A search experiment for cosmic ray magnetic monopoles was performed by means of atomic induction mechanism by using He mixture gas proportional counters of the calorimeter (130 square meters sr) at the center of the Akeno air shower array. In 3,482 hours operation no monopole candidate was observed. The upper limit of the monopole flux is 1.44 x 10 to the minus 13th power cm-z, sec -1, sr-1 (90% C.L.) for the velocity faster than 7 x 0.0001 c

Hara, T.

Hayashida, N.

Honda, M.

Kamata, K.

Kobayashi, M.

Kondo, T.

Matsubara, Y.

Mori, M.

Ohno, Y.

Tanahashi, G.

English

NASA Technical Reports Server

218
HE 6. i-2
Magnetic Monopole search by 130 m2sr He Gas Proportional Counter
T.Hara, N.Hayashida, M.Honda, K.Kamata, M.Kobayashi _, T.Kondo _,
Y.Matsubara _, M.Mori _, Y.Ohno, G.Tanahashi, M.Teshima _ and
Y.Totsuka _*_
Institute for Cosmic Ray Research, University of Tokyo, Tanashi, Tokyo,
188 Japan
National Laboratory for High Energy Physics, Oho-machi, Tsukuba,
Ibaraki, 305 Japan
*_ Department of Physics, Kyoto University, Sakyo-ku, Kyoto, 606 Japan
_ LICEPP, Faculty of Science, University of Tokyo, Bunkyo-ku, Tokyo,
133 Japan
A search experiment for cosmic ray magnetic monopoles has been
performed by means of atomic induction mechanism by using He mixture gas
proportional counters of the calorimeter(130 m_sr) at the center of Akeno
AS array. In 3,482 hours operation no monopole _@_ndid_te i_ observed.
The upper limit of the monopole flux is__.44xlO- _cm- sec- sr-_(90%
C.L.) for the velocity faster than 7xlO c.
i. Introduction.
The magnetic monopole has been one of the most charming objects not
only in experimental but also theoretical physics. There has been so
many monopole search experiments using many kinds of detectors. However,
mass of monopole which grand unification theory suggests is too heavy to
accelerate a monopole up to relativistic speed with the Galactic magnetic
fie_d. In this case the monopole is expected to have a velocity about
lO--c(where c is the light velocity) or less. For such slow monopoles,
the availability of usual detectors except super conducting coil is not
clear for monopole detection because the energy loss of such slow
monopole is expected to be extremely small in the matter. However, Drell
et al. suggested that the atomic induction mechanism in Heliwm or
Hydrogen gas is effective for monopole detection down to lO--c of
monopole velocity(l). In this paper we report a result of slow monopole
search experiment with He mixture gas proportional counters using the
above mechanism.
2. Apparatus and experiment.
__ For monopole search experiment, we
use the proportional counters of the
._ calorimeter at Akeno air shower -
75cm _ array(2). The proportional counters,
._ / > each unit size is lOcm x lOcm x 500cm,
/ concrete shieldings and arranged to
/ lie in the same direction. For
< _ monopole search experiment we changed
_ // the proportional gas to He mixture
< gas(He85% + CH415%) and provided two
/ more layers of the same proportional
counters on the top of the
Fig.l Apparatus for monopole calorimeter. The rough sketch is
detection, shown in fig.l. Though the monopole
https://ntrs.nasa.gov/search.jsp?R=19850027815 2020-03-20T17:10:15+00:00Z
219
HE6.1-2
excites only He-atoms by the atomic
.... , ..... induction mechanism, added inner methane
molecules produce free electrons in the
_ 100 f 130 m2sr proportional counter when they collidewith the excited He-atoms through Penning
effect. With the process, we can observe
t the signal of the monopole from the
10
proportional counter.0
The experiment has been continued sincei I t t ' i i J ! s
I0-3 10-2 I0-t. the beginning of Nov. in 1984.
monopoJ.evelocity/3 The apparatus is triggered when any
counter in any trigger block unit, which
Fig.2 Aperture of the detector, is composed of adjacent i0 proportional
counters in the same layer, produces a
....' J ' ' i
signal larger than i0 times of minimum
--_ ionization of single cosmic ray muons in
each layer of the counters. In order to
decrease shower events, the trigger pulse
c_. is killed whenever more than 2 trigger
o_ " /It/} !t block units in any layers satisfy the
/ trigger condition('shower veto'). With
-2 the threshold of i0 times of the minimumo
L-c_ ionization, monopol_s_ with the velocity
faster than 4.1xlO c are expected to be
L- /
"_ /} detected by our He mixture proportional
_oo _ counters from the comparison of electronpairs produced by relativistic cosmic
-3 _ ray muons with that by monopoles which is
estimated by the revised calculation of
4 Drell et al.(3) assuming 83% of Penning
t l n , ._I ,
--3 .2 effect(4) .
The aperture of the apparatus for both
* Log(inpuT _) upward and downward monopoles, which
fig.3 Availability for the varies with monopole's velocity, is
determination of calculated by Monte Carlo simulation
monopole velocity, assuming the arrangement of the
apparatus, th_ trigger condition and the
trigger gate time(46}]s), _8_d found to be 130m-sr for monopoies of the
velocity larger t_an 7xlO-_e. The detectable minimum velocity of the
monopole is 5xlO-_c as shown in fig.2.
" We record the pulse height of each proportional counter and the time
difference(resolution time is 0.5_s) between the signal from each trigger
block and the main trigger signal, with which we can estimate the
velocity of the monopole, in magnetic tapes by using the registration
system of Akeno air shower array. The time response of our proportional
counter is slow because of the drift velocity of electron in He gas(about
ips/cm). We measured the time response of our counter in the same
condition as that of the experiment by using pion beam(2 GeV) from the
KEK PS Accelerator as a function of the impact parameter to the anode
wire. Using the data, a Monte Carlo simulation was made on the
availability of our apparatus for the determination of monopole velocity.
In our apparatus we can determine monopole velocity only projected to
the vertical plane perpendicular to the long axis of proportional
220
HE 6.1-2
counters. Therefore, the velocity thus determined is always less than
the true velocity. The simulation results are shown in fig.3 which
indicates that we can determine the velocity within the error _f 50% for
the monopole passing through with the velocity less than 2xlO--c, but for
faster monopole, the systematic error is too big to determine the
velocity. Undeterminable region of the velocity for the apparatus was
also checked experimentally by using the data triggered by relativistic
cosmic ray muons. Both data are consistent with each other.
3. Analysis and results.
Almost all the triggered events are accidental ones caused by radio
isotopes contained in the concrete or the wall of our counters or small
air shower events escaped from 'shower veto'.
First of all, we reduce these events by off line computer analysis by
checking that the 'on' counters make a straight line within the allowance
of 20cm displacement and the number of 'on' counters in any layer does
not exceed more than three.
Secondly the events survived the computer reduction are checked with
more severe criterion for making a straight line(lOcm allowance) by
visual scan on graphic display and then are carefully studied for both
the energy loss along the line and the timing data. If the monopole
passes through the apparatus, the energy loss in each counter, which
depend on the velocity of the monopole, is almost same to the others
because the fluctuation of the energy loss by atomic induction mechanism
is considered to be small. On the other hand if the apparatus is
triggered by small showers or surrounding backgrounds, the signal from
each counter is expected to be different in the magnitude from the
others.
In fig.4 are shown the event
" ', , , , , _ . , _ , , survived the visual scan. The
- velocity of each event is determined
__. by _2 -fitting using the timing data
which are sometimes lacking in one ,
I03 ,.'/""_ or two counter layers because of
.-_ / unresponse of timing circuit and
m ,' is plotted the plausible lowest
/" value even if the gC_-minimum can not "
102
o /" be found. Accordingly we cannot
ill _ _ rule out that all these events have
o  tll vo oc t,to101 _ Th vertical bar of each event inthe figure shows the one standarddeviation f energy losses in 6
layers of the counters. Except two
, , 1 , , I , , I , , events these are considered to be
10-5 10-2 10-I produced by small cascades developed
ve[0cityp (=_/c) in the concrete from the signal
transition in successive counters.
Fig.4 Events survived to the final The exceptions in which the signals
analysis, of all layers are almost the same to
one another may be caused by
successive cascades by high energy muons. In any case their energy
losses are still too small comparing with the calculation by Droll et
al.. We can see that there is no monopole event in our data.
221 HE 6.1-2
4. Conclusion.
Up to now we have no monopole
I0-" .event in the observation time of
i, , , .... ],,. G_.o_m_ '
J3,482 hours. Since the aperture ofinduc_ian I
(e_12verLl____.l._.__.__.._ . J our _onopole detector is about
"'--_-_g;._llt_l \/ /, .. ] 130m-sr, we have t_._ upper li_it ?f
' ! _ /Bir'e'-' ]the flux 1 44 xlO--- cm--sec--s--. __
\ / Ma for monopoles faster than 7xlO c inIO-'au _ _ \ saimo 190% c fidence lev l. We show more
Kaji¢lo\ I'; \ _I / Jldetailed flux upper bound in fig. 5
'asa functionofmonopolev locity
.....8ar.wlc_<_-...._ .,, /
• Our fesu_t._; J taking into account the
T _ aperture(fiz.2). In fig.5 we also
• 1
I0-_ I_I // ] show the results of other
= < experimental groups(5) for the
Krisnnaswamy comparison.
= Recently, Ahlen et al.
° \ ,/o.:10_i4 investizated the availability ofA[exeye' these detection methods for monopole
G detection(6). They conclude that
scintillation detectors can not be
applied to monopoles slower than
6xlO _e and Argon counters to|0-!-_ , , l , _ I , , 1 _ r ' , _ -
I0 -_. i0-_ I0-_ 10-z i0-1 2xlO c. For other experiments in
'monopoL.eveLocity_ fig.5, we show the results only for
the applicable velocity regions in
Fig.5 Upper limit of monopole flux. accordance with the discussion by
Ahlen et al.. It is seen that our
upper bound shows the lowest value in the velocity region slower than
i0 -c by counter experiment.
5. Aekngwledzments.
. The authors would like to thank the member of Akeno AS group for their
help. We also thank the member of accelerator division of National
Laboratory for High Energy Physics for the use of the accelerator beam.
Analysis and calculation were done by FACOM M380 at the computer room of
" Institute for Nuclear Study, University of Tokyo.
References
i. DrelI,S.D. et al. Phys. Rev. Lett. 50 644(1983)
2. T.Hara et al. 17th ICRC II 373(1981)
= 3. KrolI,N.M. et al. 'Monopole 83' ed. Stone,J.L. Plenum.(1984)
4. Jesse,W.P.J. Chem. Phys. 41 2060(1964)
5. Groom,D.E. et al. Phys. Rev. Lett. 50 573(1983), Higashi,S. et al.
. private communication(1985), Tarle,G. et al. Phys. Rev. Lett. 52
90(1984), Bartelt,J. et al. Phys. Rev. Lett. 50 655(1983), Mashimo,T.
et al. Phys. Lett. 128B 327(1983), Bonarelli,R. et al. Phys. Lett.
126B 137(1983), Krishnaswamy,M.R. et al. Phys. Lett. 142B 99(1984),
Alexeyev,E.N. et al. 18th ICRC 5 52(1983), Doke,T. Phys. Lett. 129B
370(1983), Kajino,F. et al. private communication(1985), Barwick,S.M.
et al. Phys. Rev. D28 2338(1983)
6. Ahlen,S.P. and Tarle,G. Phys. Rev. D27 688(1983), Liss,T.M. et al.
Phys. Rev. D30 884(1984)


Magnetic monopole search by 130 m(2)sr He gas proportional counter

Magnetic monopole search by 130 m(2)sr He gas proportional counter

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