Precision measurements of beauty decays and the W boson mass at LHCb

LHCb 的美衰变和 W 玻色子质量的精确测量

• 批准号: ST/N004892/2
• 负责人: Mika Vesterinen
• 金额: $ 44.52万
• 依托单位: University of Warwick
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=ST%2FN004892%2F2
• 关键词: Precision; measurements; beauty; decays; boson

In elementary particle physics we study the basic building blocks of Nature including those that have not naturally existed since the earliest stages of the Universe. In our Standard Model theory (SM) there are 12 fundamental matter particles, each with its antimatter twin. They interact by exchanging one of four types of "bosons". Over 40 years, this elegant theory has proven remarkably accurate in explaining what we see in our experiments. However the SM is not the final word. For example it fails to explain why the present day Universe contains any matter at all. The Big Bang should have created matter and antimatter in equal quantities, but we know that matter and antimatter "annihilate" when they meet, producing photons (one of the four types of bosons). Almost 14 billion years later, all that should remain is the annihilation photons. That is very nearly true, except that our Universe appears to possess one matter particle for every few billion photons. This seemingly insignificant imbalance is what makes up everything from the the stars and galaxies, to you and I. The SM simply cannot explain it. This is just one example of why we are certain of "new physics" beyond the SM. The Large Hadron Collider is built to search for heavy new particles that are expected to exist. It does so by smashing protons (a type of "hadron") together at high energy. Bunches of 100 billion protons collide 30 million times each second. The energy is critical because Einstein's famous equation (E=mc^2) tells us that energy can be transformed into mass. The new particles are expected to be massive (heavy), so according to the equation we need large energy to produce them. After its first run in 2010-2012, the LHC has just begun a new journey into the unknown, with a three year "Run-II" at almost double the energy.Of the four main LHC experiments, LHCb has a cunning strategy to look for new physics. Rather than search for the direct production of new particles it makes extremely precise measurements of "beauty hadrons". They have been known for decades, yet are of great interest because their behaviour can be indirectly affected by new particles. The theory of Quantum Mechanics allows particles to flicker in and out of existence in so called "loops", and the b-hadrons exhibit various phenomena that depend on them. The goal is to see the effects of loops containing new particles. We must study huge quantities of b-hadrons to discern tiny differences compared to the calculations of the SM theory. LHCb sees some million-billion of them each year. With the three years of Run-II data, I will make two measurements related to differences between matter and antimatter versions of b-hadrons. A key challenge will be to avoid being fooled by fake effects due to imperfections in the apparatus.Quantum loops also affect the masses of the force carrying bosons. The mass of the W-boson is notoriously difficult to measure. While an uncertainty of 2 parts in 10,000 might seem impressive, a further reduction could reveal a deviation from the expectation of the SM. Two of the LHC experiments have already set out on a mission to do this, but their ultimate precision will be limited by how well we understand the details of proton collisions. I have shown that LHCb, which wasn't designed for this purpose, can actually make a similarly precise measurement and its special features will crucially reduce our dependence on how well we understand proton collisions.One of the biggest challenges in all LHC experiments is to decide, within less than a second, which collisions to save for further study. More than 99.9% of them need to be discarded. This is the task of the "trigger" system and I have long been involved with the LHCb trigger and I will continue my prominent role. This is a challenging but exciting programme of research with the potential for great rewards - deviations from the SM predictions that would point us to new physics.

在基本粒子物理学中，我们研究了自然的基本基础，包括自宇宙最早阶段以来自然存在的基本构建基块。在我们的标准模型理论（SM）中，有12个基本物质颗粒，每个粒子都有其反物质双胞胎。他们通过交换四种类型的“玻色子”之一来进行交互。在40年的时间里，这种优雅的理论在解释我们在实验中看到的内容非常准确。但是，SM不是最终单词。例如，它无法解释为什么当今的宇宙根本包含任何问题。大爆炸本应该以相等数量的形式产生物质和反物质，但是我们知道物质和反物质会遇到时“歼灭”，产生光子（四种类型的玻色子之一）。将近140亿年后，静止不动的是歼灭光子。这几乎是正确的，除了我们的宇宙似乎每亿个光子具有一个物质粒子。这种看似微不足道的失衡是构成从星星和星系到您和我的所有事物的原因。SM根本无法解释它。这只是为什么我们确定SM以外的“新物理学”的一个例子。大型强子对撞机旨在寻找预期存在的重型新粒子。它通过在高能量上将质子（一种“强子”）粉碎在一起来做到这一点。 1000亿质质子的束相撞，每秒碰撞了3000万次。能量至关重要，因为爱因斯坦著名的方程式（E = MC^2）告诉我们，能量可以转化为质量。预计新颗粒将庞大（重），因此根据方程式，我们需要大量能量才能产生它们。在2010年至2012年首次运行之后，LHC刚刚开始了新的未知之旅，三年的“ run-ii”几乎是四个主要LHC实验的能量的两倍，LHCB有一个狡猾的策略来寻找新的物理。而不是寻找新粒子的直接生产，而是对“美容黑人”的极为精确的测量。它们已经闻名了数十年，但引起了人们的极大兴趣，因为它们的行为可能会受到新粒子的间接影响。量子力学的理论使粒子可以在所谓的“环”中闪烁和出现，而b-hadrons则表现出依赖于它们的各种现象。目的是查看包含新颗粒的环的效果。与SM理论的计算相比，我们必须研究大量的B- had子来辨别微小的差异。 LHCB每年看到其中的数百万。有了三年的II数据数据，我将进行两个与B-HADRON的物质和反物质版本之间的差异有关的测量。一个关键的挑战将是避免由于设备中的不完美而被虚假效果愚弄。Quantum循环还会影响携带玻色子的力量的质量。众所周知，W-Boson的质量很难测量。虽然10,000中有2个部分的不确定性似乎令人印象深刻，但进一步的减少可能揭示了SM的期望。 LHC的两个实验已经开始执行任务，但是它们的最终精度将受到我们了解质子碰撞细节的程度的限制。我已经表明，不是为此目的而设计的LHCB实际上可以进行类似的精确度量，其特殊功能将至关重要地减少我们对我们了解质子碰撞程度的依赖。所有LHC实验中最大的挑战之一是在不到一秒钟内决定，以便在不到一秒钟之内，以节省进一步的研究。其中超过99.9％需要被丢弃。这是“触发”系统的任务，我长期以来一直参与LHCB触发器，我将继续我的重要角色。这是一个充满挑战但令人兴奋的研究计划，具有巨大的奖励 - 与SM预测的偏差，这将使我们指向新的物理学。

项目成果

Understanding and constraining the PDF uncertainties in a W boson mass measurement with forward muons at the LHC

• DOI: 10.1140/epjc/s10052-019-6997-8
• 发表时间: 2019-02
• 期刊: The European Physical Journal C
• 作者: S. Farry;O. Lupton;M. Pili;M. Vesterinen

A Comparison of CPU and GPU Implementations for the LHCb Experiment Run 3 Trigger

LHCb 实验运行 3 触发器的 CPU 和 GPU 实现比较

• DOI: 10.1007/s41781-021-00070-2
• 发表时间: 2021
• 期刊: Computing and Software for Big Science
• 作者: Aaij R

A comprehensive real-time analysis model at the LHCb experiment

• DOI: 10.1088/1748-0221/14/04/p04006
• 发表时间: 2019-03
• 期刊: Journal of Instrumentation
• 影响因子: 1.3
• 作者: R. Aaij;S. Benson;S. Neubert;E. Govorkova;O. Lupton;M. Vesterinen;R. Matev;C. Fitzpatrick;H. Schreiner;A. Pearce;M. Cian;A. Dziurda;S. Stahl

Simultaneously determining the $W^±$ boson mass and parton shower model parameters

同时确定$W^±$玻色子质量和部分子簇射模型参数

• 作者: Lupton Olli

A simple method to determine charge-dependent curvature biases in track reconstruction in hadron collider experiments

确定强子对撞机实验轨道重建中电荷相关曲率偏差的简单方法

• DOI: 10.1140/epjc/s10052-021-09016-9
• 发表时间: 2021
• 期刊: The European Physical Journal C
• 作者: Barter W