CERN: A needle in a million different haystacks

15 May 2012

Leif Lönnblad

The task is comparable to looking for a needle in a million different haystacks. The tool is a computer programme that sifts out the interesting events in the proton collisions.

At Lund University, world-leading research is underway on the computer programmes required in the particle hunt at CERN.

Leif Lönnblad is a professor of theoretical physics. He is not working on the experiment itself at CERN but instead with the theoretical models and computer programmes which are to help analyse the results of the experiment. He looks quite pleased when he talks about the successes of the Lund theoreticians.

“Grab any researcher you like in particle physics and tell them you are from Lund University. They will answer: “Ah, the Lund model!” he says.

The computer programmes from Lund are used by particle physicists from all over the world. The programmes simulate the proton collisions carried out at CERN’s ATLAS experiment station. In the previous issue of LUM, some researchers from Lund told us about their work at ATLAS, including the hunt for dark matter and the Higgs boson.

”The computer programmes are absolutely essential if we are to have any chance at all to understand what emerges in the detectors”, explains Leif Lönnblad.

The computer programmes help the experiment to sift out the events that can be interesting to study. Leif Lönnblad compares this to the needle in the haystacks. And it is not only about having to look in a million different haystacks but also about learning the difference between a needle and a straw. In our ordinary world it is not difficult to distinguish what is a needle from what is a straw, simply by its appearance, but in the world of accelerator physics it is not as easy to establish what is what when millions of particles are swirling forth and colliding almost at the speed of light.

Leif Lönnblad emphasises the fact that Pythia, the most important computer programme, is the brainchild of his colleague Torbjörn Sjöstrand. At the time of LUM’s visit, however, Torbjörn Sjöstrand is in the US to receive a prestigious scientific award and therefore unable to take part in the interview.

One of this year’s honorary doctors at the Faculty of Science, Bryan Webber from Cambridge University, also has a connection to the computer programmes from Lund. Webber is considered to be one of the world’s leading theoretical experts within the subject and has developed a computer programme that stands in direct competition to the Lund model. Even so, Lönnblad and Sjöstrand chose to nominate Bryan Webber for an honorary doctorate. Leif Lönnblad explains that Webber’s successful research spurred on the Lund team over more than two decades in a spirit of friendly competition, giving the research field many new findings and insights.

“Even though he is a tough competitor he is also a good friend to our research team,” says Leif Lönnblad.

Text: Lena Björk Blixt

*Footnote. The computer programme from Lund is called Pythia after the oracle at Delphi in ancient Greece.

Read more about CERN in themed articles first published in the Lund University Magazine - LUM.

CERN: Basic research and business
CERN: How does matter really hold together?
CERN: The key to creation