# Parsons (2014) - A Monte Carlo template based analysis for air-Cherenkov arrays
###### tags: `IACT` `Monte Carlo` `annotating` `translating`
> 基於蒙地卡羅範本的大氣契忍可夫陣列分析
## :information_source: Information *資訊*
* URLs:
* [arXiv:1403.2993v2](https://arxiv.org/abs/1403.2993v2)
* [ScienceDirect] [*Astroparticle Physics* **56** pp.26--34 (2014)](https://doi.org/10.1016/j.astropartphys.2014.03.002)
* cited by
* [227 in ScienceDirect](https://www.sciencedirect.com/science/article/pii/S0927650514000231#section-cited-by)
* [arbeletche2021](https://hackmd.io/@siniu-thesis/arbeletche2021-3) as Ref. 177
* cite as BibLaTeX

    @article{parsons2014,
        author    = {R.D. Parsons and J.A. Hinton},
        title     = {A Monte Carlo template based analysis for air-Cherenkov arrays},
        journal   = {Astroparticle Physics},
        publisher = {Elsevier},
        volume    = {56},
        pages     = {26--34},
        year      = {2014},
        issn      = {0927-6505},
        doi       = {10.1016/j.astropartphys.2014.03.002},
    }

## :star2: Highlights *重點整理*
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## :page_with_curl: Table of Contents *目錄*
[TOC]

## 0. Abstract *摘要*
We present a high-performance event reconstruction algorithm: an **Image Pixel-wise fit for Atmospheric Cherenkov Telescopes** (ImPACT). The reconstruction algorithm is based around the likelihood fitting of camera pixel amplitudes to an expected image template. A maximum likelihood fit is performed to find the best-fit shower parameters. A related reconstruction algorithm has already been shown to provide significant improvements over traditional reconstruction for both the CAT and H.E.S.S. experiments. We demonstrate a significant improvement to the template generation step of the procedure, by the use of a full Monte Carlo air shower simulation in combination with a ray-tracing optics simulation to more accurately model the expected camera images. This reconstruction step is combined with an MVA-based background rejection.

我們提出了一種高性能的事件重建演算法——**適用於大氣契忍可夫望遠鏡的逐像素式圖像擬合法**（ImPACT）。這種重建演算法是基於相機像素幅度與預期圖像範本的概似擬合。我們執行最大概似擬合，以找到擬合度最佳的簇射參數。已證實有一種相關的重建演算法可為 CAT 和 H.E.S.S. 實驗的傳統重建提供顯著改進。我們使用完整的蒙地卡羅簇射模擬，結合光線追蹤的光學模擬，更準確地模擬了預期的相機圖像，在重建過程的模板生成階段展現出顯著的改進。此重建步驟亦結合了基於 MVA 的背景拒斥。

Examples are shown of the performance of the ImPACT analysis on both simulated and measured (from a strong VHE source) gamma-ray data from the H.E.S.S. array, demonstrating an improvement in sensitivity of more than a factor two in observation time over traditional image moments-fitting methods, with comparable performance to previous likelihood fitting analyses. ImPACT is a particularly promising approach for future large arrays such as the Cherenkov Telescope Array (CTA) due to its improved high energy performance and suitability for arrays of mixed telescope types.

範例展示的是 ImPACT 分析 H.E.S.S. 陣列模擬和測量（來自強 VHE 源的）伽馬射線數據的性能，此分析證明了：與傳統的「圖像動差擬合法」相比，觀察時間的靈敏度提高了兩倍以上，其性能與先前的「可能性擬合分析」相當。 ImPACT 是一種前景可期的方法，適用於未來的大型陣列，例如契忍可夫望遠鏡陣列（CTA），因為它改進了高能性能並且適用於混合望遠鏡類型的陣列。

## 1. Introduction *簡介*
about ground-based γ-astro
about IACT, H.E.S.S. as an example

> The process of reconstruction/estimation of the properties of the primary photon (direction and energy), and the rejection of events likely to belong to the background of hadronic showers, makes use of image information from each telescope. Traditionally this event reconstruction is performed using the Hillas parameters of the camera images [2], derived after an image cleaning step (described in [3]). The Hillas parameters are the moments of the camera image which, given the approximately elliptical nature of typical camera images, already capture much of the available image information. In the most commonly used stereoscopic reconstruction method the major axes of images are calculated in a common camera reference frame and the intersection points of all axes found. A weighted average (based on image amplitude and the angle between the axes) is then taken of all crossing points to provide an estimate of the arrival direction of the primary gamma-ray. A similar procedure involving the intersections of the directions between the image centroid and the optical axis is then performed in a common plane perpendicular to the pointing direction, to determine the shower impact point on the ground.

重建/估計初級光子屬性（方向和能量）的過程，以及排除可能屬於強子簇射背景的事件，都是利用來自每個望遠鏡的圖像資訊方能達成。傳統上，此事件重建是使用相機圖像 [^2] 的 Hillas 參數執行的，這些參數是在圖像清理步驟（在 [^3] 中描述）之後得出的。 Hillas 參數是相機圖像的動差，考慮到典型相機圖像有近似橢圓讀性質，它已經捕獲了許多可用的圖像信息。在最常用的立體重建方法中，圖像的主軸在相機共同參考系中計算，並找到所有軸的交點。 然後對所有交叉點進行加權平均（基於圖像振幅和軸之間的角度），以提供對主要伽馬射線到達方向的估計。 然後在垂直於指向方向的共平面中執行涉及圖像質心和光軸之間方向的交叉點的類似過程，以確定簇射在地面上的衝擊點。

[^2]: [2] A. M. Hillas, [Cerenkov light images of EAS produced by primary gamma](https://ui.adsabs.harvard.edu/abs/1985ICRC....3..445H/abstract), in: The 19th International Cosmic Ray Conference, vol. 3, 1985, pp. 445–448. ==**[My annotation](https://hackmd.io/@siniu-thesis/hillas-icrc1985)**==
[^3]: [3]