Tsuji, S

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29th International Cosmic Ray Conference Pune (2005) 6, 213216Momentum Spectrum of Muons Associated with Cosmic-Ray AirShower at Sea LevelS. Tsuji , T. Wada, N. Ochi, A. Iyono, S. Lan, M. Okita, N. Takahashi, K. Okei, Y.Yamashita, T. Katayama, M. Tokiwa, S. Liang, H. Matsumoto, T. Morita, T. Nakatsukaand I. Yamamoto(a) Department of Information Sciences, Kawasaki Medical School, Kurashiki 701-0192, Japan(b) Department of Physics, Okayama University, Okayama 700-8530, Japan(c) Yonago National College of Technology, Tottori 683-8502, Japan(d) Department of Computer Simulation, Okayama University of Science, Okayama 700-0005, Japan(e) Okayama Shoka University, Okayama 700-8601, Japan(f) Faculty of Engineering, Okayama University of Science, Okayama 700-0005, JapanPresenter: S. Tsuji (tsuji@med.kawasaki-m.ac.jp), jap-tsuji-S-abs2-he12-oralThe compact extensive air shower (EAS) array and the solid iron magnet spectrometer have been used to mea-sure momentum spectrum of muons associated with air showers. The EAS array which is a part of Large AreaAir Shower experiment is also operated, and telescope is located almost right under of this array. From January2004, we started observation between the EAS array and the Okayama telescope. By means of analyzing thosedata, we attempt to obtain momentum spectrum of muons associated with EAS.1. IntroductionThe atmospheric muons are produced by decay of charged mesons. These muons give us the informationsof the atmospheric neutrino flux, the ratio of decaying mesons, i.e. K/  ratio and the primary composition.Muons are also generated by charged mesons in EAS.The investigation of the muon component in EAS is to study the charged mesons and primary particles gener-ated EAS. The momentum spectrum of the EAS muon was measured by several experiments at sea level andunderground. By using both the EAS array and the magnet spectrometer, Bennett and Greisen studied the EASmuon spectra for some core distances, and sought the following equation in the reference [1]:	ﬀ	ﬁﬂﬃ "! #%$'&(*),+.-0/! 1"23$14(65 (1)with 7 894;:<2=?>@ A0B .Grishinia et al. also measured the EAS muon spectrum in the similar way.[2]In Okayama University, both a compact EAS array (the OU array) and a magnet spectrometer (the Okayamatelescope) are located. From January 2004, the Okayama telescope was synchronized with the OU array andobserving muons associated with EAS was starting. In this paper, we present the results of the momentumspectrum and the positive excess of muons obtained by coincidence observation between the EAS array andthe magnet spectrometer.2. ApparatusThe Okayama telescope was synchronized with the OU array. The OU array is a part of Large Area Air Shower(LAAS) group arrays [5, 6]. The OU array is equipped with 8 detectors, each consist of a plastic scintillator214 S.Tsuji et al(50 cm C 50 cm C 5 cm) and a fast PMT. The Okayama telescope [3, 4] is located almost right under of the OUarray as sown in figure 1.Figure 1. The arrangement of detectors, the OU arrayand the Okayama telescope. An EAS event come inboth detectors within D*E0F sec, EAS signal is recordedby the telescope.The telescope consists of trigger counters (2 scintilla-tion counters), position chambers (3 multi-wire propor-tional chamber sets used as drift chambers), an iron coremagnet (thickness: 32 cm), a theodolite and azimuthalboards. The main characteristics are summarized in thereferences [3], and detailed arrangement of the detectorsare shown in the reference [4]. If an EAS event come inboth detectors within G2Hsec, EAS signal is recorded bythe telescope.3. Results3.1 Coincidence eventsThe coincidence events have been accumulated betweenthe Okayama telescope and the OU array from January2004. These events are hereafter determined ‘coincidenceevents’. In coincidence events, the events reconstructedsingle track in the Okayama telescope (see in the reference[4] , figure 4-(c) ) are hereafter determined ‘single muonevents’. Analyzed data are used from 18th January 2004to 30th April 2005. Total observation time is 380.2 days.The total number of coincidence events and single muonevents are 299306 and 195 respectively.Figure 2 shows the distribution of the number of trigger counters in the OU array. The dashed histogramcorresponds to all EAS events and the solid histogram corresponds to coincidence events.It is clear that 2 trigger counters are dominant among all EAS events, since the trigger signal occurs in caseof 2 counter hits or more. On the other hand, the rate of the 8 trigger counters is the most frequent amongcoincidence events. The primary energies of coincidence events are estimated to be higher than those of EASevents without coincidence events.3.2 EAS muon momentum spectrumFigure 3 shows the integral momentum spectra of the muons. The solid circles corresponds to the muon fluxassociated with EAS analyzing single muon events. The open circles corresponds to the atmospheric muonflux. The dashed curve indicate the calculated flux using Greisen’s equation (1). In the calculation, equation(1) is convolved with the core distance distribution (Figure.3) and the Okayama telescope’s response functionin which effects of multiple coulomb scattering and the telescope’s angular resolution are taken account of [7].The three spectra are normalized at 10 GeV/c to be compared with each other. The result spectrum associatedwith EAS show the good agreement with the calculation flux (1) and the spectrum shows harder than theatmospheric muon’s. The integral momentum spectrum of muons associated with EAS is different from theatmospheric muon one.Momentum Spectrum of Muons Associated with Cosmic-Ray... 2150204060801002 3 4 5 6 7 8percentage for all events [%]number of trigger counters in the OU arraytotal EAS eventscoincidence eventsFigure 2. The distributions of the number of trigger counters in the OU array. The dashed histogram: for all EAS events inthe OU array. The solid histogram: for coincidence events between the OU array and the Okayama telescope.0.11101 10 100relative intensity (Arbitrary unit)muon momentum [GeV/c]Atmospheric µCoincidence µGreisenFigure 3. EAS muon momentum spectrum. The solid circles: the muon ux associated with EAS. The open circles: theatmospheric muon ux. The dashed curve indicate the calculated ux using Greisen’s equation (1).3.3 EAS muon positive excessThe Okayama telescope can measure the charge sign from the curvature of incident single muons. Using thepositive muon flux IﬁJ and the negative muon flux ILK , the positive excess M is defined as a following equation.MNIJPOIKQ"IJ$IK (2)Here the error bar R showsR%&TS IKVURJXWY$%IJZURKXW,Q;IJ$IKW216 S.Tsuji et alwhere RJ shows positive muon flux error and R"K shows negative muon flux error.The positive excess of the atmospheric muons with the momentum more than 1 GeV/c is4T: 4\[]4\[G4T: 4\4]4_^. Onthe other hand, the positive excess analyzing coincidence events is O4T: 4\4\1G4;:<2?^4in spite of large error bars.The result is not conflict with Greisen’s result [1], since the multiplicity of EAS generating muons is largerthan that of the atmospheric muons.References[1] S.Bennett and K.Greisen, Phys. Rev. 6, 1982 (1961)[2] N.V.Grishinia et al., 17th ICRC, Paris(1981) v.6, 3.[3] M.Tokiwa et al., 28th ICRC, Tsukuba(2003) HE2, 1171.[4] S.Tsuji et al., 29th ICRC, Pune(2005) HE. 1. 5,Proceeding in this conference,“The Observation System of EAS Muon Component with the EAS Arrayand the Muon Spectrometer”[5] N.Ochi et al., J. Phys. G:Nucl. Part. Phys. 29, 1169 (2003).[6] T.Wada et al., Nuclear Physics (Proc. Suppl.) 75A, 330 (1999).[7] J.Tada et al., 13th ISVHECRI Pylos, Greece(2004), In press.

Momentum Spectrum of Muons Associated with Cosmic-Ray Air Shower at Sea Level

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