Slow magnetic monopoles in cosmic rays have been searched at sea level with the detector which consists of seven layers of proportional counters filled with a mixture of He + 20% CH4. The velocities and the energy losses of the incident particles are measured. The upper limit of flux for the monopoles in the velocity range of 1 x 0.001  Beta  4 x 0.001 is 2.78 x 10 to the minus 12th power square centimeters sr sec of 90% confidence level

Cho, C.

Higashi, S.

Hiraoka, N.

Maruyama, A.

Ozaki, S.

Tsuji, K.

English

NASA Technical Reports Server

2|4 HE 6.1-1
SEARCH FOR MAGNETIC MONOPOLES USING
PROPORTIONAL COUNTERS FILLED WITH HELIUM GAS
C. Cho, S. Higashi, N. Hiraoka, A. Maruyama, S. Ozaki
T. Sato, T. Suwada, T. Takahashi and H. Umeda
Physics Department, Osaka City University
Sugimoto, Sumiyoshi-ku, Osaka, Japan
K. Tsuj i
Physics Department, Kinki University
Kowakae, Higashi-Osaka, Osaka, Japan
ABSTRACT
Slow magnetic monopoles in cosmic rays have
been searched at sea level with the detector which
consists of seven layers of proportional counters
filled with a mixture of He + 20% CH 4. The
velocities and the energy losses of the incident
particles are measured. The upper limit of flux
for the monopoles in the velocity range of
1x10-3<_<4x10 -3 is 2.78x10-12/cm 2 sr sec of 90%
confidence level.
I. INTRODUCTION
The prediction of the primordial production of super
massive magnetic monopoles (MC2_1016GeV) by Grand
Unification Theories (I), and of the subsequent acceleration
of \these monopoles to the velocities of v=6c with
_Ix10-3_1x10 -2, have caused interest in experimental search
for slowly moving magnetic monopoles in the cosmic rays (2). o
Many methods to detect the monopoles have been used, but all
experimental results except Cabrera (3) are negative.
First, we have searched the monopoles with five layers of
proportional counters filled with a mixture of 90% Ar + 10%
CH4, to measure velocity by time-of-flight method and track
positions for incident particles (4). The upper limits of
the flux for the monopoles in the velocity range of
1x10-3>B>4x10 -3 at 90% confidence level is
1.5x10-12/cm 2 sr sec, which is slightly higher than the
value reported in (4), because of the inc-ease in running
time. Second, mixed gas of 80% He + 20% CH 4 is used for the
counters, since a CH 4 molecule is ionized through the
Penning effect by a He metastable state excited by the
monopole. More two layers of proportional counters are
added to measure energy losses and track position along the
https://ntrs.nasa.gov/search.jsp?R=19850027814 2020-03-20T17:10:13+00:00Z
216 HE 6. I-I
wire. Experimental results at second stage are described in
this paper.
2. EXPERIMENTAL APPARATUS
The apparatus consists of
seven layers of proportional
counters, hhe aperture of /////////////_
2.24m2sr, 3m height as shown /J/Jf/_///JJ
in Fig. I. Each of 2 and 6- Loyer
1layer has an area of
120cmx5OOcm, the others 5[0_ .,..__
120cmx450cm. Each layer
consists of 12 counters; each
of which is made of a 50 /_ 's---_ll _ l[_ee_ _/'_4'' _re_
rectangular alminium tube
with a cross section of
5cmx1Ocm" Tw° kinds °f 5S0 /,,_5. _
counters are used; a T- 300 ....
counter which has two anode
wires of 5Ou_ g°id plated _.5 '_l__ro___
tungsten and a ground wire at
the center of the tube, and a ! _ 6,. ....._///J/
Z-counter which has a 50U_
nichrom wire at the center. 3i-5 _/, 7,....._5nl/mI ,3,4,5 and 7-1ayer which 120 _ u t c_consist of T-counters measure
the velocities by time-of-
flight method and position of Fig. I The apparatus
incident particles, but 2 and
* 6-1ayer which consist of Z-counters measure the energy
losses and the position along the wire using a charge
division method. A mixed gas of 80% He + 20% CH 4 which is
• chosen on the basis of the measurements of the velocity and
stability for different ratio of mixture, flows through all
counters at a rate of 200cc/min. The high voltage is 2.3KV,
and the discriminator level for trigger signals is 7 times
of minimum ionization of cosmic rays.
Each signal from 1,3,4,5 and 7-1ayer, 24 signals in a
layer, a total of 120 goes through a amplifier/discriminator
on the counter, and delayed by 10_sec. Any signals from the
each layer are used to make trigger pulse using a sort of
succesive delayed coincidence method. The time between
trigger and delayed signal from each wire is measured by
20MHz clock, 8 bit scaler and 8 bit shift resister (TDC) for
all 120 wires. Each of 2 and 6-1ayer has 12 anode wires,
and the adjacent two wires are connected at one ends of the
both wires. Pulse heights from both ends of the wire with
length of 10m are measured with 11 bit analog to digital
216 HE 6.1-I
converter (CAMAC ADC), the ratio and the sum of two heights
gives the position along the wire with the accuracy of about
20cm and the energy losses, respectively for a incident
particle. Data are taken by a on-line micro-computer and
recorded on floppy diskets.
The drift velocity of electrons in the gas used in this
experiment are about 100ns/mm which is very slow compared
with that of 90% Ar + 10% CH4, 20ns/mm. So this time jitter
of the pulses is at most 2.5Us for drift space of 25mm. A
veto pulse, which prevent cosmic ray muons and reduce
trigger rate, is generated by the 4 fold coincidence among
1,3,5 and 7-1ayers with the time resolution of 2.5usec .
With this data taking system, •'the velocity range to be
observed is between 3m/2.5 _ s ec;8 =4xi 0-3 and
3m/10_sec;8=Ix10 -3 for the virtical incidence of the
particle to the apparatus.
3. ANALYSIS AND RESULTS
Each event has data on positions and, times from 120
wires of T-counters and on pulse heights from 24 wires of Z-
counters. The following requirements are applied to select
the monopole candidate. First, the total number of hit-wire
of T-counters in a event is less than 10. Second, the wires
hitted have to draw a straight line, and the least square
method is applied to positions of the anode wires fired to
measure the straightness. The resultant root mean square
deviation of the wire positions from the straight line; 0(L)
is calculated. Third, the arriv_l times of the pulses from
the wires have a linear relation to the virtical position of
the player. The gradient of the straight line gives the .
the velocity for the monopole candidates, the distribution
of D(L) and D(I/8) for cosmic ray muons are obtained and
80
701 cosmicmuon cosmic muon
601 D(I/_]-distributlon D(L)-distribution
40
u 30- _t uo
20_ L t_
_o_
N,i,,, ,i, , , ° • •S 6 ? 8 (=m)'_
0.5 1.0 1.5 (_sec) $ 2 3 4 D(L) '_
O(11_)
Fig. 2 D(1/8) and D(L) distribution
for cosmic ray muons.
21T
HE 6.1-I
shown in Fig. 2, where D2(L) and D2(I/8) is the sum of
squares of the deviations from the straight line for
position and time data respectively. From these results,
selection criteria for the monopole candidates are D(L)<4cm;
o(L)<2.31cm; and D(I/_)<1_s; _(I/8)<577ns, which gives
selection efficiency of 85%. After observation from
January I, 1984 to May 28, 1985; the running time of
2.17x107sec, 95,000 events
are recorded, on which
selection criteria mentioned 103
above are applied• Until
December 12, pulse heights __/
are not measured, then
monopoles are searched only 102 _//
by the velocity. No track _/
has been found to have _/
V 1
velocity range of
1x10-3<8<4x10 -3 for the c i",11 3'
"--E 111 11 1 1
running time of 1.82x107sec• 10 1 ,3 1121,
12 2 1 2
111 2 21 " 11Fig. 3 shows ionization. I _21_z32_ 12146122111 1
losses as a function of the 22_14n_,1456643746382
I_4A_gAA_S627
velocities for monopole runs 2_l_k_,_sT_29_s.
after the selections are 1 1247_zc.A,_aes_e..._?_.3_scccma_A_5
carried out The energy 113_31,4_I
• 158B/SA4AA4AA/_
loss calculated by Drell at 122332121113 22121 1 2
13383/04325 2
el (5) is also shown• No I,
111
track has been found to have 21 211I I , I l
energy loss corresponding to
° the velocity• Combining two _0-& 10-3. 10-2 10-1
results, the upper limit of
the monopole flux in cosmic Fig. 3 The energy loss and
" ray at sea level is 8 correlation for
2.78x10 -12/cm2sr sec at 90% monopole candidates,
confidence level in the where the number
v e 1 o c i t y r a n g e o f increases as 1,2,..,9
1x10-3<_<4x10 -3 ,A,B,C, . ,Z
REFERENCES
I. Georgi, H. et al, (1974) Phys.Rev.Lett., 32, 438
2. Kajino, F. et al, (1984) Phys.Rev.Lett., 52, 1373
3. Cabrela, b. , (1982) Phys.Rev.Lett., 43, 1378
4. Higashi, S. et al, (1983) 18th I.C.R•C., 5, 6"9
5. Drell, S.D• et al, (1983) Phys.Rev.Lett., 50, 644
ACKNOWLEDGEMENTS
We wish to thank Prof. T. Kitamura for his help and
encouragement.


Search for magnetic monopoles using proportional counters filled with helium gas

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