The pisa group is involved in the Virgo collaboration since its beginning. The group organized itself in 1985 around dr. Adalberto Giazotto, which together with his colleague dr. Alain Brillet in France put the basis for the interferometric detection of gravitational waves in Europe. The initial group of physicists and engineers, mainly with a background in high energy physics, started to investigate one of the main issue for an earth bound interferometric gravitational wave detector, namely the possibility of building suspended optical cavities. Suspensions are needed to maintain the mirrors in their working position. But they should not couple the apparatus to the seismic motion of the ground. The basic idea that was implemented is the one of a chain of pendula, which produces the requested noise rejection in the relevant frequency band, typically above few Hertz. Below this frequency there is no attenuation of noise, and in order to reduce the mirror motion sophisticated active control strategies are needed. The group expanded from its initial nucleus including physicists with competences in optics and data analysis. It had a key role in the construction, commissioning and data taking of Virgo and Virgo+. Several young physicists, which now have key roles in gravitational waves experiments all over the world, did their first steps inside the group. The Pisa group has a fundamental role in the implementation of Virgo Advanced: it is still working on its “traditional” responsibilities, but has a growing interest in data analysis which will be exploited in the next scientific runs.
The two main responsibilities of the group are the mechanical design and implementation of the seismic attenuation systems for the “large” optics and their control. Mechanical attenuators were designed and produced with all their details, and in the past years several R/D projects were developed to improve them. The implementation of the active control is deeply connected with the details of mechanical suspensions. For the advanced detectors both the control strategy (with the introduction of advanced techniques) and the needed hardware (with the design and the production of advanced DSP boards) were improved.
A dedicated subgroup works on data analysis activities. The main field of interest are continuous sources, detection of stochastic background, parameter estimation and multi messenger strategies. Several members were actively involved in commissioning activities.