Sandra Berni
Nationality: French
As one of CERN’s thirty-strong survey team, Sandra Berni is responsible for measuring the precise position of the different parts of the LHCb detector.
“I work with Jean-Christophe Gayde - the person in charge of surveying at LHCb - and with the help of physicists and technicians we measure a different part of the detector each day,” explains Sandra. "We check the position, shape and the alignment of the detector components in relation to the beam line. We give these measurements to the physicists and they use it to make adjustments to the detector. We then re-measure to check that everything’s correct.”
These surveys are important for LHCb because each part of the detector (such as a straw of the outer tracker, or a silicon strip of the VELO) records only one point on the trajectory of each particle. In order to piece together the complete trajectory of a particle, physicists must ‘join the dots’ between the hits in the detector, to form what are called ‘tracks’. To do so successfully, they need to know precisely where each detector element is with respect to the other ones hit by the same particle, and it is this information that surveyors like Sandra provide.
Originally from the town of Valence in southern France, Sandra studied at the Institut National des Sciences Appliquées in Strasbourg (INSA). “It’s an engineering school and I specialized in topography and land surveying,” she explains.
“After finishing my masters' degree I went travelling in South America for a few months. When I came back to France in June 2006 I saw a job at CERN advertised on the INSA website. “I didn’t know a lot about CERN before coming here, except that it’s a huge project, really international, and I thought I could meet people from all over the world and improve my English,” Sandra recalls.
Although Sandra possessed many of the skills required for her new role at LHCb from her training at INSA, there were certain new techniques she had to master. “We use several different instruments for measuring at CERN, mainly the theodolite, which measures angles and distances, and also digital photogrammetry and laser trackers,” she says. “I learnt how to use the theodolite at school, but I also had to learn special techniques that have been developed here to improve the acuracy of the measurements.”
One of the main dificulties for Sandra was adjusting to the unusual working conditions. “I spend about 50% of my time down in the cavern,” she explains. “At first I found it hard at first to adapt to the conditions – it's always twenty degrees, the light is always the same, and the weather can be a bit surprising when you back to the surface. It took a few months to adjust, but I'm used to it now - the friendly atmosphere helps.”
Now that the LHCb experiment is about to begin, Sandra’s time at CERN is coming to an end. “We’re almost finished with the surveying now,” she says. "During the shutdown some people will realign and re-survey some things if there are any problems, but for me this job finishes in June.”
Sandra hasn’t yet decided what she’s going to do next. “It’s very interesting to work on this level of accuracy - only a handful of people in the world do survey work for particle physics - but maybe I’ll do something completely different. CERN has been a great experience for me, but I’m not sure I want to be specialized in one field yet.”