- Email: [email protected]
BESS data on primary cosmic rays and muons
UCLEAR PHYSICS:
PROCEEDINGS SUPPLEMENTS ELSEVIER
Nuclear Physics B (Pro¢. Suppl.) 100 (2001) 121-123
www.elsevier.nl/loeate/npe
BESS Data on Primary Cosmic Rays and Muons T. Sanuki a for the BESS Collaboration* aDepartment of Physics, Graduate school of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. We have measured absolute fluxes of primary protons, helium nuclei and atmospheric muons with the BESS spectrometer. Precise measurement of these cosmic-ray particles is indispensable for improving the accuracy in the atmospheric neutrino calculations.
1. I N T R O D U C T I O N The flux of atmospheric neutrino of flavor i (¢,,) is
TOF
¢,,, = Cp® Rp® Yp~,,, + C CA ® RA ® YA~,,,,(1 ) A
where Cp(A) is the flux of primary protons (nuclei of mass A). Rp(A) and Yp...,~, represent the effect of the geomagnetic field and the yield of neutrinos per primary particle, respectively [1]. In order to improve the accuracy in the atmospheric neutrino calculations, these three factors (¢p(A), Rp(a), and Yp(A)~,,,) have to be known precisely. We have measured absolute fluxes of primary protons, helium nuclei and atmospheric muons with the BESS spectrometer. The precise measurement of primary cosmic rays improves the accuracy of Cp(A). The fluxes of atmospheric muons at different sites provide useful information about Rp(A) and Yp(A)~,.
0.....
q.5m
/m
Particte
Figure 1. Cross-sectional view of the BESS.
2, B E S S S P E C T R O M E T E R
The BESS (Figure 1) is a high-resolution spectrometer with a large acceptance to perform highly sensitive searches for rare cosmic-ray components, as well as precise measurement of the absolute fluxes of various cosmic rays [2-4]. *BESS Collaboration formed with The University of Tokyo, High Energy Accelerator Research Laboratory (KEK), Kobe University, NASA Goddard Space Flight Center, University of Maryland, and The Institute of Space and Astronautical Science.
A magnetic-rigidity of charged particle is measured by a spectrometer, which consists of a thin superconducting solenoidal magnet, a JET-type drift chamber, and two inner-driftchambers (IDC's). Time-of-flight (TOF) hodoscopes provide the velocity (fl) and energy loss (dE/dx) measurements. An electromagnetic shower counter has been equipped for e/p separation. Detailed analysis procedures and the discussion of errors are described in [5] and [6].
0920-5632/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII S0920-5632(01 )01423-2
122
T Sanuki/Nuclear Physics B (Proc. Suppl.) 100 (2001) 121-123
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0 Webber el ~ . 1987 A Boezio et al." 1999
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o. Sepie:ieal~21791193~ ~.ileC~teatla/i~O00
--
.... Honda et al. 1 9 9 5 ( M I N so ar mod.) I I I i I I Ill i i i i i i i i]
10
102 KineticEnergy Ek(GeV/n)
8
7 6
et
Allkofcr al. Rastin MASS-89 CAPRICE-97 CAPRICE-94 BESS-95 BESS-97/98/99
,,,I
i
1
i
altitude
R¢
Kiel 10m 2.4GV Nottingham 50rn 2,6GV Prince Albert 6 0 0 m 0,7GV Ft. Summner 1270m 4,2GV Lynn Lake 360rn 0.SGV Tsukuba 30m l l . 2 G V Lynn Lake 3 6 0 m 0.5GV t
i
i
i I t [
10 Momentum P (GeV/c)
Figure 2. Absolute differential p and He spectra.
Figure 3. Absolute differential muon spectrum.
3. R E S U L T S
deviation among the two spectra becomes larger with decreasing momentum. The deviation comes from the influence of the geomagnetic filed. This influence is demonstrated more clearly by # + ~ p ratio as shown in Figure 5 [6].
3.1. Primary cosmic rays Figure 2 shows the absolute differential proton and helium spectra at the top of the atmosphere measured by a BESS-1998 balloon experiment [5] in comparison with other experiments [7-17].
3.2. A t m o s p h e r i c m u o n s Figure 3 and 4 shows the absolute differential spectrum of muons (p+ + p - ) at sea level [6] together with other measurements performed at various sites [18-21]. The muon intensity varies depending on environmental conditions. The altitude and cutoff rigidity for primary cosmic rays (Re) are indicated in the figures. As is seen in Figure 3, the muon spectra measured by BESS in Tsukuba and in Lynn Lake are in good agreement in higher momentum region, where the cutoff rigidity for primary cosmic rays can be neglected. Figure 4 shows, however, a
4. C O N C L U S I O N As for primary protons and helium nuclei, i.e., Cp(A) in Eqs. (1), BESS results, as well as other recent measurements, are more favorable to lower fluxes than the ones assumed in the atmospheric neutrino calculation [22] above a few tens of GeV. It may suggest importance of reconsideration for the atmospheric neutrino flux predictions. The absolute fluxes of atmospheric muons are directly related to the yield of neutrinos, Yp~,, in Eqs. (1). T h e / t + / / l - ratio in a low momentum region is sensitive to the effect of the geomagnetic field, Rv(A ) in Eqs. (1). Detailed study of the atmospheric muons will improve the accuracy in
123
7:. Sanuki/Nuclear Physics B (Proc. Suppl.) 100 (2001) 121-123
o
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,
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.
.
.
.
.
.
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Re
Kiel 10m 2.4GV Nottingham 50m 2.6GV Prince Albert 600m 0.TGV Ft. Sumnmer 1270m 4.2GV Lynn Lake 360m 0.5GV Tsukuba 30m I1.2GV Lynn Lake 360m 0.5GV I
site t3 BESS-95 Tsukuba • BESS-97/98/99 Lynn Lake
I
1
t
12"
l~_
Figure 5. p + / p - ratio at sea level.
I [
10 Momentum
P (GeV/c)
7. Figure 4. Absolute differential muon spectrum. 8. 9. the estimation of the neutrino yield and the effect of the geomagnetic field. REFERENCES
1. See, for example, T. K. Gaisser, Proc. Neutrino Oscillations and their Origin, ed. Y. Suzuki, M. Nakahara, N.Shiozawa, and K. Kaneyuki (Tokyo, UAP Inc.) (2000) 45 2. S. Orito, Proc. A S T R O M A G Workshop, ed. J. Nishimura, K. Nakamura, and A. Yamamoto (Ibaraki, KEK) (1987) KEK Report KEK87-19 111 3. A. Yamamoto et al., Adv. Space Res. 14 (1994) 75. 4. Y. Ajima et al., Nucl. Instr. and Meth. A443 (2000) 71. 5. T. Sanuki et al. ApJ 545 (2000) 1135. 6. M. Motoki, Proc. Neutrino Oscillations and their Origin, ed. Y. Suzuki, M. Nakahara,
10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.
N.Shiozawa, and K. Kaneyuki (Tokyo, UAP Inc.) (2000) 19 M . J . Ryan et al., Phys. Rev. Lett. 28 (1972) 985. L.H. Smith et al., ApJ 180 (1973) 987. W. R. Webber et al., Proc. 20th ICRC(Moscow) 1 (1987) 325. E. S. Seo et al., ApJ 378 (1991) 763. P. Papini et al., Proc. 23rd ICRC(Calgary) 1 (1993) 579. J. Buckley et al., ApJ 429 (1994) 736. W. Menn et al., Proc. 25th ICRC(Durban) 3 (1997) 409 R. Bellotti et al., Phys. Rev. D60 (1999) 052002. M. Boezio et al., ApJ 518 (1999) 457. J. Alcaraz et al., Phys. Lett. B490 (2000) 27. J. Alcaraz et al., To be published in Phys. Lett. B. O. C. Allkofer, K. Carstensen, and W. D. Dau, Phys. Lett. B36 (1971) 425. B. C. Rastine, J. Phys. G10 (1984) 1609. M. P. De Pascal et al., J. Geophys. Res. 98 (1993) 3501 J. Kremer et al., Phys. Rev. Lett. 83 (1999) 4241. M. Honda, T. Kajita, K. Kasahara, and S. Midorikawa, Phys. Rev. D52 (1995) 4985.
PROCEEDINGS SUPPLEMENTS ELSEVIER
Nuclear Physics B (Pro¢. Suppl.) 100 (2001) 121-123
www.elsevier.nl/loeate/npe
BESS Data on Primary Cosmic Rays and Muons T. Sanuki a for the BESS Collaboration* aDepartment of Physics, Graduate school of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. We have measured absolute fluxes of primary protons, helium nuclei and atmospheric muons with the BESS spectrometer. Precise measurement of these cosmic-ray particles is indispensable for improving the accuracy in the atmospheric neutrino calculations.
1. I N T R O D U C T I O N The flux of atmospheric neutrino of flavor i (¢,,) is
TOF
¢,,, = Cp® Rp® Yp~,,, + C CA ® RA ® YA~,,,,(1 ) A
where Cp(A) is the flux of primary protons (nuclei of mass A). Rp(A) and Yp...,~, represent the effect of the geomagnetic field and the yield of neutrinos per primary particle, respectively [1]. In order to improve the accuracy in the atmospheric neutrino calculations, these three factors (¢p(A), Rp(a), and Yp(A)~,,,) have to be known precisely. We have measured absolute fluxes of primary protons, helium nuclei and atmospheric muons with the BESS spectrometer. The precise measurement of primary cosmic rays improves the accuracy of Cp(A). The fluxes of atmospheric muons at different sites provide useful information about Rp(A) and Yp(A)~,.
0.....
q.5m
/m
Particte
Figure 1. Cross-sectional view of the BESS.
2, B E S S S P E C T R O M E T E R
The BESS (Figure 1) is a high-resolution spectrometer with a large acceptance to perform highly sensitive searches for rare cosmic-ray components, as well as precise measurement of the absolute fluxes of various cosmic rays [2-4]. *BESS Collaboration formed with The University of Tokyo, High Energy Accelerator Research Laboratory (KEK), Kobe University, NASA Goddard Space Flight Center, University of Maryland, and The Institute of Space and Astronautical Science.
A magnetic-rigidity of charged particle is measured by a spectrometer, which consists of a thin superconducting solenoidal magnet, a JET-type drift chamber, and two inner-driftchambers (IDC's). Time-of-flight (TOF) hodoscopes provide the velocity (fl) and energy loss (dE/dx) measurements. An electromagnetic shower counter has been equipped for e/p separation. Detailed analysis procedures and the discussion of errors are described in [5] and [6].
0920-5632/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII S0920-5632(01 )01423-2
122
T Sanuki/Nuclear Physics B (Proc. Suppl.) 100 (2001) 121-123
-~10
a
9
.,o,on Lk"k '
200 . . . . . . . . . . . .
:, :i .
~ /
~ . ~ ~ _
90
~'E 80~ g
~
o x ~10
3
",~* 0 -¢
*
~x 60
• BESS-98 Flight (This experiment)
* ¢r
zx.~u
u. 40 '::t. ++
.
Helium
2~I
~: ..~-w
70
_~
Ejt ~,
~_ -//--
_~ 30
T
z~m
Ii
.
site
! ~ i~~ ; 10 2
1197723 ~ BU~lklte~eta~l1994
0 Webber el ~ . 1987 A Boezio et al." 1999
:~ ~ -*
R~fia~heett%
0 0 * A • D •
o. Sepie:ieal~21791193~ ~.ileC~teatla/i~O00
--
.... Honda et al. 1 9 9 5 ( M I N so ar mod.) I I I i I I Ill i i i i i i i i]
10
102 KineticEnergy Ek(GeV/n)
8
7 6
et
Allkofcr al. Rastin MASS-89 CAPRICE-97 CAPRICE-94 BESS-95 BESS-97/98/99
,,,I
i
1
i
altitude
R¢
Kiel 10m 2.4GV Nottingham 50rn 2,6GV Prince Albert 6 0 0 m 0,7GV Ft. Summner 1270m 4,2GV Lynn Lake 360rn 0.SGV Tsukuba 30m l l . 2 G V Lynn Lake 3 6 0 m 0.5GV t
i
i
i I t [
10 Momentum P (GeV/c)
Figure 2. Absolute differential p and He spectra.
Figure 3. Absolute differential muon spectrum.
3. R E S U L T S
deviation among the two spectra becomes larger with decreasing momentum. The deviation comes from the influence of the geomagnetic filed. This influence is demonstrated more clearly by # + ~ p ratio as shown in Figure 5 [6].
3.1. Primary cosmic rays Figure 2 shows the absolute differential proton and helium spectra at the top of the atmosphere measured by a BESS-1998 balloon experiment [5] in comparison with other experiments [7-17].
3.2. A t m o s p h e r i c m u o n s Figure 3 and 4 shows the absolute differential spectrum of muons (p+ + p - ) at sea level [6] together with other measurements performed at various sites [18-21]. The muon intensity varies depending on environmental conditions. The altitude and cutoff rigidity for primary cosmic rays (Re) are indicated in the figures. As is seen in Figure 3, the muon spectra measured by BESS in Tsukuba and in Lynn Lake are in good agreement in higher momentum region, where the cutoff rigidity for primary cosmic rays can be neglected. Figure 4 shows, however, a
4. C O N C L U S I O N As for primary protons and helium nuclei, i.e., Cp(A) in Eqs. (1), BESS results, as well as other recent measurements, are more favorable to lower fluxes than the ones assumed in the atmospheric neutrino calculation [22] above a few tens of GeV. It may suggest importance of reconsideration for the atmospheric neutrino flux predictions. The absolute fluxes of atmospheric muons are directly related to the yield of neutrinos, Yp~,, in Eqs. (1). T h e / t + / / l - ratio in a low momentum region is sensitive to the effect of the geomagnetic field, Rv(A ) in Eqs. (1). Detailed study of the atmospheric muons will improve the accuracy in
123
7:. Sanuki/Nuclear Physics B (Proc. Suppl.) 100 (2001) 121-123
o
1.6
.
.
.
.
.
.
.
.
.
.
.
i
•
1.4
1.2 ~ : " . £ ~ " - ~ g
1.1
,rr
*
A
0
0.9
'::L ++ 2I.
0.8 0.7 0.6
site O O ,t. ,'. • [] •
-! 10
*04" l ~ l ' ~ ' ~ ' -
1
I
AlIkofcretal. Rastin MASS-g9 CAPRICE-97 CAPRICE-94 BESS-95 BESS-97/98/99 I
I
[
altitude
I
I
*
I
•
.
,
I
.
.
.
.
.
.
.
altitu0e R= 30m 11.2GV 360m 0.5GV I
lO Momentum P (GeV/c)
Re
Kiel 10m 2.4GV Nottingham 50m 2.6GV Prince Albert 600m 0.TGV Ft. Sumnmer 1270m 4.2GV Lynn Lake 360m 0.5GV Tsukuba 30m I1.2GV Lynn Lake 360m 0.5GV I
site t3 BESS-95 Tsukuba • BESS-97/98/99 Lynn Lake
I
1
t
12"
l~_
Figure 5. p + / p - ratio at sea level.
I [
10 Momentum
P (GeV/c)
7. Figure 4. Absolute differential muon spectrum. 8. 9. the estimation of the neutrino yield and the effect of the geomagnetic field. REFERENCES
1. See, for example, T. K. Gaisser, Proc. Neutrino Oscillations and their Origin, ed. Y. Suzuki, M. Nakahara, N.Shiozawa, and K. Kaneyuki (Tokyo, UAP Inc.) (2000) 45 2. S. Orito, Proc. A S T R O M A G Workshop, ed. J. Nishimura, K. Nakamura, and A. Yamamoto (Ibaraki, KEK) (1987) KEK Report KEK87-19 111 3. A. Yamamoto et al., Adv. Space Res. 14 (1994) 75. 4. Y. Ajima et al., Nucl. Instr. and Meth. A443 (2000) 71. 5. T. Sanuki et al. ApJ 545 (2000) 1135. 6. M. Motoki, Proc. Neutrino Oscillations and their Origin, ed. Y. Suzuki, M. Nakahara,
10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.
N.Shiozawa, and K. Kaneyuki (Tokyo, UAP Inc.) (2000) 19 M . J . Ryan et al., Phys. Rev. Lett. 28 (1972) 985. L.H. Smith et al., ApJ 180 (1973) 987. W. R. Webber et al., Proc. 20th ICRC(Moscow) 1 (1987) 325. E. S. Seo et al., ApJ 378 (1991) 763. P. Papini et al., Proc. 23rd ICRC(Calgary) 1 (1993) 579. J. Buckley et al., ApJ 429 (1994) 736. W. Menn et al., Proc. 25th ICRC(Durban) 3 (1997) 409 R. Bellotti et al., Phys. Rev. D60 (1999) 052002. M. Boezio et al., ApJ 518 (1999) 457. J. Alcaraz et al., Phys. Lett. B490 (2000) 27. J. Alcaraz et al., To be published in Phys. Lett. B. O. C. Allkofer, K. Carstensen, and W. D. Dau, Phys. Lett. B36 (1971) 425. B. C. Rastine, J. Phys. G10 (1984) 1609. M. P. De Pascal et al., J. Geophys. Res. 98 (1993) 3501 J. Kremer et al., Phys. Rev. Lett. 83 (1999) 4241. M. Honda, T. Kajita, K. Kasahara, and S. Midorikawa, Phys. Rev. D52 (1995) 4985.