Ultraperipheral Collisions: Intro

1 minute read


Hello. This is my first serious post. At the very beginning of my website, I promised to talk more about the type of physics I am involved with.

The official name is Ultraperipheral Collisions, but it is usually abbreviated with UPC. Firtly, let us talk a bit about a few Particle Physics basics.

Particle physics is easy to understand. This is, in my opinion, certainly not true… However, very basic ideas are easy to pick up and comprehend.

There is something called space contraction. It is a very basic relavistic phenomenon.

Basically, what happens is that if you see an object who is moving at speeds comparable to the speed of light c (something like 300000 km/s…!), then you see it squeezing, contracting. When I was a student I used to think of a spring who was launched somewhere and it was being compressed by the air… It is not the same, but it works to have an idea.

A particle, or a heavy ion, who is accelerated at the top accelerator energies, squeezes… Instead of the original ball, we find ourselves with a very energetic pancake…!

So now you have two pancakes moving towards each other, to collide. This is called an event in jargon. If these two pancakes, which are extended objects, pass close to each other, without touching, but we see that something has happened, chances are that we have a UPC event!

What probably happened was that a pancake emitted a photon (what the light is made of) towards the other pancake. And this produced magic…

Next time a bit more!