High Energy Particle Physics: A Concise Guide For Beginners

By Paul Bennett

The 'Holy Grail' of physics, is to obtain a “Theory of Everything”, from quarks to cosmology. This book is aimed at introducing the layman to some of the modern scientific ideas of high energy particle physics. It begins by giving a brief historical account and then introduces some of the key concepts that scientists have developed in order to get a unifying understanding of these laws. Most of the explanation is given in terms of coloured diagrams and simple descriptions, without recourse to the difficult mathematics that is inherent in this subject. The book gives an overview of some of the cutting edge areas of physics, with no previous knowledge assumed. Topics covered include gravity, electromagnetism, the strong and weak nuclear interactions, quantum theory and cosmology. It is just one of a series of books based on modern physics. Other titles include;
Special Relativity: A concise guide for beginners
General Relativity: A concise guide for beginners
Quantum Theory: A concise guide for beginners

• Language: English
• Publisher: Lulu.com
• Release date: Oct 1, 2011
• ISBN: 9781291916256

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High Energy Particle Physics: A Concise Guide For Beginners

High Energy Particle Physics: A Concise Guide for Beginners

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Chapter 1

This book has been adapted from PowerPoint slides that were used for a series of lectures on ‘Unification’ and high energy particle physics theory. Some of the graphics and colours have been removed from the original, in order to make it amenable for print and to reduce the cost of the book. This has also resulted in the addition of extra text, so as to clarify and expand upon some of the contents of the original slides.

The quote above by Newton appears around the side of a £2 coin. It relates to a letter he sent to Robert Hook, who had complained that he had not received due credit from Newton, for contributing to his success in formulating the laws of motion and unifying celestial and terrestrial motion under his law of gravity. Newton’ vitreous reply was, If I see further than others it is because I stand on the shoulders of Giants (Hook was rather small in physical stature.)

Today we realise that all physical phenomena can be explained in terms of just 4 fundamental interactions viz.

Gravity.

Electromagnetism.

Weak nuclear interaction (e.g. responsible for beta decay).

Strong  nuclear interaction (e.g. holds protons together in the nucleus).

It was Einstein’s dream to combine all physical phenomena/forces into a Unified Field Theory, a quest which was dismissed by many at the time but one which has gained great prominence in recent decades.

What God has torn asunder, let no man put together   Wolfgang Pauli

The greatest adventure of the human mind        Richard Feynman

Learn from yesterday, live for today, hope for tomorrow. The important thing is not to stop questioning   A. Einstein

Decades of effort aimed at sculpturing the fundamental particles with quantum theory, resulted in the ‘Standard Model’ which best describes the electroweak theory and the strong nuclear force. The holy grail of physics is therefore to combine all 4 fundamental ‘forces’ into one unified field. This effort of trying to explain a myriad of phenomena in terms of common laws and principles is historically depicted in the diagram below. Note that I have whimsically equated the theory of everything, with a theory of nothing. The reason for this is that our best theories require a quantum descriptions, which in turn predict that any fields of particles that can exist, do exist, even in a vacuum (however the latter consist of transient, virtual particles.) We can therefore regard any permanent entities, as being exited energy states of these quantum fields of virtual particles. Now the recently observed accelerated expansion of the universe, is believed to be due to a mysterious dark energy, that pervades all space, even between the galaxy clusters. Hence if we can explain the nature of this vacuum energy, in terms of fluctuating fields of quanta, then we would to some extent understand the unified theory. Hence a ‘theory of everything’ necessitates an understanding of a theory of ‘nothing’ (the vacuum). In the diagram below, start from the bottom and progress upwards through Man’s intellectual ascent. It is not important to have familiarity with all the concepts and theories depicted below, they are merely there to give an overview of some of the important topics that will be outlined in the following pages. [Symmetry is common in many of the physical theories depicted below and is particularly important in

Symmetry is an operation that does not change how something (laws of physics), behaves relative to the outside world. In fundamental physics, the notion of symmetry breaking is important, in which although the laws of physics are symmetrical the resulting solutions (which determine how the world looks) are not symmetric. As an analogy, the symmetry we have at birth, is usually broken by situations and choices we make. Also the laws of economics may exhibit symmetry but these often produce an asymmetric distribution of wealth in society.

NB.  Some of the symmetry is broken in a Rubic cube, since squares are given different colours. This makes it more interesting, just as the symmetry breaking in physics makes the world a more interesting place. Other examples of everyday symmetries are those that occur in snowflakes (rotational symmetry), rock crystals, butterfly and wallpaper (translational symmetry). In the hexagon depicted above, there is also a reflection symmetry of order six. This shape occurs naturally in basalt formations, such as the Giant’s Causeway in Northern Ireland and also in a bees honeycomb. It is a theorem due to Emmy Noether, which demonstrates that symmetry implies the conservation of a physical quantity. Einstein regarded Noether as the most important woman in the history of mathematics. There are 4 kinds of symmetry used extensively in particle physics viz;

Continuous space-time symmetries, leading to conservation of energy and momentum etc.

Discrete symmetries --- Charge, Parity, Time, symmetries of improper Lorentz transformations.

Dynamical symmetries. The requirement of the Lagrangian to be invariant under a phase shift of the wavefunction, leads to the conservation of electrical charge.

Internal symmetries, which help to categorise particles, giving them additional quantum numbers such as strangeness and charm.

The fact that experiments reveal the same laws of physics yesterday as they do today (and tomorrow), implies a conservation of