japan, 53,
1983, (1984)
(3) Inoue, N. et al, : HE 4. 7-2 of this conference


Search for long-lived massive particles in extensive air showers

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