29th International Cosmic Ray Conference Pune (2005) 00, 101–104

Telescope Array; Simulation and Data Analysis

N. Sakurai , S. Yoshida , S. Ozawa , A. Taketa , K. Hibino , N. Inoue , Y. Wada ,
K. Kasahara , R. Minagawa , T. Iguchi(a) Chiba University, 133 Yayoicho, Inageku, Chibashi, Chiba, 263-8522 Japan(b) ICRR, University of Tokyo, 515 Kashiwanoha, Kashiwa, Chiba, 277-8582 Japan(c) Kanagawa University, 3271 Rokkakubashi, Kanagawaku, Yokohama, Kanagawa, 221-8686 Japan(d) Saitama University, 255 ShimoOkubo, Sakuraku, Saitama, 338-8570 Japan(e) Shibaura Institute of Technology, 307 Fukasaku, Minumaku, Saitama, 337-8570 Japan(f) Tokyo Institute of Technology, 2121 Ookayama, Meguroku, Tokyo, 152-8550 Japan

Presenter: N. Sakurai (nsakurai@hepburn.s.chiba-u.ac.jp), jap-sakurai-N-abs1-he15-oral
Telescope Array (TA) is a EAS detector which is now building in the western desert in Utah, USA. In orderto estimate the performance of TA, a detailed detector simulation is being developed in Java. The numberof particles produced during the development of the EAS shower with various inclinations is calculated by
COSMOS code. The detection efficiency of each detector is evaluated by using the various calibration data
and the results of GEANT4 simulation. And it is taken into account in estimating the signal. The analysis
methods of the EAS data are also being developed using TA simulation. This report describes the structure ofour simulation code, the analysis methods and the TA performance estimation based on our simulation.

1.

Introduction

The AGASA observes 11 cosmic rays above  eV in 12 years operation and shows the extension of thecosmic ray energy spectrum above the GZK cut-off.[1] Although the arrival direction distribution of EHECRs
observed by AGASA is almost isotropic, some events shows an indication of point sources, from which 2 ormore EHECRs arrived. High energy astronomical objects such as quasar remnants and BL Lac objects havebeen searched behind these events, but nothing have been found. There have been several hypothesis to explainthese super-GZK events and point sources : super-heavy relics, Z-burst, the violation of Lorentz invariant atextremely high energy, and so on. Hires group have also studied the EHECRs and they reported that theirenergy spectrum is consistent with the existence of the GZK cut-off.[2] [3] From discussions of these twogroups, it seems clear that a part of the inconsistency is due to the systematic error of both experiments in thedetermination of primary cosmic ray energy.
In order to dissolve the difference between AGASA and Hires, we are now constructing a hybrid detector
which has an AGASA type ground array ( SD ) and 3 air fluorescence telescope stations like Hires detector( FD ) as the first step of TA experiment.[4] The West Desert in Utah, USA is the experimental site. TheHybrid-TA consists of 576 plastic scintillation counters which cover the ground area of 760 km in 1.2 km
mesh and 3 telescope stations ( FD stations ) which surround the array and look inward. The field of view (FOV ) of each FD station is   in elevation angle and   in azimuthal angle. There are telescopes in each FD station. The FOV of each telescope is   in elevation and     in azimuthal. Eachtelescope has spherical mirror of 3.3 m diameter and the shower image is recorded by a camera composed of
"!$#%! 2-inch hexagonal PMTs placed on imaging plane. The separation of the FD station is &'  km andstereo acceptance of FD is about 670 km sr for EHECRs falling within 45 km of the FD station. Each particle
detector of the SD is a plastic scintillator of 3m area and 2 cm thickness. The scintillation photons are fed into
PMT via wave length shifter fibers installed in grooves cut on the surface of the scintillator.

1022.

N. Sakurai et al.

Simulation
Physics

FDMC
Ray trace
DAQ
simulator

FDdataPhotonpropagation

EAS cascadeAir
fluorescence

Cherenkov
radiation

Atmosphere
Atmosphere
Rayleighscattering

SDMC
Particle
tracking
DAQ
simulator

SDdataParticles

Particles

Hit data

Hit data

Figure 1. The schematic view of the TA simulation class

In this section, the components of the TA simulation are described. Simulation code is written in JAVA. It is said
that the maintenance by a lot of people is comparatively easy for an object-oriented language as compared withlanguages, such as the C language and FORTRAN. This characteristic is indispensable when collaborators’
activity place reaches far and wide. Figure 1 gives a schematic view of the TA simulation class.
Physics This class contains the classes which describe the physics processes. EAS cascade is the class tosimulate the shower development. There are two methods to simulate the shower development: Onemethod uses the Geisser-Hillas function for longitudenal development and the NKG function as thelateral distribution. But the correlation of the scale of these functions is unknown currently and it is oneof the aim of our experiment. therefore, it is needed that the correlation of these functions is decided bya shower simulation when we adopt this method. The other is a method which uses the cascade shower
data made by air shower simulation programs such as COSMOS, CORSIKA and some other full Monte
Carlo code. Simulation program is designed so that it can cope with both methods. Air fluorescence andCherenckov radiation are the class to simulate the emittion of photons by shower particles. In Photopropagation, the propagation of photons in the atmosphere is described.
Atmosphere This class describes the atmosphere. The density profile and temperature profiles are included.
The elementary process of photon in atmosphere such as rayleigh scattering is also described.
FDMC,SDMC This class contains the classes to simulate the TA detectors. Reflection by telescope components is simulated in FDMC. In SDMC, the interactions of shower particles in the surface detector issimulated. Detection efficiency of the Surface detector is estimated by using of GEANT4. DAQ of eachdetectors is also described in this class.
FDdata,SDdata This class is for the simulation data.

Telescope Array; Simulation and Data Analysis

3.

103

Status and prospects

Figure 2. Event display of a typical Super-GZK event of the TA simulator.

The simulation code is develloping now. Figure 2 gives the event display of the TA simulation. In this simulation, the Geisser-Hillas function is used for the longitudial development of air shower and the NKG function
modified by Linsley is used for the lateral distribution of shower particles. Muon component has not been
included yet.

References[1] M. Takeda, et al., Astropart. Phys. 19 (2003) 447[2] T. Abu-Zayyad et al., Astropart. Phys. 16 (2001) 1[3] K. Griesen Phys. Rev. Lett. 16, 748 (1966).
G.T. Zatsepin and V.A. Kuzmin, JETP. Lett. 4, 78 (1966).
[4] M. Fukushima, et al., Proc. 29th ICRC (Pune) in these proceedings, (2005)