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Energy spectrum of muon in EAS
Nuclear Physics B (Proc. Suppl.) 175–176 (2008) 350–353 www.elsevierphysics.com
Energy spectrum of muon in EAS H. Matsumotoa , A. Iyonoa , C. Nodaa , M. Masudaa , I. Yamamotoa , T. Wadab , K. Okeib, S. Tsujic , T. Moritab, M. Okitab , N. Takahashib, S. Liangb , Y. Yamashitab , T. Nakatsukad and N. Ochie a
Okayama University of Science, Okayama 700-0005, Japan
b
Okayama University, Okayama 700-8530, Japan
c
Kawasaki Medical School, Kurashiki 701-0192, Japan
d e
Okayama Shoka University, Okayama 700-8601, Japan
Yonago National College of Technology, Yonago 683-8502, Japan
The compact extensive air shower (EAS) array which consists of 8 scintillation counters, and the solid iron magnet spectrometer (the Okayama muon telescope) have been used to measure energy spectrum of muons in EAS from January 2004 in Okayama University. We compared the result of the muon energy spectrum tagged by EAS trigger signals with EAS simulations which agreed with higher energy hadronic interaction models such as QGSJET and SYBILL, and lower energy hadronic ones such as Hillas Splitting Algorithm, GHEISHA and UrQMD, in order to verify the influence of the hadronic interaction model upon properties of EAS particles, especially the energy spectrum of muons.
1. Introduction Hadronic interaction models play an important role in air shower simulations in order to estimate the primary energy from EAS lateral distributions, to deduce primary species from the ratio of electron size to muon size, and to understand exotic phenomena of cosmic rays. Recently, hadronic interaction models have been discussed theoretically and experimentally. For observations carried out near ground level, the low energy hadronic interaction model is crucial because the shower particles are generated by low energy mesons. It was reported that the lateral distribution for shower particles in EAS simulations at quite a large lateral distances from the core position depend on low energy hadronic interaction models [1,2]. Studies of the muon component should focus on investigating the influence of the low energy hadronic interaction model on EAS particles because muons observed at sea level are produced by the decay of rather low energy charged mesons. In this experiment, we used a compact EAS 0920-5632/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2007.11.029
array and a momentum spectrometer to observe EAS particles. This compact EAS array of area about 600 m2 [3,4] located in Okayama University, OU, has observed EAS particles. A momentum spectrometer called the Okayama muon telescope is also located on the same campus [5,6]. In this paper, we compare muon spectra in EAS with various simulation results in order to evaluate the model dependence on hadronic interaction models.
2. Apparatus 2.1. EAS array The OU array is installed on the rooftop of Okayama University, and consists of 8 scintillation counters. Each counter is equipped with a scintillator disk, of size and thickness 50cm ×50 cm and 5cm respectively, and a fast photomultiplier (PMT). The scintillation counters are distributed over an area of about 30 m × 20 m (fig.1).
351
H. Matsumoto et al. / Nuclear Physics B (Proc. Suppl.) 175–176 (2008) 350–353
Scintillation counter Drift chamber Iron magnet
3.5 m
20 m X
30 m
Y
Scintillation counter Muon telescope
Figure 1. Arrangement of the OU array and the muon telescope (top view).
Z
2.2. Momentum spectrometer The Okayama muon telescope is installed on the 6th floor of the same building just under the OU array. The telescope is a momentum spectrometer and is equipped with a scintillation counter, drift chambers consisting of 20 layers, and a solid iron magnet (fig.2). It can determine muon momenta from 0.9 to 150 GeV/c and has an angular resolution of 1 mrad. The acceptance is 24.4 cm2 sr. Details of the arrangement and properties of the detectors are described in references [5–8].
Z
1.5 m
( a)
X-Z plane
( b)
X-Z plane
Y-Z plane
Figure 2. (a) The section of X-Z plane of the telescop. (b) Imaging of a typical event in projection of X-Z plane and Y-Z plane of the telescope.
sis, because it is harder to reconstruct the trajectories and less accurate to determine the muon momenta than for single trajectory events. We chose events such as a trajectory reconstructed singly in X-Z plane and Y-Z plane respectively in fig.2-(b). Details of the determination of muon momenta are reported in reference [6].
3. Data analysis The data period used for this analysis is from 1 February 2004 to 30 June 2006 and the total observational time is 790 days. We observed 6.2× 105 events in this period. The following event selection criteria were applied in order to determine each muon momentum. Fig.2 (a) shows the projection of X-Z plane of the telescope. Fig.2 (b) shows a typical event with the muon momenta displayed visually in the projections of X-Z plane and Y-Z plane of the telescope. The event selection criteria are that an incident particle penetrates the magnet, all drift chambers register information and a trajectory identifies the same particle. If more than two trajectories satisfy the above criteria at the same time, those events are rejected in this analy-
4. Simulation 4.1. Simulation programs To investigate hadronic interaction models in EAS, the AIRES [9] and the SENECA [10] programs are used in this simulation study. In both simulation programs, the transition energy region from the high energy hadronic models to the low ones is around 80 GeV for particle energies. In the AIRES program, we used QGSJET01 (QGS) [11] and SIBYLL2.1 (SIB) [12] in the high energy model and the Hillas Splitting Algorithm (HSA) [13] in the low one. In SENECA, the high energy model is the same model as the AIRES and the low ones are GHEISHA (GHE) [14] and UrQMD (UrQ) [15] models.
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H. Matsumoto et al. / Nuclear Physics B (Proc. Suppl.) 175–176 (2008) 350–353
0.016 data QGS+HSA QGS+GHE QGS+UrQ
0.014 EdN/dE (normalized)
relative number of events
1
0.1
0.01
0.001 1012
0.012 0.01 0.008 0.006 0.004 0.002
13
10
10
14
15
16
10 10 primary energy [eV]
17
10
18
10
0 1
10
100
energy [GeV]
Figure 3. Relative primary energy distribution.
Figure 4. Energy spectra of muons. The high energy model used is QGSJET01.
5. Result 4.2. Simulation parameters The primary energies of events are sampled using effective energy distributions of 1.58 × 1013 to 2.51 × 1016 eV (fig.3). The sensitive area for EAS particles is within about 20 m. Details of the calculations for this distribution are reported in reference [7]. The number of primary particles used is 600 at 3.98 × 1014 eV. We assume the primary cosmic ray to be a proton. The zenith angle distribution is not taken into account. The thinning energy is Ethinning /Eprimary = 10−5 .
4.3. Energy spectra of muons We used QGSJET01 and SIBYLL2.1 in the high energy interaction models and for the low ones HAS, GHEISHA, UrQMD. Fig.4 and fig.5 show the muon energy spectra obtained by this experiment and various simulations. Each graph is normalized in the fig.4 and the fig.5. The experimental values are compared with the result of simulations using QGSJET01+HSA, QGSJET01+GHEISHA and QGSJET01+UrQMD in fig.4. The comparison between the result of experiment and simulations using SIBYLL2.1+HSA, SIBYLL2.1+GHEISHA and SIBYLL2.1+UrQMD is shown in fig.5
The muon energy spectrum obtained by this experiment agrees with ones obtained by various simulations within statistical errors. The muon energy spectra with SIBYLL2.1 in the high energy interaction model is in better agreement with the experimental value than for QGSJET01. For comparison of the low energy models, the difference of shape of muon energy spectra is shown for muon energy from 1 to 20 GeV in fig.4 and fig.5. 6. Conclusion We measured the energy spectrum of muons in EAS using the muon telescope in coincidence with EAS events. The comparison between the muon spectra obtained by experiment and simulations, and of the muon energy spectra by various simulations are discussed in this paper. Muon spectra could show the difference of the influence of the low energy hadronic model upon shower particles in EAS around center of distance from core position. Acknowledgements This work was partially supported by the Academic Frontier Project from Ministry of Educa-
H. Matsumoto et al. / Nuclear Physics B (Proc. Suppl.) 175–176 (2008) 350–353
0.014 data SIB+HSA SIB+GHE SIB+UrQ
EdN/dE (normalized)
0.012 0.01 0.008 0.006 0.004 0.002 0 1
10
100
energy [GeV]
Figure 5. Energy spectra of muons. The high energy model used is SIBYLL2.1.
tion, Culture, Sports, Science and Technology in Japan. REFERENCES 1. H.J.Drescher et al., Astropart. Phys. 21 (2004) 87 2. D.Heck, Nuclear Physcs B (Proc. Suppl.) 151 (2006) 127-134
353
3. T.Wada et al., Nuclear Physics B (Proc. Suppl.) 75A (1999) 330-332 4. N.Ochi et al., J. Phys. G: Nucl. Part. Phys. 29 (2003) 1169-1180 5. T.Wada et al., Nuclear Physics B (Proc. Suppl.) 151 (2006) 465-468 6. S.Tsuji et al., ’The atomospheric muon flux and the charge ratio using a magnet spectrometer’, this volume 7. J.Tada et al., Nuclear Physics B (Proc. Suppl.) 151 (2006) 333-336 8. A.Iyono et al., ’Muon components detected by EAS array and Okayama muon Telescope experiments’, this volume 9. S.J.Sciutto, astro-ph/9911331 (1999); http://www.fisica.unlp.edu.ar/auger/aires 10. H.J.Drescher, Nuclear Physics B (Proc. Suppl.) 151 (2006) 151-158; http://www.th.physik.unifrankfurt.de/˜drescher/SENECA/ 11. N.N.Kalmykov, S.S.Ostapchenko, and A.I.Pavlov, Nucl. Phys. B (Proc. Suppl.) 52B (1997) 17-28 12. R.Engel et al., Proc. 26th Int. Cosmic Ray Conf., Salt Lake City (USA) 1 (1999) 415 13. A.M.Hillas, Nucl. Phys. B (Proc.Suppl.) 52B (1997) 29-42 14. H.Fesefeldt, PITHA85/02, RWTH Aachen, 1985 15. M.Bleicher et al., J. Phys., G 25 (1999) 1859
Energy spectrum of muon in EAS H. Matsumotoa , A. Iyonoa , C. Nodaa , M. Masudaa , I. Yamamotoa , T. Wadab , K. Okeib, S. Tsujic , T. Moritab, M. Okitab , N. Takahashib, S. Liangb , Y. Yamashitab , T. Nakatsukad and N. Ochie a
Okayama University of Science, Okayama 700-0005, Japan
b
Okayama University, Okayama 700-8530, Japan
c
Kawasaki Medical School, Kurashiki 701-0192, Japan
d e
Okayama Shoka University, Okayama 700-8601, Japan
Yonago National College of Technology, Yonago 683-8502, Japan
The compact extensive air shower (EAS) array which consists of 8 scintillation counters, and the solid iron magnet spectrometer (the Okayama muon telescope) have been used to measure energy spectrum of muons in EAS from January 2004 in Okayama University. We compared the result of the muon energy spectrum tagged by EAS trigger signals with EAS simulations which agreed with higher energy hadronic interaction models such as QGSJET and SYBILL, and lower energy hadronic ones such as Hillas Splitting Algorithm, GHEISHA and UrQMD, in order to verify the influence of the hadronic interaction model upon properties of EAS particles, especially the energy spectrum of muons.
1. Introduction Hadronic interaction models play an important role in air shower simulations in order to estimate the primary energy from EAS lateral distributions, to deduce primary species from the ratio of electron size to muon size, and to understand exotic phenomena of cosmic rays. Recently, hadronic interaction models have been discussed theoretically and experimentally. For observations carried out near ground level, the low energy hadronic interaction model is crucial because the shower particles are generated by low energy mesons. It was reported that the lateral distribution for shower particles in EAS simulations at quite a large lateral distances from the core position depend on low energy hadronic interaction models [1,2]. Studies of the muon component should focus on investigating the influence of the low energy hadronic interaction model on EAS particles because muons observed at sea level are produced by the decay of rather low energy charged mesons. In this experiment, we used a compact EAS 0920-5632/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2007.11.029
array and a momentum spectrometer to observe EAS particles. This compact EAS array of area about 600 m2 [3,4] located in Okayama University, OU, has observed EAS particles. A momentum spectrometer called the Okayama muon telescope is also located on the same campus [5,6]. In this paper, we compare muon spectra in EAS with various simulation results in order to evaluate the model dependence on hadronic interaction models.
2. Apparatus 2.1. EAS array The OU array is installed on the rooftop of Okayama University, and consists of 8 scintillation counters. Each counter is equipped with a scintillator disk, of size and thickness 50cm ×50 cm and 5cm respectively, and a fast photomultiplier (PMT). The scintillation counters are distributed over an area of about 30 m × 20 m (fig.1).
351
H. Matsumoto et al. / Nuclear Physics B (Proc. Suppl.) 175–176 (2008) 350–353
Scintillation counter Drift chamber Iron magnet
3.5 m
20 m X
30 m
Y
Scintillation counter Muon telescope
Figure 1. Arrangement of the OU array and the muon telescope (top view).
Z
2.2. Momentum spectrometer The Okayama muon telescope is installed on the 6th floor of the same building just under the OU array. The telescope is a momentum spectrometer and is equipped with a scintillation counter, drift chambers consisting of 20 layers, and a solid iron magnet (fig.2). It can determine muon momenta from 0.9 to 150 GeV/c and has an angular resolution of 1 mrad. The acceptance is 24.4 cm2 sr. Details of the arrangement and properties of the detectors are described in references [5–8].
Z
1.5 m
( a)
X-Z plane
( b)
X-Z plane
Y-Z plane
Figure 2. (a) The section of X-Z plane of the telescop. (b) Imaging of a typical event in projection of X-Z plane and Y-Z plane of the telescope.
sis, because it is harder to reconstruct the trajectories and less accurate to determine the muon momenta than for single trajectory events. We chose events such as a trajectory reconstructed singly in X-Z plane and Y-Z plane respectively in fig.2-(b). Details of the determination of muon momenta are reported in reference [6].
3. Data analysis The data period used for this analysis is from 1 February 2004 to 30 June 2006 and the total observational time is 790 days. We observed 6.2× 105 events in this period. The following event selection criteria were applied in order to determine each muon momentum. Fig.2 (a) shows the projection of X-Z plane of the telescope. Fig.2 (b) shows a typical event with the muon momenta displayed visually in the projections of X-Z plane and Y-Z plane of the telescope. The event selection criteria are that an incident particle penetrates the magnet, all drift chambers register information and a trajectory identifies the same particle. If more than two trajectories satisfy the above criteria at the same time, those events are rejected in this analy-
4. Simulation 4.1. Simulation programs To investigate hadronic interaction models in EAS, the AIRES [9] and the SENECA [10] programs are used in this simulation study. In both simulation programs, the transition energy region from the high energy hadronic models to the low ones is around 80 GeV for particle energies. In the AIRES program, we used QGSJET01 (QGS) [11] and SIBYLL2.1 (SIB) [12] in the high energy model and the Hillas Splitting Algorithm (HSA) [13] in the low one. In SENECA, the high energy model is the same model as the AIRES and the low ones are GHEISHA (GHE) [14] and UrQMD (UrQ) [15] models.
352
H. Matsumoto et al. / Nuclear Physics B (Proc. Suppl.) 175–176 (2008) 350–353
0.016 data QGS+HSA QGS+GHE QGS+UrQ
0.014 EdN/dE (normalized)
relative number of events
1
0.1
0.01
0.001 1012
0.012 0.01 0.008 0.006 0.004 0.002
13
10
10
14
15
16
10 10 primary energy [eV]
17
10
18
10
0 1
10
100
energy [GeV]
Figure 3. Relative primary energy distribution.
Figure 4. Energy spectra of muons. The high energy model used is QGSJET01.
5. Result 4.2. Simulation parameters The primary energies of events are sampled using effective energy distributions of 1.58 × 1013 to 2.51 × 1016 eV (fig.3). The sensitive area for EAS particles is within about 20 m. Details of the calculations for this distribution are reported in reference [7]. The number of primary particles used is 600 at 3.98 × 1014 eV. We assume the primary cosmic ray to be a proton. The zenith angle distribution is not taken into account. The thinning energy is Ethinning /Eprimary = 10−5 .
4.3. Energy spectra of muons We used QGSJET01 and SIBYLL2.1 in the high energy interaction models and for the low ones HAS, GHEISHA, UrQMD. Fig.4 and fig.5 show the muon energy spectra obtained by this experiment and various simulations. Each graph is normalized in the fig.4 and the fig.5. The experimental values are compared with the result of simulations using QGSJET01+HSA, QGSJET01+GHEISHA and QGSJET01+UrQMD in fig.4. The comparison between the result of experiment and simulations using SIBYLL2.1+HSA, SIBYLL2.1+GHEISHA and SIBYLL2.1+UrQMD is shown in fig.5
The muon energy spectrum obtained by this experiment agrees with ones obtained by various simulations within statistical errors. The muon energy spectra with SIBYLL2.1 in the high energy interaction model is in better agreement with the experimental value than for QGSJET01. For comparison of the low energy models, the difference of shape of muon energy spectra is shown for muon energy from 1 to 20 GeV in fig.4 and fig.5. 6. Conclusion We measured the energy spectrum of muons in EAS using the muon telescope in coincidence with EAS events. The comparison between the muon spectra obtained by experiment and simulations, and of the muon energy spectra by various simulations are discussed in this paper. Muon spectra could show the difference of the influence of the low energy hadronic model upon shower particles in EAS around center of distance from core position. Acknowledgements This work was partially supported by the Academic Frontier Project from Ministry of Educa-
H. Matsumoto et al. / Nuclear Physics B (Proc. Suppl.) 175–176 (2008) 350–353
0.014 data SIB+HSA SIB+GHE SIB+UrQ
EdN/dE (normalized)
0.012 0.01 0.008 0.006 0.004 0.002 0 1
10
100
energy [GeV]
Figure 5. Energy spectra of muons. The high energy model used is SIBYLL2.1.
tion, Culture, Sports, Science and Technology in Japan. REFERENCES 1. H.J.Drescher et al., Astropart. Phys. 21 (2004) 87 2. D.Heck, Nuclear Physcs B (Proc. Suppl.) 151 (2006) 127-134
353
3. T.Wada et al., Nuclear Physics B (Proc. Suppl.) 75A (1999) 330-332 4. N.Ochi et al., J. Phys. G: Nucl. Part. Phys. 29 (2003) 1169-1180 5. T.Wada et al., Nuclear Physics B (Proc. Suppl.) 151 (2006) 465-468 6. S.Tsuji et al., ’The atomospheric muon flux and the charge ratio using a magnet spectrometer’, this volume 7. J.Tada et al., Nuclear Physics B (Proc. Suppl.) 151 (2006) 333-336 8. A.Iyono et al., ’Muon components detected by EAS array and Okayama muon Telescope experiments’, this volume 9. S.J.Sciutto, astro-ph/9911331 (1999); http://www.fisica.unlp.edu.ar/auger/aires 10. H.J.Drescher, Nuclear Physics B (Proc. Suppl.) 151 (2006) 151-158; http://www.th.physik.unifrankfurt.de/˜drescher/SENECA/ 11. N.N.Kalmykov, S.S.Ostapchenko, and A.I.Pavlov, Nucl. Phys. B (Proc. Suppl.) 52B (1997) 17-28 12. R.Engel et al., Proc. 26th Int. Cosmic Ray Conf., Salt Lake City (USA) 1 (1999) 415 13. A.M.Hillas, Nucl. Phys. B (Proc.Suppl.) 52B (1997) 29-42 14. H.Fesefeldt, PITHA85/02, RWTH Aachen, 1985 15. M.Bleicher et al., J. Phys., G 25 (1999) 1859