Feynman Diagrams and the CMS

 Bonjour! Bonjour!

Louis came back today to talk to us about Feynman diagrams.  It really is amazing how useful they really are.  You see, Feynman diagrams are more than just pictures that represent particle interactions, they are actually the terms of the equations that  help determine the probabilities of each possible outcome of the interaction going forward in time.  Each kind of vertex, like the ones up on the screen in the image, carries with it a unique term that represents that interaction.  So if you draw every possible interaction to get from the starting constituents to the ending constituents, you can just add up the terms to find the equation that represents that interaction.  You might say, "but what if I make a super long random chain that eventually gives the things that I want?" Well that would be one of the possibilities but each vertex added makes the term that is a factor of 37 times smaller, so adding more and more vertices, although possible would eventually make the process so unlikely as to be negligible and also, probably impossible to find in the first place.

It was for the reason of turning a complex mathematical process into a graphical and manipulatable format that Richard Feynman was awarded the Nobel Prize.  His advancement allows for rapid advancement of both ideas and the science behind them. 

This is me with my colleague from Bhutan where I am wearing a shirt that has a Feynman diagram representing an electron and a positron interacting through a photon and then moving on as a positron and an electron.  The positive time direction is upward, so the the arrow on the bottom left is an electron, but notice that the arrow on the bottom right is aimed backward in time, showing that it is an antiparticle (in this case a positron). The photon acts in no time, hence why it is horizontal, then the photon creates a positron on the top left and an electron on the top right.  If you were trying to figure out all the way an electron and a positron could become a different electron and positron you could draw a million versions of this, but each time you add a vertex it become less and less likely (although not impossible).  To find the probability of getting this outcome, you would add up all of the possible solutions. 

 I know that is not the easiest thing to understand, but this is the basis for more complicated interactions like ones where you start with 2 protons and end with two photons.  This is one of the ways in which you could find a Higgs, because a Higgs could decay into two photons with the same energy as the mass of the Higgs (around 125 GeV). So if I find two photons, I could look for every possible way and many different amounts of Energy are possible.  The random distribution should look like the blue dotted line in the graph below:

However, notice that there is an extra peak at 125GeV.  THIS is the evidence for the Higgs.  It was confirmed by both the CMS and the ATLAS experiments independently and at a 5σ significance!!  

So this leads us to the CMS, which was the second part of the day. I'm going to photo dump here to show you some amazing things I saw and did at the CMS.

LED showing from where and to where the PETAbytes of data is traveling and at what speed the data travels.

Behind this 7.5 meters of door is the CMS detector.

This is me in front of a life sized image of the CMS experiment

87.9 meter below the Earth's surface

We took some data on the pressure difference from the top to the bottom of the elevator. 

This is the crane that dropped some of  the pieces of CMS

Cool image superimposing model into an image of the CMS

When the LHC stops next July, the CMS will be modified to a hexagonal sensor on the end caps.

CMS sign off

We ended the night watching a movie about the discovery of the Higgs so here is me sitting in the chair Peter Higgs was when her heard the news that he was likely going to be awarded the Nobel Prize.