H. Tokuno

The atmospheric transparency measured with a LIDAR system at the Telescope Array experiment

An atmospheric transparency was measured using a LIDAR with a pulsed UV laser (355 nm) at the observation site of Telescope Array in Utah, USA. The measurement at night for two years in 2007–2009 revealed that the extinction coefficient by aerosol at the ground level is 0.033−0.012+0.016km−1 and the vertical aerosol optical depth at 5 km above the ground is 0.035−0.013+0.019. A model of the altitudinal aerosol distribution was built based on these measurements for the analysis of atmospheric attenuation of the fluorescence light generated by ultra high energy cosmic rays.

The Energy Spectrum and the Chemical Composition of Primary Cosmic Rays with Energies from 1014 to 1016 eV

We have measured extensive air showers with primary energies above 6 TeV at Mount Chacaltaya in Bolivia. The data were collected by an air shower array called the Minimum Air Shower (MAS) array starting in 2000 March. We applied an equi-intensity analysis method to the extensive air showers extended over the region of their maximum development. We varied the mixture of protons and iron in our simulations and compared these to the data to determine the mixing ratio of protons as a function of the primary energy. Using this, we derived the primary energy spectrum from 1014 to 5 × 1016 eV. Consequently, we conclude that the power-law index of the spectrum changes gradually around 1015.5 eV and that the obtained proton ratio decreases with increasing energy. We directly measured the longitudinal development of air showers generated by primaries with energies around the knee. We found that the average mass number of primary cosmic rays shows a steady increase with energy above 1014.5 eV and that the dominant component around the knee is not protons.

Calibration of photomultiplier tubes for the fluorescence detector of telescope array experiment using a Rayleigh scattered laser beam

Abstract We performed photometric calibration of the PhotoMultiplier Tube (PMT) and readout electronics used for the new fluorescence detectors of the Telescope Array (TA) experiment using Rayleigh scattered photons from a pulsed nitrogen laser beam. The experimental setup, measurement procedure, and results of calibration are described. The total systematic uncertainty of the calibration is estimated to be 7.2%. An additional uncertainty of 3.7% is introduced by the transport of the calibrated PMTs from the laboratory to the TA experimental site.

An Event Reconstruction Method for the Telescope Array Fluorescence Detectors

We measure arrival directions, energies and mass composition of ultra‐high energy cosmic rays with air fluorescence detector telescopes. The longitudinal profile of the cosmic ray induced extensive air shower cascade is imaged on focal plane of the telescope camera. Here, we show an event reconstruction method to obtain the primary information from data collected by the Telescope Array Fluorescence Detectors. In particular, we report on an “Inverse Monte Carlo (IMC)” method in which the reconstruction process searches for an optimum solution via repeated Monte Carlo simulations including characteristics of all detectors, atmospheric conditions, photon emission and scattering processes.

Measurement of ultra-high energy cosmic rays by telescope array (ta)

The Telescope Array (TA) is a large scale ground experiment in Utah, USA for the measurement of extensive air showers from the ultra-high energy cosmic rays. Its construction is completed in March, 2008 and the data taking started.

Central Laser Facility Analysis at The Telescope Array Experiment

The Central Laser Facility (CLF) is the laser device which shoots the vertical laser. CLF is located at the Center of the Telescope Array (TA) experiment site. The TA has three fluorescence detectors. CLF is equidistant from three FD stations. We made the CLF simulation using the same program as the cosmic‐ray simulation. Using the CLF simulation, we reconstruct the energy shot by the CLF. In this paper, we describe some results of CLF reconstruction comparing the difference of reconstructed energy between two fluorescence telescopes.

The hybrid trigger system in the Telescope Array experiment

We report the development of a “hybrid trigger” system for the fluorescence detectors (FDs) and the surface detectors (SDs) in the Telescope Array (TA) experiment. It is shown from our Monte‐Carlo studies that geometry determination accuracies of monocular FD events are significantly improved using SD information (position at the ground level, timing of arrival, etc…). On the other hand, in a lower energy event, the trigger efficiency of SD for lower energy showers is smaller than that of FD. Therefore no SD information is available for events with energies below 1018.5 eV taken with the TA original data acquisition system. In order to collect the small SD signals, we developed an FD‐driven SD triggering system: this introduces an external triggering scheme to the TA‐SD using triggering signals from FD. We present the design of the system, installation and the operational stabilities in TA observation from October 2010.

The effect of the atmospheric condition on the extensive air shower analysis at the Telescope Array experiment

The accuracies in determination of air shower parameters such as longitudinal profiles or primary energies with the fluorescence detection technique are strongly dependent on atmospheric conditions of the molecular and aerosol components. Moreover, air fluorescence photon yield depends on the atmospheric density, and the transparency of the air for fluorescence photons depends on the atmospheric conditions from EAS to FDs. In this paper, we describe the atmospheric monitoring system in the Telescope Array (TA experiment), and the impact of the atmospheric conditions in air shower reconstructions. The systematic uncertainties of the determination of the primary cosmic ray energies and of the measurement of depth of maximum development (Xmax) of EASs due to atmospheric variance are evaluated by Monte Carlo simulation.