The existence of significant amounts of antimatter in the Universe is demonstrated through cosmic radiation. The data from the Danish-French Cosmic Ray Spectrometer on the HEAO-3 satellite offers an opportunity to search for heavy antinuclei, since all the relevant parameters (charge, velocity, arrival direction, and satellite position at the time of arrival) are measured for each recorded nucleus. Using the 22676 positive only events in the data seletion corresponding to L  1.5 as a measure of our exposure factor to heavy antinuclei and noting that no corresponding antinuclei were found, an upper limit (95% confidence) is given to the ratio of antinuclei to nuclei as 1.4 x .0001 for particles with Z 9. The upper limit resulting from this work is compared with previous results of searches for heavy antimatter in the cosmic radiation. It is seen that, if one regards only antiparticles heavier than fluorine, then the present result represents a reduced upper limit over previous data. When taken together, all the available experiment data now push the upper limit for the ratio of antiparticles to particles well below .0001

Lund, N.

Rotenberg, M.

English

NASA Technical Reports Server

aao 
SEARCH FOR HEAVY ANTINUCLEI IN THE COSMIC RADIATION 
Niels Lund and Miriam Rotenberg 
The Copenhagen-Saclay HEAO Collaboration 
Danish Space Research Institute, Lundtoftevej 7, DK-2800 Lyngby 
Introduction 
The cosmic radiation is one of the few channels through which the 
existence of significant amounts of antimatter in the Universe may be 
demonstrated. Such a finding would be of fundamental importance for 
cosmology as well as for particle physics. 
The data from the Danish-French Cosmic Ray Spectrometer on the HEAO-3 
satellite offers an opportunity to search for heavy antinuclei, since 
all the relevant parameters (charge, velocity, arrival direction, and 
satellite position at the time of arrival) are measured for each 
recorded nucleus. 
Instrumentation and initial data selection 
The HEAO-3 instrument is described in detail in (3). The charge and 
velocity of each particle is determined from the signals produced in a 
stack of five Cerenkov counters. 
The consistency of the signals are used to check for particles 
undergoing nuclear interactions while traversing the instrument. For 
this investigation, however, the consistency requirements have been 
relaxed somewhat from the values used generally, in order not to reject 
antinuclei, which are expected to yield sigflals differing slightly from 
those of their positive counterparts. 
The particle velocity is determined from a fit to the Cerenkov signals. 
We use a routine which determines not only the best fit velocity, but 
also the lower and upper bounds for a velocity inte val outside which 5 the true values should only lie in one case out of 10 . 
Particles with inconsistent values of the velocity signals have been 
rejected. 
The present analysis is limited to elements'heavier than fluorine since 
the reliability of the time-of-flight system has been found to degrade 
somewhat for lighter elements. 
Pilot runs showed that the number of particles with zenith angles less 
than 90° which could be assigned a unique charge is quite small. 
Consequently we restrict the data base to particles with zenith angles 
greater than 90°. 
Trajectory tracings 
Before beginning the trajectory tracings the acceptable velocity range 
mentioned above is converted to a rigidity interval by using a very 
wide range of possible isotopic masses for each element. This procedure 
OG6.1-2 
ttO 
SEARCH FOR HEAVY ANTINUCLEI IN THE COSMIC RA ATION 
N s Lund and Miriam R enberg 
The C lay HEAO C labo ion 
D sh Space R earch In titute, L t tevej 7, D 800 Lyngby 
Introduction 
The cosmic radiation is one of the few channels through w ch the 
existence of significant am ts of antim ter in the U v rse m y be 
de st ated. Such a finding w ld be of fundam tal im tance for 
cosmology as w l as for p ticle ph cs. 
The data from the D sh-French Cosm c Ray Sp ctrom ter on the HEA 3 
sate lite offers an op tunity to search for heavy antinuclei, since 
all the relevant param ers (charge, velocity, arrival direction, and 
sate lite p tion at the time of arrival) are m red for each 
recorded nu leus. 
Instrume ation and initial data selection 
The HEA 3 instrument is described in d a l in (3). The charge and 
v lo ty of each p icle is determined from the signals produced in a 
stack of five C renkov cou ers. 
The con istency of the signals are used to check for p ticles 
undergoing nu lear interactions w le traversing the instrument. For 
this investigation, how r, the con istency requirements have been 
relaxed somew at from the values used gen ally, in order not to reject 
antinuclei, w ch are expected to yield signals differing slightly from 
those of their p tive co s. 
The p icle v lo ty is determined from a fit to the C renkov signals. 
We use a routine w ch determines not only the b t fit v o ty, but 
also the lower and upper bounds for a velocity inte~val outside w ch 
the true values should only lie in one case out of 10 . 
P ticles w th inco stent values of the v lo ty signals have been 
rejected. 
The present analysis is limited to elem ts heavier than fluorine since 
the reliability of the tim flight system has been found to degrade 
somew t for lighter elem s. 
P lot runs showed that the num r of p icles w th zenith angles less 
than 90 0 w ch could be assigned a unique charge is q te sm l. 
C ly we restrict the data base to p ticles w th zenith angles 
greater than 90 0 • 
T ajectory tracings 
B fore beginning the trajectory tracings the acceptable velocity range 
m ioned above is con ted to a rigidity interval by using a very 
w de range of p ible isotopic m ses for each elem . T s procedure 
https://ntrs.nasa.gov/search.jsp?R=19850025780 2020-03-20T18:00:20+00:00Z
takes into account the possibility that a short lived fragment produced 
in the atmosphere may follow a different trajectory than the ones 
available to the stable isotopes. 
The helix-method (4) is used for the trajectory tracings. The magnetic 
field model used is a 14. order model based on MAGSAT data (5). For 
each rigidity value it is checked if any of the two possible charge 
signs corresponds to an acceptable arrival situation. Dependent on the 
outcome of the tracings the particles are divided into four classes: 
1) Both charge signs are possible. This class contains all events for 
which at least one positive rigidity and at least one negative 
rigidity are acceptable. 
2) Only a positive sign is possible, i.e., particles for which at 
least one positive rigidity is acceptable and none of the negative 
rigidities are acceptable. 
3) Only a negative sign is possible, i.e., all positive rigidities 
forbidden, but at least one negative is allowed. 
4) Neither sign is allowed, all positive as well as negative 
rigidities are forbidden. 
A very conservative criterion for classifying a rigidity as "forbidden" 
has been used. It is demanded that the corresponding trajectory 
intersects the solid Earth within a trajectory length of one Earth 
radius from the satellite position. 
In order to allow for some error in the determination of the particle 
arrival directions, any particle which is initially in class 2, 3 or 4 
is recalculated using a zenith angle diminished by 2 degrees relative 
to the measured value. 
Results 
Of the initial data set about 25% or 34070 events are classified as 
positive only, 15 events are negative only (antiparticle candidates) 
and 10 events are impossible regardless of the sign assumed. The rest, 
103266 events, are consistent with either charge sign. 
Details on the 25 particles of classes 3 and 4 can be found in tables 1 
and 2. 
Inspection of these 25 events reveals that 7 antiparticle candidates 
and 2 impossibles were all recorded on one single day (Nov. 11, 1979). 
The total set comprises data from over 400 days. We have found no 
satisfactory explanation for this burst of unusual trajectories. There 
were no signs of instrument or satellite malfunctions. A Forbush 
decrease occurred on this day, but we see no particular reson to 
connect the two events. The geomagnetic activity index was between 1 
and 2+. We have noted that 8 of the 9 unusual events were recorded in 
the vincinity of the Sourth Atlantic Anomaly. The instrument was 
switched off during the passages through the Anomaly and the 8 events 
occurred in the first few minutes after switch on. The connection 
331 
OG6.1-2 
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between the switching of the experiment and the peculiar events is not 
obvious, however, because in the total data set there are several 
thousand such passages without irregularities. We have therefore 
decided to reject all events (of all classes) recorded on this day from 
this work. 
The remaining 8 impossible events indicate the level of background for 
the antiparticle search. This background may be due to inadequacies of 
the measured data (charge, velocity, and arrival direction for the 
particles) or it may arise due to inadequacies of the magnetic field 
model. The MAGSAT model does not describe local crust related magnetic 
anomalies and does not take into account magnetic disturbances which 
might exist at the specific'time of our particle recordings. 
When analyzing the geographic distribution of the remaining "impossi- 
bles", it appears that the problem lies with the magnetic field data 
because these particles have preferentially been detected at low 
geomagnetic cut-off values where magnetospheric disturbances have the 
largest effect. We have therefore investigated the effect of excluding 
data obtained at locations with geomagnetic L-values greater than 1.5. 
It turns out that most of the "particle" candidates remain in this 
selection whereas all the "antiparticle" candidates and all but one of 
the "impossibles" are gone. This last "impossible" event may be 
reasonably attributed to the uncertainty of the time-of-flight 
imformation. In fact, an indepqent analysis leads us to suspect a 
residual contamination at the 10 level for the time-of-flight system. 
We also note that all but one of the Nov. 11 events have L-values 
greater than 1.5. 
Conclusion 
Using the 22676 "positive only" events in the data selection 
corresponding to L11.5 as a measure of our "exposure factor" to heavy 
antinuclei and noting that no corresponding antinuclei were found we 
can give an upper l'mit (95% confidence) to the ratio of antinuclei to 
-4 
nuclei as 1.4 x 10 for particles with ( z I >  9. In table 3 we compare 
the upper limit resulting from this work with previous results of 
searches for heavy antimatter in the cosmic radiation. It is seen that, 
if one regards only antiparticles heavier than fluorine, then the 
present result represents a reduced upper limit over previous data. 
When taken together, all the available experiment data now push the 
uppzr limit for the ratio of antiparticles to particles well below 
10 
As a final remark we may stress that we have found no satisfactory 
explanation for the 9 unusual particle tracks seen on November 11, 
1979. We would appreciate being informed of other geophysical 
"curiosities" which might have been observed on this date. 
Acknowledgements 
The authors would like to thank all their collaborators in the 
Copenhagen-Saclay Collaboration for their efforts in providing the data 
base for this work. In particular we want to thank Prof. B. Peters for 
his continuing interest and useful comments throughout the project. 
332 
OG6.1-2 
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TABLE 1 Ant i  p a r t i c l e  candidates 
D a t e  GMT L a t  . Long. L-value Zen. A z .  Z p GeV/c 4.3 0 r a n g e  
TABLE 2 "Impossible p a r t i c l e s "  
TABLE 3 Searches f o r  a n t i n u c l e i  
95% confidence upper 1 i m i  t 
Badhwar e t  a1 (1978) Z = 2  
Smoot e t  a1 (19751 2 7 2  
Present work Z,9 
References 
1)  G.F. Smoot, e t  a l ,  Phys. Rev. Le t t . ,  35, (19751, 258. 
2)  G.D. Badhwar, e t  a l ,  Nature, 274, (19Tg1, 137. 
3 )  M. Bouffard, e t  a l ,  As t r .  Sp. Sc. 84, 3, (1982). 
4) B. Byrnak, e t  a l ,  Nucl. I n s t r .  Meth., 16, 303, (1979). 
5 )  R.A. Langel , e t  a l ,  Geoph. Res. L e t t  .,7, (19801, 793 
- 
333 OG6.1-2 
nti  
t   t. - al e . . P e /c 4 .  0 r  
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791111 07 59 -43.3 32.3 2.51 123 44 14 1. 58 1.52 - 1. 65 
791111 08 00 -43.5 37.0 2.52 135 18 13 4.66 4.19 - 5.54 
791111 08 01 -43.6 39.7 2.52 107 29 19 8.02 7.40 - 9.31 
791111 09 37 -43.0 27.3 2.49 119 36 14 2.16 1.98 - 2.45 
791111 09 37 -42.8 28.9 2.49 129 15 14 5.38 4.66 - 6.41 
791111 09 38 -42.4 31.6 2.49 122 36 14 2.11 1.94 - 2.35 
791215 14 46 -43.6 74.8 3.0 105 138 10 1. 17 1 .14 - 1.19 
800129 17 18 -38.0 133.4 2.5 109 79 13 7.22 6.70 - 8.22 
800205 09 08 -43.4 -175.8 2.4 130 -63 12 2.14 1.94 - 2.48 
800206 00 04 41.8 148.9 1.6 95 55 12 6.28 5.27 - 6.70 
800415 02 20 -43.6 -36.4 1.63 109 46 10 3.09 2.97 - 3.28 
800715 20 13 -36.8 61.2 2.2 114 52 18 7.15 6.73 - 7.90 
801025 09 35 -36.5 -171.7 1. 75 99 123 10 8.73 7.44 - 12.94 
801031 13 38 -41.2 102.0 3.0 107 116 12 8.81 7.66 - 11.94 
 i  rti l s" 
7-90930 20 57 -42.8° 104.8° 3.3 135° -75° 12 4.30 3.89 - 5.02 
791005 18 06 41.8 -71.3 3.1 119 -48 13 1. 21 1.20 - 1. 22 
791017 17 08 -43.3 72.2 3.0 134 86 13 1. 97 1.82 - 2.21 
791111 10 05 16.2 116.3 1.0 146 114 16 56.36 15.4 - co 
791111 11 22 -25.9 48.2 1.6 109 171 12 6.73 6.34 - 7.44 
791208 21 04 -43.5 18.2 2.3 168 70 10 1.28 1.26 - 1.32 
800628 17 08 -43.6 -176.0 2.4 147 -107 20 5.43 4.87 - 6.31 
800823 00 50 -43.5 57.6 2.4 152 -54 14 2.68 2.34 - 2.97 
800912 05 19 35.6 2. 6 1.5 144 -79 10 16.36 10.13 - co 
801105 06 32 38.7 -12.3 1.8 129 14 20 20.07 11 .42 - co 
LE  earc s f r nti clei 
dhwar et a  (1978) 
Smoot et a1 (1975) 
resent ork 
   
Z > 2 
Z > 9 
95 confi e er li i  
1.7 x 10-44 0.8 x 10-4 1.4 x 10-
ef r s 
1) .  Smoot, et a1, Phys. Rev. lett 35, ( ),258.
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3) M. Bouff rd, et a1, tr. Sp. Sc. 84, 3, (1982). 
4) B. B r k, et a1, cl. Instr.  16, 30 , (1979). 
5) R. langel, et a1, eoph. Res. let .,-r, (1 ), 793 


Search for heavy antinuclei in the cosmic radiation

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