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Virgo at LAPP

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LAPP (Laboratoire d’Annecy de Physique des Particules) has been part of the Virgo Collaboration since its quest for approval in the early 90s. The LAPP team has been contributing to numerous aspects of the Virgo experiment : building and commissioning of the detector, calibration and characterisation of the data, data analysis with a focus on the search for signals from compact coalescing binaries (neutron starts or black holes).

On February 2016, the Virgo LAPP team is made up of 11 physicists, including one PhD student, two postdocs, and about 12 engineers and technicians in charge of developments in mechanics, electronics, and computing.

Detector construction and commissioning

The main mirrors of the Virgo interferometer are suspended on 10-meter high suspensions under vacuum. LAPP has been in charge of design and installation of the vacuum tanks containing the mirrors and their suspensions, but also of the working platforms and of the tools for vacuum tanks access.

The LAPP team was also in charge of the design and installation of the optical benches under vacuum, needed for the control of the interferometer and the detection of the gravitational wave signal. It has the responsability of those benches, their optical configuration ((mirrors, lenses, optical cavity...) as well as the electronics for the sensors.

The relative position and the alignment of the mirrors of the Virgo interferometer are controlled in real time. The numerical control loops are set up thanks to GPS-synchronized electronics and computing designed and installed by the LAPP team.

Finally, the LAPP team takes care of the commissioning, monitoring and improvements of the different subsystems under its responsability, with close interaction with other subsystem teams. The team has thus a regular presence on the experiment’s site.

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From the detector data to the gravitational wave signal

At the interface between the detector and the data analysis, the LAPP team is in charge of the interferometer calibration and data reconstruction : using different signals from the instrument, the amplitude of the gravitational wave is computed as a function of time, then sent to the various gravitational wave signal searches.

LAPP also contributes to the detector characterization, on one hand to improve the detector components and to understand the noise sources that compromise the detector’s sensitivity, on the other hand to improve the data analysis efficiency by reducing the number of false alarms.

Searching for coalescences of binary compact objects

The LAPP team contribute to data analysis by searching for gravitational waves signals from coalescences of binary compact objects, neutron stars and black holes. Since 2007, this search is run online on the data of the three detectors Virgo and LIGO. It aims at triggering alerts for telescopes and satellites (optical, Xray...) to perform follow-up observations and localize more precisely the gravitational wave sources in the sky, which could be crucial to understand the physics of these sources.

A data format for the gravitational waves interferometric detectors

Within the LAPP team, has been developed the Frame format : a data format common to the gravitational waves interferometric detectors.

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