Search for Supernova Relic Neutrinos

核心崩塌超新星是宇宙中能量最大的事件之一。一颗超新星会让整个星系黯然失色，但光还不到释放出的能量的1%。超新星释放的绝大多数能量(99%)是以中微子的形式释放出来的，中微子是一种几乎从不与物质相互作用的“幽灵”粒子。三十多年前，从超新星1987A探测到了24个中微子；这些中微子提供了我们目前所知的大部分超新星。来自下一颗银河系超新星的中微子目前正在前往地球的途中。当它们到达时，我们将对它们进行研究，以极大地提高我们对大质量恒星如何死亡的了解。然而，无法预测这种情况发生之前需要多少年(或几十年)。在我们等待的同时，也有可能搜索来自银河系外超新星的信号，试图进行中微子宇宙学研究。核心塌缩超新星被认为是在恒星形成后不久就在宇宙中开始的。因此，应该存在一个弥散的中微子背景，这些中微子来自之前爆炸的所有超新星。这些粒子被称为超新星遗迹中微子，我们可以利用它们来了解宇宙中超新星爆炸的历史和相关的宇宙量，如恒星形成速率和宇宙化学演化。以前曾对超新星遗迹中微子进行过搜索，但信号被地球背景掩盖了。Super-Kamiokande(SK)探测器将很快升级为Gd，并重新命名为SK-Gd。在Gd标记的帮助下，SK-Gd将能够识别超新星遗迹中微子，并最大限度地减少地球背景，使超新星遗迹中微子很有可能在未来几年内最终被探测到。这次PHD将前往日本参加SK-Gd实验，包括在Gd加载后校准探测器。它还将涉及数据简化、模拟和分析，最终目的是产生第一个成功观测到的超新星遗迹中微子。

Core-collapse supernovae are amongst the most energetic events in the Universe. A single supernova will outshine an entire galaxy, yet the light is less than 1% of the energy that is released. The vast majority of energy released in a supernova (99%) is emitted in the form of neutrinos, a 'ghostly' particle that almost never interacts with matter. Over thirty years ago, 24 neutrinos were detected from Supernova 1987A; these have provided most of what we currently know about supernovae.Neutrinos from the next galactic supernova are currently on their way to Earth. When they arrive, we will study them to greatly advance our knowledge of how massive stars die. However, it is impossible to predict how many years (or decades) it will be before this happens.While we wait it is also possible to search for the signal from extra-galactic supernovae in an attempt to do neutrino cosmology. Core-collapose supernovae are believed to have started in the universe shortly after star formation began. Thus, there should exist a diffuse background of neutrinos throughout all of space, originating from all of the supernovae that have previously exploded. These particles are called 'supernova relic neutrinos', and we can use them to learn about the history of supernova explosions in the universe and related cosmological quantities, such as the star formation rate and cosmic chemical evolution.Previous searches for supernova relic neutrinos have been performed, but the signal has been masked by terrestrial backgrounds. The Super-Kamiokande (SK) detector will soon be upgraded with gadolinium and re-christened as SK-Gd. With the aid of gadolinium tagging, SK-Gd will be able to identify the supernova relic neutrinos and minimise the terrestrial backgrounds, making it very likely that the supernova relic neutrinos will finally be detected in the next few years.This PhD will involve travel to Japan for participation in the SK-Gd experiment, including calibration of the detector following gadolinium loading. It will also involve data reduction, simulation, and analysis, ultimately aimed at producing the first successful observation of the supernova relic neutrinos.