No Arabic abstract
Preliminary results on the development of a separation method for Cerenkov (CL) and fluorescence (FL) light from EAS are shown. The results are based on the measurement of attenuation coefficients of CL and FL for different filters. A total of six optical filters were investigated: filters from optical glass UFS-1, UFS-5, FS6 (analogue BG3) and interference filters SL 360-50, SL 280-380, FF01-375/110. The measurements were performed using silicon photomultipliers (SiPM). To improve existing fluorescent light detectors, a segment of 7 SiPM was developed, which would be able to separate both components of the light flux from EAS at the level of primary data processing.
A novel photon detector, the Silicon Photomultiplier (SiPM), has been tested in proximity focusing Ring Imaging Cherenkov (RICH) counters that were exposed to cosmic-ray particles in Ljubljana, and a 2 GeV electron beam at the KEK research facility. This type of RICH detector is a candidate for the particle identification detector upgrade of the BELLE detector at the KEK B-factory, for which the use of SiPMs, microchannel plate photomultiplier tubes or hybrid avalanche photodetectors, rather than traditional Photomultiplier Tubes (PMTs) is essential due to the presence of high magnetic fields. In both experiments, SiPMs are found to compare favourably with PMTs, with higher photon detection rates per unit area. Through the use of hemispherical and truncated pyramid light guides to concentrate photons onto the active surface area, the light yield increases significantly. An estimate of the contribution to dark noise from false coincidences between SiPMs in an array is also presented.
UHE particle detection using the lunar Cherenkov technique aims to detect nanosecond pulses of Cherenkov emission which are produced during UHE cosmic ray and neutrino interactions in the Moons regolith. These pulses will reach Earth-based telescopes dispersed, and therefore reduced in amplitude, due to their propagation through the Earths ionosphere. To maximise the received signal to noise ratio and subsequent chances of pulse detection, ionospheric dispersion must therefore be corrected, and since the high time resolution would require excessive data storage this correction must be made in real time. This requires an accurate knowledge of the dispersion characteristic which is parameterised by the instantaneous Total Electron Content (TEC) of the ionosphere. A new method to calibrate the dispersive effect of the ionosphere on lunar Cherenkov pulses has been developed for the LUNASKA lunar Cherenkov experiments. This method exploits radial symmetries in the distribution of the Moons polarised emission to make Faraday rotation measurements in the visibility domain of synthesis array data (i. e. instantaneously). Faraday rotation measurements are then combined with geomagnetic field models to estimate the ionospheric TEC. This method of ionospheric calibration is particularly attractive for the lunar Cherenkov technique as it may be used in real time to estimate the ionospheric TEC along a line-of-sight to the Moon and using the same radio telescope.
We study the azimuthal distributions of Cherenkov photons in Extensive Air Showers (EASs) initiated by $gamma$-ray, proton and iron primaries of different energies incident at various zenith angles over a high altitude observation level. The azimuthal distributions of electrons and positrons along with their asymmetric behaviour have also been studied here to understand the feature of azimuthal distributions of Cherenkov photons in EASs. The main motivation behind this study is to see whether the azimuthal distribution of Cherenkov photons can provide any means to distinguish the $gamma$-ray initiated showers from that of hadron initiated showers in the ground based $gamma$-ray astronomy experiment. Apart from this, such study is also important to understand the natures of $gamma$-ray and hadronic showers in general. We have used the CORSIKA 6.990 simulation package for generating the showers. The study shows the double peak nature of the azimuthal distribution of Cherenkov photons which is due to the separation of electron and positrons in the azimuthal plane. The pattern of distribution is more sensitive for the energy of the primary particle than its angle of incidence. There is no significant difference between distributions for $gamma$-ray and handron initiated showers.
We give an overview of the SPHERE experiment based on detection of reflected Vavilov-Cherenkov radiation (Cherenkov light) from extensive air showers in the energy region E>10^{15} eV. A brief history of the reflected Cherenkov light technique is given; the observations carried out with the SPHERE-2 detector are summarized; the methods of the experimental datasample analysis are described. The first results on the primary cosmic ray all-nuclei energy spectrum and mass composition are presented. Finally, the prospects of the SPHERE experiment and the reflected Cherenkov light technique are given.
This paper describes an experimental setup that has been developed to measure and characterise properties of Silicon Photomultipliers (SiPM). The measured SiPM properties are of general interest for a multitude of potential applications and comprise the Photon Detection Efficiency (PDE), the voltage dependent cross-talk and the after-pulse probabilities. With the described setup the absolute PDE can be determined as a function of wavelength covering a spectral range from 350 to 1000nm. In addition, a method is presented which allows to study the pixel uniformity in terms of the spatial variations of sensitivity and gain. The results from various commercially available SiPMs - three HAMAMATSU MPPCs and one SensL SPM - are presented and compared.