Observation of heavy cosmic-ray primaries over the wide energy range from 100 GeV/particle to 100 TeV/particle

Is the celebrated knee actually so prominent?

Masakatsu Ichimura, Masataka Kogawa, Shuichi Kuramata, Hiroyuki Mito, Takayuki Murabayashi, Hirotada Nanjo, Takahiro Nakamura, Katsuyuki Ohba, Tatsumi Ohuchi, Tomohiko Ozawa, Yoshiyuki Yamada, Hideya Matsutani, Zenjiro Watanabe, Eiji Kamioka, Keisuke Kirii, Motoyasu Kitazawa, Tadashi Kobayashi, Atsusi Mihashi, Toru Shibata, Kazuo Shibuta & 2 others Hisahiko Sugimoto, Kazuma Nakazawa

Research output: Contribution to journalArticle

98 Citations (Scopus)

Abstract

We have exposed a new type of emulsion chamber of area 1.53 m2 at an atmospheric depth of 11.7 g/cm2 for 22.2 h. The chamber makes extensive use of screen-type x-ray films, which have recorded the tracks due to over 100 000 cosmic-ray heavy primary nuclei of Z8. With this experiment we have succeeded in determining the absolute intensities of the heavy primaries over a pretty wide energy range from a few GeV/nucleon up to 1 TeV/nucleon, using a single detector and a unified charge-and-energy determination method. In the present paper we give a report of our results on silicon and heavier components, accompanied by a detailed account on our newly adopted energy determination method and a discussion of its accuracy. Our iron flux is in agreement with that obtained by Spacelab-2, the integral spectral index being nearly constant, 1.5, up to a few TeV/nucleon. Of peculiar interest is our silicon flux, which is again consistent with the Spacelab-2 result. The energy spectrum gets softer beyond 100 GeV/nucleon, being as high as 1.95 there. Current interstellar acceleration and propagation models will meet difficulty in explaining this result. We also report about the abundance ratio of the subiron group to iron, which is strongly sensitive to the escape length of cosmic rays in the Galaxy, and find that it decreases in the form of power laws over the wide energy range from a few GeV/nucleon to a few TeV/nucleon, though a quantitative study in connection with a particular propagation model is reserved to the future. Our all-particle spectrum deviates significantly from that of the proton satellites beyond 50 TeV/particle, while both agree rather well with each other in the lower energy range. When we investigate individual heavy components, we find that all their respective fluxes multiplied by EP2.5 (EP is the primary energy per particle) show a decreasing tendency around 10 TeV/particle and beyond, no indication of recovery being observed as the energy gets even higher. This means that the heavy components, paricularly iron, do not increase so drastically as to cover the excess in the knee region. Extrapolation of our all-particle spectrum up to 10151016 eV/particle indicates a milder knee shape than that found by the air shower experiments. If the break is as sharp as hitherto reported, then it will suggest either (i) there is a sharp break which might be due to a drastic advent of new components (other than heavy primary nuclei), or a drastic change in nuclear interaction, or (ii) the break just appears to be sharp due to a 20% (or more) systematic overestimation in converting the air shower sizes into the primary energy values in the knee region.

Original languageEnglish
Pages (from-to)1949-1975
Number of pages27
JournalPhysical Review D
Volume48
Issue number5
DOIs
Publication statusPublished - 1993
Externally publishedYes

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heavy cosmic ray primaries
Spacelab
energy
cosmic ray showers
iron
Proton satellites
chambers
nuclei
propagation
nuclear interactions
silicon
emulsions
escape
extrapolation
cosmic rays
indication
tendencies
energy spectra
recovery

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)

Cite this

Observation of heavy cosmic-ray primaries over the wide energy range from 100 GeV/particle to 100 TeV/particle : Is the celebrated knee actually so prominent? / Ichimura, Masakatsu; Kogawa, Masataka; Kuramata, Shuichi; Mito, Hiroyuki; Murabayashi, Takayuki; Nanjo, Hirotada; Nakamura, Takahiro; Ohba, Katsuyuki; Ohuchi, Tatsumi; Ozawa, Tomohiko; Yamada, Yoshiyuki; Matsutani, Hideya; Watanabe, Zenjiro; Kamioka, Eiji; Kirii, Keisuke; Kitazawa, Motoyasu; Kobayashi, Tadashi; Mihashi, Atsusi; Shibata, Toru; Shibuta, Kazuo; Sugimoto, Hisahiko; Nakazawa, Kazuma.

In: Physical Review D, Vol. 48, No. 5, 1993, p. 1949-1975.

Research output: Contribution to journalArticle

Ichimura, M, Kogawa, M, Kuramata, S, Mito, H, Murabayashi, T, Nanjo, H, Nakamura, T, Ohba, K, Ohuchi, T, Ozawa, T, Yamada, Y, Matsutani, H, Watanabe, Z, Kamioka, E, Kirii, K, Kitazawa, M, Kobayashi, T, Mihashi, A, Shibata, T, Shibuta, K, Sugimoto, H & Nakazawa, K 1993, 'Observation of heavy cosmic-ray primaries over the wide energy range from 100 GeV/particle to 100 TeV/particle: Is the celebrated knee actually so prominent?', Physical Review D, vol. 48, no. 5, pp. 1949-1975. https://doi.org/10.1103/PhysRevD.48.1949
Ichimura, Masakatsu ; Kogawa, Masataka ; Kuramata, Shuichi ; Mito, Hiroyuki ; Murabayashi, Takayuki ; Nanjo, Hirotada ; Nakamura, Takahiro ; Ohba, Katsuyuki ; Ohuchi, Tatsumi ; Ozawa, Tomohiko ; Yamada, Yoshiyuki ; Matsutani, Hideya ; Watanabe, Zenjiro ; Kamioka, Eiji ; Kirii, Keisuke ; Kitazawa, Motoyasu ; Kobayashi, Tadashi ; Mihashi, Atsusi ; Shibata, Toru ; Shibuta, Kazuo ; Sugimoto, Hisahiko ; Nakazawa, Kazuma. / Observation of heavy cosmic-ray primaries over the wide energy range from 100 GeV/particle to 100 TeV/particle : Is the celebrated knee actually so prominent?. In: Physical Review D. 1993 ; Vol. 48, No. 5. pp. 1949-1975.
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T1 - Observation of heavy cosmic-ray primaries over the wide energy range from 100 GeV/particle to 100 TeV/particle

T2 - Is the celebrated knee actually so prominent?

AU - Ichimura, Masakatsu

AU - Kogawa, Masataka

AU - Kuramata, Shuichi

AU - Mito, Hiroyuki

AU - Murabayashi, Takayuki

AU - Nanjo, Hirotada

AU - Nakamura, Takahiro

AU - Ohba, Katsuyuki

AU - Ohuchi, Tatsumi

AU - Ozawa, Tomohiko

AU - Yamada, Yoshiyuki

AU - Matsutani, Hideya

AU - Watanabe, Zenjiro

AU - Kamioka, Eiji

AU - Kirii, Keisuke

AU - Kitazawa, Motoyasu

AU - Kobayashi, Tadashi

AU - Mihashi, Atsusi

AU - Shibata, Toru

AU - Shibuta, Kazuo

AU - Sugimoto, Hisahiko

AU - Nakazawa, Kazuma

PY - 1993

Y1 - 1993

N2 - We have exposed a new type of emulsion chamber of area 1.53 m2 at an atmospheric depth of 11.7 g/cm2 for 22.2 h. The chamber makes extensive use of screen-type x-ray films, which have recorded the tracks due to over 100 000 cosmic-ray heavy primary nuclei of Z8. With this experiment we have succeeded in determining the absolute intensities of the heavy primaries over a pretty wide energy range from a few GeV/nucleon up to 1 TeV/nucleon, using a single detector and a unified charge-and-energy determination method. In the present paper we give a report of our results on silicon and heavier components, accompanied by a detailed account on our newly adopted energy determination method and a discussion of its accuracy. Our iron flux is in agreement with that obtained by Spacelab-2, the integral spectral index being nearly constant, 1.5, up to a few TeV/nucleon. Of peculiar interest is our silicon flux, which is again consistent with the Spacelab-2 result. The energy spectrum gets softer beyond 100 GeV/nucleon, being as high as 1.95 there. Current interstellar acceleration and propagation models will meet difficulty in explaining this result. We also report about the abundance ratio of the subiron group to iron, which is strongly sensitive to the escape length of cosmic rays in the Galaxy, and find that it decreases in the form of power laws over the wide energy range from a few GeV/nucleon to a few TeV/nucleon, though a quantitative study in connection with a particular propagation model is reserved to the future. Our all-particle spectrum deviates significantly from that of the proton satellites beyond 50 TeV/particle, while both agree rather well with each other in the lower energy range. When we investigate individual heavy components, we find that all their respective fluxes multiplied by EP2.5 (EP is the primary energy per particle) show a decreasing tendency around 10 TeV/particle and beyond, no indication of recovery being observed as the energy gets even higher. This means that the heavy components, paricularly iron, do not increase so drastically as to cover the excess in the knee region. Extrapolation of our all-particle spectrum up to 10151016 eV/particle indicates a milder knee shape than that found by the air shower experiments. If the break is as sharp as hitherto reported, then it will suggest either (i) there is a sharp break which might be due to a drastic advent of new components (other than heavy primary nuclei), or a drastic change in nuclear interaction, or (ii) the break just appears to be sharp due to a 20% (or more) systematic overestimation in converting the air shower sizes into the primary energy values in the knee region.

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