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### Poisson d’Avril and Poisson Probabilities

Giant yoyo with sidebar. I imagine I'll get funny looks on the train!

Bonjour,

Today I want to tell you just a bit about my work. It’s just a brief outline today as I am off to a school this morning in East Croydon. The lovely Birmingham Particle Physics technician has finished my rather wierd request for a giant yoyo with a detachable sidebar. It looks great!

I am going to get the kids to guess which way it will roll if I pull towards me
a. the string wound one way, b. the string wound the other way and c. the bar. It works a treat for demonstrating that physics wins out over instinct!

I am also preparing a talk on some of the work I have been doing. Let me explain. I am interested in events that produce lots and lots of particles. When you collide Lead ions at high energy, as the LHC eventually will, you can get THOUSANDS of particles produced. However, for protons, a few hundred is fairly rare. What is not always as rare is the rather annoying possibility of two events (that don’t make very many particles) happening at once. If you try to select the ones you want, you end up with these too. We call them “pile-up”.

What does this mean? Well, if you took two single protons and tried to collide them you would be waiting a long time. At the LHC, many (of the order of 10,000,000,000!) protons are bunched tightly together in a “bunch”. These bunches, once accelerated, cross each other and then there is some probability ONE of the protons from each bunch will interact. This actually follows a Poisson distribution. If there is a probability that you will get 1 interaction then there is some, smaller probability you will have 2 interactions, 3 interactions and so on. It all depends on how tightly compact and full of protons this “bunch” is. Of course, two events with, say, an average of 50 particles produced looks, at first, very similar to one event with 100 particles produced. Imagine disappointed physicists faces as they look through their sample and find all these events are actually “pile-up”. Luckily, thanks to Simeon-Denis Poisson, I am working on a way to understand what we expect to see.

So what is the fish all about?

Fish pranks are funny 🙂

Well yesterday was of course April fool’s day, and this is celebrated in different ways around the world. In France, so I hear, they do something called “April Fish”, where the practical jokes include pinning paper fish to people’s backs. I looked for some fish-shaped chocolate before I came back but couldn’t find any.

So why does that matter? Well, my boyfriend and I have been together for 4 years from yesterday. We have our anniversary on April fool’s day so as you might expect, I like to play tricks on him. Yesterday morning he found a fish in his dressing gown and a wind-up one in the shower. There was one in his wallet and a blow-up, helium-filled fish-balloon at the foot of the bed. He had never heard of “Poisson d’Avril” so he was more than a little confused!

And don’t I feel guilty now… he bought me my very own copy of the Feynman lectures vol 1 to 3 (and “tips on physics”)! To translate this to non-physicists, this makes me very happy! (It’s basically my equivalent of diamonds!)

We went to a very fancy restaurant and enjoyed the yummiest chocolate tart I have ever had, so I am determined to find some time to try and replicate it!

After the school visit, I am off to see my boyfriend’s band play in Cheltenham. I think I will take some pictures and at some point do an “electric guitar” related physics post 🙂