Status and result from BESS

Adv.

0273-l

Spacr

Res.

Vol.17.

Rioted in

177(95)00684-2

No.

9. pp. (9)101-(9)110.

1996

Copyright 0 1995 COSPAR GreatBritain.Allrightsreserved. 0273-l

177196

$9.50

+ 0.00

STATUS AND RESULT FROM BESS BESS Collaboration* K. Anraku,l R. Golden,2 M. ImorL3 S. Inaba, 1 B. KimbelL N. Kimura,l Y. Makida,l H. Matsumoto,4 H. Matsunaga,3 J. Mitchell,5 M. MotokiP J. NishimuraP M. No~aki,~ S. Orito,3 J. Ormes,S D. Righter,5 T. Saeki? R. Streitmattex,5 J. Su~uki,~ K. Tanaka,l I. Ueda,3 N. YajimaP T. Yamagami,6 A. Y amamoto,l T. Yoshidas and K. Yoshimura3 1National Laboratory for High Energy Physics (KEK), Tsukuba, Ibaraki 305, Japan 2 New Mexico State University, Las Cruses, NM 88003, U.S.A. 3 University of Tokyo, Bunkyo-ku, Tokyo 113, Japan 4 Kobe University, Kobe, Hyogo, Japan 5 NASA, Goddard Space Flight Center, Greenbelt, MD 20771, U.S.A. 6 Institutefor Space and Astronautical Science (ISAS), Sagamihara, Kanagawa 229, Japan AIISTRAC’I

A balloon-borne cxpcrimcnt using a supcrconducling at making

a prccisc mcasurcmcnt

primordial

antimallcr

in the Univcrsc.

superconducting

solcnoidal

ballooning

was successfully

llight

prepnrcd

to bc carried out

experiment

of low cncrgy

magnet

solcnoidal

antiproton

The spcctromctcr and is realizing

magnet spcctromctcr

has a unique cylindrical a geometrical

carried out in northern

carried out with aims

is being

flux in cosmic rays and a highly configuration

sensitive

search for

associated with a thin

of 0.5 m*sr. The first scientific 1993, and the second flight is being

acceptance

Canada, in summer,

in summer, 1991. Pcrformancc of the spcctrometcr in the first flight and progress of the

arc dcscribcd.

INTRODUCTION The BESS expcrimcnt

(Balloon-Borne

planned

a fundamental

to invcsGgatc

expcrimcnd primordial

approach antimaucr

of prccisc measurcmcnt

with a Superconducting

on mattcr/antimattcr

superconducting

cnablcs a spcctromctcr

solcnoidal

magnet Spectrometer)

in the Universe

spectrum and highly

has a unique cylindrical

mognct, which allows

design having

solcnoidal

asymmetry

of low cncrgy anliprolon

in cosmic rays 12-51. The BESS spcctromacr

with a thin (transparent) This configuralion

Expcrimcm question

[l]

sensitive

was

through

an

search for

dctcctor configuration

cosmic rays to traverse the spectrometer.

a large gcomctrical

acceptance

to search for evidence

of

in antiparticle/particle ratio in one-day flight. Dcvciopmcnt of the spcctromctcr has been carried out in collaboration amongst University of Tokyo, KEK, ISAS, New Mexico State Uni\tcrsity, Kobc University and NASA Goddard Space Flight Center. The BESS fist scientific flight (BESS-93) was succcssl’ully carried out from Lynn Lake, Manitoba, Canada, in summer of 1993 as a balloon cooperation program bctwccn ISAS and NASA. Performance of the spcctrometcr and progress of the experiment are dcscribcd in the following sections. The second flight is being prcparcd at Lynn Lake in summer of 1994. antimatter

WSS

in cosmic

rays at a sensitivity

lcvcl

of

10T6 LO 10e7

SPIXTROMET~R

The BESS spcctromctcr was specially dcsigncd to rcalizc a large gcomctrical acceptance using a thin superconducting solcnoidal magnet and a cylindrical dctcctor configuration. The particle detector consists of drift chambers, time-of-flight counters, and data acquisition system [SJ. All of the components are arranged horizontally in the cylindrical configuration shown in Fig. 1. The spccvomctcr struclurc including the magnet wall and pressure vessel is dcsigncd to bc as transparent as possible to cnablc the cosmic rays to traverse the spectrometer system. The cylindrical spcctromctcr configuration is efficiently used in the compact volume to provide the large geometrical acccptancc of 0.5 m2sr. The main paramctcrs of the spcclromacr are summarized in Table 1.

K.AN&U et al.

(9)1(=

Scinlillalian

SuperconductIng

Counters :

\

Magnet

Outer DC

Inner DC

Layout of the BESS spcctromctcr.in

Fig. 1.

cylindrical

configuration

with a thin supcrconducitng

magnet.

The superconducting

magnet

magnet wall transparency ray particles

passing through

superconductor field.

A Iicld uniformity

As a central particle transvcrsc

detectable

rigidity

a solcnoidal

wall [6,7].

The coil is wound

field

1 tesla with minimizing

of

length (Ai),

in order to allow

by using aluminum

stabilized

tracking

dctcctor,

magnet.

field.

in a warm, cylindrical

cooled through an aluminum

bore (tracking

volume)

outer support cylinder,

a cylindrical

drift chamber

(known

of 85 cm in diameter

as the JET chamber)

The JET chamber makes prccisc mcasuremcnts field

providing

continuous

Each of the track mcasurcmcnts

of 300 GV.

1

TABLE

An axial position

rcsolulion

measurement

is located

of the particle

of a particle’s

is made with 200 pm precision of 1 cm may bc expcctcd

trajectory

giving

Gcomclrical

by using “charge division”

0.5 m2sr

acccptancc rigidity

Anti proton dc[ccLablc rigidily Anti helium dctcclablc

in tracking region

> 1GV

rigidity

1-2kHz 100 - 200 Hz

Eveni rate to bc rccordcd Ma[crial

- 1.2 GV

0.6

rate

Sensitivity

300 GV

region

for antimatter

starch

in the spcctromctcr

(per wall)

10-6 - 10-7 7.5 g/cm2

Prcssurc Vcsscl Dimensions

1.5 rn$ x 3.2 m

Total spcctromctcr

2.1 ton

weight

in the

a maximum

Main dcsign paramclcrs of the BESS spectrometer.

dctcctablc

in the

trajectory in a

_______________ _____-. _________.,________

Trigger

NbTi/Cu

which conducts heat to

read-out.

Maximum

the

cosmic

in the dcwar located at one axial end of the solenoid coil.

to the magnetic

magnetic

to provide

length (Xo) or 0.04 interaction

of +/- 15 “/n is obtained

of the solenoid

solcnoidal

dcsigncd

with 4 layers in the central part and 8 layers at both axial ends to shape the

The coil is indirectly

the liquid helium (LHc)

direction

the magncl

in a coil configuration

and 1 m in Icngth.

warm-bore

is specially

to bc 0.2 radiation

1.2 kW Power consumption ________________________________________~~~~~~________~___~~~~~~~~~~~___~_~~~~~~~~~~~~~~ ___-___________

(9)103

Status and Result from BESS

Surrounding

the JET chamber, both inside and ouddc

are located. Those arc socially

dcsigncd

hence the charge of the incident cosmic-ray chambers incident

have radially particle

will

double

azimuthal

direction.

for USCin the on-lint

provide

two of thcsc double

The subdivided

an accurate axial (z) position

operated with “slow gas”, C02+Ar(lO%),

Time-of-Flight

(TOF) scintillation

six paddle configuration, trigger

at

chambers

photo-multiplier

ends of the scinlillalor

resolutions

to make the rapid identification pad” read-out.

paddles

provides

a gcomctrical

direction.

The scintillation

tubes (PMT

under magnetic

signal initiated

field cnvironmcnl

process, and provide

identification.

in TDC (time to digital

thresholds

to their cncrgy

loss in the scintillalor.

of 0.2 T.

v&city

flight.

in four and

of 0.5 m2sr with a cosmic ray is viewed

through light-guides The TOF counters

and cncrgy-loss

convcrtcr)

feature to

All of the chambers are

in the paddle (NE102A)

: Hamamatsu H26l I-SXA)

An

of the track and its

during the scientific

acceptance

and Those

of 300 pm in the

The IDC and ODC have a further

of 230 brn by using “vcmicr

trigger signals to start the data acquisition charged nuclei, according

(circumferential)

having

1 atm. absolute without gas circulation

which

rate of a few thousands per second.

magnetic-field-resistant

summarized

deflection

(track trigger).

counter hodoscopcs arc located at top and bottom of the spccrrometer

respectively,

The dual lcvcl

cvcnt sclcction

cells in the azimuthal

layer drift

system and cvcnt sclcction.

resolution

of the sign of the angular

a fast on-board

small cells arc csscntial

triggering

“cell type” drift chambers (IDQODC)

ordinal

identification

and to provide

layers of about 5 cm drift

cncountcr

deflection

the solenoid,

to make a quick

identify

generate initial

measurements incident

by

at both axial

singly

for particle or multiply

Main parameters of those detector components

are

in Table 2.

TABLE

2

Main design paramctcrs of the dctcctor components.

____-------_____________________________~~________________~~~~~~______~~~_~___________~---~~~~~~~~_____~~~~~~_. .SuncrconductincT

MaPnct (MAC):

Central magnetic

Opcriltional

1.2 tcsla

field

current

520 A

Stored cncrgy

0.X MJ

Material

4 s/cm*

in the wali

Tr:msp:ucncy (Rxl.

Icngth)

0.2 x0

Coil size LHc RcIN

1 m@x 1.3 m inter-period

Central Tracker (JET) Tracking

(Capacity)

volume

0.75 m@ x 1.0 m

point (max.)

Meximum

drift Icngth

50 per track +I- 95 m

T;Il;l;;$

ID

;

c 0

1” / z)

Angle covcrcd

0.20 mm / 10 mm 78 deg.

# ofcclls

per chamber

1 l/l2

Tracking

mean radius

0.393fl.4

Axial

tracking

(150 1)

days

;

Sampling ,,,;rp;;l:, 7

5 -6

region

11 m

Im

Spatiill resolution (Q/z) Outer Drift Chambers (ODQ

0.3 mm / 0.2 mm 7 1.5 deg.

Angle covcrcd # ofcclls

per chamber

15/16

Tracking

mean radius

0.605/0.627

Axial

tracking

region

Spatial rcsolulion (Q 1 d Time of Flirrht Counters (TOF); Solid angle covcrcd Stint. paddle config.

m

1.08 m 0.3 mm / 0.2 mm 0.5 m2sr (top/hot)

416

Mean radius of the paddle

0.68 m

Paddle size (w x z x t)

0.2 x 1.1 x 0.02 m3

Time resolution

200 pscc

Block diagram of the cvcnt processing subsystem.

Fig.2. The BESS

data acquisition

communication

system

consists

18.91. Each subsystem

other sub-systems

through

of subsystems

is controlled

serial bus-lines

for event

process,

by a microprocessor

(Omni-net).

data storage,

(NEC-V40

monitoring

and

or V50) and is linked

with

Event data from the dctcctors are selected and compressed

in the event processing subsystem, and arc tronsfcrrcd

to the

data

storage subsystem consisting

of dual EXABYTEs

with 8 mm lapcs, as shown in Fig. 2. The cvcnt sclcction and data reduction

arc proccsscd through three stages of

(i) Ist-lcvcl

(Software)

(TOF) trigger,

(ii) 2nd-lcvcl

trigger starts the data acquisition trigger provides signal.

dala or' the

dcllcction

The master trigger

rcccivcs

event data to bc sent to further memories through

(ROM).

computer

charged

on momentum

carefully

decision

particle

cvcnt

and other data characteristics.

and the IDC/ODC algorithm with

track data and quickly

(paramctcrs

the single

track (clean event)

(EXABYTE).

time and, thcrcforc,

negatively

charged

the maximum

limited by this process time.

In the prcscnt system, the maximum

The tape capacity of 10 Gbytcs will allow the data recording

For the purpose to normalize

anti-particlc/particlc

rccordcd scientific

through a simple count down process without flight as well as house-keeping BESS-93

spectromctcr

by using

any cvcnt sclcction. any bias

TOF trigger

may be cycle

rate is also

is 200 Hz with the averaged for a period of 20 hours. sample

The full data from all detectors are

. In parallel, indcpcndent

system for monitoring

particles

bias in the sclcctcd data, non-biased

sample data (C 1 %) are

gcncral spectrometer

performance

during the

ba.

balloon llight

was successfully

carried out in northcm Canada, in summer,

was launched by using a balloon of 29 MCF from Lynn Lake, Manitoba,

It achieved to an altitude of 36.5

shown in Fig. 4. The scientific

observation

of 14 hrs. The IOR cosmic rays were passing through the spcctromctcr

selected wcrc storagcd into the on-board magnetic tapes with a data capacity of 5 Gbytes. around Pcacc River, Alberta,

in the afternoon

1993. The BESS

in the evening on July 26. Figure 3

shows the BESS payload suspcndcd by a launcher to bc launched at the Lynn Lake airport. km (120 kft) with a residual prcssurc of 5 mbas shcmntically carried out for a duration

may be selected analysis

PERFORMANCE

FLIGHT

The first BESS scientific

cvcnt rate (storagcd)

ratio or to calibrate

arc taken without

to the ground through the tclcmctry

selects the

The present data acquisition

data size of 500 bytcs/cvcnt.

transmitted

track

in tables) stored in read-only-

is made with software

The low energy

data rccordcr

1 mscc mainly due to the cvcnt building

data (1 - 2 % ) after the TOF triggers

The TOF

The IDC/ODC

f2irm). The prccisc on-line analysis can bc made to select the events

sclcctcd and bc stored into the on-board

time is about

event filtering.

single or multiple.

of the charged particle tracks, associated with the TOF trigger

later. The final cvcnt sclcction

banks in the cvcnt filter (Transputcr

depending

and (iii) 3rd-lcvcl

the TOF charge-trigger

process, rcfcrring

;IS discussed

process

trigger,

angle (polarity)

The ncgativcly

this trigger

(Master)

cycle and also provides charge separation;

was successfully

and 4 x lo6 events

The ballooning

on July 27, and the BESS payload was safely recovered

was terminated

in the next day.

Status and Result from BESS

Fig.3

Balloon launching at Lynn Lake in BESS-93.

Atomsphere

___----

(9)105

Limit

II

_-_-----------r--FLI\,_________

Cosmic

Rays

--

Balloon

1174

Termination

P

-----c-__._,

Altitude,

36.5

km

treasure,

5 mbar

//

./

1’

piiimza] ‘. ‘1

I’G5J E

1’

Data Transfer

by Telemetry

Telemetry Alberta.

Fig. 4.

CANADA

Station

Manitoba.

CANADA

BESS-93 flight with an alutitude of 36.5 km from Lynn Lake to Peace River

Figure 5 shows house-keeping data for the magnetic field, the TOF/PMT temperature and the JET chamber temperature according to the ballooning process. Fig. 6 shows the gravity acceleration load measurement in typical cases during the BESS-93 ballooning process. Table 3 gives the ballooning and operational performances of the spectrometer in BESS-93. Resolutions of detector componencts were determined from data analysis using flight data of singly charged, high cncrgy particle resulting straight tmck even in the magnetic field of 1 tesla. To obtain a time resolution of 290~s to the TOF, the event path length between the top and bottom TOF counters was precisely calculated by using the drift-chamber data and its extrapolation to the TOF counters. The time difference measured between the left and right PMTs in the scintillator paddle was also used to provide a consistency check of the axial position. Based on those result, the maximum dctcctable rigidity of 200 GV has been verified and the performance in particle identification below 1 GeV/c has been verified.

K. Anraku et al. 60

50

40

30

20

10

0

35

25

15

Time

45

[hour]

Fig. 5. Payload house-keeping

data in BESS-93.

12

0 Launching

Tsrminatian

Recovery

Landing

Balloon Flight Process Fig. 6.

Accclcration

loads rccordcd during the flightprocess.

PROGRESS IN DATA ANALYSIS Based on the spcctromctcr

pcrlbrmancc

carried out to the point of starching reduction I)

was made according

N-track = I:

dctcrmincd

from the BESS-93

flight data, scicntiPic data analysis has been

for candidates of low energy antiprotons

to the following

off-lint

below 1 GeV/c.

The preliminary

cvcnt sclcction process.

Clean cvcnt having single track in JET and IDC/ODC.

2) N-good=l:

At Last 14 wires hit (N-hit>=14)

3) N-TOF=IIl:

Only one pair of TOF scgmcnts at top and bottom have PMT signals at both right and left PMTs, and position

should be consistent with JET and IDC/ODC

particle should bc downward 4) $,q<

5:

5) IZvk - Ziofi c 70

The ~$9

in JET chamber and the ratio of N-hit to N-should

moving

z=0.8.

track (r@)signals, and

(to rcjcct albcdo).

for the fit of the track in r@ plant

in the JET and IDC/ODC

is less than 5.

mm:: The cvcnt position of the TOF signal in z coordinate should bc consistent with position cxtrapolatcd IDC/ODC.

dctcrmincd

from left and right PMT

from the uack signals fit from JET and

data

Statusand ResultfromBESS

TARLE

(9W

BESS-93 ballooning & spectromctcr performances.

Locations

(launching) (landing) Cut-off Rigidity Floating altitude Residual air Floating time Payload weight Suspcndcd weight (w/ ballast etc.) Balloon size

56” 53’ N, 101” 25’ W 57” 52’ N. 1170 30’ W 0.5 GV 35.4 - 36.6 km 5mb 17 hrs 2,060 kg 2,720 kg 29.47 MCF

Gcomclrical acccplancc Central Magnetic field Scientific obscrvalion time Data taking efficiency TOF (Lcvcl 1) trigger rate Master (Lcvcl 2) trigger ralc Cosmic rays passing through. spccvomctcr Events sclcctcd and storagcd TOF time resolution spatial rcsolulion (z, timing / dE/dx) JET spatial resolution (x I z) sampling points (x,y I z) IDC/ODC spatial resolution (@I z) Max. Dctcctablc Rigidity Tcmpcraturc stability

0.5 m*.sr 1T 14 hrs 70 % >2kHz > 80 Hz 1OR triggers 4 x IO6 events 290 ps 30 mm / 120 mm 0.18mm20mmx 16~s 24/ 16mm 0.21mm / 0.23 mm 200 GV 40 - 10 “C

For events which passed the above cuts, masses (m) wcrc calculated by using the momentum (p) and the velocity (p) of the cvcnt according to the following equation;

m*=tl/p*- ljxp*. where p was dctcrmined from JET/lDC track curvature in B field. The velocity square , p*, was calculated from the time of flight (7) bctwcen TOF at top and bottom according to p = L/CT, where L is path length and c is light velocity. p* was also indcpcndcntly calculated by using dE/dx signals in TOF according to dE/dx = (z*/p*).f(p). Figure 7 shows mass scaucr plots for positive parliclcs that have momenta below 1 GeV/c. The vertical axis indicates mass square, m*, calculated by using the dE/dx signal from the TOF paddles and the horizontal axis indicates m* calculated from the time of flight bctwccn the lop and bottom TOF counters. In order to separate particles corresponding to protons from other particles, events observed in a region of 1.4 GeV* > m*(dE/dx)> 0.5 GeV* were sclcctcd. This cut cffcctively eliminates background particles such as e+, IF+, p+ and heavier particles such as Hc, etc. Figure Bshows mass histograms (hatched) for positive particles resulting from this selection for each bin width of 0.1 GcV/c. For compnrison, data without this cut are also shown as the unhatched histograms. By using the same method, m* scatter plots arc made for ncgativc particle, as shown in Fig. 9, Two clear events, well separalcd from c-, II-, pL- cvcnts, can bc seen bctwccn m* region bctwecn 0.9 -1 .O GeV* on the horizontal axis. Figure 10 shows mass square histogram for negative particles in four momentum bin with 0.1 GeV/c width, before and aficr cutting data for m*(dE/dx) > 1.4 GcV* or m2(dE/dx c 0.5 GcV*. In a momentum range of 0.9 - 1.0 GeV/c, two well scparatcd particles arc dctcctcd at the m* corresponding to antiprotons. We consider that these events are the antiproton candidates dclcclcd during in lhc BESS-93 balloon flight in Canada. Figure 11 shows an event display for one of the antiproton candidates at p = 0.96 GcV/c, dctcctcd through the data reduction process dcscribcd above. An cvalualion of ihc dctcction cfficicncy for antiprotons and precise normalization to proton flux (the corresponding number of protons is in a range of 105) arc being carried out. Corrections for secondary protons and antiprotons produced in air above the spcclromctcr or produced in the spcctrometcr system must be determined. Studies are also under way on annihilation processes of low energy antiprotons in the spectrometer that would affect the detection cfficicncy. .Wl1&D-H

Fig. 1.

1

M* scatter plot, M*(dE/dX) V.S.M*(tof)nt p
Fig. 8.

M* disrtograms bctwccn 0.6cpcl GeV/c in 0.1 GeV/c bins with dE/dX cut (hatched) and without cut (un-hatched).

; : ..f

0.6

-

0

-

4.3

-

.:,

:

i

Fig. 9. M* scatter plot for ncgativc particlcs with pcl GcV/c.

Fig. 10. M* histrogram b/w 0.6~pcl.O GeV/c in 0.1 GcV/c bins with dE/dX cut (hatched) and without cut (unhatched).

(9w9

11. An antiprotons candidate cvcnts at p=O.961 GeV/c.

Fig.

Data analysis to starch for anti helium is in progress and it is cxpcctcd anti-hclium/hclium

SUMMARY Balloon-borne

with a superconducting

asymmetry

with a thin superconducting

balloon

1993. The spcctromctcr at an altiludc

essentially Scientific

in the Univcrsc. solenoid

Ilight

magnet.

(BESS)

data analysis

curvature

a gcomctrical

configuration

acceptance of 0.5 m2sr

associated

with a magnetic

for anti helium

is continuing.

Further

their abundance rclativc

capability antiproton

rccordcd

onto magnetic sampling

dctailcd

two antiproton

in the BESS-93

antiproton

flight.

for a flight

from north Canada to Greenland

candidates

events.

have been detected these

range.

dctcction

sensitivity

and sensitivity

to the trigger system and the

in the summer of 1994 and beyond.

by using acryiic Chcrcnkov and/or in Antarctica

curvature

is being carried out to verify

Improvcmcnts

The second

counters is planned to be carried out at

Lynn Lake, Canada, in summer of 1994. In the longer term, further upgrading flighls

14 hour include

to protons in the same momentum

arc being implcmentcd identification

during

tape for data analysis

of positives

data analysis

arc planned to improve

starch based on the cxpcricnce

identification

cvcnts

At this stage of the analysis,

in the range of 0.9 - 1 .O GcV/c.

with improved

carried out from Lynn Lake to Pcacc River, Canada, in summer,

cvcnts and a partial or fractional

Further up-grades of the BESS spcctromctcr

duration

is being carried out to investigate

has a unique cylindrical

well and IOx cosmic rays passed through the BESS spectrometer

of 36.5 km. The four million

candidates and to dctcrminc

flight

It rcalizcs

was successfully

pcrformcd

all the ncgativc

with momenta

particle

magnet spcctromctcr

The spectrometer

I 1csla.m in the spcctromctcr.

The first scientific flight

for the upper limit in

AND FU’I’URE PLANS

cxpcrimcnt

maucr/amimattcr impulse of

to achieve a sensitivity

ratio to bc a lcvcl of 1O-5 as a result of data analysis in the BESS-93.

possibly

of the dctcctor is under way for long in 1996 or 1997.

(9)llO

K. Aru&u et al.

ACKNOWLEDGMENI The authors would

like to thank Dr. V. Jones of NASA

would cxprcss their sinccrc apprcciadon The authors deeply thanks Prof. R. Akiba, for lhcir continuous General

of KEK,

encouragement.

supporl Prof

Hcadquartcrs

10 NASA/GSFC/WFF Director

and encouragcmcm.

H. Hirabayashi,

Prof.

Balloon

for his support and encouragement. They office

and NSBF for iheir skillful

Gcncral of ISAS, Prof. A. Nishida The authors

S.Koizumi

This work is supported by Inlcmationnl

would

and Prof.

Scientific

support.

and Prof. H. Okuda of ISAS

like to lhank Prof. H. Sugawara. S. Iwata

of KEK

for

Rcscarch Grant in Monbusho,

their

Director

support

and

Japan.

REFERENCES 1. J. F. Ormes and R. E. Strciimaucr,

Physics, World Scicntilic, 2. S. Orito, Anliprolon Workshop,

614-

and antimaucr:

KEK Rcporl,

4. A. Yamamoto Space Rcs. U(2), 5. A. Yamamolo

for primordial

A balloon cxpcrimcnt

Ill-

KEK-87,

3. J. Ormcs cl al, Scorching with a superconducting

Starching

anlimaucr,

Ctrrrenr Topics in Asfrofundamental

, (1991)

for primordial

solcnoidal

anlimaucr

spccuometcr

CLal, Balloon-borne

with the model solenoid, Proc. of ASTROMAG.

, (1987) at discancc of 30 LO300 Mpc using a balloon borne experiment

(BESS), Proc. ICRC, Calgary,

expcrimcnt

with a superconducting

(1993).

solcnoidal

magnet spectrometer,

Adv.

75-87. (1994) Editor,

Balloon-hornc

cxpcrimcnt

with superconducting

magna

spcctrometirs,

Proc. of the 3rd

BESS workshop, KEK Proceedings 92-2, I- 173, (1992) 6. A. Yamamolo

CLal., Conceptual

design of a thin superconducting

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