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 Back to the Big Bang! presentation on the science behind 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, Extreme Machine, further explores how the LHC works. The presentations can be given in either order, but it is suggested that this one is used first.

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

Slide 1 - Back to the Big Bang!
The Large Hadron Collider, or LHC, is part of the biggest physics experiment in history.

Its purpose is to find out what the universe and everything in it, including us, is ultimately made of.

This presentation tells the story of this amazing quest for knowledge. And it's a story that begins at the dawn of time itself�

Slide 2 - The Universe
This is the Hubble Ultra Deep Field photo of a tiny portion of sky - about the area you'd see if you looked through a 2m long drinking straw. It took the space telescope 400 orbits to take this 1 million second exposure, collecting just a single photon of light per minute from the dimmest objects. It is the deepest portrait of the visible universe ever taken.

The smudges and dots aren't stars, they are whole galaxies made of hundreds of billions of stars. There are about ten thousand of them here. This isn't a special part of the sky, if you point a powerful enough telescope in any direction this is what you will see.

The closer galaxies have familiar shapes - spirals and ellipses. The furthest are very strange. Light from these odd-looking smudges has taken around 13 billion years to reach us. We are looking at the earliest galaxies emerging from the "dark ages" when the universe was less than a billion years old. This is the very edge of the visible universe, about as far back in time as we will ever see.

Slide 3 - The B of the Bang
Most scientists believe the universe popped into existence around fourteen thousand million years ago. Asking �What was there before?� doesn�t really make sense, because there was no time for there to be a �before� in.

It sounds crazy, but there�s lots of evidence to support the idea of the Big Bang. If it�s correct, the conditions just after the Big Bang must have been unrecognisably different from today�s universe.

Slide 4 - The B of the Bang
The raw ingredients of the universe we see today must have all been there, but the conditions were far too hot and dense for anything like atoms or even photons to exist. Until now, the only way to think about how the universe began has been through equations and theories.

If we could hop aboard a time machine and go back to study what was happening in the first fraction of a second after the Big Bang, we could see how well our ideas about what makes the universe the way it is hold up. And probably get one or two surprises.

The next best thing to actually being there is to try to reproduce the conditions just after the Big Bang, and see what we find.

Slide 5 - What Would We Find There?
It sounds like science fiction, but that's exactly the plan: to recreate the beginning of everything.

Slide 6 - The Large Hadron Collider

Slide 7 - What is CERN?
CERN is a huge international laboratory. For over 50 years, scientists from around the world have been coming to CERN to study the building blocks of matter and the forces that hold them together.

CERN provides them with the tools they need to do this. These are accelerators, which accelerate particles to almost the speed of light, and detectors to make the particles visible. The LHC is the largest and most powerful in a series of particle accelerators, each more powerful than the one before. Over the last five decades each new accelerator has been enabling scientists to probe deeper and deeper into the structure of the atom.

Slide 8 - What is The Large Hadron Collider?
Hadrons are the group of sub-atomic particles that experience the strong nuclear force: baryons (protons and neutrons) and mesons (pions and kaons). For a while scientists thought protons and neutrons were "fundamental particles" that weren't made of anything smaller, just like earlier scientists thought the atom couldn't be split into smaller parts.

Experiments with atom-smashing particle accelerators at places like CERN have revealed that hadrons are made of even smaller things: quarks. Two up and one down quark for protons, two down quarks and an up for neutrons, held together by force-mediating gluons. Could it be that we're finally down to the ultimate building blocks of everything?

If you crash hadrons together hard enough, you get loads of other particles. These don't come from inside quarks - the LHC isn't a quark-smasher. Instead, the collisions have so much energy that some of the energy converts into mass and actually creates particles that weren't there before. These are particles that haven't been around since the Big Bang. And the more energy you put into the collision, the more massive the particles that you can conjure into existence.

The LHC collides hadrons at much higher energies than previous accelerators, which physicists are expecting will reveal massive particles we've never seen before.

Will they fit in with existing theory? Or will we have to re-think the Standard Model?

Slide 9 - How Does It Work?
If you have an old-style TV or PC monitor with a cathode ray tube, that's a mini particle accelerator. The LHC is the same, only a bit bigger.

The idea is simple: use a pulsed electric field to accelerate bunches of charged particles (protons or lead nuclei), steer them round a ring with powerful magnets, then collide them and record what happens.

A circular accelerator like this is called a synchrotron. The particle beam energy is measured in TeV (tera-electronvolts). 1TeV = 10¹² eV. We need such a big unit because 1eV is tiny: it's the kinetic energy one electron gains when it's accelerated by a potential difference of 1V. It's about the kinetic energy of a flying mosquito.

The Tevatron at FermiLab was the highest-energy synchroton before the LHC, capable of achieving 1TeV. The LHC can attain 14TeV. Giving protons this much energy without them flying out the side of the circular tunnel isn't easy. In fact, it's taken 25 years and billions of pounds to achieve.

So, what are the big mysteries the LHC experiments might help us crack?

Slide 10 - And What's It For?
For a start, 96% of the universe is missing. Measurements of the way galaxies move have led scientists to think only 4% of the universe is made of normal matter we can see and touch, and energy we can detect like heat and light. The rest of it seems to be made of something completely different that we can't perceive directly, so it's called dark matter and dark energy.

The trouble is nobody knows what this mysterious matter actually is, so scientists are pretty keen to find out. The LHC just might make us some particles of dark matter so we can take a look. Or if it doesn't, maybe that means we've got it all wrong. Maybe gravity works differently than we thought.

What causes gravity isn't fully understood either. Are there interaction particles that mediate gravity, like the way photons convey electromagnetism? We've made up a name for them - gravitons - as we expect they might exist, but again no one has actually detected them. In fact, gravity doesn't fit into the Standard Model at all.

Next there's mass itself. Why do different particles have different masses? Why does anything have mass in the first place? In other words, what gives stuff stuff? Sometimes the very simplest questions are the toughest. Might the LHC experiments show us a particle that confers mass onto the other particles? Lots of scientists are betting on it, and they call it the Higgs particle after the scientist who first predicted that it should exist.

The theory suggests that equal amounts of matter and antimatter were made just after the Big Bang, but we can't find any antimatter in the modern universe. So where did it all go?

String theory might provide a way to unify all four fundamental interactions: gravity, the strong nuclear force, the weak nuclear force and electromagnetism. The trouble is it needs at least ten dimensions for the theory to work. Could the LHC experiments provide evidence for extra, unseen dimensions?

And there are other possible discoveries. The real point is you can dream up all the theories you like about what the universe is made of, but sooner or later you have do some experiments to see if your ideas hold up.

And sometimes finding out we were completely wrong turns out to be the most exciting result of all.

Slide 11 - How Can You See What's Happened?
There are four main detectors around the LHC tunnel. They're big, complex pieces of kit. This is a simulation of the pattern a Higgs particle might make in one of them.

The trouble is, with hundreds of millions of collisions every second, picking out the interesting ones is like trying to find a particular grain of sand on a beach. And the experiments will run for at least ten years.

Slide 12 - That's a LOT of Data�
You know what a scientist at CERN did last time they needed to share lots of information between scientists around the world? He invented the World Wide Web.

Now, because of the vast amount of data that the LHC is going to produce, the scientists at CERN are using the Grid. The Grid networks computers around the world in order to share processing power as well as information.

It's the ultimate supercomputer, and they're going to need it to find that grain of sand as the total amount of data that the LHC will produce will be about equal to writing down every word spoken by everybody in the world, ever!

Slide 13 - Watch This Space!
The most exciting part of this experiment is that nobody knows for certain what will happen. If they did, the whole thing would be a huge waste of time and money. The only thing everyone is pretty sure about is that the experiments will reveal something, and that it will change our understanding of how the universe works. And the people in this control room at CERN will be at the centre of it!