The energy spectrum of cascade showers induced by electromagnetic interactions of high energy muons of horizontal cosmic ray flux in iron absorber was measured. The total observation time exceeded 22,000 hours. Both the energy spectrum and angular distributions of cascade showers are fairly described in terms of the usual muon generation processes, with a single power index of the parent meson spectrum over the muon energy range from 150 GeV to 5 TeV

Ashitkov, V. D.

Kirina, T. M.

Klimakov, A. P.

Kokoulin, R. P.

Petrukhin, A. A.

Yumatov, V. I.

English

NASA Technical Reports Server

•77 HE 5.2-_
ENERGY SPECTRUM OF CASCADE SHOWERS INDUCED BY COS_IC RAY
MUONS IN THE RANGE FROM 50 GEV TO 5 TEV
Ashitkov V.D., Kirina T.M., Klimakov A.P.,
Kokoulin R.P., Petrukhin A.A., Yumatov V.I.
Moscow Physical Engineering Institute, Moscow 115@09, USSR
Abstract. Results of a new measurement of the energy
spectrum of cascade showers induced by electromagnetic
interactions of high energy muons of horizontal cosmic
ray flux in iron absorber are presented. The total
observation time exceeded 22,000 hours. Both the energy
spectrum and angular distributions of cascade showers
are fairly described in terms of the usual much genera-
tion processes (i.e. through _- and K-decays in the
atmosphere) with a single power index of the parent
meson spectrum over the much energy range from 150 GeV
to 5 TeV.
1. Introduction. Recent magnetic spectrometer measurements
of cosmic ray rouen spectrum at large zenith angles [q,2]
agree well with each other and are successfully interpreted
within the frames of the conventional much generation pro-
cesses with a value of the differential parent particle
spectrum index of about 2.7 up to several TeV muon energies.
A similar result was obtained earlier in the ionization
calorimeter measurements of the spectrum of cascade showers
initiated by muons F3] and was confirmed by the _TRON ca-
data Plorimeter ublished recently _]. However, a number of
experiments _5-8] give appreciably more rigid shower spec-
trum ......around I TeV, what is claimed to be caused either
by some additional flux of muons (or some other penetrating
particles) or by an anomalous muon interaction increasing
with energy. On the other hand, in the experiments [9,10]
the steepening spectrum of cascade showers was observed.
Here we present the first results of a new measurement
of the cascade shower spectrum using an ionization calori-
meter. Compared to our old data [3], the energy range has
been extended to lower energies.The exposure time and hence
" statistics of high energy events have been doubled.
2. Experimental. A schematic diagram of the experimental
. arrangement is given in Fig.1. The arrangement consists of
the six-layer calorimeter and G.M. counter hodoscope detec-
tors. Two trigger modes have been used in the operation.
The first one required the coincidence of any three layers
of ionization chambers (ionization m/80 cascade particles)
together with the total energy deposition exceeding 60 GeV.
The second trigger was organized to study the low energy
part of the spectrum and included a coincidence of two
hodoscope detectors and triggering of any pair of adjacent
layers of the calorimeter with the above ionization thresh-
https://ntrs.nasa.gov/search.jsp?R=19850027777 2020-03-20T17:03:48+00:00Z
78
HE 5,2-I_
. old. The cascade energy threshold in
_c the latter case corresponded to app-
roximately 20 GeV. A veto signal from
A ic s an air shower shield was formed by a
@-fold coincidence in AC detector
sensitive area each. A more detailed
description of the experimental arra-
ngement has been published in [11 ].
During five experimental runs in
1980 to 198@ with the total observa-
tion time of 8.0x10_s of about 250000
Fig.1 events have been recorded and ana-lysed. Only cascade showers initiated
by muons crossing hodoscope detectors with zenith angles
e _6o ° have been selected to study the shower energy spect-
rum and angular distribution. Edge events and a small amo-
unt of nuclear showers (which are very different from elec-
tromagnetic ones in longitudinal development) have been re-
jected.. The total number of reconstructed events equals to
8.2x10" for trajectories traversing both A and B hodoscope
detectors .with _2 triggered layers of the calorimeter,
and 3.8×10" for three-layer events (_3) with at least one
hodoscope detector (A or B) discharged. The maximum detected
shower energy was about 16 TeV.
3, Data analysis and results. To derive cascade shower gene-
ration spectrum from the observed distributions the accurate
account for experimental conditions (arrangement geometry,
trigger and selection criteria, hodoscope and reconstruction
efficiency, the difference between the real shower energy
and its estimate _, and so on) is necessary. We used the
trial spectrum method to analyse our data. Calculations
started from the expected (or "trial") spectrum of cascade
shower generation in a unit target mass :
where J_ff(E,e)is the differential muon spectrum at the ob-
servation level (has been calculated after [12]), and6(E,_)
is the sum of the cross sections of electromagnetic muon
interaction processes [13-15]. A Monte Carlo technique was
used to calculate the response of the experimental arrange-
ment - the matrix of the numbers of events N,(A_ ,A e)
expected in the energy estimate interval A_ and zenith angle
interval A e. The experimental values of the differential
cascade shower generation spe_ctrum were then derived from a
comparison of the observed N_Ag,Ae) and calculated No(AS,Ae )
matrices using the following relation:
,=- Ae). (2)
Here e* is the avera6e zenith angle in the Ae interval,and
?@ HE 5.2-I_
6* is a logarithmi- 10 i , , i ,
tally averaged value 8 o - (A B)(A_2)
(i.e., = exp( )) 6 .-
Of the cascade she- __._o--_-__
wer energy_ contribu-
ting to AE interval.
Such a choice of the L _.2.75.K/_O.15 __
reference energy mi-
nimizes the sensiti- 2
vity of the derived n(_,'1_'__,1o'Tg_s"_r_c_v_
spectrum to the slo-
pe of the trial one. _ I J , i ,
The experimen- 50 _ioo 200 500 woo _,Gev
tal spectrum of cas- Fig.2
cads shower genera-
tion in iron is presented in Fig.2 for two selection crite-
ria discussed in the previous section. Error bars indicated
in the figure are statistical only. The systematic uncer-
tainties may reach-_q5%. The best-fit value of the pion
generation spectrum index is 2.75+0.02 in the shower energy
interval 50 GeV -<_ -< 2 TeV for tee events selected accor-
ding to (AB)(A>,2) criterion, and 2.68+0.03 for (A+B)(A>.3)se-
lection in the range 200 GeV.<Z.<3 TeVT.Effective much energy
range covered by this experiment is
I _' ' ' ' approximately from 150 GeV to 5 TeV.
3.o Jt_,e)/.n(,_,oo') Angular distributions of cas-
cade showers initiated by muons are
2.sLT/'-x given in Fig. 3. The theoretical
curves are calculated with _¢= 2.70
:lTeV and K/_ = 0.15 and normalized to
2o[i T ,_ _ the experimental data. The agree-
. . ment of the observed distributions
with th theoretic l prediction is
I exoxeoCascade shower intesity above
2,OT/_'_'_T._,[,/_ / _=0.STeV f""_ a certain energy _o may be conver-ted into absolute much intensity
I__....... above rouen energy Eo. With an app-
ropriate choice of the relation
. '._ between So and Eo, the estimated
much intensity does not strongly
_._ depend on the spectrum model and
1.0 relies mainly upon the electromag-
_o,2"rev netlc interaction cross sections
F_ used in the conversion. Absolute
"_ muon intensities above 1 TeV at
_,.. large zenith angles derived fromthe pr sent experimental data are
_,o given in Flg._ together with the
' ' ' ' recent magnetic spectrometer re-
_,0 o, 0.2 0_ 0.4_o._O sults. Errors quoted (except MUTRON
Fig. 3 point ) are pure statistical. The
80
HE 5.2-14
systematic uncertainty of , , , ,
ou.r data is of about 15% 2.0 3_¢']_(_ITeV,@),
and is related mainly to _ I + 1o.Tc.%.,sr.,the absolute normalization _
of shower energy measure- ,s _ §_ }ments.
4. Conclusions. The energy 10
spectrum of cascade showers o _E,s
= -HUTRON
initiated by cosmic ray mu- •-P_ENT_ATA
ons and their angular dis- o.s , , , J
tribution have been measu- 90 s_ 80 _ 70 eo
red in a wide energy range
with a good statistical ac-
curacy. Both the spectrum Fig.4
and the angular distribution are fairly described by a con-
ventional picture of muon generation in_- and K-decays with
a single power index _ = 2.68 - 2.75 and K/_-ratio of 0.15
over the muon energy range from 150 GeV to 5 TeV. The abso-
lute muon intensity at large zenith angles derived from the
cascade shower intensity agrees with the recent magne-
tic spectrometer data and does nob support the hypothesis of
the additional much interaction around I TeV much energies.
References
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Energy spectrum of cascade showers induced by cosmic ray muons in the range from 50 GeV to 5 TeV

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