Correlations between hadrons and electromagnetic particles were studied in the hadron-gamma families observed in the Chacaltaya emulsion chamber experiment. It is found that there exist a number of hadrons which associate electromagnetic showers in extraordinarily close vicinity. The probability to have such a large number of hadrons associating electromagnetic showers, expected from background calculation, is found to be negligibly small and it means there exists anomalous correlation between hadrons and electromagnetic particles in the characteristic spread of atmospheric electromagnetic cascade

Tamada, M.

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288 HE 3.3-6
Anomalous correlation between hadron and electromagnetic
particles in hadron and gemma-ray femilies
M. T&MADA
Science and Engineering Research Laboratory,Waseda
University, Tokyo 162, JAPAN
Abstract
Correlations between hadrons and electromagnetic particles are
studied in the hadron-gamma families observed in Chacaltaya emulsion
chamber experiment. It is found that there exist a number of hadrons
which associate electromagnetic showers in extraordinarily close
vicinity. The probability to have such large number of hadrons
associat ing electromagnet ic showers, expected from background
calculation, is found to be negligibly small, _I0-5 , and it means
there exists anomalous correlation between hadrons and electromagnetic
particles in the characteristic spread of atmospheric electromagnetic
cascade.
I. Introduction.
Through the analysis on the structure of hadron and galsa-ray
families, especially of the families with ha&con-rich nature, we have
noticed that there were a number of showers which penetrate through the
hole chamber, the upper and the lower chamber. The core structure seen
in the lower chamber tells us that considerable number of those
penetrating showers are not simply pure electromagnetic cascades but
are coming from nuclear interaction of hadrons in the chamber, that is,
they are hadronic origin. [1] [3] During studying on the core
-_tructure of those penetrating showers, we found some of showers which
are considered as hadronic origin have separate multi-core structure in
the upper chamber, not single core structure. That is, there exist
hadron and electromagnetic showers which are located extraordinarily
close each other, in the extreme case the relative distance between the
two is _ 30 _ m. Here we show how closely a hadron accompanies
electromagnetic showers in its neighbourhood in the high energy hadron
and gamma-ray families observed in Chacaltaya chamber no.19.
2. Experimental procedure.
Chacaltaya chamber no. 19 The Chacaltaya chamber no.19 has two-
storey structure with air-gap, that is, the upper chamber of 6 cmPb
thick, target layer of 23 cm pitch, air-gap of 1.5 m and the lower
chamber of 8.4 cmPb thick. The special character of the chamber "
no. 19 different from the other chamber is that in all'the area of the
upper chamber nuclear emulsion plates together with X-ray films are
inserted under 3, 4 and 6 cm lead plates. Then we can study very
precisely on the core structure of showers, with accuracy of 10 _m,
observed in the upper chamber as well as in the lower chamber.
The energy of each shower is estimated by track-c_unting method.
Photometric measurement is also applied for high-energy showers.
Selection of the events Among the events observed in the chamber
no. 19 we pick up only the events which have at least one identified
hadron and pass through the whole chamber, in order to get enough
information on hadron component. In the Japanese part ( _30 m2year
, a half of the total area) of the chamber no. 19, we found 19 events
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289
with l_Otal observed energy greater than 100 TeV, incident energy
Eo_10 eV, which satisfy the above criteria. The detection threshold
energy is put to 2 TeV.
Identification of hadrons The showers in the lower chamber are
those from local nuclear interactions in the target layer (C-jet with
clean multi-core structure), those from local nuclear interactions in
the lower chamber (Pb-jet-lower with clean single-core structure) and
tails of showers from the upper chamber (with diffuse core structure).
Thus almost all showers observed in the lower chamber are hadronic
origin. The showers observed in the upper chamber are mixture of
electromagnetic showers from the atmosphere and those from local
nuclear interactions in the upper chamber itself (Pb-jet-upper).
Among showers observed in the upper chamber, we consider the showers as
hadrons when the showers can be seen only after 8 cascade unit of
emulsion plate, that is, no electron shower track can be seen at the
expected place of emulsion plate at 6 cascade unit, and/or when the
showers continue to the lower chamber and new core can be seen in the
lower chamber. The above procedure for identification of
hadrons in the upper chamber can not pick up all hadrons interacted in
the upper chamber, 20 %30_ of them are left unidentified.
3. Results.
Here we study how closely hadrons accompany electromagnetic
showers in their neighbourhood by comparing with background calculation
where only azimuthal angle _ of observed hadrons are randomly chosen
in the observed families. Fig. la shows a distribution of relative
distance, Rmin, between a hadron and its nearest neighbouring shower,
and Fig.lb shows a distribution of energy-weighted relative distance,
Xmin, between a hadron and a shower nearest neighbouring in Xij-space
for the events of Chacaltaya chamber no. 19. Xij is defined by
Xij= J EiE j ×Rjj where EL and Ej are visible energy of hadrons and of
electromagnetic showers and Rij is relative distance between the two.
The distributions are compared _¢ith background calculation. As is
seen in the figures, there exists a bump above the background
distribution both in small Ruin region, l_in < 400 _m and in smu11
Xmin region, Xmin < 2 GeV.m. Figs.2a and 2b are the same
distributions shown above in logR and in logX scale but here hadrons
are divided into four parts depending on their distance Rh measured
from energy-weighted center of a fomily. The background
. distribution in small l_in and in small X_in becomes negligibly small
when distance Rh of hadrons becomes larger, in contrast to that in the
experimental data there still exist hadrons which accampany a shower in
very smaU Ruin and Xmin even when I_ is large. There exist two
" hadrons which accompany a shower in l_ain less than 160 _ m and in Xmin
less than 0.6 GeV.m for the case of Rh 5 cn where no hadrons are
expected to accompany a shower in such smull l_in and Xmin region from
the background calculation. The probability, p, that a hadron
accompanies a shower at (energy-weighted) relative distance less than
_in or Xnin is given by the background calculations. Then the
probability On that at least n ha&cons accompany a shower at (energy-
weighted) relative distance less than Ruin or _iu is given by a
binomial formula,
nh
r(i nh-r
= Y nhCr p -p) (i)Qn r=n
here nh is the total number of observed ha&cons. The observed number
290
HE 3.3-6
of hadrons which accompany a shower in small Rmin or Xmin is very large
compared with background distributions and the probability that such
large number of hadrous accompany a shower in such small Rmin or Xmin
is negligibly small, for example, we have 21 hadrons which accompany a
shower in Rmin less than 400 _m and 19 hadrons which accompany a shower
in Xmin less than 2 GeV.m. The probability that these two cases
are realized , expected from background calculation, is % 8.3×10 -7 and
%2.1× 10 -5 respectively. Thus we can conclude that there exist
hadrons which accompany electromagnetic showers extraordinarily close
to them, and such closeness in relative distance Rmin and in energy-
weighted relative distance Xmin can not be reproduced simply by chance.
4. Discussions.
Those hadron and accompanied electromagnetic showers form isolated
cluster of collimated showers, mini-cluster[2] [3]. Then one may
say that those cluster of showers are due to nuclear interaction at low
altitude. However, if we interpret those clusters of showers as
products of atmospheric nuclear interaction of normal type, < Pt >_350
MeV/c, the interaction height of them always gives very small value,
around several to several ten meters above the chamber. We can
estimate the number of hadrons arriving at the chamber by the observed
number of C-jet and Pb-jet-lower under the assumption of a collision
mean free path of hadrons. Then we can estimate the number of
atmospheric interactions at low altitude, H 50 m above the chamber
for example. Table 2 shows a summary of the above argument for
hadrons with visible energy, Kh(Y) ,greater than 10 TeV. Almost all
of shower clusters have their energy greater than 10 TeV. The
estimated number of atmospheric interactions should be compared with
the number of hadrons which accompany electromagnetic showers in the
close vicinity of them. As one can see in the Table, the number of
atmospheric interactions at such low altitude is very small compared
with those hadrons unless we assume very short collision mean free path,
_1/5 _eo., of hadrons. The effect of the zinc roof of %lmm thick
(_0.01 _eo) which is located 3m above the chamber is also negligible.
Thus if we assume that those mini-clusters are due to nuclear
interaction in the atmosphere, the interactionpoint should be much
higher and the average transverse momentum of produced particles should
be much smaller ( _I0 times smaller) than normal one. In many of
mini-clusters, a hadron carries a large portion of energy of a cluster.
This fact indicates that a hadron is a core of a cluster and *
electromagnetic showers are accompanied by unknown mechanism.
Acknowledgement
The author would like to express his gratitude to Professors
Y.Fujimoto and S.Hasegawa and to all the members of Chacaltaya emulsion
chamber experiment for their valuable discussions and comments.
References
[ 1] Y. Funayama and M.Tamada ; 19th ICRC HE 3.3-5
[2] Brasil-Japan collaboration ; AIP Conf. Proceedings No.85(1981) p.500
S.Hasegawa ; Proceedings of Int. Sympo. on Cosmic Rays and
Particle Physics, Tokyo(1984) 319
[3] R.Bielawska et al. ; Proceedings of Int. Sympo. on Cosmic Rays and
Particle Physics, Tokyo(1984) 374
291 HE 3.3-6
no. of hadrons number of "single hadrons" arriving number of hsdrons expected
with _inin:_ 400 from C-jet and Pb-jet-lower
/z m Pb-j et-upper C-jet Pb-j et-lower
identified Z 8co. 1/22, geo. ]/3Z geo. I/SA geo.
21 12 8 I 23± 7 21± 7 24± 8 41+14(I. o± o.3) (i. 8+ o. s) (3. 2__.I. I) (9. s± s, 2)
Figures in parenthesis are estimated number of atmospheric interactions at the
heiohts less than 50 m above the chamber.
0,I0_ " . . " , , .... , O.lO
I ]
o.o it t
0 ! 2 3 4 0 I 2 3 4 5 6
R,t,j. (ram) X_,. (GeV.m)
Fig. la: Distribution of relative Fig. lb: Distribution of energy-
distance, Rmin, between a hadron and weighted relative distance,
its nearest neighbouring shower. Xmin, between a hadron and its
Histogram is a background nearest neighbouring shower in
distribution. Y_lj -space.
..05 .0_
_h _h--
/
... , ,,.
, _ _: . ,
r," _l.5_Bt_,5.em .c: I < Ft_l_.5_m
o .Io _ .lo-
•,_ .05 c .05
L+$ ++
05
,o2 !6' ,o° ,o' Io2 ,03 ,0 162 ,6' to to' 1o2 Io3 I
Rml n (mr'n) 'X,rnin (GeV.m)
Fig. 2a: Distribution of relative Fig. 2b: Distribution of energy-
distance, Rmin, between a hadrons weighted relative distance, Xmin,
and its nearest neighbouring shower between a hadron and its nearest
for four different intervals of neighbouring shower in Xii-space
distance Rh of hadrons measured for four different intervals of
from the energy-weighted center of distance Rh of hadrons.
the event. Histograms are
bacnkground distributions.


Anomalous correlation between hadron and electromagnetic particles in hadron and gamma-ray families

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