The properties of 10 to the 18th power - 10 to the 19th power eV EAS showers such as the electron lateral distribution, the muon lateral distribution ( 1Gev), the ratio of muon density to a electron density, the shower front structure and the transition effects in scintillator of 5cm thickness are investigated with the Akeno 4 sq km/20sq km array at far core distances between 500m and 3000m. The fluctuation of densities and arrival time increase rapidly at core distances greater than 2km

Hara, T.

Hatano, Y.

Hayashida, N.

He, C. X.

Honda, M.

Ishikawa, F.

Kamata, K.

Matsubara, Y.

Nagano, M.

Teshima, M.

English

NASA Technical Reports Server

320 !tE_.7-3
Properties of 1018-1019eV gAS at far core distance
M.Teshima*, M.Nagano, T.Hara, Y.Hatano, N.Hayashida, C.X.He**
M.Honda, F.Ishikawa, K.Kamata, Y.Matsubara*, M.Mori*,
H.Ohoka and G.Tanahashi
Institute for Cosmic Ray Research, University of Tokyo, Tokyo, 188 Japan
*Department of Physics, Kyoto University, Kyoto, 606 Japan
**Institute of High Energy Physics, Academia Sinica, BeiJing, China.
Abstract
Properties of I018-I019eV gAS such as the electron lateral
distribution, the muon lateral distribution (E>IGeV), the ratio of muon
density to electron density, the shower front structure and the transition
effects in scintillator of 5om thickness are investigated with the Akeno
4km2/20km 2 array at far core distances between 500m and 3000m. The
fluctuation of densities and arrival time increase rapidly at the core
The 4km2 array has been in 5 o art charoed --
o muon(>lGeV) _
continuous operation for two years[l] o
and the expanded array of 20km212] from \
the end of 1984. Properties of I018- _ o
1019eV extensive air shower(EAS) at far _ Eofl_S'S~lO19aeV
core distances are studied with 2 - \
4km2/20km 2 array in conjunction with A - o -
the data of the dense Akeno Ikm2 _ \
array[3] which consists of 151 _ o _
scintillation counters of Im2 area and _I - \ -
9 muon stations of 25 m2 area. The oresults are important not only for _ •
determining electron size, muon size _ \
and arrival direction of the large _ o
showers and estimating their errors, _O
but also for designing the future huge
surface array of 100km2 area. The
reliability of the Linsley proposal for
the detection of giant air shower with
"mini array"J4] is also discussed using -1
the data obtained.
The data observed with 4km 2 array 4 _during a period between Dec. 1982 and
Oct. 1984 and with 20km2 between Sep.
1984 and May. 1985 are analyzed. -2 I I I
During this operation time about 250 2.0 5.0 4.0
EAS of energies above 1018eV are COREDISTANCE LOG(R) (m)
observed. Fig.1 The lateral distribution
of electrons and muons.
2. The lateral distribution of eleotrons(LDE)
The LDE is expressed by the function with two parameters _ and _ [5].
_e(R) = C(R/Rm)-g(I+R/Rm)-_ -_). Rm = 91.6m ; Moliere unit. ---(I)
https://ntrs.nasa.gov/search.jsp?R=19850027741 2020-03-20T17:04:49+00:00Z
321 XE _.7-3
O_Is 1.2, to which our experiments is not sensitive. _ _ can be measured
precisely with many detectors. For the EA3 of 3x1018ey _ is about 3.8.
The LDE becomes steeper as the energy increases and is expressed by
= 3.80±0.05+(0.10_0.05)LOG(E/IOI9ev) _ (2)
between 100m and 1000m. This energy dependence is a llttle larger than
the result reported by Linsley[6],
At core distances above Ikm, the LDE becomes steeper than the
extraporation of the above formula. In flg.1 the average LDE of I018.5eV-
I019.5eV for vertlcal EA3 is shown.
The fluctuations of electron densities after subtr_otlng statistical
ones(Poisson) are shown by solid linesin fig.2(a) and expressed as a
function of core distances as follows.
_p e(R)/p e(R) = 0.20x(l+R/1500) 2.0. - ............... (3)
At core distances near 2km, the fluctuations become abo_t 100%.
Ap/p=O.2*(l+R/1500)_°
z s._/
0 1.0 /.sT_
_------ ....
41_
U
_J
UL
P 0.1I--
I I , i i I I
-I O 1 2
2.0 2.5 3.0 3.5 LOG( PULSE HEIGHT)
. COREDISANCE LOG(R) (m)
(a) , (b)
Fig.2 The fluctuation of eleotron densities(a). The broken line is
derived from pulse height distribution of single partloles. That
" is shown in (b).
3. Ionization losses in sclntillator at far core distances
At far core distances the fluctuations of electron densities become
larger. The followlng causes are possibly related to its increment; the
transition effect in scintillator, slow neutrons, large core angle
distributions of electrons or broad arrival time distribution of
- electrons. The last one is important when the densities arq_measured by
one detector of large area.
The transition effect in scintillator is examined by comparing the
ionization losses of 16 Scintillation detectors of Im2 area with 5cm
thickness and those of 25 detectors of 0.25m2 area with 0,3cm thickness.
The ratio of them is 1.05±0.05 and the transition effect is negligible.
The slow neutrons may be partly responsible, since the delayed pulses
are frequently observed at far from the core[7].
322 HE q.7-3
We are measuring the density with the logarithmic amplifier by
discriminating the exponential pulse of decay constant 10 _sec. Therefore
the successive particle incidence with broad arrival time distribution
described in section 5 may contribute to the fluctuation. The fluctuation
due to this is estimated to be about 5% at Ikm and 60% at 2km, which are
less than the observed values. The pulse height distribution of a single
particle which traverse the scintillatXor is measured at core distances
around 2km and is shown in fig.2(b). This distribution is obtained with
151 scintillators of Ikm2 array when the average density is smaller than
0.2 per detector. Therefore this distribution shows the energy loss
distribution of a single particle and is free from the pile up of the
exponential pulses. The FWHM is about 100% and is the same with the value
of Eq(3). This shows that the large density distribution is not due to
the spurious one of the used amplifier.
The large core angle distribution of electrons is expected to be
originated from multiple scattering, which is also concerned with time
structure of shower front reported in section 5.
4. The lateral distribution of muons(LDM) and the ratio of muon density
to electron
The LDM(>IGeV) between 200m and 3km is well expressed by Greisen's
formula[6].
p#(R) = C(RIRO) -0-75 (I+RIRO) -2"5. RO=280m (4)
The average LDM for 1.0 I I I _ T
vertical EASof P_(>IGeV) I l1018.SeV-1019-5eV is _T
shown in fig. 1. P_[_d ?IT
The average ratio 0.20*0,07IT_ |
of muon density to "_" _'_
electron is shown by _ III_lIhorizontal bars as a 0.1--
function of core _ -- Idistances between 100m
and 3km in fig.3. The
points with error bars --
are the individual
events which are
observed by usin_ the 0.01 l I l I .
detectors of Ikm_ array 2.0 2.5 3.0 3.5
triggered by 20km2 COREDISTANCE LOG(R) (m)
array. The average
ratio at core distances Fig.3 The ratio of muon density
between 2km and 3km is to electron.
0.20±0.01, but the
fluctuation of each event is large.
5. The time structure of shower front
The arrival time of the fastest particle of each detector is measured
to determine the arrival direction of EAS. There are 53 fast timing
channels with 10nsec resolution in Ikm2 array and 23 channels with 20nsec
in 20km2. The time structures of shower front are studied by using these
76 channels. Our information is the arrival time of the fastest particle,
323
rm JI.7-3
but it gives the shower 4 I I Ifront structure at far _/
from the core where the Llnstey ....""
average density per Ot=_R/3__._
detector is less than I.
In fig.4 the _ 5 -
dispersion of arrival S
time is shown. The
dispersion increases
rapidly at core _ /
distances above 2km, and _ 2 --/-
deviates from the
extrapolation of the
formula given by
Linsley[4]. The
curvature of shower I J J J
front shows the similar 2.0 2.5 5.O 3,5
tendency. COREDISTANCE LOG(R) (m)
Fig.4 The thickness of shower
front.
6. Discussion and Conclusion
At core distances above Ikm, the LDE becomes steeper than the
extraporation of that within Ikm. The density fluctuation increases with
distances and exceeds 100% above 2km. The causes of the increment of
fluctuations are possibly related to the broad arrival time distribution
and the large core angle distribution originated from multiple scattering
of electrons. The curvature and the thickness of shower front increase
more rapidly above 2km. Therefore, it is necessary to arrange the
detectors within Ikm spacing.
The observation of Giant Air Shower with "mini array" proposed by
Linsley[4] has serious limitations, because the lateral distribution of
electrons becomes steeper and its fluctuations become large above Ikm.
Furthermore fraction of low energy muons to total charged particles
" fluctuate largely in shower to shower. This method requires the detectors
of large area.
Acknowledgements
The authors wish to thank the other members of Akeno A.S. Group for
their help and fruitful discussions. The analysis was carried out with
FACOM M380 at the Computer Room of Institute for Nuclear Study, University
of Tokyo.
Reference
[I] T. Hara et al., Proc. 18th ICRC, Bangalorell (1983) 276.
" [2] M. Teshima et al., This conf., La Jolla OG 9.4-8
[3] T. Hara et al., Proc. 16th ICRC, Kyoto 8 (1979) 135.
[4] J. Linsley, Proc. 18th ICRC, Bangalore 12 (1983) 135.
[5] J. Linsley, Prom. 15th ICRC, Plovdiv 12 (1977) 56.
[6] K. Greisen, Ann. Rev. Nucl. Sci. 10 (1960) 63.
[7] F. Kakimoto et al.,This conf., HE4.7-5.


Properties of 10 (18)-10 (19)eV EAS at far core distance

Properties of 10 (18)-10 (19)eV EAS at far core distance

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