Atlas – simulating Big Bang in search of the Higgs particle and nature beyond the Standard Model
Person photo Prof Kerstin Jon-And
Elementary Particle Physics (Department of Physics)


Svensk sammanfattning
Dagens partikelfysiska teorier kan bara delvis beskriva hur universum fungerar. Gravitation och uppkomsten av massa och mörk materia kan inte förklaras. Dessutom har Higgspartikeln, som förklarar varför andra partiklar har en viss massa, aldrig observerats. I en gigantisk partikelaccelerator återskapar vi de förhållanden som rådde precis efter Big Bang i ett försök att hitta Higgspartikeln och lära oss om de grundläggande krafter som skapat universum.

English summary
Today’s theories of particle physics only describe parts of the workings of the Universe. Gravity and the origin of mass and dark matter cannot be explained. Also, the Higgs particle that explains why other particles have certain mass, has never been observed. In a gigantic particle accelerator we recreate the conditions just after the Big Bang in an attempt to find the Higgs particle and learn about the basic forces that have shaped Universe.

English article
The Large Hadron Collider (LHC) is a gigantic scientific instrument at the European Organization for Nuclear Research (CERN) near Geneva, where it spans the border between Switzerland and France about 100 meters underground. It is a particle accelerator which recreates the conditions just after the Big Bang in order to study the smallest known particles – the fundamental building blocks of all things.

Two beams of particles will travel in opposite directions inside the 27 km circular accelerator, gaining energy with every lap. Eventually, the two beams smash into each other at very high energy, creating simulations of Big Bang, in the centre of special detectors. The biggest of the detectors is the Atlas detector.

In search of new particles
With the Atlas detector we investigate a wide range of physics in an attempt to answer fundamental questions of science and the universe itself. The Standard Model is currently the best description we have of the subatomic world, but it does not explain the complete picture. The theory incorporates only three out of the four fundamental forces, omitting gravity. The project might shed light on new theories of particle physics beyond the Standard Model. Among the possible unknowns are the origin of mass, extra dimensions of space, microscopic black holes, and evidence for dark matter candidates in the Universe. One of the most important goals is to find the missing piece of the Standard Model, the Higgs particle.

What do Stockholm physicists do?
The project is a collaboration between 169 universities in 37 countries. At Stockholm University we are building electronics which will allow us to measure the amount of energy the particles produce when they collide. Crashing together in the Atlas detector, the particles produce tiny fireballs of primordial energy. The fireballs are first converted into analog energy signals. These signals then have to be converted into whole numbers which can be stored and analyzed digitally.

We are also working on the so called trigger, a processor which uses simple information to identify, in real time, the most interesting events to retain for detailed analysis. Around 800 million collisions occur every second. But only a few of these are of any interest. New exciting phenomena and particles are only expected to occur once in 100 billion collisions. With other words we have to accumulate an enormous quantity of data in order to get good statistics. The trigger helps us with that. There are three trigger levels and by preliminary analyses at each level, data will be reduced from 800 million collisions per second to a few hundred. At Stockholm, we work with the trigger which is used at the first of the three levels.

Work in progress
The LHC started up on 24 November 2009 with the first collision events. The first papers with early results may come in the summer of 2010. Continued data taking will be made during the next 15-20 years with publications of results on an ongoing basis.


Researchers (5)
Research fields (1)
Contracts (1)
Dr Christophe Clément
Prof Sten Hellman
Prof Per-Olof Hulth
Prof Klas Hultqvist
Prof Barbro Åsman