Most ATLAS users know Emil Obreshkov only as a man at the end of a mysterious e-mail address. Ceri Perkins went along to meet the man himself, and find out a bit more about him.

“Every experiment needs its librarian,” says Emil Obreshkov modestly, but his role as ATLAS software librarian is a far cry from the peaceful, contemplative one of the stereotypical cataloguing bookworm. Together with a small, closely-working team of colleagues, Emil, a member of the DESY group, is responsible for building major in-house software releases for ATLAS physicists.

The software itself is unique to ATLAS, and is a huge collaborative effort. In fact, it is written by more than 1,000 developers from institutions all over the world. Each of them writes code which will identify the signatures of specific particles in the detector, amongst the reams and reams of data that will eventually come off the experiment. But at around 5 gigabytes in size, building the software into a fully functioning system is a massive undertaking, to which Emil can attest.

To tackle this problem, each developer focuses on just a tiny portion of the full code; the portion which relates to a specific sub-detector, particle type, condition database, simulation software, etc. that their own research group is responsible for. Periodically, they use the Internet to feed their changes and improvements into the central system, which is tested overnight each night at the Meyrin site.

Occasionally, altering the code so that it performs well for one group of researchers can cause problems in other areas where it was previously functioning well. Part of Emil’s job is to monitor the researchers’ feedback on the night-runs, and to notify the specific developers who can help with any problems that have arisen. He receives up to 150 emails each day from researchers who have noticed snags in the previous night’s run, and must decide exactly which expert to send each query to, even on weekends.

“If I didn’t check my emails on Saturday and Sunday, I would have 300 emails by Monday morning!” he explains. “Our developers don’t sleep; they’re based all over the world.”

As you might imagine, organisation on such a grand scale requires a special kind of person. Emil credits his previous experience in his home country of Bulgaria for developing his skills in this area:

“The process here is very specific, and it’s something I’ve never seen before. But I think I am able to manage this because I used to work for a software company where we also had to be able to react very quickly,” he says. “At ATLAS, we have to solve software problems fast, in order to provide some kind of schedule. The work here is heavy, and there are a lot of things to be done. But that’s OK with me!”

Emil has been at ATLAS for almost four years now, but the software project began back in 2002. It is currently in its 13th version, and is piece-by-piece becoming better and better tailored to the needs of all the ATLAS physicists. Eventually, when the night-runs become stable, and both users and developers are happy with the state it has got to, Emil and the team will release Version 14. This, they predict, will be the one which will be used when real data-taking begins later this year.

Although he has work commitments almost seven days a week, Emil still finds time to socialise and ski, making the most of Geneva’s local mountains. But when he first arrived here, aged 28, he says it was a bit of a culture shock.

“It was the first time I had ever been abroad, and it was really surprising,” he remembers. “Switzerland and Bulgaria are very different. When I went back, I went into a shop and said, “morning,” or, “hi, how are you,” normal things in Switzerland, and people looked at me very suspiciously!”

For now, he is happily settled into his busy CERN life, and doesn’t have any plans to return to Bulgaria, saying, “For me, I never thought that one day I would go to Switzerland. It was a great chance for me, so I feel very lucky. Maybe one day I will take off and explore the rest of the world too!”