A Search for Exotic Higgs Decays: Or: How I Learned to Stop Worrying and Love Long-Lived Particles

Burzynski, Jackson

A Search for Exotic Higgs Decays: Or: How I Learned to Stop Worrying and Love Long-Lived Particles
  • 出版商: Springer
  • 出版日期: 2024-05-25
  • 售價: $7,030
  • 貴賓價: 9.5 折 $6,679
  • 語言: 英文
  • 頁數: 193
  • 裝訂: Quality Paper - also called trade paper
  • ISBN: 3031304683
  • ISBN-13: 9783031304682

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商品描述

The absence of new physics at the TeV scale observed thus far at the Large Hadron Collider (LHC) motivates an increasing focus on searches for weakly-coupled new particles and exotic signatures. In particular, particles with macroscopic mean proper lifetimes, known as long-lived particles (LLPs), are of significant interest due to their ability to elude the majority of searches which rely on the assumption that Beyond Standard Model particles decay close to the primary interaction point. Many models which aim to solve various issues with the Standard Model (SM) introduce new particles with lifetimes that are either unconstrained, or even shown to prefer the macroscopic regime. These theories often point to the Higgs boson as a possible portal to new physics, with exotic Higgs decays being the primary phenomenological consequence and means of discovery. It is well motivated both from theory and experimental constraints to consider the scenario in which the particles produced in these exotic decays have macroscopic proper lifetimes and give rise to unique detector signatures.

This work describes a search for exotic decays of the Higgs boson to two long-lived, neutral, spin-0 particles which subsequently decay to pairs of b quarks, giving the striking signature of displaced hadronic jets in the ATLAS inner detector. Several other ATLAS searches have probed this decay topology previously, excluding branching ratios of the Higgs boson to LLPs of more than 10% for proper lifetimes greater than 100mm. These searches relied on dedicated triggers designed to select events with LLPs decaying in the ATLAS calorimeter or muon spectrometer. The lack of an equivalent trigger for LLP decays in the ATLAS inner detector has been a limiting factor in probing LLP lifetimes less than 100mm. To circumvent the difficulty of triggering on LLP decays, the search presented in this thesis exploits the ZH associated production mode, relying on leptonic trigger signatures to select interesting events. This is the first search for Higgs boson decays into LLPs to exploit this analysis methodology and additionally makes use of several novel methods for both background rejection and background estimation.


No excess over Standard Model predictions is observed, and upper limits are set on the branching ratio of the Higgs boson to LLPs . Depending on the mass of the LLP, branching ratios greater than 10% are excluded for lifetimes as small as 4mm and as large as 100mm, probing an important gap in the ATLAS exotic Higgs decay programme. In comparison to the previous searches for Higgs decays to LLPs, these are among the most stringent limits placed on this scenario, and for LLPs with masses below 40 GeV these results represent the strongest existing constraints on the branching ratio of the Higgs boson to LLPs in this lifetime regime.

商品描述(中文翻譯)

迄今為止，在大型強子對撞機（LHC）上觀察到的TeV尺度上沒有新物理的存在，促使人們越來越關注對弱耦合新粒子和異常特徵的搜尋。特別是，具有宏觀平均壽命的粒子，即長壽命粒子（LLPs），因其能夠逃避大多數基於超越標準模型粒子在主要交互點附近衰變的搜尋而引起了重大興趣。許多旨在解決標準模型（SM）各種問題的模型引入了壽命不受限制，甚至顯示出偏好於宏觀範疇的新粒子。這些理論通常指出希格斯玻色子可能是通往新物理的入口，異常希格斯衰變是主要的現象學結果和發現手段。從理論和實驗限制的角度來看，考慮在這些異常衰變中產生的粒子具有宏觀平均壽命並產生獨特的探測器特徵是有充分動機的。

本研究描述了對希格斯玻色子進行異常衰變的搜尋，該衰變產生兩個長壽命、中性、自旋0的粒子，隨後衰變成一對b夸克，形成ATLAS內部探測器中的位移強子噴流的顯著特徵。ATLAS的幾項其他搜尋先前已探測到這種衰變拓撲，排除了希格斯玻色子對LLPs的分支比大於10％且平均壽命大於100mm的情況。這些搜尋依賴於專門設計用於選擇在ATLAS量能器或μ子譜儀中衰變的LLPs的觸發器。ATLAS內部探測器中沒有相應的LLP衰變觸發器一直是探測LLP壽命小於100mm的限制因素。為了克服對LLP衰變的觸發困難，本論文提出的搜尋利用ZH相關產生模式，依賴於帶有輕子觸發特徵的選擇有趣的事件。這是首次對希格斯玻色子衰變為LLPs的搜尋利用這種分析方法，並且還使用了幾種新的方法來進行背景抑制和背景估計。

未觀察到超出標準模型預測的過量，並對希格斯玻色子對LLPs的分支比設置了上限。根據LLP的質量，對於壽命小至4mm和大至100mm的分支比大於10％的情況進行了排除，探測了ATLAS異常希格斯衰變計劃中的一個重要空白。與先前對希格斯衰變到LLPs的搜尋相比，這些結果是對這種情況設置的最嚴格限制之一，對於質量低於40 GeV的LLPs，這些結果代表了對希格斯玻色子對LLPs在這個壽命範圍內的分支比的最強現有限制。

作者簡介

Jackson Burzynski is a high energy particle physicist working on the ATLAS experiment at CERN. His research is centered around searches for new physics with unconventional detector signatures, such as those originating from the decays of metastable particles that travel considerable distances through the ATLAS detector before decaying.

In addition to performing fundamental research, Jackson also works to study and improve the algorithms used by the ATLAS experiment to reconstruct charged particle trajectories. He played a crucial role in the optimization of the algorithm used to search for charged particles produced at large radii which helped to revolutionize the long-lived particle search programme in ATLAS. He is also passionate about analysis software and efficient data pipelines, and is working to streamline and improve the way that physics analysis at the LHC is performed.

Jackson received his PhD from the University of Massachusetts Amherst under the supervision of Benjamin Brau. He currently holds a postdoctoral research fellow position at Simon Fraser University.

作者簡介(中文翻譯)

Jackson Burzynski 是一位在歐洲核子研究組織（CERN）的ATLAS實驗中從事高能粒子物理學研究的科學家。他的研究主要集中在尋找具有非傳統探測器信號的新物理現象，例如來自於在ATLAS探測器中行進一段距離後衰變的亞穩定粒子的衰變。

除了進行基礎研究外，Jackson還致力於研究和改進ATLAS實驗中用於重建帶電粒子軌跡的算法。他在優化用於搜索在大半徑處產生的帶電粒子的算法方面發揮了關鍵作用，這有助於改變ATLAS中長壽命粒子搜索計劃的方式。他對分析軟件和高效數據管道也充滿熱情，並致力於簡化和改進LHC物理分析的方式。

Jackson在馬薩諸塞大學阿默斯特分校獲得了博士學位，他的導師是Benjamin Brau。他目前在西蒙菲莎大學擔任博士後研究員職位。

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