Matsushiro Underground Cosmic-Ray 0bservatory (220 m.w.e ... · Matsushiro Underground Cosmic-Ray...

J, FAC. SCI., SHINSHU UNIVERSITY, Vol. 24, No. 1, 1989

Matsushiro Underground Cosmic-Ray 0bservatory

(220 m.w.e. Depth) and the 0bservation of

High Energy (〓10〓 eV) Cosmic Ray

Intensity Variation

Satoru MORi, Shinichi YASUE, Shuji SAGiSAKA,

Masaoki ICHINOSE*, Kizuku CHINO,

Shigenobu AKAHANE, and Toshihiko HIGUCHI

Department of Physics, Faculty of Science and Faculty of Liberal Arts"

Shinshu University, Matsumoto 390, Japan

Abstract

A new underground cosmic-ray observatory was opened in Matsushiro,

Nagano City, Japan on March 22, 1984, ancl amulti-directionalmuontelescope

has been installed at an effective vertical depth of 220 m.w.e. underground.

The telescope consists of 50 plastic scintillation detectors totally, arranged in

two layers of 25 detectors each and has 17 directional channeis of observation.

We have made the continuous observation of the intensity variation of cosmic

ray muons (median primary energies of detection ;EllOi2 eV) since that date.

The intensity has been recorded every hour, and the average muon counting-

rates are; -J8.7×10` counts per hour for a wide-angle vertical telescope (two-

fold coincidence between upper and lower arrays of detectors) and ･v2.0×10`counts per hour for a vertical component-telescope, for example. In the pres-

ent report, we describe briefly the underground observatory of Matsushiro

and its surroundings, including the underground tunnel, the muon detector,

the multi･directional telescope constructed and some of its related character-

ristics. We also present some of the observed intensity variations of cosmic

ray muons for a fuli five-year period from April 1984 through March 1989

and discuss preliminarily the analyzed results of them in solar and sidereal

time.

Introductiem

The continuous observations of the time variations of high energy galactic

2 MoRI,S. YAsuE,S. SAGIsAKA,S. ICHINOSE, M. CHINO,K. AKAHANE,S. HIGUcHI,T,

cosmic rays (;lblOi' eV), particularly in sidereal time, provide information of

its dlstribution and its propagation of cosmic rays inside and outside the helio-

magnetosphere, and in turn information of the electromagnetic conditions in

the magnetized space. For those purposes, the long-running observations of

the comsic ray intensity variations have been performed by many researchers

since the discovery of cosmic radiations, by means of a variety of detectors

at various levels at the ground and underground (e. g･, ELLIoT, 1952; DoRMAN,

1974). Among those, at the present moment more than a dozen underground

telescopes (its median energies of detection >10i' eV) have been actively in

operation and accumulated valuable data worlclwidely. Those stations are shown

in Fig. 1 and listed in Table 1. By using those data, a great many investiga-

tions of the anisotropy, particularly in sidereal time, of galactic origin has

been performed, and some indications have been obtained about a nature of

the anisotropic fiows of cosmic rays around the inner and outer heliomagne-

tosphere (e.g･, NAGAsHIMA and MoRI, 1976, references therein), cooperated

with recently developed small air-shower measurements (its effective energies

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Figure

O 30 60 90 120 150 180 -150 -120 -90 -60 -3C

Geographic Longitude t")

1 A worldwide location of the underground cosmic-ray observatoriesin operation (in parenthesis, each depth i's indicated).

Matsushiro Underground Cosmic-Ray Observatory

Table 1 List of worldwide underground cosmic-ray observatories and some of its characteristics.

3

Station GeographicLat. (') Long. (')

Depth"(m. w. e.)

EmpS

(GeV)

Artyomovsk'BaxanBolivia**

Budapest**

EmbudoHobrat

Hong KongKamioka"London**

Matsushiro

MawsonMisato

ottawa #

Poatina

Sakashita

Socorro

Takeyama**

Vtah**

Yakutsk

48. 8N

43. 0N

16. 3N

47. 5N

35. 2N

42,9S

22. 0N

36. 3N

5L 5N36. 5N

67. 6 S

36. 0N

･51. 0N

41.8S

35. 6N

34. 0N

35. 2N

40. 6N

62. 0N

38. 0E

42. 5E

68. 2E

18. 9E

106. 4W

147. 2E

114. 0E

137. 5E

e. IW

137. 8E

62. 9E

137. 8E

78. 0W

147. 9E

137. 5 E

105. 6W

139. 6E

111. 5W

129. 5

575

850

25 40 27 36 577

27oe

60 220

40 34 o 365

80 74 54

4297, 20, 60

1600

2000

117-180

187-209

125-159

･ 184-195

1500

7000

261-421

6oo-13eo

164-188

145-2e9

80-900

1400

331-595

280-364

212-299

130O

80-264

" Vertical depth, "" ceased, tt at grotind (inclined),

' S Emp (median primary energy) for Matsushiro (IMAIzuMI, 1988), and for otherwise (FuJiMoTo et al,, 1984), and

' originally not for modulation observation.

of response >10i3 eV) (e.g., SAKAKIBARA et al･, 1984, references therein). A

complete picture, however, of the anisotropies of galactic origin, including

its three-dimensional nature, its energy spectrum, and furtheritsmoclulation 'in the heliomagnetosphere, particularly in the energy regions >10i2 eV, have

not yet been fully documented.

Here we can refer to one of the recent summaries of the observations of

the siclereal anisotropy, given at 'the Moscow･Conference (KRisTiANsEN, 1987),

for example. That states that i/'the,energy regions 10i2ct-10i` eV, to which

the deep underground observations 'and 'small air-shower measurements may

respond, the sidereal diurnal aniSotropy obtained shows the aniplitude approx-

imateiy O. 1% and the phase around 2 hr LST, and that those are almost invar-

iant with energy. On the basis of that observed constancy, some authors

(e.g., KIRALyand KoTA, 1979) have interpreted that the anisotropic-fiows.of

cosmic rays may mairily be produced by the so-called CoMpToN-GETTr'NG effect;

4 MORI,S. YAsuE,S. SAGIsAKA,S. IcHINosE,M. CHINo,K. AKAHANE, S. HIGUCHI,T.

a simple drift of cosmic rays through a smoothly flowing local (in some tens

of Lamor radii for the energies in question) interstellar medium. We should

also refer to the other important observational and theoretical views, given

by JACKLYN (1970) and NAGAsHiMA (1971). Those state that in addition to the

diurnal term, the semi-diurnal and higher terms have definitely been observed

in the sidereal wave, and that those terms may play an essential role for dis-

cussing the anisotropy model of cosmic rays.

We may further refer to a series of works, recently developed by NAGA-

SHIMA et aL (1982, 1983, 1985; references therein). That concerns the helio-

magnetospheric modulation of the sidereal tirne anisotropies, being presumabiy

predominant in the energy regions iess than 10i3 eV, to which the underground

observations at the depth of 200 m.w.e. or above may respond. They have

made an extensive theoretical calculation of modlfications of the anisotropy

inside the heiiosphere (its dimension roughly 100 AU), due to the orbital deflec-

tion of cosmic ray particles in the magnetosphere. Using models of the helio-

magnetosphere, which may change its state every 11-year, particularly of the

field polarities in the northern and the southern hemispheres with respect to

the neutral current sheet with its different degrees of waviness. NAGAsHiMA et

aL (1983) have presented, in a tabular form, comprehensive predictions of the

field modulated characteristics of the anisotropies of arbitary orientation, as

functions of primary bosmic ray particle rigidity and Iatitude of the viewing.

The following reference may be added as a milestone of observation of the

sidereal signal of cosmic rays, which is very recently reported by NAGASHIMA

et aL (1989; references therein). That concerns an observational summary of

the sidereal anisotropy and its modulation in the heliosphere, based on their

long-running observations by means of small air showers at Mt. Norikura

for almsot 20-year period (1970-1988). First, a significant sidereal diurnal varia-

tion has been well established with enough statistics, showing that an amplitude

is O. 06e±O. O03% and a phase O.8±O.3 h LST for -1.5･ 10i3 eV, together withstatistically significant higher terms (semi- and tri-diurnal variations) in the

sidereal wave. The results are definitely proved to be free from the atmospheric

effects, with a method of the difference between two simultaneous directional

(eastward and westward) air-shower measurements. We may regard the above

result as a `standard' of the anisotropic flows of cosmic rays outside the helio-

sphere. Secondly, the observation of the heliosphereic modulation of the side-

real daily variations have been discussed, showing that the annual variations

of the observed phases of both sidereal and solar daily variations may respond

significantly to the polarity reversal of the polar magnetic field of the Sun at

the transition period 1979-1980. If that were the case, such modulation would

Matsushiro Underground Cosmic-Ray Observatory 5

be predominant in the energy regions >.vlOi2 eV, then the observations at the

deep underground depths of approximately 220 m. w. e. or above, may be ex-

pected to appreciably suffer that modulation in the heliomagnetosphere. Thirdly,

a rather negative spectrum of the sidereal diurnal variations has been observed

with their multi'fold air-shower measurements; the diurnal amplitudes may

show a slightly decreasing form in the energy range of t--10i2 to --10i` eV.

This may be rather strong contrast to a flat or rather increasing spectrum

so far discussed (e.g., KIRALy et al., 1979; KRIsTIANsEN, 1987). If that would

be the case, greater amplitudes of about O. 1% or more might be expected to

be observable in the energy regions of >.wlO'2 eV, and the expectation of larger

amplitudes will be referred to later.

In those observational and theoretical situations, we have been expecting

the deep underground observations of cosmic rays promising, at the depths of

200 m.w.e. or above and much better with a multi-directional telescope in

the following several reasons. First, the observations in the energy regions

around 10i2 eV, to which the present observations at Matsushiro may respond,

may be important and interesting for establishing a sidereal anisotropy itself,

particularly in a sense of a connective role of observations between the higher

(>2.10i2 eV) and the lower energy regions (<5.10ii eV). In the higher energy

regions the measurements by means of air showers are available, and may

give the anisotropic flows outside the heliosphere. In the lower energy regions

there have been a great many observations at the ground and the shallow

underground for a long period of time, but the observations themselves may

be too severly modulated by the heliomagnetosphere to discuss the anisotropies

of galactic origin. Secondly, as have been comprehensively predicted by NAGA-

sHIMA et aL (1982, 1983, 1985), the heliomagnetospheric modulation of the

galactic anisotropy of cosmic rays must be predominant in -vlOi2 eV regions.

This may imply that conversely, the observations of modulation of the aniso-

tropies in the magnetized space make it feasible the electromagnetic diagnostics

about the heliosphere. Such diagnostics using cosmic ray modulation observation

may be promising for exploring the heliosphere, but this still be left fully

unsolved yet (BERcovlTCH, l984). Thirdly, a multi-clirectional observation

may be certainly effective for confirming the observationai facts themselves.

With comparison of the observed results in a multi-directional way we may

confirm them on a firm basis. Fourthly, the multi-directional telescope has a

wide scanning ability over the celestial space ; with the present telescope,

from the north polar regions (700t--800N) to the southern latitudes (･N･200S),

for example. The scanning around the Earth's rotational axis may lead to an

observation with its small amplitude of the anisotropic flows of cosmic rays,

6 MoRI,S. YAsuE,S. SAGIsAKA,S. IcHINosE,M. CHINo,K. AKAHANE,S. HIGucHI,T.

and the viewings beyond the equatorial regions may reveal some of the south-

ern characteristics, which may be different from the northern ones in the

observation. Fifthly, on the' basis of the multi-directional observation vtre may

check and eliminate the inherent atmospheric effects to the observing muons

by a method of the difference between the directional measurements (e.g･,

ELLIoT, 1952). With such･ a process we may check the spurious components of

atmospheric origin, otherwise there would be no means to test for the possi-

bility of that kind of effects.

Matsushiro underground observatory itself was completed in l983. We

started the observations of the intensity variations of cosmic ray muons on

March 1984, and have continued them since that date, whose duty operation

time rate (complete. days/total days in operation) is as high as 95%. In this

report we present a brief description of Matsushiro underground cosmic-ray

observatory, the muon detectors, the multi-directional telescope constructed

and some of its related characteristics. We also present some of the observed

results of the daiiy intensity variations of cosmic ray muons in solar and sidereal

times, and discuss the analyzed results of them preliminarily.

Underground site

Matsushiro underground cosmic-ray observatory is located in Matsushiro,

Nagano City, Nagano Pref. in a central part of Japan, as shown in Fig. 2.

Locality of Matsushiro is shown in Table 2; --40 1<m northeast of Matsumoto

38136VE

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14oo

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PACIFIC OCEAN

Figure 2 An outline map of a central part of Japan, showing Matsushiro, and other cities of Matsuinoto, Tol<yo, Nagoya, ancl Kyoto.

MatsushlloUnderground　Cosmlc・Ray　Observatol　y 7

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8 MORI,S. YASUE,S. SAGISAKA,S.

Table 2 Locality of

IcHINOsE,M. CHINo,K.

Matsushiro underground

AKAHANE,S.

observatory

HIGucHI, T.

Geographic

Longitude

Height(above sea Ievel)

Depth

Latitude

36. 530N 138. 010E 36em 220 m. w. e.

City, where our Department of Physics, Faculty of Science, Shinshu University

is situated. Flgure 3 illustrates a detailed map (printed by Geographical Survey

Institute) of Matsushiro and the underground site. The present underground

site is very close to the olcler Matsushiro underground observatory <tv4 km in

distance), which has been in operation since August 1980 (YAsuE et al., i97g;

lgsl; 1983). Figure 4 (photograph) shows a distant view of an area (Mt. Zohzan)

of the underground cosmic-ray observatory, for which the unused tunnel has

been re-excavated and enlarged through the hil! named Mt. Zohzan.

Figure 5 (a) shows the topography of the overburden (Mt. Zohzan), under-

neath of which the present cosmic-ray observatory is located, and Figure 5(b)

illustrated a cross-sectional profile along a line A-B of Mt. Zohzan in Fig. s(a).

As shown in the figure, the overburden rocks are mostly andesite (abbreviated

to ALdin the figure) aBd shale (also to Sh)･ The rocks were sampled by boring

at four points from the top ("v45em above s. I･ ) to the bottom (-v36em above s. 1. >

of the hill, and thelr average density is estimated at 2.54 g･cmM3. We aiso

measured directly the rock depth and is as high as 92.8m vertically, being

equivalent to 236 meter-water depth (Fig. 5 (b)).

'

#,ge,･

tt

mati/iasEieei:mees",tesgeme

wwW wwww ww"7.

･ew- ewew･

es x .T Wfljw! -...,." itX..

Figure 4 A distant view of Mt. Zehzan and the

'Ti/{zEii "ww"

underground site

es

area.

Matsushiro Underground Cosmic-Ray ObserVatory 9

Ad:Sh:

AndesitShale

<? 400 3eb

360m

A

Sh

-

OESERilATiON R(X)M pa44o h

h

II

%g>

Ad

B

hi-

5 (aj A

which

f'

Figure

A

J-t

topography ofthe underground

ENTRANCE

:

-i-

･39

(a)

the overburden (Mt. Zohzan),

tunnel has been re-excavated

-- -- -- -- - -- --4 - - -- . - --- t --- ' - t- . -: Ad ･'92'8F' .-so

-- ---- I l-l -- .-- -- .. .･ .. 65.7rn. . - ny . Sh :"

-- - -- -v t -- . i ---- .- "v.9M .. .' '..'' '. i- --4 - : - -- -tJi - 4--t -- -4- -4 -- "- T' vt - - "-

xx"

underneath of and en!arged.

.

.Im-

'

-'

an One

Figures 6 (a)

tions of the hill;

(E-W) direction,

B xX cEselsnATicNRoctvt 133m

(b)

of the cross-sections of Mt. Zohzan along a line AB in Fig. 5(at.

and 6 (b) demonstrate the simplified profiles of the .cross-sec-

(a) in the north-south (N-S) direction and (b) in the east-west

for example. In the figure, the Ietters N, NN, N3, S, SS, S3,

10 MoRI,S. YAsUE,S. SAGIsAKA,S. IcHINOsE,M. CHINo,K. AKAHANE,S. HIGucHI,T.

CROSS-SECTION OF THE TUNNEL

N3 x.lllNl X N {44

-- :- -- - -- - -t- - --- i ' '':' '53e. - - s- -.e --- i- ---- -- - ! - - - -- -tN .･.::, '･':'''･::/:: ･: ･' '

s --:- ---- -F-----i -t- - --- -l - -----.. .:630 .. t. -t ----34q..et . .- - -.- --- --- --- --- --- -t - ---- - - e--- --t T-- - ----t li -t !- i- - ' -- ---- .:::: ..: ::::

ss

S3

,

:

i-:t-. :: ---- -

: "'' :' ':':t:: ' s

100rn(360rn)

200m

E3

E

EE E

' t- -ny

-- :-:;l :f -t--

C440 - t-1

f - :-t

li

-

l'3･3.?

--- - t,

W ww

'--- 63e34e

tt ---r'--- -- - -,S e - --- -i- d- t --- - --l --

W3

w

100nt (360m} loom

Figure 6 A simplified profile of the cross-sections in the directions; (aj north-

south (N-S) direction and fo) east-west (E-W) direction, for example. Numerical values (m) in parenthesis represent a height.

etc. represent the center directions of viewing of the component-telescopes

constructed, which will be referred to later. One can see that the rock depths

are different from each direction and the median primary energies of detection

of each dlrectional component-telescope are, therefore, different from each

other (see Table 4). Figures 7 (photograph) shows the underground tunnel, in

which the cosmic-ray observatory is located; (a) the entrance of the tunnel,

and (b) and (c) the paths insicle. Figure 8 illustrates the room arrangement of

the observatory in the' tunnel; the observation room (10×10m in area) and the

recorder room, where the electronics circuits and the recording system have

been installed as shown in Fig. 9 (photograph). As mentioned earlier, the present

underground tunnel has been constructed by re-excavating and enlarging the

unused tunnel for the sake of the cosmic ray observation. The environmental

conditions in the tunnel therefore, have been kept in an exceilent state; inside

the tunnel it has been rather dry and in almost constant atmospheric tempe-

rature throughout the year; the temperature in both observation and recorder

rooms has been kept constant at 18.0±O.10C throughout the year with someheating sources. The daily variation of the temperatue has been too small

(twO. OIOC) to produce any significant effects to the cosmic ray detectors and the'

MatsushHoUnde1910u貸d　Cosm王。－Ray　Observator｝ 11

購掘

ン

ル

鮮幽嬢卿謬　　　　．．縛蹄’〆♂感

ノ／

醐　　汐匹

響灘澱

髪驚

　　　　　　　　（乱）

総

磯鰻礁

～

’

＼＼

く

ノ

（b＞

（o）

Flgure　7　Matsushuoし1nderglomld　cosmlc・1ay　observatoly；（a）the　Inam　ellt　　　rance，　and　（b）　the　path　正n　the　ttlnne1，　and　（0）　the　entlance　of　the

　　　obsel　vat！on　l　oOln．

electronlcs　clrcuits・　The　hulnidlty　111　both　roolns　has　beell　kept　collstant　at　50±

1％　（rotltinely　measured）all　the　year　l　otlnd　by　ushlg　four　dehumidi丘ers．

12 MoRI,S. YAsuE,S. SAGIsAKA,S. IcHINOsE,M CmNo,K. AKAHANE,S. HIGucHl,T.

OBSERVATiON ROOM AND RECORDER ROOM

c:gM,i:,gei " "k

e Mio2ni------,l , Os ll,l rw2 RtcsoRMDER t"x ss{kgl2:L<siei "si

F--ff'----m----t25M- Nx ,･.s,,,liJl9N

7

Figure8 An anangement of the room m the observatery; the recorder

room and the observation room <10×10 m in area).

. .." t""; fe '"b wr .gr ag ';e･k'dig

s t..Z'cr'?s ''ajth

2ngtv,,.,,.,../g.ii,lliiigttsgees. was bx.Eee,.

Figure 9 The recorder room, where the eiectronics circuits and the recording

system are mstal!ed.

Multi-direetional eosmie ray muon telescope

1. Cosmtc ray niuon detector

In the present observation, we have used plastic scmtillation detectors for

detecting the cosmic ray muons. The detector itself is of the same type as

that being used m the older Matsushiro underground observatory, some detaild


of which have already been discussed by'YAsuE et aL (1979). The detector of

a piramid-shaped iron box of 1×1 m in area, as shwon in Fig. 10, contains

four piastic scintiliators, each of which has 50×50 cm in area and 10 cm thick.

Inside the iron box we have coated white paint (Marine Paint) for reflecting

and collecting as much scintillation light as possible (-v90% in efficiency) to

the photomultipliers (PMs, 5" in diameter; Hamamatsu Photonics)L It is worth-

while noting here that in the present detector we have adopted a new optical

system, which we call `double PMs system', as shown in Fig. 10.

MAIN--AMP

E

!Mrr--

DISTRIBUTOR

COSMIC RAY DETECTOR

PRE-AMP

IT H

HIGH-VOLATGE

an!:

me.pt.y

･r:

SUPPLY

',:-=.--rw: 7====1

[1

PHOTO-MULTIPLIER

(5" ±n diameter}

PLASTIC SCINTILLATOR (100xlOOxlO cm}

Figure 10 The cosmic ray detector, including the plastic scintMators (each

being 100×100×10 cm slab), double photomultipliers (PMs; 5" in diameter), and some electronics connection.

As can be seen in the figure the scintillators are viewed with `one set of two

PMs' instead of a single PM, placed at the apex of the iron box. We then take

two-fold coincidence between those two output pulses out of the twin PMs as

an output of each detector. With this liouble PMs system' we have succeeded

in obtaining a better signal-to-noise ratio (S/N ratio), detection uniformity in

the scintillators, and finally exceilent HV-characteristics (output counts vs.

high-voltage applied to PMs) of the component-telescopes. as shown later (see

Fig. 13). We have carefully selected four plastic scintillators as well as double

PMs and their combination in each detector so as all the detectors to have

fairly equal detection sensitivity.

2. Multi-directional muon telescoPe

The present tplescope consists of 50 detectors totally. We have arranged

these detectors in two layers (upper and lower) of 25 detectors each, spaced by

150 cm verically as illustrated in Fig. 11. Figure 12 (photograph) shows the

14 rYiloRI,S. '}t'ASUE,S. SAGISAI<A,S. IcHINosE, M. CHINo,K. AKAHANE, S. HIGucm,T.

tOD- .#VleILJ

N

×

upperside-vie1･i

lower

cosmlc--ray detecrl or

5 10 15 20 25

4 9 14 19 24

3 8 13 1823

--rd-aj

-+a-di-

s

2 7 12 17 22

1 6 11 16 21

L

lvsIl1lrl

mss

-

i

l34os3.630iI.x.It

-vnH

r':

-k

lvl,I5m-- -H-l

l

I

l

bu-

S3

'

kes-1 . Snd

- o-X

fi

ln

rm - -d pt

Figure 11 An arrnagement of the cosmic ray muon detectors in the two(upper and lower) layers of 25 detectors each, spaced by 150 cm verti-

cally. Some of the component-telescopes; V-telescope, the inclined N-,

S-, SS-, and S3-te}escopes are illustrated.

,}t"f'/.･...I. .

･ ...} , t'r,.. . '. 'V.stt..g.

. le･ k t t.tt t".. t.t t.t ijtt

i

･l le" /"',

tt.. ij . ., usem . au m-

wa

ew.ssww･2.va. .rwva･va

Figure

<El)

12 The settings 'layer <exactly the

(b> in the upper

ot" the cosmic ray same setting as the

and iower layers.

muon 1oxver

(b)

detectors; (aj in the upper

Iayer; not shosvn here) and


setting of the detector arrays; (a) the upper layer in the observation room (and

in the lower layer also set in the same manner as the upper; not shown here)

and (b) two layers. On the basis of this arrangement of the detectors, whose

numberings are shown in Fig. 11, we have constructed 16 directional component-

telescopes 'as well as the vertical telescope, by taking two-fold coincidence

between the pulses out of appropriate pairs of the detectors in the upper and

lower layers. In Table 3, we summarize the present coinciclence system be-

tween them. Figure 11 also shows some of the component-telescopes thus con-

structed in a front view; the vertical telescope (abbreviated to V-telescope

hereafter), the south'pointing telescopes (S-, SS-, and S3-telescopes) and one

of the north-pointing telescopes (N-telescope), for example. As is seen in the

figure and as tabulated in Table 3, a geometrical settirigs of the component-

telescopes are as follows; the center directions of viewing of the inclined tele-

scopes, N-and S-telescopes (also E and W-teiescopes) are inclined at the angle

of ･--340 to the vertical (with angular resolution of -v±200 in latitude 2cd and

Table 3 The present coincidence system at Matsushiro

Componenttelescope

Coincidence-system Nurnber of

sub-telescope

V ==(Ul×Ll)+(U2×L2)+(U3×L3)+(U4×L4)+(U5×L5)+ ･･････････････--･･-･･･-･(25)

N =(Ul×L6)+(U2×L7)+(U3×L8)+(U4×L9)+(U5×LIO) + ･･････････`･･････････(20)

S ==(U6×L1)+(U7×L2)+(U8×L3)+(U9×L4)+(U1O×L5)+･･･････････････`････････(20)

E ==(U2×Ll)+(U7×L6)+(U12×Lll)+(U17×L16)+(U22×L21)+ ･･･････････････(20)

W = (Ul×L2) + (U6×L7) + (Ull×L12) + (U16×L17) + (U21×L22) + ････-･･････････(20)

NE == (U2×L6) -Y (U3×L7) + (U4×L8) -l- (U5×L9) +･･･････-････--･･･････+････････････････････(16)

SE = <U7×Ll) + <U8×L2) -- (U9×L3) + <Ule×L4) + ･･-･･････-･･-･･ny-････････-･････`････}･･(16)

NW - (U1×L7) + (U2×L8) + (U3×L9) + (U4×LlO) + ･･･････････････-･･-･･････････-･･-･--･･･(16)

SW=(U6×L2)+(U7×L3)+(U8×L4)+(U9×L5)+ ･･･････････････････+･･･････--･････T･-･･(16)

NN = (Ul× (Lll+L12+L13+L14+L15)) + (U2× (Lll+L12+L13+L14+L15)) +･･･(15)

S S =: (Ull× (Ll+L2+L3+L4+L5)) + (U12× (Ll+L2+L3+L4+L5)) +･･･････････････(15)

EE = (U3× (Ll -Y L6+Ll1+L16+L21)) + (U8× (Ll+L6+Ll1+L16+L21)) +･････････(15)

WW = (Ul× (L3+L8+L13+L18+L23)) + (U6× (L3+L8+L13+L18+L23)) +･ny-･--･･･(15)

N3 == (Ul× (L16+L17+L18+L19+L20>) + (U2× (L16+L17+L13+L19+L20)) +･･･(10)

S3 = (U16× (Ll+L2+L3+L4+L5)) + (U12× (Ll+L2+L3+L4+L5)> +･･･････････････(10)

E3 = (U4× (Ll+L6+Lll+L16+L21)) -F (U9× (Ll+L6+Lll+L16+L21)) +･････････(le)

W3 = (Ul× (L4-f-L9 -i- L14-i-L19+L24)) + (U6× (L4+L9+L14+L19+L24)) +･････････(10)

WV = VS×LSUS == (Ul+U2+U3+･････････+U24+U25)

L S = (Ll+L2+L3+･･･-･-･･-L24+L25)

For numbering the detectors, see Fig. 11.

× denotes coincidence and + denotes mixing of the pulses.

16 MoRI,S. YAsuE,S. SAGIsAAK,S. ICHINosE,M, CHINo,K. AKAHANE,S. HIGucHI,T.

rv }450 in azimuthgcd). More inclined SS-telescope (also NN-, EE-, and WW-

telescopes) are inclined at rv530 (with angular resolution ･v±10e in 2cd and

-- }680 in pccl), and most inclined S3-telescope (also N3-,E3- and W3-telescopes)

are inclined at A-630 (with angular resolution -v±100 in 2cd and --±590 in qccl),

respectively, Four more component-telescopes are also constructed, which are

pointing towards the intermediate directions between N-, S-, E- and W-telescopes

and inclined at --400 to the vertical with angular resolution rv±200 in Zcd and

-v }450 in pcd (abbreviated to NE-, NW-, SE-, SW-telescopes).

Figure 13 illustrates the so-called high-voltage (HV-) characteristics; the

output counting rates vs. high-volatge applied to PMs, for some of the com-

ponent-telescopes; V-telescope, mixed countings in the upper (US) and the

lowerdetectorarrays (LS), and also the wide-vertical telescope (WV; two-fold

H,V, CHARACTERISTICS

lo6

5 IOAcr=xvut

NF<ecoi2 lo48U

UT

LT

operating voltage

YIV-coMp,

V-COMP,

3 10- soo 6oe 7oo soo -goo looo H,V, SUPPLIED (VeLTS)

Figure 13 High-voltage characteristics (recorded counts vs. HV applied to

PMs), for some component-telescopes; V-, WV-telescopes and US and LS.


coincidence between US and LS). Note again here that in the present system,

the above US and LS themselves are the resultant outputs of two-fold coinci-

dence and also the 17 component-telescopes are the resultant outputs of four-

fold coincidence, thus accidental coincidence rates are very rare and negligible.

In Fig. 13 we can clearly recognize a wide plateau region in the recorded count-

ing-rates ranging approximately 200 volts or so. We have finally operated the

detectors with a common high-voltage at 790 volts, with a further fine

adjusted-voltage to each of 100 PMs through resistance-networl< of HV-distri-

butor (see Fig. 10). As mentioned earlier, with an aid of the present improved

detection system of `double PMs' we have succeeded in obtaining much improved

HV-characteristcs of the detectors and of the telescopes even in the deep under-

ground, which may ensure the present continuous observations stable and

reliable.

Figure 14 plots the asymptotic orbits of the 17 component-telescopes cal-

culated for the primary particle energies of 250, 350, 450, and 750 Gev (INouE,

personal communication, 1985). As can be seen in the figure, the present multi-

directional telescope may scan the celestial space from -v800N to --200S in

latitude and--130e wide in longitude. Among the 17 component-telescopes, three

north-pointing telescopes; N-, NN-, and N3-telescopes, can view in the direc-

tions which are almost parallel to the Earth's spin axis, while three south-

pointing telescopes; S-, SS-, and S3-telescopes can view the equatorial plane

ASYMPTOTIC LATITUDE AND LONGITUDE (MATsusttlRo: 37,5]ON, 138,02"E)

LATITuDE (O)

7S-O CV

60

90

x ];･3

N--"-H

7SO

N2 2soasto4sif'7

r' NIN'" 60

7SOCV.IgEXv

W/

-t--E

Ibl3

1750

x'W･2

307SOXE2X

sv"

! s" SEE3

x

o 120 ISG 240 20

S2.

S3"H LONGITUDE (

o)

7SO-30

Figure 14 The asymptotic orbits for the 17 component-telescopes, calculated

for primary energies of 250, 350, 45, and 750 GeV.

18 MoRI,S. YAsUE,S. SAGIsAKA,S. IcHINOsE,M. CHNIO,K. AKAHANE,S. HIGucHI,T.

or rather southern latitude regions (--20eS). Such a wide scanning ability and

the present mu!ti-channels of observation and also with its relatively high

energies of detection (as described below) may be the merits of the present

muon telescope at Matsushiro as emphasized in Introduction. In Table 4 we

summarize some of the characteristics of the 17 component-telescopes; the

center directions of viewing (in geographical latkude and longitude), averaged

hourly counting-rates, and median primary energies of detection (MoRI et al･,

1984, 1985, 1987).

Figure 15 shows the so-called integral response functions for some of the

component-teiescopes; V-telescope (in shallower depth among the 17 component-

telescopes), S-, SS- and S3-telescopes (in deeper depth among the 17 telescopes).

The calculations have been made by referring to the table of the response

functions prepared by MuRAKAMI et aL (1979) and by taking into account rather

realistic shape of the overburden (Mt. Zohzan) of each directional telescope

<IMAIzuMI, 1988). As is summarized in Table 4 and shown in Fig. 15, the median

primary energies of detection of the present component-teiescopes lie in the

range of 6.10iitvl.3 10'2 eV, and the corresponding Lamor radii are 3"v5 AU

for ･-v5nT of the magnetic field strength around the Earth's orbit and ･x･50 AU

around the Saturn's orbit.

gpE:

%g-gor e

ENliisk

g

;QO

50

10

lo2].o 10

PRIMARY ENERGY (GeV>

lo5

Figure 15 The integral response functions g!ving the percentage of the cou-

ntrate F (<Em) due to primaries of energies Em for some of component-telescopes; V-, S-, SS- and S3-telescopes, for example.

Matsushiro Underground Cesmic-Ray Observatory 19

Observational Data of Cosrnic Ray Muons

We started the observations on March 22, 1984, and have continued them

since that date, whose duty operation time-rate (complete days/total days in

operation) is as high as 95%. We have recorded real counts of the muons on an

hourly basis on paper tape, (and now in preparation on other recording medi-

ums, such as magnetic tape and floppy disk), for the 17 component-telescopes

as well as for the WV-teiescope and the upper (US) and lower (LS) arrays, whose

hourly countings are tabulated in Table 4. At persent we are also in prepa-

ration of the data-sendings and the electronics monitoring by means of the

remote-sensing with micro-computer and public telephone system between the

remote observatory (-v40 km in distance) and our laboratory in Matsumoto,

a full system of which has been in operation between the older Matsushiro

and Matsumoto (YAsuE et aL, 1979). In the followings, we will show some of

Table 4 Characteristics of 17 component-telescopes of multi-directional

muon telescope of Matsushiro underground observatory

Comp. Rcd(o) ip cd(O) n( × 10`lh) Emp(GeV) Deff(m. w. e)

VNs

E

WNENWSEswNNssEEWWN3S3E3W3WVusLS

36. 5

70. 8

3. 4

28. 1

31. 3

52. 7

58. 0

1. 5

3. 5

86. 2

-16. 7

18. 5

27. 4

79.1

-26.9

12. 6

18. 4

140. 6

146. 9

134. 1

174. 6

100. 5

199. 5

82. 6

168. 7

110. 6

223. 6

139. 6

198.6

80. 9

294. 5

139.7

20Z 7

71.6

20. 0

9.2 7. 4

9. 6

10. 6

4. 7

6. 5

4, 5

5. 6

6. 0

3. 8

5. 1

4. 3

L6 O,9

1.7 2. 4

87. 5

141.3

138. 0

660

710

730

770

630

7eo

640

73e

660

870

1050

720

660

980'1300

770

710

660

660

660

214

230

240

255

200

228

208

240

216

265

328

235

216

320

410

255

230

214

214

214

R cd and ¢ cd, asymptotic latitude and longitude in geographic coordinatesystem of center direction for 750 GeV; n, counting rate (as to January,

1986); Emp, effective median primary energy (GeV); Deff (m.w.e.),

effective depth.

20 MORI,S. YAsUE,S. SAGIsAKA,S. ICHINOSE,M. CHINo, K.AKAHANE, S.HIGUCHI,T.

the observed intensity variations of cosmic ray inuons and its analyzed results,

on the basis of the hourly data without any correction for the meteorological

effects of both the barometric pressure and the atmospheric' temperature.

1. 0bserved intensity variations of cosmic ray muons

As is well known the observed intensities of cosmic ray muons at the ground

and underground are affected not only by the primary cosmic rays themselves

in free-space but also by the atmospheric effects through its production and

propagation processes in the atmosphere. In addition to the above, the recorded

intensity variations may further be contaminated with some unknown effects

such as those of the instrumental, of background radiations, etc. Figure 16

shows the example of the observed intensity variations of muons, showing

its monthly averages for WV-telescope, for example, during the period from

April 1984 through July 1989. In the figure, first we can find a gradual de-

creasing trend in the intensity with a rate of approximately O. 3% per year. Such

decreasing may be largely due to decreasing detection efliciency of the PMs

used. Superposed on it, we can also find a trend of the semi-annual intensity

variations, that is, there would be two peaks in a year; one peak locates at

around mid-summer (June-July) and the other at around mid-winter (December-

January). The present semi-annual variation may be an identical phenomenon

to that already observed at the older Matsushiro underground by our group

(YAsuE et al･, 1981). These semi-annual variations may be of atmospheric ori-

gin, and in order to understand the atmospheric effects on the intensity vari-

ations of muons, here we summarize in brief the basic idea developed by one

of the present authors (SAGisAKA, 1986; references therein). The observed

Figure

J84

Jun

Period of time

,B5 i86 i87Jun Jun ･Jun

'88'Jun

T89

Jun

- t' 3.0 q o -H pu nt ･q 2.o as > h P 10 .H m g o p g H

16 The period

tO･5*

monthly averagedApril 1984 through

i

TW--telescope

intensity variations of WV- for the July 1989, for example..


intensity variation (dlatm) may be produced by at least two types of atmo-

spheric variations; one is due to the barometric variations (AIp) and the other

to the atmospheric temperature variations (Ah), and these are formulated

as

AIatm == riIp+dlT (1)

where ziIp ==Pe"P xoand AIT==l a(x)･AT(x)dx ･ (2) o

In the above Eqs. P denotes the barometric coefiicient, ev(x) is the partial tem-

perature coefficient at x (gr/cm2) from the top of the atmosphere and aT (x)

the hourly deviations of the atmospheric temperature. On the basis of the

data AT (x) of direct temperature soundings (routinely four times a day at the

meteorological stations in Japan), we can make a computation of Eq. (2) and can

apply them to the atmospheric effects on the observing muons. SAGisAKA

(1986) has made an extensive calculation of the partial temperature coefficients

of muons for various situations; rock depths, muon threshold energies, and

incident directions (see text in detail). With the computed results and the mete-

orological data, he has given a satisfactory explanation of the observed semi-

annual varlation of muon intensities at the older Matsushiro underground obser-

vatory. Figure l7 illustrates an example of the present analyses along SAGi-

sAKA's manner, showing a comparison between the observed and the theoret-

ically calculated variations for WV-telescope (KAJIyA, 1988). In the figure those

variations are plotted in a relative form (in %) on a monthly basis, normalized

' ' - : observed A gg ---:theoretical (100 GeV, 48b)

-H .4.J. f?,t llt N ICXx2 3 4 5 i6X7 8 9 10/ 11 12(month)

u as > h tA a s .fi

g :

Figure 17

o.o NN

-O.3

with the solicl line)

the dotted line) of

basis for the year

NNg'･

'

t

t

NN

s

N

6tl

1

t

A comparison between the observed intensity variatipns (connected

and the theoretically calculated variations (with

muons for WV-telescope, plotted on a monthly 1985.

22 MoRI,S. YAsuE,S. SAGIsAKA,S. IcHINOsE,M. CHINO,K. AKAHANE,S. HIGuCHI,T.

on June, for the year 1985; the observed variations are connected with the solid

line and the calculated with the dotted line, whose calculations are tentatively

made for primaries incident by 480 in zenith and with muon threshold energy

of 100 GeV. In the figure we can find a fairly satisfactory agreement between

the two variations. We can summarize here that as discussed by SAGIsAKA such

a semi-annual variation may be one of the characteristic features of the obser-

ved intensity variations of high energy muons at the deep underground (>100

m.w.e. depth), and that this can be satisfactorily explained in terms of the

upper atmopsheric temperature effect on the observing muons.

2. Barometric effect' on muon inteftsity variation

We have also examined the baromeric effect on the observed muon inten-

sity variations at Matsushiro, based on Eqs. (1) and (2). Figure 18 gives an exam-

ple of comparisons between the observed and the theoretically calculated

barometric coefficients for WV-telescope for the year 1985 (KAJIyA, 1988). The

calculated coefficients are obtained by taking into account two terms; one is the

term from the partial temperature coefficient and the other from the so-called

barometric coeflicient. By combining these two terms and the meteorological

data, the calculated coeflicients can be finally obtained. In Fig. 18 the observed

coeflicients are connected with the solid Iine and the theoretical ones with the

dotted line, on a monthly basis for the year 1985. We can find a fair agreement

with each other (and the yearly average of the observed coeffcient P=-O. 020±

Ae×ee

e.9

-:

u8Uo･HkpoeopasR

o

-2-5.0st10

123

- :observed----- :theoretical (100 GeV, 48e)

456 78 9 le 11 12 (month)

q. 1 .V

IG-- ---d''

ll ! s

..Ps-･o-. .. -o- -R

t s

Slt

t

s

1

1

t

Figure 18 A comparison between t'he observed barometric coefflcents (connec-

ted with the solid line) and the theoretically estimated coefficients

(with the dotted line) for WV-telescope, plotted on a monthly basis

for the year 1985.


O.O04%/mb in 1985). The present result may be consistent withthosecharac-

teristics of anomalously Iarge coefficients (B'v-O･ 05%/mb) obtained by the older

Matsushiro (YAsuE et aL, 1981) and by Poatina in Australia (365 m. w. e. depth)

(FENToN et aL, 1979). We may summarize here that the barometric effects on

the muon intensity varlatlons can be well explalned in two terms of the ap-

parent temperature effect in the upper atmosphere and.the so-called barometric

effect, as discussed by SAGIsAKA (1986).

We have further analyzed the atmospheric temperature effect on the ob-

served solar cliurnal intensity variations of cosmic ray muons at the deep under-

ground, Matsushiro, some of which have already been discussed by our group

(MoRI et al., 1988). Here we present a brief summary of their analysis and

show the resultant temperature effect vectors of the daily variations of muons

in the high energy regions .<vlei2 eV. They have examined the temperature

effect on an assumption that the observed solar diurnal variations may be pro-

duced with at least two kinds of the effect; one is the effect by the cosmic ray

anisotropies themselves including the so-called COMpTON-GETTING effect and

the other is the atmospheric temperature effect. First the solar diurnal an-

TEMPERATURE EFFECT VEcToRS DVS (TEMP)

FROM VARIOUS STATIONS Legand: eh NU:'worldwide (17 stat±ons) % NAG: Nagoya (surEace) O.eS MIS: Misato c34 m.;v.e.} TAK: Takeya!na (52 m.w.e.) SAK: Sakas,hita C80 m.:".e.} BAX: Baxan {8SO m.w.e.} MAT: Matsushiro (22o m.sf.e.)

lsh

BAX

SAK

MIS TAK

NAGO,10 %

6h

IIAT

MU

Figure

12h

19 The atrnospheric temperature vectors at Matsushiro, together with those from the underground stations at Baxan (850 rn.w.e. depth), Sakashita (80 m.w.e. depth), Takeyama (54 m.w.e. depth), and Misato (34 m. w. e. depth) and the surface stations at Nagoya and at the world-

wide location, reproduced from Mori et aL (1988).

24 MoRI,S. YAsUE,S. SAGISAKA,S. ICHINOSE,M. CHINO,K. AKAHANE,S. HIGucHI, T.

isotropy has been determined, and obtained as -vO. 35% in --18 hr LT direction,

after correcting for the COMPTON-GETTING effect. The temperature vectors are

then derived for the 17 component-telescopes at Matsushiro, and those vectors

are reproduced in Fig. 19, together with those in both lower energy regions

and higher energy regions; We can well recognize that in the high energy

regions (>6.10ii eV) the results from Matsushiro (k6.10" eV) and Baxan (850

m. w. e. depth and >tv2- 10i2 eV; ANDREyEv et al･, 1987) are in good agreement

with each other, being directed towards the evening time (-v20 hr LT). On

the contrary, the corresponding vectors in the lower energy regions (k3.10i'

eV) from the shallower underground stations are directed towards the morning

time (-v7 h LT). At the present stage we may summarize that the temperature

vectors in the low and high energy regions may be different from each other

and of reversed characters. Both of them, however, couid not be fully

understood ln terms of the temperature effect only, but may be rather owed

by the residuals of the barometric effect (NAGASHIMA, personal commu-nication, 1989).

3. Daily intensity variations of cosmic ray muons

Figures 20 (a) and (b) show the observed daily intensity variations of cosmic

ray muons by the present 17 component-telescopes, averaged over a full five-

year period l984-1989, plotted in the time-coordinate systems of the solar time

(SO), the sidereal time (SI) and the anti-sidereal time (AS), respectively. In the

figure the statistical error a of the counting-rates is given for each component-

telescope. In comparison we also plot the best-fitted curves to the above ob-

served variations in Figs. 21 (a) and21 (b), which are constructed with the first

(lst) and the second (2nd) harmonic terms, some of which will be referred to

later. In the figure also counting-rates error a is given for each component-

telescope.

Figure 22 shows the lst and the 2nd harmonic vectors of the above daily

variations in the solar time (SO), the sidereal time (SI), and the anti-sidereal

time (AS), for the 17 component-telescopes. These vectors are averaged over

a full five-year period of I984-1989, but are left uncorrected for any spurious

effects such as the meteorological effects of the barometric pressure and the

atmospheric temperature. The statistical errors are derived from dispersion of

yearly vectors. In what follows, we will present a pereliminary result of

each daily intensity variation in solar (SO) time and in sidereal (SI) and

anti-sidereal (AS) times, and the results of the detailed analysis of them will

be reported in the near future.

1984

sg

o4-89n3

IO,IZ

6 12 IB g

Sll

v

N

s

[

N

NE

NN

s[

SN

PLE

fou

E-1?i

18

fi l2 l8

AS

6 12 IB

ii g84.

se

4-89.3

IS,iz

O.O17k V

O.025kNfi..nslt..

sO.027ig

o.o24ig

lnO.023rz

o.o34F NE

NblO.029p

SEO.035ig

O.031k

Figure

SN

x.jL'tsL,-,-FL,

l,lw.,11

6 12 le

V

N

s

E

N

NE

Nli･1

SE

SFI

cr1-

"M

r-LFit.J

Vptu

srrte

20 The observed daily intensity variations

telescopes at Matsushiro, averaged solar (SO), sidereal (SI), and anti-sid

(a) is given for each component-telescope.

lx]2

S2

E2

kl2

N3

S3

Ei:

S ]2 IB o

SI

o.o3org N2

,.o3s, S2

o.o33x E2

iAl2O.036X

N3O.OS9X

o.o7gp. S3

E3O.057X

S 12 IB

AS

E l2 IS

VIT"

wotf

;,i3 o o4s: i"!3V Wtl

Ii' 1':' IS u ll .･v'' of cosmic ray muons of the 17 over five-year period 1984-1989, andereal times (AS), respectively.

N2

S2

E2

K2

N3

S3

E3

LJ---Jl

ptL.tLP

jF[3blE:LjvJL'tr"tiliii/

s i2 lg

component- plotted inCounting-rate error

Kye

9F'

o

a:nonco"ostpmo8B8'

,

Uptsc

ocrmo"<ptcto"K

8

N

IC･84,

se

4,-t,S,3

IO,IZ

S 12 Ia cr

SI

v

N

s

E

Yl

NE

"lyl

SE

Sbl

AJ

v

6 12 l6

S i2 I8

vO.O05X

O.O07MN

o .oos ¢. S

o'.oo7g E

o.oo7a

N

o.oioza NE

NFIO.O08".

o.oloz SE

O.O09M

syl

xv

-rv

6 12 18

AS 6 12 18

Y

i･1

s

:l:

rL･

VI

NE

NLil

SE

LrtVdit

[

sleJF

i

F

l/

l

Figure

b' IZ l

1 :, lil 4i ,･ll -/Ll II･ ,S

fi IV I u/t/- Eil

6 12 IS

li･,112 li ."

[ l i [ lS2Vi

E2

l･/l2

-

vxi3l !

S3

[･o

LJ

lr･]3

U

O.O09t

O.OllX

p-..,M l

tE

L-diA-I E l,Z,' IIS

SI

E 12 ia

AS

el2

S2f

o.oiog. E2

O.OIOX

o.opg

IAI2

N3

S3b.o23g

O.O14k

O.O16t

E3

hl3

-l [

u

E 12 ld

6 12 IB

N2

S2

r"ld

N2

Ig3

S3

E3

Fi3

21 The Best-fitted curves to the above intensity variations

in Fig. 20, constructed with the lst and the 2nd harmonlc (a> is given for each component-telescope.

of each

terms.

component-telescopeCounting-rate error

fi 12 IB

g

xox.H.cf)

K>m¢

o-

m.m>QHm>x>-

m.Ho:Hzom.m

g.

o:E.O

.x

>x>:>z.m

.m

m-mCam-N

8.

Matsushiro Underground Cosmlc-Ray Observatory

HARFVIONIC DIAL IN SIDEREAL, SOLAR, AND ANTI-SIDEREAL

' MATSUSHIRO (1984-198g)

OH

IHS

ARMoNIcSs! o?t ,, SO RH AS

SE s2 s E2 E eV sN l"E ;v3 lsH N3 N2NW o.io o-. tg･i u2

2NDHARfVIONICS

9H

cs

VI2

t"3

N2.t,,Te

.tgeJ'l3

E3

s[v1'"e E2

vbe

s"E

SE

E2.

N ENE SE

S3-e v S3 se

NVJ J

evlV32

TIME

OH

e

o. 05

sev L･J

. .

e s o.os g

E3elg3

N･ Ee

SE, e

e.;"e

eee

s

S2v･i

L"2

'W3

r"SI･]eN3

evN

Lee

27

6H

SH

6H 6H 6H Figure 22 The five-year averages over 1984-1989, of the lst and 2nd harmonic vectors of the daily intensity variations at Matsushiro in Fig. 21, plotted

in sidereal (SI), solar (SO) and anti-sldereal (AS) times, resspectively.

For AS, on!y five component-telescopes (V-, N-, S-, E-, W-te!escopes)

are indicatecl to avoid confusion.

3. 1 Solar daily variation of cosmic ray mttons

As mentioned earlier, our group (MoRI et al･, 1988) have already discussed

some of the solar diurnal variations and its atmospheric temperature effect for

the period 1984-1987. Figure 23 reproduces an example of the observed solar

diurnal variations (after correcting for the CoMpToN-GETTING effect) at Matsu-

shiro, together with some others in the lower energy regions at the ground

(Nagoya) and the underground stations (Misato; 34 m. w. e. depth and Takeyama;

54 m. w. e. depth). In the figure it seems highiy likely that a common, signifi-

cant anisotropy responsible for the observed variations exists in free-space for

the period 1984-1985. The analysis by means of a method of best-fitting with

the difference between the directional vectors of V-, N-, S-telescopes, etc.,

has shown that the solar diurnal anisotropy has such characteristics that the

amplitude is approximately O. 35% in around 18 hr LT direction in free-space.

28 MoRI, S. YASUE,S. SAGISAKA,S. IcHINosE,M. CHINo,K AKAHANE,S. HIGucHI,T.

SOLAR DIURNAL VARIATIONS

AT VARIOUS STATIONS

DVs <coR) (I): l984-1985

oh

lsh

MATsusHl RO

W2N

%O,2 wT s

S2 ×v

SM Sr wE N2

;"ME2VT TAKEYAMA

NT

MlsATov@bt

T･IN

ET

ts

E)I･N"1

s r･J

NN

VN

NAGoyA

EN

O,3

%

6h

12h

Figure 23 The observed solar diurnal vectors of some of the 17 component-telescopes at Matsushiro, together with those at Nagoya (surface), Misato

and Takeyama (underground) for the year 1984-1985, reproduced fromMori et aL (1988).

This result may be consistent with those so far obtained in the lower energy

regions (<5e10ii eV), with a rather higher cut-off (--300 GeV) of solar modu-

lation during the last declining period of solar activity (UENo et al･, 1985;

NAGASHIMA et al., 1987; KuDo et al., 1987). Note that the solar daily varia-

tions at Matsushiro have certainly decre' ased and diminished during the following

years of solar activity minimum (1986-1987).

It may be lnteresting to mention about another result analyzed by means

of the power spectral analysis of the intensity variation at Matsushiro (YAsu-

TANi, 1989). Figure 24 shows the power spectral density calculated for WV-

telescope for the frequency range 10-7-10-` Hz (in a period of 1 hr to 40 days).

The three-year (1985-1987) average is piotted, together with that at the Misato

underground (34 m.w.e. depth; MoRI et al-, 1976). In the figure the power

Matsushiro

bn- t

N&=el- ･

xeou -'-

)K

x6nH;X: m

-EL' l anz- b -

Underground Cosmic-Ray Observatory

J PBV"ER SPECTRUM' MISATe 1978,82 SBSERVED DATA

Jt..,.,

29

1o-7 J10'fi lo"5 FREQUENCT(HZ)

10"

t'xtri" C) -

=Xmou)K

xn×N."

LV =, u) -O- H

6 trrI

PONER SPECTRUMtrIATSUSHIRe i98S-･e7

OBSERVED )ATA

XX--.vLMv...M-KLlhJtVv-

Figure

Io ie !o io' FREGUENC¥ (HZ )

24 The averaged power spectral densities over 1987 of WV-telescope at Matsushiro, together that at Misato for 1978 and 1982.

1985-

with

density at the fiat level may correspond to that expected from the counting-

rates (white noises), indicating that the present observations at Matsushiro

have been well operated for those periods of time in a statistical point of view.

Detailed analysis of the observed intensity veriations of muons at the under-

ground as well as those of the nucleonic components, have been going on by

our gruop (YAsuE, personal communication, 1989), and will be published else-

where.

Figures 25 illustrates a summation dial showing year-to-year variation of

the observed solar semi-diurnal vectors at Matsushiro for the periods 1984

through 1989. In the figure the statistical errors for each component-telescope

are derived from counting-rates. Figure 26 shows its five-year averages over

1984-1989. The statistical significance may be rather less but the present results

of its N3 hr LT phases are in accordance with those well established in the

iower energy regions (MoRIsH!TA et al,, 1984).

30 MoRI, S. YASUE,S. SAGISAKA,S.

SUMMATION DIAL

OH

9H

9H

IcHINosE,M. CHINo,K.

OF SOLAR SE"OI-I]IURNAL

OH

go

.10

E

sv

N

IV

S2N2

zo.10

2

AKAHANE,S.

VECTORS

MATSUSHIRO(1984-Z989)

?

O.10 SE

NE

W

o.10

sw

2

3

.tpmS3

O.10 9o

N

"J

3H

3H

HIGucHI,T.

6H

6H

Figure 25 A summation dial showing year-to-year variations of the observed solar semi-diurnal variations of the 17

component-telescopes at Matsushiro for the period 1984 through 1989. Statistical errors are derived from

the counting-rates.

3. 2 Sidereal daily variations of cosmic ray mttons

Figures 27 shows the same summation dial as that in Fig. 25 but for the

observed sidereal diurnal vectors of the 17 component-telescopes at Matsushiro

during the period 1984 through 1989. In the figure the statistical errors are

derived from counting-rates. In this figure we can well recognize that the

observed diurnal vectors are statistically significant and persistent over years.

Figures 28 shows its five-year averages, whose errors are derived from

dispersion of yearly averages. In the figure we can find that the present

observed vectors may be reasonable and reliable on the basis of their mutual

consistency of the phase configuration for the directional teiescopes. Among

Matsushiro Underground Cosmic-Ray Observatory

AVERAGED SOLAR SEanI--DIURNAL VECTORS

MATSUSHIRO (1984--1989)

OH

9H

Figure

eb'

o. 03E3

S3 E2 E

rNE SE

N2-･ v,-s

S2 mu o

N

WsW

W2

N3

W3

6H

26 The five-year averages diurnal vectors over the errors are derived from

ges.

- 3H.o3g

of the observed solar semi-

period 1984-1989. Statistical

dispersion of yearly avera-

31

the 17 vectors the phases of the east-pointing telescopes (E-, EE-, and

E3-telescopes, for example) locates in the earlier directiens, while the phases

of the west-pointing telescopes (W-, WW-, and W3-telescopes, for example)

in the later directions, and the south-pointing telescopes (S-, SS-, and

S3-telescopes) and V-teiescope are in the intermediate phases within statistical

errors. Such comparison may be one of the merits of the multi-diretional

measurement for confirming the reliability of the observed results. In Fig. 28

we can also find that the observed amplitudes by the three north-pointing

telescopes (N-, NN-, N3-telescopes) are small (O. OlrvO. 02%) and not statistically

significant. This is reasonably expectable on the basis of their directions of

viewing (700N800 N), which are almost parallel to the Earth's spin axis. From

this it seems highly lil<ely that the spurios effects such as those of atmospheric

32 MoRI, S.

lsLI

YAsUE,S. SAGIsA'KA,S. IcHINOSE,M. CHINO,K. AKAHANE,S.

SUfVIMATION DIAL OF SIDEREAL DIURNAL VECTORS

g

O,20

E

v

I,J

Nq

O.20 z

lsH

Figure 27

origin and

insignificant

that the

are free

spurlous

the

the above

ors.

gO.20

E2

OH

s

SE

ixIEsw

o 20 g.-

):v -

z O.30S2

.3

t,IATSUSHIRO (1984-1989)OH

6H

W3

HIGUCHI,T.

S3

12H

The same vectors of 1984-1989.

of other environmental and

to the present

observed sidereal

from the effects, if exists,

observed anti-sidereai

component-telescopes

argument and

We have tentatively determined the direction of the observed sidereal diurnal

o.3og N3 o.4o g.- N2 W2 12H

summation dial but for the observed sidereal diurnalthe 17 component-telescopes at Matsushiro for the period

Statistica! errors are derived from the counting-rates.

instrumentai causes, may be small and

observations. We can positively draw a'conclusion

diurnal vectors of all the component-telescopes

contribution of atmospheric origin, because the above

may be common to all. We can further note that

diurnal vectors are small (O. 02% or less) for all the

as shown in Fig. 22, and this may be consistent with

also with the present significant sidereal diurnal vect-

' .

lsH

AVERAGED

OH

Matsushiro Undergrou.nd Cosmic-Ray

SIDEREAL DIURNAL VECTORS

MATSUSHIRO (l98A-1989)

o8.10

S3

SE

S2

E2s

kE

E3 eV sW--

NE

N3 N W W3

N2--NW W2'o.loe

6H

Observatory , 33

Figure 28

The five-year averages of the observed sldereal diur-

nal vectors of the 17 component-telescopes over the period 1984-1989. Statistical

errors are derived from the

dispersion ef yearly aver-

ages.l2H

DIFFERENCE VECTORSoh

h18

Figure

e/eO.05

--""xE2-W2

.NSE-SW

E3--W3

Nt/i

?NE-NW

'E-IAI/

8O.10

6h

h 12

29 The difference vectors of the observed sidereal diurnal variations between five pairs of the east- associated and the west-associated telescopes at Ma-

tsushiro. The statistical errors are derived from the

dispersion.

34 MoRI,S. YAsUE,S. SAGISAKA,S. ICHINOSE,M. CHINO,K. AKAHANE,S. HIGUCHI,T.

vectors by means of a method of difference between appropriate pairs in the

17 component-telescopes. Figure 29 shows the difference vectors thus derived

for five pairs between the east-pointing telescopes (E-, EE-, and E3-teiescopes,

NE- and SE- telescopes) and the west-pointing telescopes (W-, WW-, and W3-

telescopes, NW- and SW-telescopes). In the figure we can see that all the differ-

ences lie in almost the same direction around 19 hr LST within errors, which

may be certainly free from the atmospheric effects. By rotating the vectors

by 900, we obtain the average direction as 2.2ti/:O.3 hr LST, which is in coin-

cidence with those of the present V-, S-, SS- and S3-telescopes within statistical

errors (see Fig. 28). We can also note that the present phase of 2.2 hr may

also be in coincidence with those at the similar energies above 500 GeV; the

older Matsushiro (YAsuE et al., 1985) and the south-pointing (SS-) telescope

at Sakashita (UENo et al･, 1985).

In Fig. 30, we tentatively plot; (a) the observed diurnal amplitudes and (b)

the observed phases, as functions of median primary energies of detection for

iOii eV to 10i` eV from various underground stations and air-shower measure-

ments. Note that the data periods are different from each other, and the sta-

tistical errors are their own. The quoted vectors in the lower energy regions

(<5･10ii eV) are corrected by means of NAGAsHiMA method (1984). In the figure

the projected amplitudes onto the equatorial plane are shown, divided by coso"

(6 denotes the viewing latitude of each telescope and apparatus) (ALExEENKo

et al,, 1981; BERcovlTcH and AGRAwAL, 1981; CuTLER et al., 1981; DAvlEs

et al,, 1979; FENToN and FENToN, 1975; GoMBosl et aL, 1975; HuMBLE et al-,

1984; KoTA, 1985; LEE and NG, 1987; SAKAKIBARA et aL, 1984; SpELLER et al･,

1.0

ge v E;-' o Ll s 03 e g .4.J Hn k

O.Ol 11 12 13 14 10 '10 10 10

Median Primary Energy (eV}

(El)

+r･st

.t.tit tt

J Ba"asas-

llfg"itM t+UH -

Ba}On

ScM rxm

s A

Matsushiro Underground Cosrmic-Ray Observatory 35

p:rl!

vzz.lg

k

5

3

1

2'3'

Ee

i

..k℃twiu +Ba

-FLt.- t---t-tLLt "Ba")ln

im

Figure

11 12 13 1410 10 10 10

Median Primary Energy (eV>

to3e (at The observed diurnal amplitudes projected onto the equatorial plane (6 ==O) and fo) the observed phases,

as functions of median primary energies, from various

underground stations and by air-shower measurements, including the present results at Matsushiro. The data

periods are different from each other, and the sta-

tistical errors are taken from their own.

l972; UENo et al･, 1985; MuRAKAMI, personai communication, 1989). In the figure

we may find some energy dependent nature of both the amplitudes and phases.

First, we can note that the amplitudes range from O. 02% to O. 10% or more;

the former corresponds to the energy --100 GeV at the shallower underground

(Embudo and Misato, for example), and the latter correspond to the energy

-- 1000 GeV at the deep underground (Matsushiro, for example). Such an energy

dependent nature, particularly in the iower energy regions, <10i2 eV, might

represent the so-called iower energy cut-offs, which would result from severe

modifications by the heliomagnetosphere (NAGAsHIMA et al., 1982, 1983a). It

may be interesting to note here that the greater amplitudes have been ob-

served by thesouth-pointingtelescopes, S-, SS- and S3-telescopes at Matsu-

shiro, in particular, S3-telescope showing its amplitudes of O. 11t--O. 20% in --2

hr LST phase, whose asymptotic directions of viewing are around 200S. That

might not be far from understandable but rather consistent with the nega-

tiveiy decreasing spectrum proposed by NAGAsHIMA et aL (1989) mentioned ear-

lier. A precise detemination of the spectrum may be most important for explor-

ing the nature of the sidereal anisotropy of galactic origin, for which a fur-

ther observation and detailed analysis will be required. Secondly, the phases

may also depend on energies of detection (KoTA, 1985); the earlier phase of --1 hr

LST for air-shower measurements (represented by AS in Fig. 30), the later phase

of'-5 hr LST for the lower energies and the intermediate of 2rv3 hr LST for

36 MoRI,S. YASUE,S. SAGIsAKA,S. IcHINOSE,M CHINo,K AKAHANE,S. HIGUCHI,T.

the intermediate energies of detection including the present.

We can point out another interesting observed fact from Fig. 30 (and also

Figs. 27 and 28) that the present V-telescope at Matsushiro seems likely to be

rather smaller than those of other directional telescopes, the south-pointing

telescopes, for example. This tendepcy may be seen in those observed results

by V-telescopes at the older Matsushiro (YAsuE et al., 1985), at Sakashita

(UENo et al･, 1985) and at Utah (CuTLER et aL, 1981). In the present observa-

tion, the fact of less than one:half amplitude of V-telescope relative to S-, SS-,

and S3- telescopes may not be explained by mereiy considering each viewing

latitude; a factor of "-1.2 (==1/cos 36.50) difference at most. This may suggest

that the above facts would not be necessarily due to the energies of detection,

but be due partly to the nature of the anisotropy itself, one of which consti-

tuents may be of the north-south (N-S) asymmetric nature. From this point of

view,UENo et al. (1981, 1983, 1985) have anaiyzed the observed results in the

lower energy regions (Nagoya Misato, and Sakashita) in terms of two-way

anoisotropy (JAcKLyN, 1970); one is of the N-S symmteric type and the

other of the N-S asymmetric type. They have succeeded in separating each

contribution in the observed sidereal variations, to some extent, and have

discussed the N-S asymmteric term in the sidereal signaL Their analysis in

the energy region <5 ･ 10i' eV, however, may be still lacl<ing the consideration

about predominant modifications by the heliomagnetosphere to discuss the side-

real anisotropy of galactic origin. The modei of theanisotropy;of one-way,

two-way or more may also be another target to be explored in the near fu-

The analysis concerning `toward-away' field dependent sidereal daily varia-

tions may provide important information about modulation of the sidereal an-

isotropy in the heliosphere as comprehensively predicted by NAGAsHIMA and

MoRIsHITA (1983). As has been well known for some times, SwiNsoN (1969)

has suggested and given a definitive example of the sidereal diurnal variations

of solar origin, which critically depend on the IMF sense of `toward or away'

from the Sun, being apparently produced by the anisotropic flows (SvLTINsoN

flows) perpendicular to the ecliptic plane, due to the radial heliocentric density

gradient of cosmic rays in the presense of the IMF. That IMF-sense depen-

dent anisotropy has been certainly shown, as expected, being directed tovLTards

-- 18 hr LST direction for `toward (T) sense' of the IMF, while towards -v6 hr

LST for `away (A) sense', respectively, because the radial gradients of cosmic

rays are always positve (outwarcl from the Sun) and the IMF essentially lies

in the eciiptic plane. The observed IMF-sense dependent sideresl diurnal var-

iations; usually the difference being taken, that is, the T-A vectors between


T- and A-vectors, show the resultant phases of 18 hr LST direction, at the

ground and the shallow underground, and have perfectly supported the predic-

tions (e.g., UENo et aL, 1989; SvtqNsoN, 1988). Note that in the above

SwiNsoN's fiows there may be an underlying assumtion that the Lamor radii

of cosmic ray particles of interest may be less than the scale of the IMF

concerned. If that were the case, for Matsushiro observation we wouid expect

the T-A vectors being some different from that of SwlNsoN's because our

median energies of detection are high eonugh (tN･10'2 eV) and its Lamor radii

are greater than 5 AU or so for 5nT IMF. Figure 31 shows an example of

such sidereal diurnal T-A vectors obtained for five-directional telescopes

(V-, N-, S-, E-, and W-telescopes) at Matsushiro, which are sorted according

to `toward-away' sense of the magne'tic field as usualy made in the analysis.

In the present case, we refer to the field polarity from the table prepared by

T-･A FIELD DEPENBENT SIDEREAL DIURN,AL VECTORS MATSUSHIRO (1984-･1989) ./

OH

1.sH 6H

l2H

Figure 31 The sidereal diurnal T-A vectors for five directional telescopes, averaged over the period 1984-1989. The statistical errors are derived from dispersion of yearly averages.

Stanford Solar Observatory (Solar-Geophysical Data, 1989), We can find in the

figure that irrespective of their large statistical uncertainty the T-A vectors

for these five directional telescopes may be, on the average, directed towards

--･ 21 hr LST direction; being somewhat deviated from that of ･v18 hr LST

direction so far established in the lower energy regions. Note here that to

-hO.04Nv

W

O.02pv

E'

38 MORI,S. YASUE,S. SAGISAKA,S. ICHINOSE,M. CHINo,K, AKAHANE,S. HIGUCHI,T.

SUMMATION DIAL OF SIDEREAL SEMI-DIURNAL VECTORS

MATSUSHIRO (1984-l989)

oH oH k rg O.10

W

. X`e"x}z}?. sw

s

N2 )J2

? O.10

S2

6H 6HFigure 32 The same summation dial as that in Fig. 27 but for the sidereal semi-diurnal vectors for the 17 component-telescopes for the period 1984 through 1989. statistical errors are derived from the counting-

rates.

Or19

mu

W ×o .20

NE sE

Tts-1

wv ×"teN3

inS3o .10 g

o.. 109o

increase statistics we derive these N-, S-, E-, and W-vectors by averaging

two vectors of N- and NN telescopes for N-vector, S- and SS-telescopes for

S-vector and so on. To determine the observed fatcs themselves and identify

the anisotropic fiows responsible for them a further analysis would be required.

Figure 32 gives the same summation dial as Fig. 27 but for the observed

sidereal semi-diurnal vectors of the 17 component-telescopes for the five-year

period 1984-1989. In the figure the statistical errors are derived from counting-

rates. We can see that the sidereal semi-diurnal vectors are statistically signi-

ficant and persistent over years for almost all the component-telescopes.

Fig. 33 shows its five-year averages, whose errors are derived from dispersion

of yearly average. We can also find that the observed vectors are reliable,

showing their mutual consistency jn the phase configuration for each directional


9H

AVERAGED SIDEREAL SEMIr-DIURNAL VECTORS

MATSUSHIRO (1984-1989)

OH

8

W2

W3

o.os

S3

sw

W

Ne

s

}]2

v

S2

N3

NW

E3

6H

NE

E2

E

O.05%

SE

3H

Figure 33

The five-year averages of the sidereal semi-diurnal vec-

tors of the 17 component-tele-

scopes over the period 1984- 1989. Statistical errors are de-

rived from dispersion of year-

ly averages.

Figure

telescope,

gtiL

$

sm

O.1

OBSERVED SIDEREAL SEMI-DIURNAL VARIATIONS

At'o O.OlY.".

HAk

O.OOI

Median primary energy CeV}

34 The observed amplitudes and phases of the sidereal semi-diurnal vectors, as functions of median primary energies, from various under-

ground stations and by air-shower measurements. The errors for unclerground stations are indicated to each V-telescope only.

similarly to the diurnal vectors mentioned earlier. In Fig. 34,

oh oh oh oh

gh ghoh

3hoh

gh hh39 3h

6 6 6 6 6

MATNAG MIS SAKe UTABAX NOR MVS

seeag

e ee:esibe

eofeeeeeD

eee

e8 ee e e

e e

e

10o10 1110 12 1di3 1di4

the

40 MoRI,S. YAsUE,S. SAGIsAI<A,S. ICHINOSE,M. CHINo, K. AKAHANE,S. HIGucHI,T.

DAILY INTENSITY VAR!ATIONS OF COSMIC RAYS

Muon 11 eV)<"9,1a

Muon{"i.o･1oi2ev)

ALr-shower 13{.1.S-10 eV)

Mr--showerc?.2･1 di3 ev)

S-telescope

lo.o41

SS-telescope

MATsusHlRo

MATSUSHIRO

MT, NoRIKURA

BAXAN

6 9 12 15 18 21 24sidereal time (hr}

Figure 35

The observed daily intensity variations in sidereal time

for S- and SS-telescopes at Matsushiro, and air-shower ineasurements at Mt. Nori- kura and Baxan.

03

observed semi-diurnal vectors at Matsushiro are shown together with those from

'other underground and air-shower measurements; the phases in the upper part

and the amplitude in the lower part in the figure (ELLIoT, 1979; FuJII et aL,

1984). It seems highly likeiy that the existence of the semi-diurnal term in the

sidereal daily wave may be definite at around 6-v7 hr LST (and 18-v19 hr LST)

in a wide range of energies 10ii--10i4 eV.

Figure 35 shows the observed sideresl daily variations in sidereal time at

the three observation stations and compares with each other; from S- and SS-

telescopes at Matsushiro underground station (220 m.w.e. depth; ･N･10'2 eV),

frorn air-shower measurements at Mt. Norikura (>2.10i3 eV), and at Baxan

(l})2.10i2 eV) (NAGAsHIMA et aL, 1989). We can see in the figure that both air-

shower measurements show very similar time-profile, characterized with rather

flat nature during 19 hr to 8 hr and rather V-shape form with a minimum

around 12 hr (NAGAsHIMA et aL, 1989). The daily variations of S- and SS-tele-

scopes at Matsushiro, on one hand, show a similar time-profile to the above

two, and on the other hand, somewhat deformed in such that the intensities

may be a little bit higher than those in around 19--O hr interval, which may

Matsushiro Unclerground Cosmic-Ray Observatory 41

be very similar to that of SS-telescope at Sakashita (UENo, personal communi-

cation, 1988)'. As emPhasized by NAGAsHiMA et al. (1989), such a shape of the

daily intensity variation may indicate that the anisotropy or anisotropies respon-

sible for the observations would contain more than two anisotropies instead

of a single in free-space.

From the above descriptions of the underground observatory and some of

the observed results with the multi-directional muon telescope at the effective

vertical depth of 220 m.w.e. at Matsushiro for a full five-year period 1984

through 1989, we can summarize that;

(1) The underground cosmic-ray observatory was completed at Matsushiro,

Nagano City, Nagano Pref., Japan, in the year 1983, and the multi-directional

muon telescope has been installed at the effective vertical depth of 220 m, w. e･

' '

(2) The cosmic ray muon d6tectors used are plastic scintillator (1×1 m in

area and 10 cm thick slab) detectors, and arranged in two layers spaced by 150

cm vertically. In the detectors we have adopted a `double photomultipliers

system', and Sticceeded in obtaining better S/N-ratio and quite improved high-

volatage characteristics of the detectors. By taking two-fold coincidence be-

tween the detectors in two layers of 25 detectors each, we have constructed the

17 directional component-telescopes. We started the observations on March

22, 1984, and have continued them since that date upto the present with high

operation time-rate (complete days/total days in operation) of -v95%.

(3) We have observed some of the characteristi6 atmospheric effects at the

deep underground; large barometric coefiicients and also the semi-annual inten-

sity variations of muons. Those effects may have been weli explained by con-

sidering the atmospheric temperature effect in addition to the usual baromet-

ric effect on the observing muons.

(4) We have observed the solar diurnal variations of cosmic rays signifi-

cantly during 1984-1985, and determined the anisotropy responsible for them

as having the amplitude --O.35% in "-18 hr LT with high cut-off --300 GeV,

which is in accordance with that obtained in the lower energy regions <JS3･10i'

eV):

(5) We have also observed significant and persistent siclereal diurnal varia-

tions of cosmic rays with median primary energies of detection 6 . 10ii--1. 3 ･ 10i2

eV for a full five-year period 1984-1989. The multi-directional observation has

shown definitely that the observed vectors are originated from some sidereal

anisotropies in free-space. Less possibility of the contributionofatmospheric

'origin may be proved with the multi-channel observation. The following ob-

served facts may support the above conclusion that smaller amplitudes are ob-

42 MoRI,S. YASUE,S. SAGIsAKA,S. IcHINOSE,M. CHINO,K. AKAHANE,S. HIGUCHI,T.

served by the three north-pointing telescopes (N-, N2-, and N3-telescope), whose

asymptotic orbits are almost parallel to the Earth's spin axis, and also the anti-

sidereal diurnal vectors for all component-telescopes are small and insignifi-

cant.

(6) The present observed sidereal diurnal vectors show a good coincidence

with those obtained at the other underground stations and by air showr mea-

surements ( uO. 06% in amplitude with higher energies of detection) (NAGAsHiMA

et al., 1989).

(7) Rather larger amplitudes have been obtained by the south-pointing tele-

scopes, in particular the vectors of -vO. 12% or more in amplitude in "v2 hr

LST direction by S3-telescope. This may be consistent with the negatively de-

creasing spectrum of the sidereal diurnal variations obtained by long-running

air-shower observations at Mt. Norikura (NAGAsHIMA et aL, 1989).

(8) The observed sidereai semi-diurnal variations may also be significant,

showing lts phase at around 7 hr. These are in good agreement with other

observed results in a wide energy range 10ii-vlOi` eV (FuJil et aL, 1984).

(g) The daily intensity variations of cosmic rays in sidereal time of S- and

SS-telescopes at Matsushiro show a similar time-profile to those observed by

air-shower measurements at Mt. Norikura and at Baxan with higher energies

(>10'3 eV), characterized by a plateau during 19 hr to 8 hr and a V-shaped sink

with a bottom at around 12 hr in the variations (NAGAsHIMA et aL, 1989).

aoj We have tentatively examined `toward-away' field dependent sidereal

diurnal variations, and obtained the T-A vectors in -v21 hr LST, being somewhat

deviated from SWINSON's of "--18 hr LST in the lower energy regions.

Acknowledgements The authors would like to expresse thier great appreciation to many people

in Faculty of Sclence, Shinshu University, who kindly support and help us

to construct the present Matsushiro underground cosmic-ray observatory. The

authors have also been owed much to our students, particulariy Messrs. M.

OzAKI, H. KIMuRA, and T. IToH, who help us keeping continuous observations

wlth high operation-time. Thanks are also due to Prof. K. NAGAsHIMA of

Nagoya University for his continuous encouragement throughout the present

work.


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