You might have been wondering why one has to wait so long to see the new Higgs boson results from the 2012 data at CERN. Are we there yet? CERN announced last week that these results will be presented at special CERN seminar on July 4th at 9:00 am, Geneva time, with a live webcast.
Why does it take so long? The reason is simple. The physicists are slowly climbing over this pile of new data, one small step at a time, hoping to have some great surprises once we reach the top.
It would certainly be nice if we could simply add the new data and get the results out. But the reality is quite different.
First of all, we need to get that data. This requires having a team of people on shift 24 hours a day, and several dozen experts reachable at all times to ensure the detector in tip-top shape.
Each event looks like a mini firework. Once in a while, some heavy and unstable particle is created from the energy released when two protons collide head-on in the Large Hadron Collider (LHC) where two beams of protons circulate in the 27-km long accelerator.
Our task is to identify each tiny piece from the debris and reconstruct the initial object from the pieces that flew away in all directions.
The hope is to find new particles never seen before, like the Higgs boson that could explain how particles acquire their mass, or dark matter particles, the unidentified matter that makes up most of the universe.
The data come from millions of different parts of the detector, carrying information on where the debris flew or lost energy. That’s a huge amount of information and it takes the Grid, a network of thousands of computers, to be able to tackle this task.
Other people scrutinize these data every day, making sure they are of good quality with all information available.
In parallel, we simulate billions of events called Monte Carlo events that look just like the events recorded in the detector but that are based on current knowledge or hypothesized ideas (like the Higgs bosons or dark matter particles). By comparing the Monte Carlo with the real data, we can see if all is already known or if new particles are present.
Before using the simulated data, we must check they reproduce every single aspect of the data we collect. We must check every type of information we use for the physics analysis. If the simulation differs from the real data, we correct it until all is reliable.
Then comes the physics analysis per se where hundreds of different teams design dedicated selection criteria to extract specific types of events. This is where the simulated Monte Carlo data comes in handy. We impose selection criteria based on the characteristics of the events of interest (called the signal) and designed to reject most other types of events (called the background).
All selection criteria must be defined using only simulated data such as not to bias these criteria. When all is ready, we apply the selection to the real data .
Last but not least: getting the whole collaboration’s approval for these results. The review process is painstaking and trying. Nobody wants to risk putting out a result that would be erroneous so high scrutiny is applied. When everyone is convinced, then the results can be shown publicly.
For us physicists, there is one new added twist: pressure stemming from the public and media interest. We certainly hope to deliver exciting results at the special seminar next week on the eve of the most important physics conference of the year hosted in Melbourne, Australia from 4th-11th July.
The last data has still to be processed. Until all is finalized, patience will be required. We too are holding our breath.
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