The ratios of fluxes of heavy nuclei from sulfur (Z=16) to chromium (Z=24) to
the flux of iron were measured by the ATIC-2 experiment. The ratios are
decreasing functions of energy from 5 GeV/n to approximately 80 GeV/n, as
expected. However, an unexpected sharp upturn in the ratios are observed for
energies above 100 GeV/n for all elements from Z=16 to Z=24. Similar upturn but
with lower amplitude was also discovered in the ATIC-2 data for the ratio of
fluxes of abundant even nuclei (C, O, Ne, Mg, Si) to the flux of iron.
Therefore the spectrum of iron is significantly different from the spectra of
other abundant even nuclei.Comment: 4 pages, LaTeX2e, a paper for 23rd European Cosmic Ray Symposium
  (2012

Adams, J. H.

Ahn, H. S.

Bashindzhagyan, G. L.

Chang, J.

Christl, M.

Fazely, A. R.

Guzik, T. G.

Isbert, J.

Kim, K. C.

Kouznetsov, E. N.

Panasyuk, M. I.

Panov, A. D.

Seo, E. S.

Sokolskaya, N. V.

Watts, J. W.

Wefel, J. P.

Wu, J.

Zatsepin, V. I.

Journal of Physics : Conference Series

English

arXiv

A D Panov

N V Sokolskaya

V I Zatsepin

J H Adams

H S Ahn

G L Bashindzhagyan

J Chang

M Christl

A R Fazely

T G Guzik

J Isbert

K C Kim

E N Kouznetsov

M I Panasyuk

E S Seo

J W Watts

J P Wefel

J Wu

Crossref

Journal of Physics Conference Series

Upturn observed in heavy nuclei to iron ratios by the ATIC-2 experiment

The ratios of fluxes of heavy nuclei from sulfur (Z=16) to chromium (Z=24) to the flux of iron were measured by the ATIC-2 experiment. The ratios are decreasing functions of energy from 5 GeV/n to approximately 80 GeV/n, as expected. However, an unexpected sharp upturn in the ratios are observed for energies above 100 GeV/n for all elements from Z=16 to Z=24. Similar upturn but with lower amplitude was also discovered in the ATIC-2 data for the ratio of fluxes of abundant even nuclei (C, O, Ne, Mg, Si) to the flux of iron. Therefore the spectrum of iron is significantly different from the spectra of other abundant even nuclei

LSU Scholarly Repository (Louisiana State Univ.)

Louisiana State University LSU Scholarly Repository Faculty Publications Department of Physics & Astronomy 1-1-2013 Upturn observed in heavy nuclei to iron ratios by the ATIC-2 experiment A. D. Panov Lomonosov Moscow State University N. V. Sokolskaya Lomonosov Moscow State University V. I. Zatsepin Lomonosov Moscow State University J. H. Adams NASA Marshall Space Flight Center H. S. Ahn University of Maryland, College Park See next page for additional authors Follow this and additional works at: https://repository.lsu.edu/physics_astronomy_pubs Recommended Citation Panov, A., Sokolskaya, N., Zatsepin, V., Adams, J., Ahn, H., Bashindzhagyan, G., Chang, J., Christl, M., Fazely, A., Guzik, T., Isbert, J., Kim, K., Kouznetsov, E., Panasyuk, M., Seo, E., Watts, J., Wefel, J., & Wu, J. (2013). Upturn observed in heavy nuclei to iron ratios by the ATIC-2 experiment. Journal of Physics: Conference Series, 409 (1) https://doi.org/10.1088/1742-6596/409/1/012036 This Conference Proceeding is brought to you for free and open access by the Department of Physics & Astronomy at LSU Scholarly Repository. It has been accepted for inclusion in Faculty Publications by an authorized administrator of LSU Scholarly Repository. For more information, please contact ir@lsu.edu. Authors A. D. Panov, N. V. Sokolskaya, V. I. Zatsepin, J. H. Adams, H. S. Ahn, G. L. Bashindzhagyan, J. Chang, M. Christl, A. R. Fazely, T. G. Guzik, J. Isbert, K. C. Kim, E. N. Kouznetsov, M. I. Panasyuk, E. S. Seo, J. W. Watts, J. P. Wefel, and J. Wu This conference proceeding is available at LSU Scholarly Repository: https://repository.lsu.edu/physics_astronomy_pubs/2206 Journal of Physics: Conference SeriesOPEN ACCESSUpturn observed in heavy nuclei to iron ratios bythe ATIC-2 experimentTo cite this article: A D Panov et al 2013 J. Phys.: Conf. Ser. 409 012036 View the article online for updates and enhancements.You may also likeDark matter and collider phenomenologyof split-UEDChuan-Ren Chen, Mihoko M. Nojiri, SeongChan Park et al.-Electrons and Positrons in Cosmic RaysA D Panov-Dark matter sees the lightPatrick Meade, Michele Papucci andTomer Volansky-Recent citationsFirst results of the cosmic ray NUCLEONexperimentE. Atkin et al-Origin of the spectral upturn in the cosmic-ray C/Fe and O/Fe ratiosNicola Tomassetti-Upturn in the heavy nuclei to iron ratio inthe ATIC experiment above 100GeV/nucleonA. D. Panov et al-This content was downloaded from IP address 130.39.60.163 on 29/10/2021 at 13:49Upturn observed in heavy nuclei to iron ratios by theATIC-2 experimentA D Panov1, N V Sokolskaya1, V I Zatsepin1, J H Adams, Jr.2, H SAhn3, G L Bashindzhagyan1, J Chang4, M Christl5, A R Fazely6 T GGuzik5, J Isbert5, K C Kim3, E N Kouznetsov1, M I Panasyuk1, E SSeo3, J W Watts2, J P Wefel5, J Wu31 Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, Russia2 Marshall Space Flight Center, Huntsville, AL, USA3 University of Maryland, Institute for Physical Science & Technology, College Park, MD, USA4 Purple Mountain Observatory, Chinese Academy of Sciences, China5 Louisiana State University, Department of Physics and Astronomy, Baton Rouge, LA, USA6 Southern University, Department of Physics, Baton Rouge, LA, USAE-mail: panov@dec1.sinp.msu.ruAbstract. The ratios of fluxes of heavy nuclei from sulfur (Z=16) to chromium (Z=24) to theflux of iron were measured by the ATIC-2 experiment. The ratios are decreasing functions ofenergy from 5 GeV/n to approximately 80 GeV/n, as expected. However, an unexpected sharpupturn in the ratios are observed for energies above 100 GeV/n for all elements from Z=16 toZ=24. Similar upturn but with lower amplitude was also discovered in the ATIC-2 data for theratio of fluxes of abundant even nuclei (C, O, Ne, Mg, Si) to the flux of iron. Therefore thespectrum of iron is significantly different from the spectra of other abundant even nuclei.1. IntroductionIt is generally expected that the ratio of flux of a secondary cosmic ray nucleus to the flux ofthe corresponding parent nucleus should be decreasing function of energy. It is a very generalconsequence of decreasing the diffusion galaxy escape time with energy. This expectation wasconfirmed very well for energies up to several tens of GeV in HEAO-3-C2 experiment [1], HEAO-3-C3 experiment [2, 3, 4] and other experiments. Some essential fractions of the nuclei Ar (Z=18)and Ca (Z=20) in cosmic rays are supposed to be secondary daughter nuclei of spallation of ironas a parent [5] therefore Ar/Fe and Ca/Fe ratios may be expected to be decreasing functionsof energy. However the data of HEAO-3-C3 experiment [2, 3, 4] revealed unexpected upturnof the ratios near the energy 100 GeV/n and their increasing in the region 100–600 GeV/n.The observed upturn was not surely recognized as a real physical effect in [2, 3, 4] and possiblesystematic origin was supposed as well. Similar unexpected upturn was observed in Ti/Fe ratioin the data of the ATIC-2 experiment [6] near the energy 70–80 GeV/n, but the statistics for theenergies above 100 GeV/n were insufficient and the upturn was considered in [6] to be statisticallyinsignificant. While both in the HEAO-3-C3 experiment and in the ATIC-2 experiment theupturn in the ratio was not taken seriously, the resemblance of the observed phenomena forcesone to study the phenomenon more accurately. Careful investigation of ratios of heavy nucleifluxes to the flux of iron in the ATIC-2 experiment is the main object of the present work.23rd European Cosmic Ray Symposium (and 32nd Russian Cosmic Ray Conference) IOP PublishingJournal of Physics: Conference Series 409 (2013) 012036 doi:10.1088/1742-6596/409/1/012036Published under licence by IOP Publishing Ltd 1Hereinafter we call the range of charges Z = 16 – 24 as group H−. Manganese (Z = 25) isnot included in the group H− because it may be contaminated by iron under conditions of theATIC experiment. Note that there are a number of low-statistics data (emulsion experiments[7, 8, 9, 10], TRACER 2 TeV/n point for B/C ratio [11]) that indicate fluxes of secondary nucleiat energies above 100–500 GeV/n to be high relative to simple leaky-box predictions with escapepath length ∝ E−0.6 or to similar models. Therefore the study of secondary to primary fluxesratio at high energies is an important problem.2. MethodThe details of the ATIC long duration balloon project are descibed in [12]. There are two maindifficulties to carry out the described program in the ATIC experiment. The first one is lowstatistics at high energies (as it was noted in [6] in relation to Ti/Fe ratio), the second one isinsufficient charge resolution of ATIC experiment in the group H− that prevents to separatefluxes of adjacent nuclei carefully. The method proposed here solves both problems.Since the upturn of flux ratios in HEAO-3-C3 (Ar/Fe and Ca/Fe) and in ATIC (Ti/Fe) wasobserved for quite different charges in the group H−, one reasonably may suppose that thephenomenon is common for the total group H−. Therefore it is meaningful to study the effectaveraged on the whole group H− or for large parts of this group. One improves the statisticsby this way and at the same time solves the problem of insufficient charge resolution. If onestudies combined spectrum in terms of energy per nucleon for large charge region, then theerrors related to the low charge resolution are connected only with the margins of the regionand are relatively small.To proceed with this idea we consider the charge Z to be a continuous variable which ismeasured by the apparatus. We consider the atomic weight A to be a continuous piece-linearfunction of Z which is obtained by interpolation of actual relation Z(A). To obtain charges ofnuclei we use the usual ATIC’s silicon matrix technique with correction for relativistic increasingof ionization capability as described in [6]. To reconstruct the primary energy of particles we usethe method of differential energy shift described in [13]. To reconstruct the spectra at the top ofthe atmosphere from the spectra at the top of the calorimeter, the correction for fragmentationof nuclei in the atmosphere is carried out with coefficients calculated with FLUKA system for4.81 g/cm2 of the residual atmosphere with technique described in [14]. These coefficients are0.897, 0.843, 0.901, 0.840, 0.798, 0.715 for C, O, Ne, Mg, Si and Fe respectively.To check the method we first obtained the summary spectrum for all nuclei from carbon toiron in terms of energy per nucleon. Practically it is the spectrum obtained with the methoddescribed above for the charge range 5.5 < Z < 27. The result is shown in Fig. 1. The spectrumlooks as one could expect. Particularly, the expected hardening of the spectrum at energiesabove approximately 200 GeV/n discovered by ATIC [13] and confirmed by CREAM [15, 16] isclearly seen.3. ResultsRatio of the spectrum for the whole H− group to the spectrum of iron obtained in the ATIC-2experiment is shown in Fig. 2. Undoubtedly the upturn observed by HEAO-3-C3 for Ar/Fe andCa/Fe [2, 3, 4] is qualitatively confirmed by the ATIC data for the spectrum of H− group. Ratiosof fluxes for sub-regions of H− group (15.5 < Z < 20.5)/Fe and (20.5 < Z < 24.5)/Fe are shownin Fig. 3 and Fig. 4 respectively. The difference between the nature of regions (15.5 < Z < 20.5)and (20.5 < Z < 24.5) is that the contribution of primary nuclei to Ar and Ca fluxes expectedto be prominent in the first region, but it is generally supposed that the nuclei from the secondregion are mainly secondary [5]. Nevertheless, the upturn is clearly seen for both regions ofcharges, therefore it looks to be a general property of the whole group H−.23rd European Cosmic Ray Symposium (and 32nd Russian Cosmic Ray Conference) IOP PublishingJournal of Physics: Conference Series 409 (2013) 012036 doi:10.1088/1742-6596/409/1/0120362E/n, GeV1 10 210 310 4102.6 (GeV/n)−1 ster−1 s−2, m2.6 E×Flux 210Figure 1. The spectrum of all nuclei fromcarbon to iron (5.5 ≤ Z ≤ 27) in the termsof energy per nucleon.E/n, GeV1 10 210 310Ratio00.511.522.53Figure 2. Flux of (15.5 < Z < 24.5) to ironratio.E/n, GeV1 10 210 310Ratio00.511.522.5Figure 3. Flux of (15.5 < Z < 20.5) to ironratio.E/n, GeV1 10 210 310Ratio00.20.40.60.81Figure 4. Ratio of flux of (20.5 < Z < 24.5)to iron.4. DiscussionFrom these observations, it would be too early to deduce the conclusion that the upturn of theratio H−/iron is related to the behavior of spectra of secondary nuclei produced by spallationof iron. The ratio of oxygen to iron fluxes is shown in Fig. 5. It is seen that there exists similarupturn in the ratio. The ratios of C/Fe, (Ne+Mg+Si)/Fe measured by ATIC-2 look very similarto the O/Fe ratio. Therefore the upturn of ratios is not an attribute of the secondary nucleiexclusively. Rather it may be connected (even if partially) with some special behavior of the ironspectrum in the ATIC data relatively to the spectra of all other nuclei 6 ≤ Z ≤ 25. However, itis important that the amplitude of modulation in the ratios H−/iron (Fig. 2 – Fig. 4) is higherthan for the ratios of abundant nuclei like O/Fe (Fig. 5). Note, that the spectra of abundanteven nuclei C, O, Ne, Mg, Si measured by ATIC are in good agreement with the data of otherexperiments [17].To exclude the possibility that the observed upturn in the ratio of fluxes of various nuclei tothe flux of iron is related to some systematics in the ATIC spectrum of iron, we have calculatedthe ratio of H− group measured by ATIC to the iron measured by TRACER [18] and by CREAM[15] (there are no direct data for H−/Fe from both TRACER and CREAM). The TRACER andCREAM data were recalculated to the ATIC energies by interpolation on energy. The result ofcomparison is shown in Fig. 6. The data of HEAO-3-C2 experiment [1] are also shown here. All23rd European Cosmic Ray Symposium (and 32nd Russian Cosmic Ray Conference) IOP PublishingJournal of Physics: Conference Series 409 (2013) 012036 doi:10.1088/1742-6596/409/1/0120363E/n, GeV1 10 210 310Ratio024681012Figure 5. Ratio of oxygen flux to the flux ofiron measured by the ATIC-2 experiment.E/n, GeV1 10 210 310Ratio00.511.522.533.5ATIC, (15.5<Z<24.5) / FeHEAO−3−C2, (15.5<Z<24.5) / FeATIC(15.5<Z<24.5) / TRACER(Fe)ATIC(15.5<Z<24.5) / CREAM(Fe)Figure 6. Ratio of (15.5 < Z < 24.5)/iron inATIC and other experiments (see the text).the data are in a reasonable agreement within statistics (an exception is a bit lower absoluteratio of fluxes in HEAO-3-C2, but the shape of the curve reproduces the ATIC’s data well).Therefore, there are no signs of systematics in the discovered upturn in the ratio of fluxes. Anumber of other tests to exclude systematics that we can not mention here were also carriedout. Among other factors, we have analyzed the data on super-iron nuclei. No indications ofsystematics were found. Thus we consider the upturn of ratios to be a real physical phenomenon,and it seems to indicate that the spectrum of iron is different from other primary nuclei.The work was supported in Russia by RFBR grant number 11-02-00275.References[1] Engelmann J, Ferrando P, Soutoul A, Goret P, Juliusson E, Koch-Miramond L, Lund N and Masse P 1990A&A 233 96[2] Jones M, Klarmann J, Stone E, Waddington C, Binns W, Garrard T and Israel M 1985 Proc. of 19th Intern.Cosmic Ray Conf. vol 2 p 28[3] Israel M, Jones M, Kamionkowski M, Klarmann J, Stone E, Waddington C, Binns W and Garrard T 1987Proc. of 20th Intern. Cosmic Ray Conf. vol 1 p 330[4] Binns W, Garrard T, Israel M, Jones M D, Kamionkowski M, Klarmann J, Stone E and Waddington C 1988ApJ 324 1106[5] Shapiro M, Silberberg R and Tsao C 1972 Space Research XII (Berlin: Akademic-Verlag) p 1609[6] Zatsepin V I, et al 2009 Astronomy Letters 35 338[7] Hareyama M, Ichimura M, Kamioka E, Kobayashi T, Kuramata S, Matsutani H, Nanjo H, Shibata T andSugimoto H 1999 Proc. of 26th Intern. Cosmic Ray Conf. vol 3 p 105[8] Takahashi Y (for the JACEE Collaboration) 1998 Nucl. Phys. B, Proc. Suppl. 60 83[9] Hareyama M, et al 2005 ApJ Letters 628 L41[10] Ichimura M, et al 2005 Proc. of 29th Intern. Cosmic Ray Conf. vol 3 p 21[11] Obermeier A, Ave M, Boyle P, Höppner C, Hörandel J and Müller D 2011 ApJ 742 14[12] Guzik T G, et al 2004 Advances in Space Reseach 33 1763[13] Panov A D, et al 2007 Bulletin of the Russian Academy of Sciences: Physics 71 494[14] Panov A D, et al 2008 Proc. of 30th Intern. Cosmic Ray Conf. vol 2 p 3[15] Ahn H S, et al 2009 ApJ 707 593[16] Ahn H S, et al 2010 ApJ Letters 714 L89[17] Panov A D, et al 2009 Bulletin of the Russian Academy of Sciences: Physics 73 564[18] Ave M, Boyle P, Gahbauer F, Höppner C, Hörandel J, Ichimura M, Müller D and Romero-Wolf A 2008 ApJ678 26223rd European Cosmic Ray Symposium (and 32nd Russian Cosmic Ray Conference) IOP PublishingJournal of Physics: Conference Series 409 (2013) 012036 doi:10.1088/1742-6596/409/1/0120364

Upturn observed in heavy nuclei to iron ratios by the ATIC-2 experiment

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