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Register a new userAzimuthal distribution of Cherenkov photons and corresponding electron-positron asymmetry in EASs of different primaries
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Added by
Umananda Dev Goswami
Publication date
2018
fields
Physics
and research's language is
English
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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.
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The simulation of Cherenkov photons lateral density and arrival time distributions in Extensive Air Showers (EASs) was performed with the CORSIKA code in the energy range: 100 GeV to 100 TeV. On the basis of this simulation we obtained a set of approximating functions for the primary $gamma$-ray photons, protons and iron nuclei incident at zenith angles from 0$^circ$ to 40$^circ$ over different altitudes of observation. Such a parameterisation is important for the primary particle identification, for the reconstruction of the shower observables and hence for a more efficient disentanglement of the $gamma$-ray showers from the hadronic showers. From our parameterisation analysis, we have found that even though the geometry of the lateral density ($rho_{ch}$) and the arrival time ($t_{ch}$) distributions is different for different primaries at a particular energy ($E$), at a particular incident angle ($theta$) and at a particular altitude of observation ($H$) up to a given distance from the showe core ($R$), the distributions follow the same mathematical functions $rho(E,R,theta,H) = a E^{b}exp[-{c R + (theta /d)^{2}-f H}]$ and $t(E,R,theta,H) = l E^{-m}exp(n/R^{p})({theta}^q+s)(u {H}^2+v)$ respectively but with different values of function parameters.
We have studied the distribution patterns of lateral density, arrival time and angular position of Cherenkov photons generated in Extensive Air Showers (EASs) initiated by $gamma$-ray, proton and iron primaries incident with various energies and at various zenith angles. This study is the extension of our earlier work cite{Hazarika} to cover a wide energy range of ground based $gamma$-ray astronomy with a wide range of zenith angles ($le 40^circ$) of primary particles, as well as the extension to study the angular distribution patterns of Cherenkov photons in EASs. This type of study is important for distinguishing the $gamma$-ray initiated showers from the hadronic showers in the ground based $gamma$-ray astronomy, where Atmospheric Cherenkov Technique (ACT) is being used. Importantly, such study gives an insight on the nature of $gamma$-ray and hadronic showers in general. In this work, the CORSIKA 6.990 simulation code is used for generation of EASs. Similarly to the case of Ref.cite{Hazarika}, this study also revealed that, the lateral density and arrival time distributions of Cherenkov photons vary almost in accordance with the functions: $rho_{ch}(r) = rho_{0};e^{-beta r}$ and $t_{ch}(r) = t_{0}e^{Gamma/r^{lambda}}$ respectively by taking different values of the parameters of functions for the type, energy and zenith angle of the primary particle. The distribution of Cherenkov photons angular positions with respect to shower axis shows distinctive features depending on the primary type, its energy and the zenith angle.
We have investigated some features of the density and arrival time distributions of Cherenkov photons in extensive air showers using the CORSIKA simulation package. The main thrust of this study is to see the effect of hadronic interaction models on the production pattern of Cherenkov photons with respect to distance from the shower core. Such studies are very important in ground based $gamma$-ray astronomy for an effective rejection of huge cosmic ray background, where the atmospheric Cherenkov technique is being used extensively within the energy range of some hundred GeV to few TeV. We have found that for all primary particles, the density distribution patterns of Cherenkov photons follow the negative exponential function with different coefficients and slopes depending on the type of primary particle, its energy and the type of interaction model combinations. Whereas the arrival time distribution patterns of Cherenkov photons follow the function of the form $t (r) = t_{0}e^{Gamma/r^{lambda}}$, with different values of the function parameters. There is no significant effect of hadronic interaction model combinations on the density and arrival time distributions for the $gamma$-ray primaries. However, for the hadronic showers, the effects of the model combinations are significant under different conditions.
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.
Hard photon emitted from energetic heavy ion collisions is of very interesting since it does not experience the late-stage nuclear interaction, therefore it is useful to explore the early-stage information of matter phase. In this work, we have presented a first calculation of azimuthal asymmetry, characterized by directed transverse flow parameter $F$ and elliptic asymmetry coefficient $v_2$, for proton-neutron bremsstrahlung hard photons in intermediate energy heavy-ion collisions. The positive $F$ and negative $v_2$ of direct photons are illustrated and they seem to be anti-correlated to the corresponding free protons flow.
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