The ATIC balloon-borne experiment measures the energy spectra of elements from H to Fe in primary cosmic rays from about 100 GeV to 100 TeV. ATIC is comprised of a fully active bismuth germanate calorimeter, a carbon target with embedded scintillator hodoscopes, and a silicon matrix that is used as a main charge detector. The silicon matrix produces good charge resolution for the protons and helium but only a partial resolution for heavier nuclei. In the present paper a charge resolution of ATIC device was essentially improved and backgrounds were reduced in the region from Be to Si by means of the upper layer of the scintillator hodoscope that was used as an additional charge detector together with the silicon matrix. The flux ratios of nuclei B/C, O/C, N/C in the energy region from about 10 GeV/nucleon to 300 GeV/nucleon that were obtained from new high-resolution and high-quality charge spectra of nuclei are presented. The results are compared with existing theoretical predictions

Adams, J.H.

Ahn, H.S.

Bashindzhagyan, G. L.

Batkov, K.E.

Chang, J.

Christl, M.

Fazely, A. R.

Ganal, O.

Gunasingha, R. M.

Guzik, T. G.

Isbert, J.

Kim, K.C.

Kouznetsov, E. N.

Panasyuk, M. I.

Panov, A. D.

Schmidt, W. K. H.

Seo, E.S.

Sokolskaya, N. V.

Watts, John W.

Wefel, J. P.

Wu, J.

Zatsepin, V. I.

NASA Technical Reports Server

MS-Fc R 3 I^:_
30TH INTERNATIONAL COSMIC RAY CONFERENCE
Me
ICRC^°
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Relative abundances of cosmic ray nuclei B-C-N-O in the energy region from 19
GeV/n to 300 GeV& Results from the science flight of ATIC.
A. D. PANOV 1 , N. V. SOKOLSKAYA I , J. H. ADAMS, JR. 2 , H. S. AHN3 , G. L. BASHINDZHAGYAN I , K.
E. BATKOV I , J. CHANG4,5 ; M. CHRISTL 2 , A. R. FAZELY6 , O. GANEL3 , R. M. GUNASINGHA 6 , T. G.
GUZIK 7 , 7. ISBERT7 , K. C. KIM 3 , E. N. KOUZNETSOV I , M. I. PANASYUK', W. K. H. SCHMIDT 5 , E.
S. SE03 , JOHN W. WATTS 2 , 7. P. WEFEL 7 , 7. WU 3 , V. I. ZATSEPIN'.
1 Skobeltsyn Institute of Nccclear Physics, Moscow State University, Moscow, Russia 2Marshall Space Flight
Center, Huntsville, AL, USA 3 University of Maryland, Institute for Physical Science & Technology, College
Park, MD, USA 4Purple Mountain Observatory, Chinese Academy of Sciences, China 5 Max-Planck Institut
for Solar System Research, Katlenburg-Lindau, Germany 6 Southern University, Department of Physics,
Baton Rouge, LA, USA 7Louisiana State University, Department of Physics and Astronomy, Baton Rouge,
LA, USA
panov@decl. sinp. msu. ru
Abstract: The ATIC balloon-borne experiment measures the energy spectra of elements from H to Fe
in primary cosmic rays from about 100 GeV to 100 TeV. ATIC is comprised of a fully active bismuth
germanate calorimeter, a carbon target with embedded scintillator hodoscopes, and a silicon matrix that
is used as a main charge detector. The silicon matrix produces good charge resolution for the protons and
helium but only a partial resolution for heavier nuclei. In the present paper a charge resolution of ATIC
device was essentially improved and backgrounds were reduced in the region from Be to Si by means
of the upper layer of the scintillator hodoscope that was used as an additional charge detector together
with the silicon matrix. The flux ratios of nuclei B/C, O/C, N/C in the energy region from about 10
GeV/nucleon to 300 GeV/nucleon that were obtained from new high-resolution and high-quality charge
spectra of nuclei are presented. The results are compared with existing theoretical predictions.
Introduction
The ATIC spectrometer, the procedures of its cal-
ibration and the algorithm of trajectory of pri-
mary particles reconstruction have been described
in [3, 9, 7]. Charge resolution provided by the sili-
con matrix is sufficient to obtain spectra of primary
protons and helium [8, 61 and preliminary spectra
of some abundant heavy nuclei [5, 61.
A very important sort of data to understand mecha-
nisms of propagation of cosmic rays in the Galaxy
is boron (which is secondary and not abundant
nucleus) to carbon fluxes ratio in cosmic rays.
The problem of B/C ratio have been widely ex-
perimentally investigated in the energy range 0.5—
50 GeV/n (see [1] and references herein). The en-
ergy range of the ATIC experiment permits to ob-
tain the data for the higher energies (up to 200-
300 GeV/n). But there are obstacles to solve the
problem: 1) too low charge resolution of the sil-
icon matrix in the range of charges 5-8, 2) high
backgrounds in the silicon matrix charge spectrum
in the range of boron and carbon (see fig. 1). In this
paper we use the upper layer of the scintillator ho-
doscope to improve charge resolution of the device
and to reduce backgrounds in B-C region to solve
B/C problem in the ATIC experiment. The paper is
based on the science flight of ATIC (2002-2003.)
Improved charge spectrum
The upper scintillator layer of the hodoscope is
comprised by 42 parallel scintillator strips 1 x 2 x
88.2 cm3 . The first task is to force these scintil-
lators to work as a supplementary charge detector.
This task includes a multi-step procedure of cali-
https://ntrs.nasa.gov/search.jsp?R=20090028651 2019-08-30T07:34:16+00:00Z
A,
RELATIVE ABUNDANCES
Figure 1: The charge spectra obtained with the sili-
con matrix only and with the silicon matrix plus the
upper layer of hodoscope for the range of energy
deposit in BGO calorimeter 50-100 GeV (primary
energy per particle approximately 150-300 GeV)
bration of scintillators as a charge detector which
will be described in details elsewhere. The method
to improve charge spectrum by the charge detected
by the upper layer of the scintillators hodoscope
is the following. At the first step we use usual
method to measure the charge of primary parti-
cle by the trajectory reconstructed from signals in
BGO-calorimeter and by the charge detected with
silicon matrix . (Qsi ) by the maximal signal in the
area of confusion for the trajectory as described in
[3, 9, 7]. At the second step we find the charges de-
tected in each scintillator strip and select the strip
with the charge nearest to the charge detected by
the silicon matrix (Qs,;). The found charge is ac-
cepted if the distance from the strip to the recon-
structed trajectory is less than 5cm and is rejected
otherwise. At the third step Qs^i is rejected if
Qsc; — Qsi I > 0.25. The final result for the charge
is Q = (Qs.i
 + Qsi)/2. The described procedure
reduces the backgrounds in the charge spectrum
and improves its resolution but reduces the initial
statistics by the factor of about 4. There are other
strategies to process charge data from the scintilla-
tor hodoscope but for this paper we select the strat-
egy of "higher resolution - lower backgrounds -
lower statistics". The charge spectra obtained with
the silicon matrix only and with the silicon matrix
plus the upper layer of hodoscope are compared in
fig. 1.
Measurement of the relative fluxes
We calculate ratio of fluxes of different nuclei in
cosmic rays to the flux of carbon against energy
of particles per nucleon. It is a multi-step pro-
cedure which is designed to obtain the most ex-
act information for fluxes of nuclei with charges
4<q<14.
1. For five ranges of the energy deposit Ed in
the BGO calorimeter (50-100,100-200,200-398,
398-794, 794-1585 GeV) the charge spectra (sim-
ilar to fig. 1, the lower graph) are builded up. There
is a dependency of ionization from the energy of
particles. To account for this dependency we de-
compose each charge, spectrum by Gaussian peaks
(the value )(2 per one degree of freedom is close to
1 in all cases), calculate the positions of peaks and
produce charge boxes for each particular primary
particle such that the margins of boxes are at the
half of path between adjacent peaks. The number
of counts I° e in each charge box q for Ed range
number s is the raw data to obtain the fluxes of pri-
mary particles (s! = 0 corresponds to the energy
region of Ed 50-100 GeV, etc).
2. Protons and helium due to interaction in the
substance (aluminum honeycomb and other) of the
ATIC device above the silicon matrix could some-
times simulate heavier nuclei. This effect is energy
dependent (grows with energy). Corresponding
backgrounds BP;Qe for each value I° Q are calcu-
lated by simulation of propagation of protons and
helium through the ATIC device by the FLUKA
code [2], with simulation of the conditions of
charge selection (seeprevious section). The appa-
ratus charge line widths are accounted for as well.
This procedure produces the corrected values of in-
unarga
U
30TH INTERNATIONAL COSMIC RAY CONFERENCE
tensities 11 q
 
= I°,q — BP ,H' The value of BP;Hge
for boron (q 5) varies from 9% to 36% of 1O
3. The particles with charges q > 15 due to
fragmentation in the substance of the ATIC device
above the silicon matrix could simulate nuclei of
4 < q < 14. The corresponding backgrounds were
subtracted but the effect is small (about 0.1% for
boron) and we do not describe the method of sub-
traction here.
4. Each nuclei of 4 < q < 14 due to interactions in
the ATIC device, and due to the apparatus broad-
ening of lines produces some "charge response" of
the device which may be described for each par-
ticular nucleus q at the entrance of the device by a
set of the coefficients K4, K5, ... , Kq4 , where K4
is the probability to find nucleus q in the charge
box 4, etc. Of course the coefficient Kq dominates
strongly in the set K4,... , K14 . -In other words
the matrix KS is diagonally-dominated. Let Fq
be the intensity of the nucleus q at the entrance of
the device. Then for each energy region s the ex-
perimental charge spectrum Iq after subtraction of
p-He backgrounds (described above in the item 2,
we do not write the index s for simplicity) may be
written as
14' =K4F4+K4F5+,..+K44F14
.................................	 (1)
I14 — K14F4+K14F5+•••+K14F14
Eq. (1) is a square linear system relative to un-
known values F4 , F5 ,. - . , F14 with diagonally-
dominated matrix and it can be easily solved by
usual methods. The coefficients of the system
Kq, are calculated by simulation of propagation
of different nuclei through the ATIC device with
FLUKA and the values P are already known after
steps 2 and 3. The ratio of B/C (calculated as the
ratio of the contents of the related charge boxes)
reduces at the step 4 up to 14%-42% for different
energies (the effect is energy dependent).
5. The next step is a transition from the spectra of
fluxes per region of Ed (see step 1) as a functions
of Ed (it is the result of step 4) to the spectra of
primary energy per nucleon. For each nucleus this
procedure includes firstly a calculation of expected
primary energy for each edge of the region of Ed
(see step 1). To solve this problem FLUKA simu-
lation of energy deposition was used with supposi-
tion of the primary differential momentum spectra
to be power one with the index -y = —2.6 (there
is only a weak dependence of exact value of y in
such a calculation). After normalization of the pri-
mary energy to the atomic weight and to the width
of the related energy region it is occurred that the
fluxes for different nuclei are connected with dif-
ferent energies. But one is interested for the ratio
of fluxes at the same energy per nucleon for any
species (it is the most physically meaningful quan-
tity). To obtain the ratio of fluxes at the same en-
ergies we calculate the energy points obtained as a
geometrical mean for the corresponding points for
boron and carbon and calculate all fluxes for these
energy points by interpolation of the spectrum of
each nucleus. This procedure increases B/C ratio
of the step 4 up to 13%-23% (different for differ-
ent energies).
6. The mean altitude of the flight of ATIC-2
was 36.5 km which corresponds approximately to
4.5 g/cm2 of the residual atmosphere. To obtain
the primary fluxes of the species above the at-
mosphere the interaction of nuclei in the atmo-
sphere should be accounted fora The interaction
may be described as fragmentation of nuclei with-
out changing of the energy per nucleon. Then the
interaction for each primary energy and for each
primary nucleus q may be described by a set of co-
efficients Lq„ q' < q which show the probability
to find the nucleus q' at the entrance of the de-
vice. The coefficients Lq, were calculated by sim-
ulation of propagation of nuclei in the atmosphere
by the FLUKA. Let 0, be the flux of nucleus q in
the terms of energy per nucleon at the entrance of
the device (these values are known after step 5; we
omit the index of the energy for simplicity) and cpq
be the same values above the atmosphere for some
definite energy per nucleon. Then one can write
V)4 = L4 W4 + ... + L4 W14+ 64
.,/. ......................
	
(2)
V)14 = L"4 014 + E14,
where E4, ... , E14 are small corrections related to
the fragmentation of nuclei heavier than silicon
(q = 14). This corrections are calculated approxi-
mately (we omit the details). If Eq are known then
the system (2) to be a square linear system relative
to V4i ... , cp 14 with the triangle and diagonally-
dominated matrix Lq, and it can be solved directly
starting from the final equation. The atmospheric
I
RELATIVE ABUNDANCES
Table 1: B/C, N/C, O/C ratio against primary en-
ergy per nucleon (GeV/n).
E B/C N/C O/C
19.9 0.173(12) 0.206(10) 0.965(21)
38.3 0.160(15) 0.173(12) 0.899(36)
74.3 0.108(31) 0.183(26) 1.041(60)
149 0.144(54) 0.171(44) 1.039(124)
307 0.053(62) 0.132(65) 0.951(193)
correction reduces B/C ratio to 13%-33% for dif-
ferent primary energies.
The experimental errors were calculated as a com-
bination of the Poisson dispersion of the exper-
imental statistics and the statistical errors of the
simulations. If the desired quantities were obtained
as a solution of a linear system (as in steps 4 and
6) then corresponding complete covariation matrix
were calculated by Monte Carlo method. All re-
ported errors are the standard deviations.
Results and discussion
The results for B/C; N/C, O/C ratio are presented in
table 1. The data for B/C ratio along with the data
of HEAO-3-C2 experiment [1] and with theoretical
predictions are shown in fig. 2. One can see that
the data of present work is in a reasonable agree-
ment with the data of [I ] but are extended to higher
energies. The theoretical curves in fig. 2 are calcu-
lations in leaky box approximation. The dashed
line is based on the HEAO-3-C2 fit for the Galaxy
escape length [1] Aasc = 34.1/3R-0 .60 g cm-2 (R
is the rigidity) and the solid line is for the escape
length obtained in the model of Kolmogorov type
of magnetic turbulence and reacceleration during
propagation [4]:
Aesc = 4.2(R/Ro) —I/3 [1 + (R/Ro) -2/3] g cm-2,
where Ro = 5.5 GV. Whereas the experimental
data support general trend of decreasing B/C ratio
with energy it is impossible to distinguish between
different models of propagation of particles due to
large experimental errors.
It should be noted that our experimental data are
model dependent due to extensive simulation of
rather high background by the FLUKA system, but
the situation may be improved by usage of addi-
tional simulation codes. One can expect that the
,O-	 I 
Energy per nucleon, GeV
Figure 2: B/C ratio from this work, from HEAO-
3-C2 experiment and from theory.
experimental separation between different models
of propagation would be possible with some ad-
ditional experiments of ATIC-type (ATIC itself or,
for example, CREAM).
We only present the data for N/C and O/C (table 1)
but do not discuss them due to a lack of room.
Acknowledgements. This work was supported by
RFBR Grant 05-02-16222 in Russia and NASA
Grants Nos. NNG04WC12G, NNG04WC10G,
NNG04WC06G in the USA.
References
[1] J. J. Engelmann et al. (HEAD Collaboration).
Astron. Astrophys., 233:96, 1990.
[2] A. Fasso et al. arXiv:hep-ph/0306267, 2003.
[3] T. G. Guzik et al. (ATIC Collaboration). Adv.
Sp. Res., 33(10):1763,2004.
[4] J. L. Osborn and V. S. Ptuskin. Sov. Astron.
Lett. 14(2):132,1988.
[5] A. D. Panov et al. (ATIC Collaboration). Adv.
Sp. Res., 37:1944, 2006.
[6] A. D. Panov et al. (ATIC Collaboration). Bull.
Russ. Acad. Sc.: Physics, 71:494,2007.
[7] N. V. Sokolskaya et al. Phys. Atom. Nucl.,
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Relative Abundances of Cosmic Ray Nuclei B-C-N-O in the Energy Region from 10 GeV/n to 300 GeV/n. Results from the Science Flight of the ATIC

Relative Abundances of Cosmic Ray Nuclei B-C-N-O in the Energy Region from 10 GeV/n to 300 GeV/n. Results from the Science Flight of the ATIC

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