Natural Units

Our universe is governed by a handful of fundamental constants, such as the speed of light or the gravitational constant. In particle physics, it is often convenient to use natural units, in which key constants are set to unity, revealing the underlying simplicity of physical laws.

Spin and Polarisation

Spin is a fundamental property of particles, corresponding to their intrinsic angular momentum. Polarisation describes how the spin of a particle is oriented.

Pile-Up

The LHC collides bunches (groups of protons), which can result in multiple proton-proton collisions at each crossing. Such additional collisions are called pile-up.

ATLAS Coordinate System

The ATLAS coordinate system allows scientists to accurately and consistently describe how particles travel through the detector.

Inside a Collision

Proton collisions at the LHC generate high-energy events, initiating a cascade of processes, such as parton showering and hadronisation, which ultimately produce the particles seen in the ATLAS detector.

Particle Decay, Lifetime & Width

The lifetime (or equivalently, the width) and the different ways elementary particles can decay are fundamental properties crucial for physicists exploring the boundaries of known physics.

Monte Carlo Simulation

Monte Carlo (MC) methods help ATLAS physicists simulate data by generating theoretical collisions based on both known and theorised physics. We use the simulated data to help us understand the detector’s behaviour, optimise algorithms, and identify new physics.

4-Vectors and Particle Mass

Time and space ­coordinates vary depending on the frame of reference in which a collision event is measured. 4-­vectors are tools that can simplify the transformations between frames of reference.

Statistical Significance

When physicists make statements about whether or not a given process has been observed in the LHC data, they must back up their claim with strong statistical evidence. This is often expressed in terms of standard deviations or the p-value.

Cross Section and Luminosity

This sheet defines cross section and luminosity, presents examples of LHC cross sections, and introduces the method used to determine number of events.

Signal and Background

This sheet defines signal and background and presents some common strategies for increasing the signal-to-background ratio.

Conservation Laws

These laws govern the reactions we observe in particle physics! Their violation would be a sign of new physics.

Feynman Diagrams

A powerful tool to visually represent particle interactions, as well as to conduct elaborate calculations! Learn the basics on how to read Feynman diagrams.

The Standard Model

All fundamental particles classified based on their properties! Deviations to the Standard Model can point the way to new physics.