LHC PROJECT SIMULATOR

Simulation of a Higg's particle decay in the CMS detector of the LHC

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These notes support the Extreme Machine presentation about the LHC experiments. For a full list of curriculum links for this section please visit the Curriculum Links section.

They can be used for a teacher presentation, or students can use them to prepare and deliver a presentation of their own to their class. The presentation is designed to take 10-15 minutes.

The partner presentation Back to the Big Bang! further explores the science behind the LHC experiments. The presentations can be given in either order, but it is suggested that you use this one second.

You can use these notes as a script, or you can edit them to suit your own style and audience.

Slide 1 - Extreme Machine

Slide 2 - The Large Hadron Collider at CERN
This is the inside story of the most powerful particle accelerator on the planet. It's the most complicated machine ever built. It's called the Large Hadron Collider, or LHC. It is home to the biggest physics experiments ever, and its job is to discover what the universe is made of.

Slide 3 -
It’s taken 25 years to plan and build, involving around 8,000 scientists and engineers from all over the world.

Slide 4 - The Scale of Things
A dew drop is made of a billion trillion (10²¹) molecules of water. Each molecule is made of an oxygen atom and two hydrogen atoms (H₂O). At the start of the 20th century, atoms were the smallest known building blocks of matter. Each atom has a nucleus, surrounded by electrons. The nucleus of a hydrogen atom is just a single proton.

Experiments with earlier accelerators have shown that protons in turn consist of three quarks. Quarks are fundamental particles, not made up of even smaller particles. They are point-like particles, with no measurable volume. They're impossible to see directly, so how do we know anything about them? And how can we learn about other fundamental particles?

Slide 5 - The Limits of Light
Optical microscopes can't see details smaller than about 1 µm (a micrometer) across because of the wavelength of light. Atoms are much smaller, so you can never see them with light. Fine for studying plant and animal cells, but no use for seeing inside the atom.

Slide 6 - Seeing Smaller

This electron microscope uses a beam of electrons instead of light - it's actually a small particle accelerator. The electron beam has a much shorter wavelength than light rays, so it can make out much smaller details, right down to spotting individual molecules. But you still can't see atoms.

Slide 7 - Building Bigger to See Smaller
Investigating particles a billion times smaller needs a different approach. Instead of shining a beam on something, accelerators smash particles: either into a target if it's a linear accelerator, or against each other in a synchrotron. The faster the particles are going, the more energy they have when they hit, and the more you can learn from what happens.

To give the particles enough energy to reveal all the different particles that we think the universe is made of, you need a really big accelerator.

Slide 8 - The Ultimate Microscope…
Over the last 50 years bigger and bigger accelerators have, bit by bit, revealed a hidden world of unimaginably tiny particles inside atoms. Physicists have sorted these into a framework called the Standard Model that describes what we see pretty well, but it isn't the complete picture. It doesn't include gravity, for example. Or explain what gives particles mass.

By colliding protons (and lead nuclei) at a much higher energy than ever before, physicists are pinning their hopes on the LHC to provide the missing pieces.

Slide 9 - Particle Creator…
Smashing particles together this hard doesn't just break them open, like a nut. Einstein realized that matter and energy can be converted from one to the other.

By accelerating hadrons to relativistic speeds, within a hair's breadth of the speed of light, the collisions in the LHC are so powerful that some of the energy actually creates particles that weren't there before.

So, the more powerful the accelerator, the heavier particles you can create. And the LHC operates at energies over ten times greater than any previous particle accelerator.

Slide 10 - …and Time Machine!
When we look at distant galaxies, it's taken billions of years for the light to get here. We're looking back in time. But we can't ever see all the way back to the start of the universe because there was no light to see it by - photons just didn't exist.

By recreating the conditions just after the Big Bang, the LHC experiments are like a time machine taking us right back to the beginning of the universe, when it was unimaginably hot and dense. Understanding what happened then holds the key to understanding the fundamental nature of the universe as it is today.

Slide 11 - Detecting the Invisible
The particles created in the LHC are way too small to see directly. Many only exist for a tiny fraction of a second, decaying almost instantly into other particles. Huge, complex detectors, the size of mansions, record the energies and momentum of these particles as they zap outwards from the collision. The detectors have an onion-like layered construction, each layer designed to perform a specific task.

Most collisions reveal nothing new. Data from potentially interesting collisions is captured and stored for later analysis. Physicists can then carefully pick over these data, reconstructing what must have happened, to see if there were any new particles or phenomena.

It's painstaking work, a bit like accident investigators using data from an aircraft's "black box" flight recorder and debris from the crash scene to piece together what happened to the aircraft.

Slide 12 - Extreme Conditions…
To make electromagnets strong enough to steer and focus such a high energy hadron beam, they need to pass a current of tens of thousands of amperes with almost no resistance - otherwise they'd melt in seconds. In other words they need to be superconducting. To achieve this, they are bathed in liquid helium at just above absolute zero: 1.9K (-271.3°C). That's colder than outer space, which is 2.7K.

At such a low temperature, helium becomes super-fluid with almost no viscosity. This helps carry heat away from the superconducting magnetic solenoids efficiently. The whole thing is the biggest superconducting installation ever built.

The beam pipe also needs almost all the air pumped out of it to create an ultrahigh vacuum, where the pressure is ten times lower than on the Moon - that's emptier than outer space. Otherwise, the hadrons would keep colliding with air particles as they hurtle round the 27km tunnel 11,000 times a second. Achieving this is like creating the hard vacuum of space in a volume the size of a cathedral.

Slide 13 - For Extreme Collisions…
Pairs of protons collide with an energy of 14TeV, that's about the kinetic energy of 14 flying mosquitoes. That doesn't sound much until you realize that this energy is concentrated into a space a million million times smaller than a mosquito. Think of it this way: you could clap your hands together nice and hard, but you'd think twice before doing the same thing with a drawing pin stuck to your palm.

The total energy in the particle beam is equivalent to a 400 tonne train (like the French TGV) going at 150 km/h. Where the beams cross, they're squeezed to less than the diameter of a human hair. That's a lot of energy in a tiny volume…

Slide 14 - …And in 2008?
Here's a simulation of the particle trails left by a collision between two lead nuclei. Making sense of complex particle signatures like this is difficult, but the reward could be a major discovery that changes our understanding of how the universe works. For the thousands of physicists studying the results from the LHC, it's an incredibly exciting time.